Lasers in operative dentisry and endodontics/ dental implant courses by Indian dental academy

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INTRODUCTIOn Laser is an acronym for Light Amplification by the Stimulated Emission of Radiation. Laser is the brightest monochromatic (single color) light existing today.

Laser was invented by Dr.Maiman in 1960. Laser has found widespread application in communications, industry, defense and medicine. Lasers are the single most important advancement in surgery of the 20th century. These versatile devices have evolved from the early short-pulsed lasers to the more sophisticated continuous wave gas and solidstate lasers. Lasers have radically changed the ways in which many procedures can be done. Supermarket bar code scanners and the compact disk player have even moved lasers into everyday life.An essential condition for the proper and successful use of lasers in any specialty is an understanding of the characteristics and limitations of wavelengths, interaction with tissues, mode of transmission, delivery systems (optics, contact and non-contact modes), and settings (power, repetition rate, continuous versus pulse modes). This knowledge permits the application of the laser technology in the proper clinical setting and it provides the best results. Lack of understanding often leads to the misuse and abuse of lasers, causing detrimental results and otherwise avoidable complications. Shortly after the development of the laser in 1960, research began for the feasibility of using different types of lasers for intraoral surgical procedures. Over the past 40 years there has been significant efforts by dental researchers in developing basic workable safety parameters as well as in investigating the numerous applications of laser instruments in intraoral soft tissue surgery, hard tissue applications, dental materials and endodontics. Hence, the dental lasers of today have benefited from decades of laser research.

HISTORY Laser is an acronym for Light Amplification by the Stimulated Emission of Radiation. Albert Einstein postulated the theoretical foundation of laser action, stimulated emission of radiation, in 1917.In his now classical publication “ Zur Quantum Theorie der Strahlung ’’ (“ The Quantum Theory of radiation”) he discussed the interaction of atoms, ions and molecules with electromagnetic radiation. (Einstein 1917). He specifically addressed absorption and spontaneous emission of energy and proposed a third process of interaction: stimulated emission. Einstein postulated that the spontaneous emission of electromagnetic radiation from an atomic transition has an enhanced rate in the presence of similar electromagnetic radiation. This “ negative absorption” is the basis of laser energy.

Many attempts were made in the following years to produce stimulated emission of electromagnetic energy, but it was not until 1954 that this was successfully accomplished. In that year, Dr.Charles Townes and two of his students discussed their experiences with stimulated emission of radiation in the microwave range of electromagnetic spectrum. This represented the first MASER (Microwave Amplification by the Stimulated Emission of Radiation) and paved the way for the development of the first laser. In 1958, Dr. Townes and physicist, Dr. Arthur Schawlow published “ Infra red and optical masers” (Schawlow and Townes 1958), in which they discussed stimulated emission in the microwave range of the spectrum and described the desirability and principles of extending stimulated emission techniques to the infra red and optical ranges of the spectrum.Dr.Theodore Maiman expanded on their theoretical writings and built the first laser in 1960. (Maiman). With

2 synthetic ruby crystals, this laser produced electromagnetic radiation at a wavelength of 0.69um in the visible range of the spectrum. Although the laser energy produced by Maiman’s ruby laser lasted less than a millisecond, it paved the way for explosive development and widespread application of this technology.

BIOPHYSICS A laser is an electro optical device that emits organized light (rather than the random-pattern light emitted from a light bulb) in a very narrow, intense beam by a process of optical feedback and amplification. Because the explanation for this organization involves stimulated emission, a brief review of quantum physics is necessary. In the semi-classic picture of an atom, each proton is balanced by an electron that orbits the nucleus of the atom in one of the several shells or orbits. A shell corresponds to a specific energy level and these energy levels are characteristic of each different atom or molecule. The smaller shells, where the electron is closer to the nucleus, have a low energy than the larger shells, where the electron the farther away from the nucleus. Electrons of a particular atom can only orbit the nucleus at these levels, or “floors”. Radiation of energy does not occur while the electrons remain in any of these shells. Electrons can change their orbits or energy levels, thereby changing the energy state of the atom. During excitation, an electron can make the transition from a low-energy level to a high-energy state. If the excitation comes from the electron interacting with a discrete packet of light (a photon), this is termed absorption. The atom always seeks its lowest energy level, the ground state. Therefore the electron will spontaneously from the high –energy shell back to the lowest energy shell in a very short time (typically 10 -8 s). As the electron spontaneously drops from the high – energy shell back to the lowest energy shell, the atom must give up the energy difference. The atom emits the extra energy as a photon of light in a process termed the Spontaneous emission of radiation. Einstein postulated that an atom in a high-energy state would be induced to make the transition to a lower energy state even faster than the spontaneous process if it interacted with an existing photon of the same energy. One might imagine a photon colliding with an excited atom and the collision results in two identical photons (one incident and one produced by the delay) leaving the collision.

The two photons have the same frequency and the same energy and are traveling in the same direction in spatial and temporal phase (Einstein 1917). This process, which Einstein called Stimulated emission of radiation is the underlying principle of laser physics. All laser devices have an optical resonating chamber (cavity) with two mirrors: the space between these mirrors is filled with a lasing medium such as argon, neodymium: yttrium aluminum garnet (Nd: YAG), or carbon dioxide (Co 2). An external energy source such as an electric current excites the lasing medium within the optical cavity. This pumping causes many atoms of lasing medium to be raised to a high-energy state. When more than half the atoms in the resonating chamber have reached a particular excited state, a population inversion has occurred. Spontaneous emission is taking place in all directions: light (photons) emitted in the direction of the long axis of the laser is retained within the optical cavity by multiple reflections off precisely aligned mirrors. One mirror is completely reflective and the other partially transmissive Stimulated emission occurs when a photon interacts with an excited atom in the optical cavity, yielding pairs of identical photons that are of equal wavelength, frequency and energy and are in phase with each other. This process takes place at an increasing rate with each passage of the photons through the lasing medium: the mirrors serve as a positive feedback mechanism for the stimulated emission of radiation

3 by reflecting the photons back and forth. The partially transmissive mirror emits some of the radiant energy as laser light. The radiation leaving the optical cavity through the partially transmissive mirror quickly reaches equilibrium with the pumping mechanism’s rate of replenishing the population of high-energy state atoms* *The term atom used in the preceding discussion refers to the lasing material.

In reality, the lasing material can be molecules, ions, atoms, semi-conductors, or even free electrons in an accelerator. In these other systems it does not have to be the bound electron that is excited. It can be many different excitations, including molecular vibrational excitation or the kinetic energy of an accelerated electron.The radiant energy emitted from the optical cavity is of the same wavelength (monochromatic): is extremely intense and unidirectional or collimated, and is coherent both temporally and spatially. Temporal coherence refers to the waves of light oscillating in phase over a given time interval. *t. Whereas spatial coherence means that the photons are equal and parallel across the wave front. These properties of monochromaticity, intensity, collimation, and coherence distinguish the organized radiant energy of a laser light source from the disorganized radiant energy of a light bulb or other light source (Ossoff and Karlan, 1985) After the laser energy exits the optical cavity through the partially transmissive mirror, the radiant energy typically passes through a lens that focuses the laser beam to a very small beam diameter, or spot size, ranging from 0.1 to 2.0 mm.

When necessary, the lens system is constructed to allow visible helium-neon aiming laser beam and the invisible CO2 or Nd: YAG laser beam to be focused coplanar. The optical properties of each focusing lens determine the focal length or distance from the lens to the intended target tissue for the focused use.

CONTROL OF SURGICAL LASER With most surgical lasers, the physician can control three variables: 1. Power (measured in watts) 2. Spot size (measured in millimeters) 3. Exposure time (measured in seconds).

Of these variables power is the least useful as a parameter and may be kept constant with widely varying effects, depending on the spot size and the duration of the exposure. For example, the relationship between power and depth of tissue injury becomes logarithmic when the power and exposure time are kept constant and the spot size is varied. Power Density (PD) is more useful measure of the intensity beam at the focal spot than power because it takes into account the surface area of the focal spot.

Specifically, power density or power per unit area of the beam, expressed in watts per square centimeter, is a measure of the power output of the laser in watts divided by the cross-sectional area of the focal spot in square centimeters.

PD = Power in the focal spot ------------------------------Area of the focal spot

4 Power and spot diameter are considered together and a combination is selected to produce the appropriate power density. If the time of exposure is kept constant, the relationship between power density and depth of injury is linear as the spot size varied.

Power density is the most important operating parameter of a surgical laser at a given wavelength. Therefore surgeons should calculate the appropriate power density for each procedure to be performed. These calculations would allow the surgeon to control in a predictable manner the tissue effects when changing from one focal length to another (400mm for micro laryngeal surgery to 125mm for hand-held surgery) or when using surgical lasers with different transverse electromagnetic modes (TEM 00 versus TEM01). Power density varies directly with power and inversely with surface area (A).

This relationship of surface area to beam diameter is important when evaluating the power density. The larger the surface area, the lower the power density, conversely, the smaller the surface area the higher the power density. Surface area is expressed as: A (area) = πr2 Where r is the beam radius. Because the radius is one-half of the beam diameter (d/2), surface area also can be expressed as: A(area) = πd2 /22 or A = π d2 / 4. Surface area then, varies as the square of the beam diameter: doubling the beam diameter will increase the surface area by four times, while halving the beam diameter will yield only one-quarter the area. Therefore power density varies inversely with the square of the diameter. For example, doubling the beam diameter (from d to 2d) reduces the power density to one-forth (PD to PD/4) and halving the spot diameter (d to d/2) increases power density by a factor of four. Newer CO2 lasers emit radiant energy with a characteristic beam intensity pattern different from that produced by older-model lasers. Because this beam pattern ultimately determines the depth of tissue injury and vaporization pattern across the focal spot, the surgeon must be aware of the characteristic beam pattern of the laser. Transverse electro-magnetic mode (TEM) refers to the distribution of energy across the focal spot and determines the shape of the laser’s spot. The most fundamental transverse electromagnetic mode is TEM00 appearing circular when cut in cross section; the power density of the beam follows a gaussian distribution, with its greatest amount of energy at the center of the beam, then diminishing progressively toward the periphery. TEM 01 and TEM11 modes are less fundamental modes that have a more complex distribution of energy across their focal spot, causing predictable variations in tissue vaporization depth. Additionally, their beams cannot be focused to a point down to as small a spot size at the same working distance as TEM00 lasers. Although simple ray diagrams normally show parallel light to be focused to a point, the actual situation is a bit more complicated. A lens will focus a gaussian beam to a beam waist or finite size. This beam waist is the minimum spot diameter, d, and can be written as: d ~ 2fλ/D. Where f if the focal length of the lens, λ is the wavelength of light, and D is the diameter of the laser beam incident on the lens (Refer Fig. 4). The beam waist occurs not at one distance from the lens, but over a range of distances. This range is termed the depth of focus and can be written as: Depth of focus ~ πd²/2λ. We realize the depth of focus every time we focus a camera. With a camera, a range of objects is in focus, and we can set the focus without carefully measuring the distance between the object and the lens. Notice from the above equation that a long focal length lens (a large f) leads to a large beam waist. A large beam waist also translates as a large depth of focus.The size of the laser beam on the tissue (spot size) can therefore be varied in two ways. Because the minimum beam diameter of the focal point increases directly with increasing the focal length of the lens to obtain a particular beam diameter. As the focal length becomes smaller, there is a corresponding decrease in the size of the focal spot; also, the smaller the spot size is for any given power output, the greater the corresponding power density. The second way the

5 surgeon can vary the spot size is by working either in or out of focus. The minimum beam diameter and the highest power concentration occur at the focal plane, where much of the precise cutting and vaporization is carried out (Refer Fig. 5). As the distance from the focal plane increases, the laser beam diverges or becomes defocused (Refer Fig. 5). Here, the cross-sectional area of the spot grows larger and thus lowers the power density for a given output. As one can readily see, the size of the focal spot depends on both the focal length of the laser lens and whether the surgeon is working in or out of focus. Fig. 6 demonstrates these concepts using arbitrary ratios accurate for a current model TEM00 CO2 laser. The laser lens setting (focal length) and working distance (focus/defocus) combinations shown here determine the size of the focal spot.

The height of the various cylinders represents the amount of tissue (depth and width) vaporized after 1-second exposure at the three focal lengths.Varying the exposure time represents the third way in which the surgeon can vary the amount of energy delivered to the target tissue. Radiant exposure (RE) refers to the amount of time (measured in seconds) that a laser beam irradiates a unit area of tissue at a constant power density.

Radiant exposure is a measure, then, of the total amount of the laser energy per unit area of exposed target tissue and is expressed as joules per square centimeter: RE = Power Density × Time. The radiant exposure varies directly with the length of the exposure time. Working in either the pulsed mode can vary the exposure time, with durations ranging from 0.05 to 0.5 seconds, or in the continuous mode. In Summary, the surgeon can control the CO2 laser to incise, coagulate, or vaporize tissue by varying the power output, spot size, or exposure time of the laser unit.

TYPES OF LASERS

The wavelengths from which the surgeon can choose are CO2, Nd: YAG in contact and non-contact modes, argon, potassium titanyl phosphate (KTP / 532) and argon dye. New experimental lasers that may soon be available are the Holmium: YAG, erbium: YAG and ultimately the free electron laser. Lasers that have the widest application in medicine are those based on carbon dioxide (CO2), argon, neodymium: yttrium aluminum garnet (Nd: YAG), krypton and various dyes. In general surgery, the carbon dioxide and contact Nd: YAG lasers are the main ones used.

A. CO2 Lasers: This is the most widely used well understood and well studied of the medical lasers. It has a wavelength of: 10.6 µm at peak of absorption of water. The laser light is transformed within the tissue to thermal energy, raising the tissue temperature to 100° C and vaporizing the tissue’s water content. This wavelength makes the CO2 laser a precise cutting tool, ideal for the excision of small lesions located on delicate structures. Basic studies by Shapshay (1987) 19 showed excellent depth of penetration with minimal damage to adjacent tissues. The CO 2 beam can be focused to create a precise coagulation of small blood vessels (approx 1 mm).

Principle: When the CO2 gas mixture is energized and stimulated to emit light, there is a concomitant dissociation of the molecule into carbon monoxide and free oxygen radical. (Unlike argon or Nd atoms, which do not break apart). The resulting molecule is no longer able to produce the CO 2 laser light. This is complicated by the fact that electrodes in the laser tube emit contaminants that further degrade the mass mixture.

Flowing Gas CO2 Systems: A flowing gas system purges the tube of the contaminants and dissociated molecule by continuously replenishing the gas. Flowing gas systems are the oldest and most established technology for CO2 lasers. They require cylinders of replacement gas, pressure regulators and a vacuum pump to draw the gas through the system. Flowing gas systems do produce reliable steady outputs ans easily generate

6 powers up to 100 W for medicine. At the low end of the power scale (1-5 W) the output is stable and reliable.Companies manufacturing: Cooper, Coherent, Hi- Tech, Nippon Infrared Industries Corporation and Sharplan. Sealed – Tube, Free Space CO2 Lasers: These are new generation laser tube that eliminates the need for replacement laser gas mixture, regulators and vacuum pumps. Output produced is 100 W. It simplifies operation and maintenance of a CO2 laser. The tubes will need to be recharged after several years as the power gradually falls from the high end of output. Power output at the low end is less than 5 W and not as stable as with flowing gas systems. These lasers use DC excitation. Companies manufacturing: Heraeus Lasersonics, Surgilase, California Laboratories, and Sharplan. Radio frequency (RF) Wave guide CO 2 Lasers: These are other type of sealed-tube laser, but use a RF that is transmitted transversely across the tube to excite the gas molecules. This eliminates electrode contamination. It gives an output of: 55W – 25W. Companies manufacturing: Bioquantum Technologies, Coherent and Pfizer. Carbon Dioxide Laser Modalities: The choices for the surgeon when requesting the operational mode of the CO 2 laser include CW, Pulsed, Repeat pulsed, and Superpulse. The higher the power available on a CO 2 laser the better, but 50-60 W will perform satisfactorily for all procedures.  

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CW: In CW operation, the laser is emitted as a steady output for the entire time the beam is emitted.

Pulsed mode: A pulsed mode on a CO2 laser provides one single pulse of a predetermined length, at whatever power is set. This provides a short burst of energy that reduces heat spread and provides more reaction time and control for the surgeon. Four common settings are routinely provided between 0.05 and 0.5 seconds. The surgeon will have to “ pump” the foot pedal for each pulse.

Repeat pulse: Is the same as a pulse except that the beam will automatically keep pulsing instead of the surgeon having to pump the foot pedal. Preset rates at which pulses are emitted are approximately 0.5 seconds between each pulse.

Superpulse: It provides a high degree of precision, but at slower speeds than in a CW mode. Its other names are: megapulse, varipulse, enhanced and spiked modes.

It reduces the amount of charring created, but offers less hemostasis than a CW mode. Disadvantage of CO2 Laser: The CO2 laser has a disadvantage in that it cannot be transmitted through flexible fibers but can only be delivered through a somewhat articulated mirror system.

B. Neodymium:Yttrium-Aluminum-Garnet:Lasers (Nd:YAG ) These units have power and cooling requirements than do CO2 lasers. surgical Laser Technologies Inc (SLT) produced the first Nd: YAG laser with no requirement for external watercooling. It allows continuous operation at high power without shutting down. (Because the flash lamps that drive the YAG crystal are not left at full power when the laser is in a ready mode, instead the lamps come up to full power only when the foot pedal is depressed). These lasers have a wavelength of 1.06 µm; they are poorly absorbed by water and therefore penetrate tissue deeply. The energy is not dissipated at the surface (as is the case with CO2. KTP/532 and argon lasers), it scatters within the tissue depending on the degree of tissue pigmentation for absorption. Studies performed in laboratory on liver, skin, bone and blood vessels showed that, when used in conract mode, the Nd: YAG laser cuts bone and soft tissue readily, achieving little hemostasis on the surface. However, when larger blood vessels are approached, such as in the center of the liver, hemostasis is poor. The latest in Nd: YAG laser technology is a 100

7 W CW system that requires no external water hookups and utilizes a single, standard 110 V wall outlet for power C. Companies manufacturing: Living Technologies, Laser scope. Nd: YAG Laser Modalities: All of the surgical Nd: YAG lasers operate in the CW mode as opposed to Q-switched or mode –locked Nd: YAG laser used in ophthalmology. The surgical Nd: YAG laser may also be operated in a timed pulse, similar to the CO 2 laser bur for longer pulse lengths from 0.10 seconds up to 10 seconds or more. Aiming Beams for the Nd: YAG Laser: A red helium neon laser is the standard aiming beam for most Nd: YAG lasers. Heraeus came out with multicolored aiming beams in their high power laser, and variable intensity in their lower power 60 W lasers. Nd: YAG Laser Fibers And Probes: Some Nd: YAG laser manufacturers still offer reusable fibers, in addition to disposable ones. Sapphire probes significantly expand the versatility of any Nd: YAG laser. Contact probes originally developed by SLT Inc are available through: SLT, Heraeus Lasersonics, Surgilase, Sharplan and Living Technologies.Companies manufacturing: Laser Industries Ltd, Medical Energy Inc, Surglilase, SLT, Trimedyne and Living Technologies.

D. Green Light Lasers - Argon and KTP (Potassium Titanyl Phosphate/532): Both argon and KTP lasers produce green light, although of slightly different wavelengths. Both are fiber optically delivered lasers. They operate in visible spectrum and KTP has a wavelength of 532. They are well absorbed by pigmented tissue and hemoglobin and are poorly absorbed by pale tissue, thus making them good coagulators with fairly good ablation of pigmented tissue. The popular company making general use Argon laser is: HGM Laser. (Range: 15-20 W). The only company making medical KTP laser system is: Laserscope (Range 12-15 W and uses a Nd: YAG laser at it’s heart. Dye Lasers: CW dye lasers, producing rigid light at 630 nm are used for Photodynamic therapy (California Lab). Key to delivering the red light in photodynamic energy is the type of fiber used and accurate measurement of the output.

Pulsed dye lasers are drawing considerable interest for selective dermatological applications (Medi tech, 577-585 nm, Yellow light), and for fragmenting kidney (laser lithotripsy, Candella Corporation, 504 nm, Yellow system) and other stones.

EXPERIMENTAL LASERS Photodynamic Therapy Photodynamic therapy consists of administering a chemical agent to sensitize living tissue so that it can be activated by a light source at a given wavelength, which results in its cellular destruction. It is based on selective tissue absorption and retention of hematoporphyrin derivative. It had been known that porphyrins cause fluorescence of tumours, but Lipson et al were the first to describe the photodynamic properties of hematoporphyrin derivative. Several investigators have demonstrated the use of hematoporphyrin derivative in Photodynamic therapy in the treatment of carcinomas: (Balchum et al 1984, Cortese and Kinsey 1982, Benson et al 1983, Hayata et al 1985, Gluckman 1991, Keller et al 1985) 19. The use of hematoporphyrin derivative in photodynamic therapy is limited because it is absorbed by inflamed and traumatized tissue to some extent as well as by tumors. Most distressing are complications related to dye toxicity including severe skin photosensitivity for several weeks. Rhodamine-123 another photosensitizing agent has been subject of an increasing number of recent investigations. It localizes selectively in the mitochondria of the living tissue and is taken up and retained by many types of carcinoma cells, causing selective tumor toxicity at certain doses and significant normal tissue toxicity at high doses.

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NEW LASER WAVELENGHTS: Holmium: YAG Laser: Ho: YAG laser is a new solid – state laser operating at a wavelength of 2.1µm. It is a pulsed laser with a 250 µ sec pulse duration that is transmitted through small quartz fibres. It has the unique ability to ablate and cut bone and cartilage with a precision not seen with the commonly available CW lasers. Ho: YAG laser is a safe and useful tool in surgeries.

Erbium: YAG Laser: It is a solid – state pulsed laser that emits radiation with a wavelength of 2.94 um. It is well absorbed by water, with absorption co-efficient of 7700 cm –1. Because of it’s high water absorption, which is even greater than with CO 2 laser, and it’s high pulse energy, the erbium: YAG laser can easily ablate soft tissues and, in particular bone. It causes minimal damage to adjacent tissues. The high peak power produced in each pulse causes a rapid increase in tissue temperature leading to microexplosion and ejection of microscopic fragments of tissue. The use of this laser wavelength is still experimental.

Free Electron Laser: Madey who developed this laser in 1976 coined the term “Free Electron Laser”. It provides continuous, stable, coherent and monochromatic electromagnetic radiation that extends from the UV to the far infrared spectrum. It consists of a high-energy electron beam that passes through a periodically alternating static transverse magnetic field that is made up of a series of magnets, which are lined up so that their polarity alters.The magnetic field thus created forces the electrons in the beam to oscillate in a transverse direction and to emit a laser beam in a forward direction. The free electron laser is still under experimental investigation. It is expected to stimulate more medical applications because it provides a wide variety of wavelength from which to choose.

TISSUE EFFECTS OF LASER When electronic energy (incident radiation) interacts with tissue, the tissue reflects part, the tissue absorbs part, and the tissue transmits and scatters part of the light The surgical interaction of this radiant energy with tissue is caused only by that portion of the light that is absorbed that is, the incident radiation minus the sum of the reflected and transmitted portions (Polanyi, 1983)19.The actual tissue effects produced by the radiant energy of a laser vary with the specific wavelength of the laser used. Each type of laser exhibits characteristics and different biological effects on tissue and is therefore useful for different applications. Yet certain similarities exist regarding the nature of interaction of all laser light with biological tissue. The lasers used in medicine and surgery today can be ultraviolet where the interactions are a complex mixture of heating and photo dissociation of chemical bonds. The more commonly used lasers emit light in the visible or the infrared region of the electromagnetic spectrum, and their primary form of interaction with biological tissue leads to heating. Therefore if the radiant energy of a laser is to exert its effect on the target tissue, it must be absorbed by the target tissue and converted to heat (Refer Fig. 7). Scattering tends to spread the laser energy over a larger surface area of tissue, but it limits the penetration depth (Refer Fig. 8). The shorter the wavelength of light, the more it is scattered by the tissue.

If the radiant energy is reflected from (Refer Fig. 9) or transmitted through (Refer Fig. 10) the tissue, no effect will occur. To select the most appropriate laser system for a particular application, the surgeon must a thorough understanding of these four characteristics regarding the interaction of laser light with biological tissue (Fuller, 1984).The CO2 laser creates a characteristics wound (Refer Fig. 11). When the target

9 absorbs a specific amount of radiant energy to raise its temperature to between 60° C and 65° C, protein denaturation occurs. Blanching of the tissue surface is readily visible and the deep structural integrity of the tissue is disturbed. When the absorbed laser light heats the tissue to approximately 100° C, vaporization of intracellular water occurs.

This causes vacuole formation, catering, and tissue shrinkage. Carbonization, disintegration, smoke and gas generation with destruction of the laser-radiated tissue occurs at several hundred degrees centigrade. In the center of the wound is an area of tissue vaporization; here just a few flakes of carbon debris are noted. Immediately adjacent to this area is a zone of thermal necrosis measuring approximately 100µm wide. Next is an area of thermal conductivity and repair, usually 300 to 500 µm wide.

Small vessels, nerves, and lymphatics are sealed in the zone of thermal necrosis; the minimal operative trauma combined with the vascular seal probably account for the notable absence of postoperative edema characteristic of laser wounds (Mihashi et al., 1976)19. Comparison studies have been performed with experimental animals on the histologic properties of healing and the tensile strength of the healing wound following laser and scalpel produced incisions. It was noted that the tensile strength in a CO 2 laser induced incision was less up to the twentieth day after injury; by the fortieth day, however, it equaled that of the scalpel produced incision. Norris and Mullarry (1982)19 studied the healing properties of laser induced incisions on hogs and concluded that scalpel induced incisions exhibited better wound healing characteristics histologically up to the thirtieth day, after which time, both incisions exhibited similar result. Study compared the rate of tissue repair after CO2 laser and scalpel incisions on hogs. In this study the tensile strength of the laser incisions was less then similar scalpel incisions during the first 3 weeks after surgery; after that time, rapid increase in the tensile strength of both wounds occurred at similar rates.

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SAFETY CONSIDERATIONSEducation: The laser is a precise but potentially dangerous surgical instrument that must be used with caution. Although certain distinct advantages are associated with the use of this relatively new technology, these advantages must be weighed against the possible risks of complications associated with laser surgery. Because of these risks, the surgeon must first determine if the use of the laser affords an advantage over conventional surgical techniques. For the surgeon to exercise this required good judgment in the selection and use of lasers in his practice, prior experience in laser surgery is necessary. Therefore exposure to some type of formal laser education program has to be a prerequisite to the use of this technology.

The surgeon who has not received training in laser surgery as a resident should attend one of the many excellent hands-on training courses in laser surgery given in this country. Such a course should include laser biophysics, tissue interactions, safety precautions, and supervised hands-on training with laboratory animals. Following completion of such a course, the surgeon should practice laser surgery on cadaver or animal specimens before progressing to the more simple procedures on patients. Each hospital performing laser surgery should appoint a laser safety officer and set up a laser safety committee consisting of the laser safety officer, two or three physicians using the laser, on or two nursing representatives from the operating room, a hospital administrator, and a biomedical engineer. The purpose of his committee is to develop policies and procedures for the safe use of lasers within the hospital. As such, the safety protocols that will be established by this committee will vary with each specialty and use of the laser. In addition, the laser safety committee should make recommendations regarding the appropriate credential-certifying mechanisms required for physicians and nurses to become involved with each laser. Educational policies for surgeons, anesthesiologists, and nurses working with laser should be developed. Other responsibilities of this important committee include the accumulation of laser patient data in cases where an investigational device was used and a periodic review of all laser complications. Finally, the operating room staff must receive some education with regard to laser surgery. Attendance at an in-service workshop with exposure to clinical laser biophysics and the basic workings of the laser as well as hands-on orientation should be the minimal requirement for nursing participation in laser surgery cases (Spilman. 1983)19.Safety protocol: Development of an effective laser safety protocol that stresses compliance and meticulous attention to detail by the surgeon, and operating room nurse (laser surgery team) is probably the single most important reason this potentially dangerous surgical instrument can be used so safely in treating patients.

Such a laser safety protocol is usually general enough to list all the major and most minor precautions necessary when laser surgery is being performed. General considerations concern the provision for protection of the eyes and skin of patients and operating room personnel, as well as the provision for adequate laser plume (smoke) evacuation from the operative field.

11 Eye protection: Depending on the wavelength, corneal or retinal burns, or both, are possible from acute exposure to the laser beam. The possibility for corneal or lenticular opacities (cataracts) or retinal injury exists following chronic exposure to excessive levels of laser radiation. Several different structures of the eye are at risk; the area of injury usually depends on which structure absorbs the most radiant energy per volume of the tissue. Retinal effects occur when the laser emission wavelength occurs in the visible and near-infrared range of the electromagnetic spectrum (0.4 to 1.4 µm). When viewed either directly or secondary to reflection from a specular (mirror-like) instrument surface, laser radiation within this wavelength range would be focused to an extremely small spot on the retina, causing serious injury. This occurs because of the focusing effects of the cornea and the lens. Laser radiation in the ultraviolet (less than 0.4 micrometers) or in infrared range of the spectrum (greater than 1.4 micrometers) produce effects primarily at the cornea, although certain wavelengths also may reach the lens (“American National Studies 1981). To reduce the risk of ocular damage during cases involving the laser, certain precautions should be followed. Protection of the eyes of the patient, surgeon and other operating room personnel must be addressed .The actual protective devise will vary according to the wavelength of the laser used. A sign should be placed outside the operating door warning all persons entering the room to wear the protective glasses because the laser is in use. In addition, extra glasses for the specific wavelength in use at the time should be placed on a table immediately outside the room. The doors to the operating room should remain closed during laser surgery with the CO2 laser and locked when working with Nd:YAG or argon laser. all operating room personnel should wear protective glasses with side protectors. When working with operating microscope and the CO2 laser, the surgeon need not wear protective glasses; here the optics of the microscope provides necessary protection (Ossiff et al.1983a). When working with the Nd: YAG laser, all operating room personnel must wear wavelength specific protective glasses that are usually of a blue-green colour. The patient’s eyes should also be protected with a pair of these glasses. Though it may appear that the beam direction and point of impact are confined, inadvertent dereflection of the beam may occur because of a faulty contact, or a break in the fiber. Special wavelength –specific filters are available, when those filters are in place, the surgeon need not wear protective glasses.When working with the argon, KTP, or dye lasers, all personnel in the operating room, including the patient, should again wear wavelength –specific protective glasses, which are usually of an amber colour. When performing photocoagulation procedures for the selected cutaneous vascular lesions of the face, protective metal eye shields rather than protective glasses are usually used on the patient. Similar precautions are necessary for newer visible and near infrared wavelength lasers. The major difference is the type of eye protection that is worn.

Skin protection: A double layer of saline saturated surgical towels, surgical sponges, or lap pads should protect all exposed skin and mucous membranes of the patient outside the surgical field. Great care must be exercised to keep the wet draping from drying out, it should be moistened from time to time during procedure. Teeth in the operating field also need to be protected. Saline saturated telfa, surgical sponges, or specially constructed metal dental impression trays can be used. Meticulous attention is paid to the protective draping procedures at the beginning of the surgery; the same compulsion should be displayed for the continued protection of the skin and teeth during the surgical procedure.

12 Smoke evacuation: Two separate suction setups should be available for all laser cases.

One provides for adequate smoke and steam evacuation from the operating field, while the second is connected to the surgical suction tip for the aspiration of blood and mucus from the operating field. When performing laser surgery with closed anesthetic system, constant suctioning should be used to remove laser-induced smoke from the operating room. This helps to prevent inhalation by the patient, surgeon, or operating room personnel. A recent report has suggested that the smoke created by the interaction of the CO2 laser with tissue is probably mutagenic (Tomita et al. 1981) 19. Filters in the suction lines should be used to prevent clogging by the black carbonaceous smoke debris created by the laser. Instrument selection: The surface characteristics of instruments used in laser surgery should provide for low specular or direct reflectance and large diffuse or scattered reflectance of the laser beam, should the beam inadvertently strike the instrument. Plastic instruments should be avoided since they can melt with the laser irradiation. Use of instruments with these characteristics will contribute to minimizing tissue injury from direct or reflected laser beam irradiation.

Anesthetic Considerations: Optimal anesthetic management of the patient undergoing laser surgery must include attention to the safety of the patient, the requirements of the surgeon, and the hazards of the equipment. Effectiveness of a safety protocol: Strong and Jako (1972)19 and later Snow et al (1976)19 warned of the possible complications associated with laser surgery (like tissue damage) from reflection of the laser beam.

Following these early warnings, several reports of complications uniquely attributable to use of CO2 laser appeared in the literature. In a survey of laser-related complications reported by Fried (1984)19 49 of the 152 surgeons who used the laser reported 81 compications. Paper published by Ossoff on laser related compications concluded that: first certain precautions are necessary when performing laser surgery, second, adherence to a rigid safety protocol allows laser surgery to be performed safely and with an extremely small risk of serious complications.

LASERS IN ENDODONTICS Since the development of the ruby laser by Maiman in 1960 and the application of the laser for endodontics by Weichman in 1971, a variety of papers on potential applications for lasers in endodontics have been published. Laser applications in endodontics, include their use in pulp diagnosis, dentinal hypersensitivity, pulp capping and pulpotomy, sterilization of root canals, root canal shaping and obturation, apicectomy, and the effects of laser on root canal walls and periodontal. The essential question is whether a laser can provide equal or improved treatment over conventional care? Secondary issues include treatment duration and cost/benefit ratio.

13 Detection Of Pulp Vitality by Laser: Use of Laser Doppler Flowmetry: HeNe and GaA1As semiconductor diode lasers at a low power of 1 or 2 Mw are used in laser Doppler flowmetry. The wavelength of the HeNe laser is 632.8 nm and that of the semiconductor diode laser, 780 to 820 nm. To prevent laser beams from reflecting off of the surrounding gingival, the measurement of the laser beams reflected from the dental pulp should be carried out under the rubber dam. The principle in the diagnosis of pulp vitality by laser Doppler flowmetry is based on the changes in red blood cell flux in the pulp tissue. It is difficult to obtain the laser reflection from some teeth. The anterior teeth, in which the enamel and dentin are thin, generally do not present a problem. In the molar teeth, the enamel and dentin are thick however. The advantage of this diagnostic method is that it allows painless diagnosis. The laser Doppler flowmetry method is useful in detection of pulp vitality of immature or traumatized teeth and for patients who are sensitive to tooth pain. Odor, T.M., Pitt_Ford, T.R., McDonald, F. (1996)84 investigated the effect of wavelength and bandwidth on laser Doppler flow meter signals from vital and root-filled teeth, and to establish their sensitivity and specificity. There was a highly significant difference between readings from vital and root-filled teeth for the 3.1-kHz/810 nm wavelength combination (p<0.003) and a significant difference for the 3.1-kHz/633 nm wavelength group (p<0.02). The 810 nm wavelength showed good sensitivity but poor specificity at 14.9 and 22.1 kHz bandwidths. The 633 nm wavelength showed good specificity, but poor sensitivity, at 14.9 and 22.1 kHz bandwidths. The 3.1 kHz bandwidth showed the best sensitivity and specificity for both wavelengths. The 810-nm/3.1 kHz combinations offered the greatest sensitivity and specificity as a test to distinguish between root-filled and vital teeth. This combination was best.

Application Of Transmitted Laser Light For The Assessment Of Human Pulpal Vitality: The purpose of a study by Sasano, T., Nakajima, I., et al (1997) 94 was to determine whether use of transmitted laser light would enable a better assessment of human pulpal vitality than back-scattered light does (LDF: laser Doppler flowmetry).

The experiments were carried out on ten upper central incisors in six subjects aged 2328 years; five of the teeth were vital with no restoration, and five were non-vital. For use with transmitted laser light, the fibers within the probe of a conventional LDF apparatus were used, one for transmitting light onto the buccal surface, the other for receiving it at the palatal surface of the same tooth. For LDF, the probe was fixed at the buccal surface. Blood flow was measured at three different locations on each experimental tooth: the incisal third, the center and the cervical third of the tooth crown. The results indicated that transmitted laser light would be useful for the assessment of tooth pulp vitality both because the blood flow signals did not include flow of non-pulpal origin, and because its output signals and response to blood flow changes were clear and could easily be monitored. The pulpal blood flow rate, pulpal responsiveness, systemic blood pressure, and pulse rate during Nd: YAG laser irradiation of an isolated tooth in vivo was evaluated by Kobayashi, K., Sato, Y., Osada, R., et al 200053. For all subjects involved in this study, the pulpal blood flow rate increased during laser irradiation. Threshold values of the electric pulp tests increased in six cases and decreased in six cases. One case showed no change. After 1 month, the threshold values for each subject had returned to previously recorded values.

Neither systemic blood pressure nor pulse rate was affected during Nd: YAG laser irradiation. Pulpal blood flow was strongly influenced immediately after Nd: YAG laser irradiation, seen as an increase in the flow rate. The results of this study suggest that effects of the Nd: YAG laser irradiations are similar to those of low power laser for

14 the improvement of local blood flow. Chaiyavej, S., Yamamoto, H. et al (2000)15 investigated the response of intradental A- and C-fibers during tooth cutting by Er: YAG laser. They concluded that during the tooth cutting, Er: YAG laser was more effective in activating intradental A-fibers compared with micro motor and also caused the activation of intradental C-fibers. The effect of irradiation with a galliumaluminum-arsenide semiconductor laser on responses evoked in trigeminal subnucleus caudal neurons by tooth pulp stimulation was investigated electrophysiologically in Wistar rats anesthetized with urethane plus alpha-chloralose by Wakabayashi, H., Hamba, M. et al (1993)116. The study indicated that low power laser irradiation (semiconductor laser: 830 nm, 350 mW, CW, through the tooth structures, for 120 s) inhibited the excitation of unmyelinated fibers of the pulp without affecting fine myelinated fibers. Hence the results suggest that low power laser irradiation has a suppressive effect on injured tissue by blocking the depolarization of C-fiber afferents.

Heat Stimulation by Laser Instead of Hot Gutta-Percha The hot gutta-percha method is commonly applied for the differential diagnosis of vital versus non-vital dental pulp.

This method has a disadvantage in that pain response cannot always be obtained because of the thick enamel and dentin or the high pain perception threshold of the dental pulp. The laser stimulation method by pulsed Nd: YAG laser was reported to be mild and tolerable compared with the pain induced by the conventional electric pulp tester. In addition to the pulsed Nd: YAG laser, other lasers may be used to diagnose the difference between vital and non-vital dental pulp in the future. Intra-canal lasersoftened gutta-percha, Ultrafil, and intra-canal laser-cured composite resin techniques were compared with respect to the temperature elevation induced on the outer root surface in a study by Aniâ&#x20AC;Ą, I., Matsumoto, K. (1995)3. The temperature at the root surface of 50 single-rooted teeth was measured using a thermovision camera. Argon laser produced a rise in temperature of +12.9 degrees C (gutta-percha) and +13.3 degrees C (composite resin), respectively. The CO2 laser produced +10.3 degrees C and Nd: YAG laser produced the highest temperature elevation of +14.4 degrees C. Lowtemperature gutta-percha obturation technique did not produce a measurable temperature change on the external root surfaces. Aniâ&#x20AC;Ą, I., Matsumoto, K.(1995)2, compared the effectiveness of four different techniques used for obturation of single rooted-teeth: lateral condensation, low-temperature gutta-percha (Ultrafil), vertical condensation of gutta-percha softened by means of three different laser devices (argon, CO2, and Nd:YAG), or composite resin photo-polymerized by argon laser. The most extensive dye penetration (4.3 mm) was observed in teeth obturated with composite resin, followed by gutta-perch laser with CO 2 (2.15 mm), and the Nd: YAG laser (3.54 mm). Gutta-percha softened with argon laser created an apical seal almost identical to that obtained with the lateral condensation and Ultrafil techniques (1.50, 1.45, and 1.48 mm of leakage, respectively). These results indicate that the argon laser can be used for gutta-percha softening to produce good apical sealing results.

Differential Diagnosis Of Pulpitis By Laser Stimulation Normal Pulp and Acute Pulpitis: When normal pulp is stimulated by the pulsed Nd: YAG laser at 2 W and 20 pulses per second (pps) at a distance of approximately 10 mm from the tooth surface, pain is produced within 20 to 30 seconds and disappears a couple of seconds after the laser stimulation is stopped. In the case of acute pulpitis, the pain is induced immediately after laser application and continues for more than 30 seconds after stopping the laser the laser stimulation.

15 Acute Serous Pulpitis and Acute Suppurative Pulpitis: Differential diagnosis of acute serous pulpitis and acute suppurative pulpitis can be obtained by combining the measurement of electric current resistance of caries and the pain duration induced by laser stimulation. If the electric current resistance is greater than 15.0 mΩ and the patient experiences continuous pain for more than 30 seconds, the diagnosis is acute serous pulpitis. When the value of the resistance is less than 15.0 mΩ and there is continuous pain for more than 30 seconds, the diagnosis is acute suppurative pulpitis.

Carious impedance of less than 15.0 mΩ indicates that no hard healthy dentin exists between the caries and the pulp chamber.

Effect Of Different Types Of Lasers On The Pulp-Dentin Complex GaA1As Semiconductor Diode Laser: Previous studies on semiconductor diode laser irradiation of dental pulp have reported no dental pulp damage. High-power semiconductor lasers of 3 to 30 W have been developed; however, and soon will be applied to dental pulp treatment. To confirm the effect of dental pulp of high-power semiconductor diode lasers, histopathologic examination must be performed. An in vitro thermometric study was conducted by Arrastia, A.M., Machida, T., et al 1994 9, on various GaAlAs semiconductor lasers emitting at wavelengths between 750 nm and 905 nm, to verify whether these lasers produced significant heating during application to tooth structure. Measurements were conducted in vitro, using a thermal camera and a thermocouple during a 60, 120, and 180 s laser exposure at energy densities between 1.5 and 2,400 J/cm2. Intrapulpal temperature elevations measured > or = 3 degrees C. An in vivo study was also conducted to determine whether perceptible stimuli are experienced by patients during this time of laser treatment and to verify results of the in vitro study. The results did not conform well with the in vitro study because of uncontrollable variables. None of the patients who received irradiation treatment described any perceptible stimuli.

HeNe Lasers: The commercial HeNe lasers of more than 15 Nw have not been used for dentistry. There is no possibility of dental pulp tissue damage by this laser.

Nd: YAG Laser: Because the Nd: YAG laser has a wide energy emission range, the clinician should take into careful consideration such parameters as the exposure time, power, whether the laser emission is continuous or pulsed, the type of laser tip, and the distance between the laser tip and the surface to be irradiated. The characteristics of the individual target teeth must be considered at the time of laser therapy. For example, if the tooth surface is enamel or dentin, the thickness between the carious surface and the pulp chamber, and the color of the target area all must be taken into consideration.

Dental pulp tissue irradiated at 3 W and 20 pps for 0.5 second, at 2 W and 20 pps for 1 second, and at 1W and 20 pps for 2 seconds by the pulsed Nd: YAG laser (ADL 300, ADL Inc., Chicago, IL) showed no adverse effects. When black India ink was applied to the tooth surface and laser irradiation was conducted at 2 W and 20 pps for 1 second, the temperature rise of the pulp chamber was less than 3˚C and completely disappeared after 5 seconds. Laser anesthesia of dental pulp, sedative treatment of temporomandibular arthrosis, and laser acupuncture therapy as well as treatment of the reduction of hypersensitive dentin can be performed without producing dental pulp damage or severe pain without tissue burn. A study to assess whether "scan irradiation" with a pulsed Nd: YAG laser could produce changes in intrapulpal nerve activities and pulpal blood flow and to investigate whether it would cause tissue damage in the pulp

16 was done by Sunakawa, M., Tokita, Y., Suda, H. (2000)104 in cats. They concluded that "Scan irradiation" with the pulsed Nd: YAG laser of cat's teeth produced alterations in the intrapulpal nerve activities, as well as caused tissue damage in the pulp. The authors also did a study to evaluate physiologically pulpal nerve responses and to elucidate histopathologically the pulp tissue reactions to "spot irradiation" with a pulsed Nd: YAG laser and concluded that spot irradiation with a pulsed Nd: YAG laser risks producing nerve injury and irreversible tissue damage in the pulp with lasing for the purpose of desensitizing hypersensitive dentin.

CO2 Laser: The CO2 laser, similar to the Nd: YAG laser can emit at high energy. The dental pulp tissue is affected by parameters such as waveform, power, and time of laser exposure. The wavelength of the CO2 laser is easily absorbed in water. However, there is little carbonization or heat penetration on the surface of substances that contain water. If the substance contains no water, carbonization and crack formation occur easily on the surface of the substance. The CO 2 laser also is used for ablating dental pulp tissue and soft dentin. When ablating carious enamel and dentin, pain and pulp damage may occur depending on the laser power, the exposure time, and the wetness of the surface. Generally the CO2 gas laser should be used at less than 1 W for less than 1 second under anesthesia and under air-cooling. If the tooth is treated under these conditions, dental pulp damage and postoperative pain may be avoided. The thermal effects of continuous wave carbon dioxide laser irradiation on human teeth were investigated (Miserendino, L.J., Neiburger, E.J., et al 1989)74 and it suggests a direct relationship between the independent variable, exposure energy (joules), and the dependent variable, internal temperature. The effect of CO 2 laser irradiation on pulpal microcirculation was studied in cat canines. The enamel surfaces of 4 teeth were exposed with energy densities of 304-1440J/cm2, using either a handpiece or a micros lad, with a focal spot of 0.21mm and 0.33mm respectively. Pulpal blood flow (PBF) before and following lasing was recorded through the intact tooth surface by a laser Doppler flow meter. CO2 laser irradiation caused an increase in PBF, which was immediate and transient. The PBF increase was higher in a large pulp than in a small pulp, and it was inversely related to the focal spot size. These findings confirm that the dental pulp is thermally affected by CO2 lasing of the tooth surface, however, without extensive pulp coagulation. It is concluded that the effects of laser irradiation on the pulpal microcirculation may be studied in situ by means of the presented methodology.

Er: YAG Laser: The 2.940 Îźm wavelength of the Er: YAG laser makes it possible to ablate hard and soft tissue under water spray. Previous investigations have reported no pulp damage if the cavity preparation is carried out under copious water spray. It is necessary, however, to spray water mist just under the hard tissue surface that is to be ablated by laser. Sonntag, K.D., Klitzman, B., et al 199696 evaluated the pulp response to class V cavity preparation with the use of the Er: YAG laser and free electron laser and concluded that the pulp response to Er: YAG laser and free electron laser application appeared to be similar to the response from speed handpiece application.

Takamori, K.(2000)106 investigated the histopathological changes in the dental pulp after Er:YAG laser irradiation compared with those after high-speed drill preparation.

The Er: YAG lasers group a marked fibroblast proliferation and the formation of reparative dentin was observed relative to the high-speed drill group. In the Er: YAG laser group an increase in calcitonin gene-related peptide-immunoreactive fibers was seen earlier than in the high-speed drill group, and 7 days after operation these fibers decreased to control level. The results suggested that the Er: YAG laser leads to pulpal

17 repair earlier than the high-speed drill. Studies to evaluate the pulpal response to the Er: YAG laser after accidental exposure of the pulp was done by Jayawardena, J.A., Kato, J., Moriya, K., Takagi, Y.200143. The Er: YAG laser group showed no bleeding and no dentin chips at the exposure site immediately after pulp exposure. However, they displayed an area of blood extravasation near the exposure site. Subsequently, the Er: YAG laser group formed dentin bridges at the exposure site more frequently than the control group (slow speed conventional hand-piece). The Er: YAG laser group demonstrated more reparative dentin formation near the exposure site than the control group, especially at 2 weeks, which was highly significant. According to the results of this study, Er: YAG laser-exposed pulp tissue demonstrated good healing capacity with the formation of a dentin bridge and reparative dentin. However, further investigations are suggested to study the effect of the blood extravasation, which appeared near the laser exposure sites. Er, Cr: YSGG Laser: The Er, Cr: YSGG laser also can be used to ablate hard and soft tissues because the wavelength is 2780 Îźm, which is similar to that of the Er: YAG laser. It has been reported that dental pulp damage can be prevented if cavity preparation under sufficient water spray. Too much water decreases the ablation ability of this laser, however. Laser systems are known to raise pulpal temperatures when applied to tooth surfaces. Dental biocalcified tissues can be cut with an erbium, chromium: yttrium-scandium-gallium-garnet-laser-powered hydrokinetic system. This device is effective for caries removal and cavity preparation in vitro. Pulpal monitoring of temperature changes during hard tissue cutting by a hydrokinetic system has not been reported. Therefore a study compared the effects of hydrokinetic system, dry bur, and wet bur tooth cutting on pulpal temperature (Rizoiu, I., Kohanghadosh, F., et al 1998)91. Pulpal temperatures associated with the hydrokinetic system either showed no change or decreased by up to 2 degrees C. Wet bur preparations resulted in a 3 degrees to 4 degrees C rise. With dry bur preparations, a 14 degrees C rise in temperature was recorded. Hence the erbium, chromium: yttrium-scandium-gallium-garnet laserpowered hydrokinetic system, when used for cavity preparation, had no apparent adverse thermal effect as measured in the pulp space.

Argon Laser: The argon laser can be used to cure composite resin quickly. This laser also can be used to ablate soft tissue. Dental pulp damage may be avoided if laser irradiation is performed for a short time at 1 W, while maintaining the laser tip at a distance of approximately 10 cm from the tooth surface.

Ho: YAG: In a study by Goodis, H.E., White, J.M. et al (1997)30 dentine specimens were prepared from freshly extracted third molars and initial permeability was measured. Each specimen was subjected to Nd: yttrium-aluminium-garnet (YAG) (1.06 or 1.32 microns wavelength) or Ho: YAG (2.10 microns wavelength) laser energy while temperatures in the pulp chambers were recorded. The results showed that all wavelengths reduced permeability but temperature rises were high enough to have caused pulpal damage, indicating that shorter treatment times and lower power settings may be necessary if used in vivo.

De-Sensitization of Hypersensisitive Dentin and Teeth by Laser Stimulation. Since the development of the ruby laser by Maiman in 1960, a variety of papers on potential applications for lasers in dentistry have been published. To date, 4 kinds of lasers have been used for the treatment of dentine hypersensitivity, and the effectiveness ranged from 5.2 to 100%, which was dependent on the laser type and parameters used. The mechanism involved in laser treatment of dentine hypersensitivity is relatively

18 unknown. Kimura, Y., Wilder_Smith, P et al (2000) 48 in their review on “Treatment of dentine hypersensitivity by lasers’’ suggest that in general, the efficiency for the treatment of dentine hypersensitivity using lasers is higher than other methods, but in severe cases, it is less effective. Therefore it is necessary to consider the severity of dentine hypersensitivity before laser use. Indication: Conditions such as cervical dentin hypersensitivity caused by tooth abrasion, dentin hypersensitivity after vital tooth cavity and crown preparation, and hypersensitivity of acute partial closed pulpitis are indicators of desensitization of hypersensitive dentin by laser stimulation.

Laser Devices, Techniques, Assessments, and Mechanisms: Semiconductor Diode Laser: Carious 30 Mw GaA1As semiconductor laser devices have been commercially developed for desensitization treatment. After drying the hypersensitive dentin as much as possible, the laser tip is placed in direct contact with the tooth surface, which is then irradiated for a period of 30 seconds to 3 minutes. If the desired effect cannot be obtained, the treatment is carried out once more after a couple of days. According to the author’s clinical assessment after a postoperative period of 4 months, 73% of cases of slight cervical dentin hypersentivity. A shorter exposure time and higher effectiveness are expected for the 3-W and 20-W semiconductor lasers. The mechanism of pain reduction by the laser stimulation is thought to be clarified by electro physiologic and laser transmission studies. These studies indicate local changes around the dentin and the nerve endings as well as changes in the central pulpal neuron.yamaguchi, M., Ito, M. et al (1990)124 conducted a study to evaluate the results of treating hypersensitive dentin with a GaAlAs semiconductor laser diode using the double blind test. A continuous wavelength of 790 nm and laser strength of 30 mW was used and the results obtained indicated that laser irradiation might possibly be effective in decreasing pain when treating hypersensitive dentin.

HeNe Laser: A treatment method similar to that of semiconductor diode laser is used with 6-Mw and 15-Mw HeNe lasers. The clinical assessment and mechanism are thought to be identical to those of the semiconductor diode laser.

Pulsed Nd: YAG Laser: Previous scanning electron microscopic studies showed that Nd: YAG laser could cause melting of dentin and closure of exposed dentinal tubules without dentin surface cracking. Therefore, in a study Liu, H.C., Lin, C.P., Lan, W.H. (1997)66 evaluated the sealing depth of Nd: YAG laser on human dentinal tubules. Nd: YAG laser at energy of 30 mJ with 10 pulses/s for a stroke along the dentin surface was used. Lased specimens showed melting of dentin and closure of exposed dentinal tubule orifices. The sealing depth of Nd: YAG laser on human dentinal tubules was approximately 4 microns. There have been no reports on the irradiated area(s) except the cervical region for dentin hypersensitivity treatment using pulsed Nd: YAG laser.Therefore Yonaga, K., Kimura, Y., Matsumoto, K. (1999)127 evaluated the results of two irradiated regions, the cervical and apical, for cervical dentin hypersensitivity treatment using pulsed a Nd:YAG laser with or without black ink. Results showed that the methods of irradiation at the cervical regions were better than those at the apical regions except for the period 2 months later. The laser effect was enhanced by black ink at both areas. SEM observation at the tooth surfaces showed that dentinal tubules were occluded or narrowed after laser irradiation. These results show that the method of irradiation by a pulsed Nd: YAG laser at cervical regions with black ink is the most effective for cervical dentin treatment of hypersensitivity and recurrence by this method is less than in other methods. Lan, W.H., Liu, H.C., Lin, C.P. (1999) 56 evaluated the

19 combined occluding effect of sodium fluoride varnish and Nd:YAG laser irradiation on human dentinal tubules. Under SEM observation, the control group (specimens not varnished with sodium fluoride) showed numerous exposed dentinal tubule orifices, and the sodium fluoride varnished specimens showed closure of exposed dentinal tubule orifices. After electrical tooth brushing, most of the sodium fluoride varnish was brushed away, except in the specimens that were irradiated by Nd: YAG laser. Over 90% of the dentinal tubule orifices were occluded by sodium fluoride varnish combined with Nd: YAG laser irradiation.

Stimulation Method for toothache Acupuncture Points: Laser stimulation is performed at the points of the same side as that of the tooth pain and 20 pps for 1 to 2 minutes at about 10 cm from the acupuncture point. The Goukoku and the ear lobe are usually used as acupuncture points. The laser exposure time can be shortened by coating the acupuncture point with black ink; using this technique, the exposure time is only 10 seconds. With respect to clinical assessment, incases of slight or mild pain, the percentage of pain reduction is 90% to 100%. In cases of severe pain, the percentage of pain reduction is less than 60%, however. The mechanism of pain reduction is thought to be the same as that for the semiconductor laser.

Stimulation Method for Foramina Mentale, Mandibulae, and Infraorabitale: The laser parameters are the same as those used for laser stimulation of tooth acupuncture points. According to the authorâ&#x20AC;&#x2122;s clinical experience, foramina related to the trigeminal nerve are effective as laser stimulation points. Laser stimulation of the foramen infraorbitales must be carried out while wearing eye protection.

Stimulation Method for the Mucosal Corresponding to the Root Apex: The parameters are identical to those of the other indications for use for the pulsed Nd: YAG laser. This stimulation method is more effective than the two aforementioned techniques. Almost all cases in which the degree of dentin hypersentivity is not too severe can be improved by this method. It is important to perform this laser stimulation for a short duration at a distance of 2 to 3 mm from the mucosal surface that has been painted with black ink and dried. This treatment takes only about 10 seconds.

Stimulation Method for the Crown Portion: The above-described parameters are applicable for this stimulation technique, but to avoid pain and dental pulp damage, only the tooth surface that is not painful should be exposed to the laser by a quick pass.

The laser exposure time must be kept to within 0.5 second per exposure. Generally the laser exposure is performed two or three times until the dentin hypersentivity has disappeared completely. This method is the best laser stimulation method by which to treat dentin hypersentivity because the patientâ&#x20AC;&#x2122;s experiences almost no pain, and only a short exposure time are required for the method to be effective.

Stimulation Method for the Surface of Dentin Hypersensitivity: The laser parameter must be changed according to the degree of pain induced by air blast or tactile examination using an explorer. Laser parameters of 1 W and 20 pps for less than 0.1 second with black ink are recommended for this treatment. This method should be applied only after sufficient training and only after all other laser treatment have been tried. Assessment by this method shows the most effective results because of the morphologic change produced in the dentin and the stimulation of the central pulpal neurons.

20 CO2 Laser: Stimulation Method on Acupuncture Points of toothache: Although pain reduction of dentin hypersensitivity can be achieved by CO2 laser stimulation, the effectiveness of this technique is less than that of the pulsed Nd: YAG laser, and the laser exposure technique is difficult to perform without inducing pain. Usually the laser is used at 0.5 to 1W, and the end of the laser tip is moved quickly, maintaining a distance of 10 cm from the tooth surface for a couple of minutes, until the pain induced by an air blast disappears completely. Goukoku, lobe, and the area related to the trigeminal nerve are used as the acupuncture points.

Stimulation Method for the Mucosal Surface Corresponding to the Root Apex: Pain reduction by CO2 laser can be performed by this method, but the effectiveness is less than that of the pulsed Nd: YAG laser. Pain is easily induced, even if the laser tip is moved quickly in circles on the mucosal surface at a power of 0.5 W. It is recommended that this method be performed under air spray cooling.

Stimulation Method On The Tooth Crown Surface: CO2 laser exposure must not be done on the dried tooth crown surface because not only pain, but also carbonization in induced. Sodium fluoride paste or petroleum jelly is coated on the tooth surface, then the tooth surface is exposed to the CO 2 laser to prevent the occurrence of pain and the carbonization on the tooth surface by the laser. Output powers used for the treatment ranged from 0.5 to 3 W, and a success rate of greater than 90% was reported.

Stimulation Method for the Surface of Dentin Hypersensitivity: Although this method is not recommended, it is not so difficult to perform if the laser exposure is done at 0.5W under air-cooling after painting sodium fluoride paste on the surface of dentin hypersentivity. A caries prevention effect is derived by laser irradiation with sodium fluoride paste on the exposed dentin surface. This method offers the highest effectiveness with pain reduction of dentin hypersensitivity of the three abovementioned CO2 laser methods.The effectiveness of CO2 laser therapy in the reduction and elimination of dentinal hypersensitivity in vivo and its thermal effects on tooth surfaces in vitro were investigated by Zhang, C., Matsumoto, K., et al (1998) 131. The parameters used with CO2 laser were 1 W in a continuous wave mode and irradiation time ranging from 5 to 10 s. Hypersensitivity was assessed by thermal stimulus (a blast of air from a dental syringe). Thermal effects were measured by thermography using 10 extracted human teeth. After laser treatment, all patients were immediately free from sensitive pain. Over 3 months, the CO2 laser treatment reduced dentinal hypersensitivity to air stimulus by 50%. All teeth remained vital with no adverse effects. Thermography revealed no temperature increase on irradiated tooth surfaces subjected to water coolant. These results show that the CO2 laser is useful in the treatment of cervical dentinal hypersensitivity without thermal damage to pulp.

Soft Lasers:The use of soft lasers in dental therapy has increased dramatically in recent years. However, there is a dearth of reports in the literature of controlled in vivo and in vitro studies of soft laser effectiveness with respect to dentinal pain.Hoji,T (1990)37 assessed the analgesic effects of soft laser treatment by the following five studies: (1) Clinical evaluation of soft laser irradiation of hypersensitive dentin. (2) Morphological study of dentinal surfaces following soft laser irradiation. (3) Study of the effect of soft laser irradiation on dentinal fluid movement. (4) Study of the effect of soft laser irradiation on the jaw-opening reflex (JOR) in rats. 5) Study of thermal changes on the internal wall of pulp chamber with soft laser irradiation. After soft laser treatment of 3

21 min to hypersensitive dentin, 86% of the patients experienced diminished sensitivity.

In model experiment with extracted human teeth, the energy levels of this laser were too low to produce any morphological changes on the surface of exposed dentin, and dentinal fluid movements induced by air blasts for 15 sec to exposed dentin were not affected by laser irradiation to the dentin for 3 min. Moreover, there was an immediate 0.7 degree C increase in the temperature of the internal wall of the pulp chamber by laser irradiation to the tooth surface. These results suggest that soft lasers have an analgesic effect, but the latter is affected by the degree of stimuli-elicited pain, and may be due in addition to descending inhibition in the central nervous system.

XeCL Excimer Laser: A study by scanning electron microscope of the effects of XeCl excimer laser on exposed dentinal tubules of human extracted teeth was done by Stabholz, A., Neev, J. et al (1993) 97. The samples were lased for 4 s by XeCl excimer laser with fluences ranging from 0.5 to 7.0 J/cm2 and pulse repetition of 25 Hz. All specimens lased at fluences of up to 1 J/cm2 showed the presence of melted dentin which closed the dentinal tubules. At fluences of 4 J/cm2 and higher, rupture of molten materials and exposure of dentinal tubules were noted. The results indicate the application of XeCl excimer laser at specific fluences can cause melting of dentin and closure of exposed dentinal tubules.

Accessory Treatment By Laser For Indirect Pulp Capping As lasers were introduced to dentistry, nobody thought that the treatment of indirect pulp capping could b performed by laser. The discovery of closure of dentinal tubules by laser energy and the sedative effects on pulpitis has led to the development of several new treatments that are soon to be put into practice. Deep cavities, and cavities that require sedative treatment are some of the indications for this treatment. When using the pulsed Nd: YAG laser, it is necessary to combine the application of black ink o the tooth surface and air spray cooling to prevent dental pulp damage resulting from the laser energy provided by 2 W and 20 pps for less than 1 second on the area. A few articles have examined this clinical treatment. According to the authorâ&#x20AC;&#x2122;s experience, clinical cases treated using this method produced no postoperative pain. The mechanism of this treatment has been proved by various studies that described the degree of dye penetration as having decreased after laser irradiation of the dentin surface. The mechanism of sedation by the laser is thought to be identical to that of dentin hypersensitivity by the laser. When using the CO 2 laser, the dental tissue must not be irritated by exposure to high-energy lasers for long periods of time. In some cases, it is recommended that this laser be used with 38% silver ammonium solution. These treatments should be performed under local anesthesia. Clinical data soon will be summarized, and the clinical results will be published. The mechanism of sedation of dental pulp by CO2 laser may be the same as that of the pulsed Nd: YAG laser.

Treatment By Laser For Direct Pulp Capping Because laser treatment had advantages with respect to control of hemorrhage and sterilization, laser use for direct pulp capping has attracted dentistsâ&#x20AC;&#x2122; attention. Various studies have examined this treatment, and some researchers have recommended the laser as a treatment method for direct pulp capping. Textbooks of endodontics report that the indications for direct pulp capping are extremely limited. The diameter of pulp exposure must be 2 mm or less, and there must be no infection in the pulp. Further research on this subject is anticipated. When using the CO2 laser for this treatment, laser irradiation of the exposed dental pulp must be performed to stop bleeding and sterilize the area around the exposure. Laser

22 irradiation should be performed at 1 or 2 W after irrigating alternatively with 8% sodium hypochlorite and 3% hydrogen peroxide for more than 5 minutes. Calcium hydroxide paste must be used to dress the sealed with cement such as carboxyl ate cement. An 89% success rate is reported. The high success rate is thought to be due to control of hemorrhage, disinfection, sterilization, carbonization, and stimulation effects on dental lasers is found to be valid, the indication of this treatment may become more widespread in the future. Studies have examined the application of the pulsed Nd: YAG, argon, semiconductor diode, and Er: YAG for direct pulp capping. Future applications of these lasers are expected. The CO2 laser seems to be a valuable aid in direct pulp capping. In a study conducted by Moritz, A., Schoop, U., et al 1998, direct pulp capping performed with the CO2 laser (with recall examination at 12 months) demonstrated a success rate of 89% (teeth remaining vital) as compared to 68% success rate with those teeth treated with calcium hydroxide.

Laser Ablation And Accessory Treatment For Vital Pulp Amputation Vital pulp amputation by laser therapy was one of the most highly anticipated laser treatments in endodontics because this treatment appeared to offer amputation of the pulp tissue at a satisfactory level. Control of hemorrhage and amputation of pulp tissue without producing pulp damage was not always easy in narrow root canals, however.

Histopathologic experimental research indicates that results of pulp tissue amputation are not always good. For pulp amputation, the laser should be used to stop bleeding and for cell stimulation. In addition to the previously mentioned indications for this laser treatment, vital pulp amputation at the coronal portion or at the middle or apical part of the root may be an indication on the future. The CO 2 laser usually is used at a power of 1 to 4 W. The laser irradiation should be conducted as intermittently as possible to prevent excessive exposure of laser energy. When it is necessary to ablate the pulp tissue into apical portion of the root canal, several laser exposures are required. As a result, the carbonization layer formed on the surface of the pulp tissue by the laser energy must be removed by irrigating alternatively with 3% hydrogen peroxide and 5.25% sodium chloride. Although it is possible to use only the CO 2 laser, this requires significant time, and the pulp tissue may be damaged by the laser energy. A CO 2 laser technique that is carried out only for pulpal hemostasis after vital pulp amputation with an excavator or a bur is recommended. Various problems must be resolved before this laser can be used widely. There are some problems concerning the application of the pulsed Nd: YAG laser for vital pulp amputation. This laser should not be used instead of an excavator and a bur. In the authorâ&#x20AC;&#x2122;s histopathologic experimental research on dogâ&#x20AC;&#x2122;s canine teeth, the success rate was about 50%. Laser heat damage to the pulp tissue was the primary reason for the low success rate. Based on these results, we recommended that the pulsed Nd: YAG laser should be used only for pulpal hemostasis, sedation, anti-inflammatory effects, and stimulation of the remaining pulpal cells. The HeNe and low-power semiconductor diode lasers are alternative lasers for these purposes. The middle-power semiconductor diode lasers are alternative lasers for these purposes. The middle-power semiconductor diode laser is being developed and out into practice for this purpose.

Access Cavity Preparation And Enlargement Of The Root Canal Orifice By Laser Access cavity preparation had been performed by air turbine, and enlargement of the root canal orifice has been carried out using a Peeso (Melfer, Zurich, Switzerland) reamer or a gates Glidden drill or bur. The Er: YAG and Er, Cr: YSGG laser, which ablates enamel and dentin, have been developed and improved. As a result, these layers

23 may soon replace the air turbine, Peeso reamer, and Gates Glidden drill as the primary method of treatment. Vital extirpation of infected root canals is one indication for these layers. In particular, this technique seems applicable for cases in which the Peeso and Gates Glidden instruments cannot be inserted into the tooth because of difficulty of opening the mouth and for cases in which it is difficult to find the root canal orifices. A new type of Er, Cr: YSGC laser has been developed and put into practice. If this laser is applied for cutting enamel and dentin at 5 W and 6 Hz under water spray, access cavity preparation and enlargement of root canal orifices can be performed easily. Detailed examination must be done to prevent perforation into the periodontium and step formation on the root canal wall, however.

Pulpotomy And Root Canal Wall Preparation By Laser A laser that can cut enamel and dentin with fine optical fibers has been developed, making it possible to remove pulp tissue and prepare root canals. A few problems remain to be solved in the near future, however only straight and slightly curved canals are indications for applying this treatment. The author uses an Er: YAG laser at 8 Hz and 2 W produced by KaVo Co. (Ulm, Germany) to prepare root canals. The laser tip must slide gently from the apical portion to the coronal portion, while pressing the laser tip to the root canal wall under water spray. During laser exposure of the apical portion at more than 1.0 mm from the root apex, the debris at the apical foramen must not be pushed into the periapical tissue.

When the laser fiber is unable to be inserted into root canals, the laser treatment should be performed after carrying out the usual root canal preparation using reamers and files.

Various studies have shown the smear layer was removed completely and that the dentinal tubules on the root canal wall opened using this technique, For this purpose, the laser irradiation must be performed after or in combination with the usual root canal prepartion. Nd: YAP laser is a dental laser with a 1340 nm wavelength. The laser beam is carried by a 200 to 300 microns fiberoptic and is suitable for endodontic therapy.

Farge, P., Nahas, P., Bonin, P.(1998)24 used the Nd: YAP laser in an in vitro experiment to study its effectiveness in endodontic re-treatment. The Nd: YAP laser irradiation was used, alone or in combination with hand instruments, to remove various canal sealers and broken instruments. Clinical parameters were monitored and scanning electron microscopic observations were conducted. When used at 200 mJ--with a pulse duration of 150 ms, an exposure time of 1 s and a frequency of 10 Hz--Nd: YAP laser preserved the dentinal walls of the root canal and enabled root canal re-treatment without thermal elevation harming periodontal tissue. It was therefore concluded that, in combination with hand instruments, the Nd: YAP laser is an effective device for root canal preparation in endodontic re-treatment. Arrastia_Jitosho, A.M., Liaw, L.H. et al (1998)10 studied to determine whether a nanosecond-pulsed, frequency-doubled Nd:YAG laser emitting at 532 nm can be used as an alternative to mechanical methods of root canal treatment or as an adjunct to conventional endodontic preparation. Root canals were irradiated for 30 to 60 s at fluences of 2 to 2.2 J/cm2, and 10 Hz. Samples were observed using SEM. Laser irradiation could achieve smear layer removal after minimal manual preparation. However, results were inhomogeneous, and at higher energy densities thermal damage was observed, especially in the fully manually prepared samples. Nanosecond-pulsed irradiation at 532 nm achieved complete smear layer removal. However, the authors suggest that mechanisms must be developed to monitor laser effects and avoid potential damage to collateral structures. To solve the problem of mechanical instrumentation, Shoji, S., Hariu, H., Horiuchi, H. (2000) 95 developed a cone-shaped laser irradiation tip. This tip equipped with a water nozzle delivered 80% of the energy of the laser laterally and 20% of the energy forward. The

24 effect of Er: YAG laser irradiation using this tip on root canal enlargement and debridement was examined. The power of 10 mJ x 10 pps caused enlargement of the canal dimension by 106.5%. 20 and 40 mJ x 10 pps caused enlargements of 116.3 and 118.6%. 30 mJ x 10 pps caused the biggest change (129.8%). Scanning electron microscopic observations indicated that the dentin surface after laser preparation appeared cleaner than that obtained after preparation by drilling. This technique may have the advantage of decreasing the preparation time.

Laser Application For Removing Pulp Remnants And Debris At The Apical Foramen The pulsed Nd: YAG laser was used for removing pulp remnants and debris that are deposited at the apical foramen. A power of 2 W at 20 pps for 1 second is recommended. A 5-second interval should be used if laser irradiation is performed two or three times. A little black ink should be applied to the root canal wall or to the apical foramen. The effects of this laser irradiation on the apical foramen include sterilization, removal of pulp remnants, control of hemorrhage, and stimulation of cells surrounding the root apex as well as debridement of the surface.

Root Canal Sweeping And Irrigation In Combination With Irrigators And Lasers Some laser devices produce cavitation effects in root canals in a manner similar to that of the ultrasonic irrigator. At present, the effect is weaker than that of ultrasonic irrigation. This laser technique is likely to be improved in the future. Straight and slightly curved root canals as well as wide root canals are indications for this treatment.

The pulsed Nd: YAG laser, Er: YAG laser, and Er, Cr: YSGG laser are recommended, but the laser fiber still requires slight improvement. The laser irradiation is not carried out by the laser alone, a solution such as 5.25% sodium chloride or 14% ethylenediaminetetra-acetic acid (EDTA) also must be used. A power of 2 to 5 W usually is used for approximately 2 minutes.

Morphological Changes In The Root Canal After Laser Irradiation The use of a new, modified Nd: YAG laser called the KTP/532 laser was evaluated within root canals to determine whether it would modify dentin permeability or alter the scanning electron microscopic appearance of canal dentin. This study was done by Tewfik, H.M., Pashley, D.H., et al (1993)112. The results showed that this laser did not change the permeability of the smear layer-covered dentin, although scanning electron microscopic examination revealed modifications to the surface of smear layer. Lasing of etched dentin produced modest increases in root permeability which were associated with enlargement and cracking of tubule orifices Thermal and micro structural events resulting from KTP laser use during root canal preparation were investigated (Machida, T., Wilder_Smith, P., et al, (1995)68 in 30 extracted single-rooted human teeth.

Thermal events occurring on the root surfaces of 18 teeth during and after exposure of the root canal were measured using thermography. Root canals of 12 teeth exposed to KTP laser irradiation were evaluated using Scanning electron microscopy. KTP laser application at a power setting of 3 W, an exposure time of 2 s, and a frequency of 5 Hz, applied five times, removed smear layer and debris from the root canal surface at temperatures below the thermal injury threshold for periodontal tissue. The effects of the Luxar LX-20 CO2 dental laser on resected apical root dentin were examined using stereomicroscopy and scanning electron microscopy by Read, R.P., Baumgartner, J.C., Clark, S.M. (1995)90. The effects of the laser energy on the dentin ranged from no visible effects, to charring, cracking, cratering, and glazing. The most dramatic effect was cracking. It was also noted that the curved tip did not deliver laser energy to the

25 dentin as efficiently as a straight tip. They concluded that the CO 2 laser radiation did not consistently obliterate dentin tubules. Khan, M.A., Khan, M.F., Khan, M.W., Wakabayashi, H., Matsumoto, K. (1997)45 examined the morphological and temperature changes of the apical portion of human extracted teeth treated by Nd: YAG, CO2 and Argon-lasers. The scanning electron microscopic evaluation showed that the laser energy vaporized the deposited debris, producing a glaze-like surface. The histopathological investigation revealed a tapered, enlarged apical lased area. All threelaser devices were capable of vaporizing the debris in this way but the degree of morphological change was highly dependent on energy level and duration. The Argonlaser produced the highest temperatures. The application of erbium: YAG laser (Er: YAG) irradiation has been investigated for periodontal therapy. Yamaguchi, H., Kobayashi, K., et al (1997)123 evaluated the effects of Er: YAG laser irradiation on root surfaces using a scanning electron microscope (SEM) and to determine the laser's ability to remove lipopolysaccharides (LPS). Infrared spectrophotometry was used to investigate the effects of the laser on LPS applied to root dentin pellets. Based on their findings they suggested that Er: YAG laser irradiation might be useful for root conditioning in periodontal therapy. However, clinical testing is necessary to establish what, if any, utility the Er: YAG laser has as a part of periodontal therapy. Nd: YAG lasers have been suggested as a potential tool in endodontic therapy because of their sterilizing and sealing effects on the dentinal tubules. However, the generation of heat in the root canal by laser irradiation may produce potentially harmful effects on adjacent tissues. The effects of a thermally cooled pulsed Nd:YAG laser on the permeability and structural appearance of the root canal wall were investigated in vitro

by Miserendino, L.J., Levy, G.C., Rizoiu, I.M.(1995)75 . Laser parameters were set at 5 W, 50 Hz, using a simultaneous air/water coolant spray of 10 psi air and 2 psi water.

The results indicated that the permeability of laser-treated teeth was significantly less than untreated specimens. Root canal preparation using Nd: YAG laser has been introduced. Laser interaction with matter may generate cavitation and subsequent pressure waves. The study by Levy, G., Rizoiu, I., Friedman, S., Lam, H. (1996) 61, characterized the pressure waves induced in root canals by either Nd: YAG laser, sonically vibrated files, or ultrasonically vibrated files. A piezoelectric transducer detected the pressure waves induced in the canals. Laser irradiation resulted in pressure waves with amplitudes varying from 35.78 to 79.26 mV, being positively correlated with the laser power density (R2 = 0.870). Sonic and ultrasonic vibrations resulted in pressure waves with mean amplitudes of 60.51 mV and 7.02 mV, respectively. It was concluded that Nd: YAG laser irradiation induced pressure waves, with different characteristics from waves induced by freely vibrating sonic and ultrasonic endodontic instruments when applied to water-filled root canals. Nd: YAG laser-induced modification of the root surface may inhibit development of external inflammatory resorption in replanted teeth. A study tested this hypothesis in vivo. Friedman, S, Komorowski, R., Maillet, W., et al (1998) 27 study results did not support the hypothesis, and questioned the clinical validity of the surface modification in Nd:YAG laser-irradiated dentin. Therefore, the clinical application of Nd: YAG laser to the root surfaces of replanted teeth is not warranted. Lan, W.H (1999) 55 evaluated the temperature elevation on the root surface when Nd: YAG laser was irradiated in the root canal and found that temperature elevation did not exceed 10 degrees C only when the laser energy output was below 100 mJ/pulse and under 20 pulses/s. The effects of pulsed Nd: YAG laser irradiation during root canal treatment of infected teeth were investigated histopathologically in dogs by Koba, K., Kimura, Y., Matsumoto, K., et al (1999)50. The canal was irradiated using the following parameters: 1 W, 30 pps, for 1

26 and 2 s, and 2 W, 30 pps, for 2 s. Inflammation of the periapical regions in the lasertreated groups was significantly less than that in the control group at 4 and 8 wk (p < 0.05). These results suggest that pulsed Nd: YAG laser is useful for root canal treatment of infected teeth, if appropriate parameters are selected. The purpose of a study by Kimura, Y., Yu, D.G., Kinoshita, J. et al (2001) 49 was to investigate the morphological and atomic changes on the root surface by stereoscopy, field emissionscanning electron microscopy (FE-SEM), and energy depressive X-ray spectroscopy (SEM-EDX) after erbium, chromium: yttrium, scandium, gallium, garnet (Er, Cr: YSGG) laser irradiation in vitro. Results showed craters having rough but clean surfaces and no melting or carbonization was observed in the samples. An atomic analytical examination showed that the calcium ratio to phosphorus showed no significant changes between the control and irradiated areas (p > 0.01). These results showed that the Er, Cr: YSGG laser has a good cutting effect on root surface and causes no burning or melting after laser irradiation.

Effect Of Laser On Smear Layer And Debris Conventional cleaning and shaping of root canal spaces involves the use of hand and rotary instruments with irrigation. The procedure results in the formation of a smear layer consisting of dentin shavings, organic tissue remnants and microorganisms. Endodontic instrumentation, irrigation, or intra-canal medication is unable to totally remove intra-canal debris. The laser has been suggested as an aid in root canal preparation. In a study by Goodis, H.E., White, J.M., et al (1993)31, pulsed and continuous wave 1.06 microns wavelength Nd: YAG lasers were used to compare their abilities to clean and shape root canal spaces to conventional methods. After preparation, the test teeth were sectioned longitudinally and examined by scanning electron microscopy. The results demonstrated that the laser was capable of removing the smear layer in its entirety and could occasionally alter dentin walls. Moshonov, J., Sion, A., Kasirer, J., et al (1995)80 evaluated the efficacy of argon laser irradiation in removing debris from the root canal system. A 300 microns argon laser fiber optic was introduced into the root canal of each tooth, to its working length. Fifteen pulses of 100 msec each with energy of 2 watts were delivered for 5 seconds at the apex. The lasing procedure was repeated at 1 mm intervals along the root canal, and the fiber tip was retrieved from the apex to the orifice. Computerized scanning electron microscopy analysis revealed that the amount of debris in the lased group was significantly lower than that in the control (p = 0.0001). On the basis of their result, it appears that intra-canal argon laser irradiation is an efficient mean of removing intra-canal debris. Blum, J.Y., Abadie, M.J (1997)13â&#x20AC;&#x2122;s study was to evaluate the canal cleanliness achieved by five different preparation techniques, including use of the laser.

The following techniques were studied: (A) manual instrumentation (serial preparation), (B) laser preparation (Nd: YAP laser), (C) manual preparation with laser as adjunct, (D) manual preparation with a subsonic device as adjunct (MM 3000 with shapers), and (E) manual instrumentation with a subsonic device and laser as adjuncts (MM 3000 with shapers, Nd: YAP laser). The canal wall surfaces were examined under a scanning electron microscope at all levels with a new method using grid incrustation on the microscope screen. Techniques A and C differed from each other only by the size of the debris particles, which were smaller for the C preparation. For laser preparation (B) there was little increase in canal diameter increase, and a substantial amount of debris was present. The differences between techniques A, C, and D were not significant. The use of the subsonic device and laser together as adjuncts (E) showed the cleanest preparation with very little debris, opened tubules, and very small particle size. This result suggests that the laser has a potential in ensuring optimal canal

27 cleanliness. There have been some contradictory reports about the efficacy of Nd: YAG laser to remove debris and smear layer. Harashima, T., Takeda, F.H et al (1997) 35â&#x20AC;&#x2122;s objective was to evaluate the efficacy of Nd:YAG laser to remove debris and smear layer on the instrumented root canal walls in vitro. Specimens lased with 2 w and 20 pps showed very clean root canal walls with debris and smear layer evaporated, melted, fused, and re-crystallized in most cases (when compared with 1 W and 20 pps). These results suggest that Nd: YAG laser is useful to remove debris and smear layer and causes melting of internal structures on the instrumented root canal walls at the parameters of 2 W and 20 pps. Takeda, F.H., A Harashima, T., Eto, J.N et al (1998) 109 studied and observed the morphological changes on root canal walls after instrumentation and irrigation, and assessed the efficacy of conventional cleansing procedures and the effectiveness of Er: YAG laser in removing debris and smear layer from the root canal walls. The root canal walls irradiated by Er: YAG laser was free of debris, with an evaporated smear layer and open dentinal tubules. These results suggested that Er: YAG laser irradiation had an efficient cleaning effect on the prepared root canal walls. Harashima, T., Takeda, F.H., Zhang, C., et al (1998) 34 examined whether argon laser has a property to remove debris and smear layer from root canal walls. The root canals were irradiated by argon laser (laser parameters were set at 1 W and pulse duration and pulse frequency fixed at 0.05 s and 5 Hz) and observed with a scanning electron microscope and evaluated as to how clean the surfaces of root canal walls were. Root canal surfaces free of debris and vaporized pulpal tissue remnants were observed, suggesting that argon laser irradiation has an efficient cleaning effect on instrumented root canal surfaces. Takeda, F.H., Harashima, T., et al (1998) 110 analyzed the effectiveness of three types of laser, argon, Nd:YAG, and Er:YAG, to remove the smear layer from the prepared root canal walls in vitro. Root canals in group 1 (G1) were unlased and were irrigated by 17% EDTA. In group (G2), root canals were irradiated by argon laser at the parameters of 1 W, 50 mJ, and 5 Hz. In group 3 (G3) root canals received Nd:YAG laser irradiation at 2 W, 200 mJ and 20 Hz. Teeth in group 4 (G4) were irradiated by Er: YAG laser at the following parameters: 1 W, 100 mJ and 10 Hz. The middle third of the teeth from G1 showed clean wall surfaces with open dentinal tubules. In G2, at the middle third, the smear layer was free and vaporized pulpal tissue remnants were observed. In G3, most of the specimens showed very clean walls with the smear layer evaporated, melted, fused, and re-crystallized in both the middle and apical thirds. The walls of G4 revealed the evaporated smear layer and open dentinal tubules in the middle and apical thirds. These results show that the argon laser and Nd: YAG laser are useful to remove the smear layer and that the Er: YAG laser irradiation is the most effective to remove the smear layer on root canal walls. There has been no report to evaluate residual debris in root canals after Er: YAG laser irradiation using a fiberscope. Therefore a study was done to investigate the effect of Er: YAG laser to remove debris near the apical seats in root canals and to evaluate the efficacy of a fiberscope for the assessment of remnant debris on the root canal wall in vitro. This study was done by Matsuoka, E., Kimura, Y., Matsumoto, K. (1998) 70. Er irradiated the teeth of groups 1, 2, and 3: YAG laser at the parameters of 1 W, 2 W, and 3 W, respectively. Group 4 was comprised of control specimens that were not lased.

After laser irradiation, the remnant debris on the apical portions of all root canals was evaluated by fiberscopy. Te specimens were observed by stereoscopy and scanning electron microscopy (SEM). The degree of remaining debris on the apical seats was scored. RESULTS: The degree of remaining debris observed by fiberscopy coincided with the results by SEM. There was no significant difference between groups 1 and 4, and also between groups 2 and 4, but the remaining debris in group 3 was significantly

28 decreased after Er: YAG laser irradiation compared with that in group 4 (p < 0.01).

CONCLUSIONS: These results suggest that Er: YAG laser irradiation is effective for removal of debris near the apical seats and that a fiberscope is useful for the evaluation of the remaining debris near the apical seats of intact teeth. In a very detailed study the effects of three endodontic irrigants and two types of laser on a smear layer created by hand instrumentation were evaluated in vitro in the middle and apical thirds of root canals by Takeda, F.H., Harashima, T. et al (1999) 108. Group 1 (G1) were control specimens that were irrigated with a final flush of 17% EDTA. The teeth in-group 2 (G2) was irrigated with a final flush of 6% phosphoric acid, and group 3 (G3) with 6% citric acid. In the specimens of group 4 (G4) the root canals were irradiated with a carbon dioxide (CO2) laser, and specimens of group 5 (G5) were irradiated using an Er: YAG laser. Control specimens (G1) showed clean root-canal walls with open dentinal tubules in the middle one-third, but in some specimens thick smear layer was observed in the apical one-third. Specimens irrigated with a final flush of 6% phosphoric acid (G2) or 6% citric acid (G3) were cleaner than with 17% EDTA, showing very clean root canal surfaces in the middle one-third but in the apical one-third the smear layer was not completely removed, especially at the openings of the dentinal tubules. The specimens irradiated with the CO2 laser (G4) showed clean root-canal walls with the smear layer absent, charred, melted, recrystallized and glazed in both middle and apical thirds. The root-canal walls of the specimens irradiated with the Er:YAG laser (G5) revealed an absent smear layer with open dentinal tubules in the middle and apical thirds. There were statistically significant differences (P < 0.01) between G1 and G4, and G1 and G5 in the cleanliness of the middle and apical one-thirds of the root canals.

CONCLUSIONS: Irrigation with 17% EDTA, 6% phosphoric acid and 6% citric acid did not remove all the smear layer from the root-canal system. In addition, these acidic solutions demineralized the interbular dentine around tabular openings, which became enlarged. The CO2 laser was useful in removing and melting the smear layer on the instrumented root-canal walls and the Er: YAG laser was the most effective in removing the smear layer from the root-canal wall. Goya, C., Yamazaki, R., Tomita, Y. et al (2000)32 evaluated the removal of smear layer at the apical stop by pulsed Nd: YAG laser irradiation with or without black ink, and the degree of apical leakage after obturation in vitro. The laser was operated at 2 W and 20 pp for 2 s, and irradiation was performed twice with a 30-s interval. The smear layer in the laser-treated groups almost melted or evaporated, and was removed significantly compared with the control group (unlased teeth). Leakage was observed in 60% of samples in-group 1 (unlased teeth) and in 20% of samples in-group 2 (lased teeth). No leakage was observed in-group 3 (lased teeth with Black ink). These results suggest that pulsed Nd: YAG laser irradiation with black ink increases the removal of smear layer compared with that without black ink, and reduces apical leakage after obturation significantly.

Sterilization Or Disinfection Of Infected Root Canals The laser is an effective tool for killing microorganisms because of the laser energy and wavelength characteristics. To prevent thermal damage to the periodontium surrounding the tooth, various techniques are considered and recommended. Infected root canals are an indication for this laser treatment, but application to be extremely curved and narrow infected root canals appears difficult. Pulsed Nd: YAG, argon, semiconductor diode, CO 2, Er: YAG, and other lasers have been considered for use in this treatment. The pulsed Nd: YAG laser has been recommended for this treatment because of the ease with which the laser fiber can be controlled. To increase the effect of sterilization in the infected root canal, about 38% silver ammonium solution was placed into the root canals and irradiated the canals

29 using the pulsed Nd: YAG laser at 2 W and 20 pps for 5 seconds, 5.25% sodium chloride or 14% EDTA also has been used. Rooney et al reported sterilization rates of 80% to 90%, whereas others have reported rates of 60%, depending on the condition of the root canals, the type of laser device, the application parameters, and the techniques.

In the future, lasers in combination with certain drugs may perform sterilization by the laser. Lasers are gaining increasing importance in the field of endodontics. Numerous studies have shown the beneficial effects of laser treatment in disinfecting root canals.

The effect of XeCl excimer laser irradiation on the growth of Streptococcus mutans in liquid media and on agar plates was studied by Stabholz, A., Kettering, J et al 1993).

The bactericidal effect of the laser applications was directly related to the amount of radiation time. Laser irradiation for 4 and 8 s resulted in bactericidal effect that was statistically significant compared with no treatment or to 2-s exposure. The zones of inhibition produced by higher energy levels (0.5 J/cm2, 0.7 J/cm2, and 1.0 J/cm2) were larger in comparison to the lowest fluence used (0.1 J/cm2). Based on this result it appears that the XeCl 308-nm excimer laser can kill S. mutans. Hardee, M.W., Miserendino, L.J., et al (1994) in their study on evaluation of the antibacterial effects of intra-canal Nd:YAG laser irradiation, concluded that there was no significant difference between groups exposed to pulsed Nd:YAG laser radiation or 0.5% NaOCl alone and in combination. The purpose of a study by Moshonov, J., Orstavik, D., et al (1995) 179 was to assess the efficacy of Nd:YAG laser irradiation in disinfecting the root canal system. Root canals were infected for 60 min with an overnight culture of Enterococcus faecalis in Tryptic Soy Broth. SEM analysis of teeth split longitudinally was used to illustrate the effect of treatment on the smear layer and on surface bacteria. Nd: YAG laser irradiation significantly reduced the number of bacteria while NaOCl irrigation effectively disinfected the canals. Fegan, S.E., Steiman, H.R. (1995)25 determined the capability of Nd: YAG laser in disinfecting contaminated root canals in vitro.

Extracted single-rooted teeth were sterilized with ethylene oxide gas and then inoculated with Bacillus stearothermophilus. The Nd: YAG laser was effective in inhibiting the growth of B. stearothermophilus. The effects of the Nd: YAG laser on other bacteria more commonly found in root canal systems should be evaluated. Blum, J.Y., Michailesco, P., Abadie, M.J.(1997)14â&#x20AC;&#x2122;s in vitro study was to compare the efficacy of a classical irrigant with that of a laser in disinfecting a contaminated root canal. The teeth were inoculated with Streptococcus mitis ATCC 33399, and the canal was then lased with different frequencies as follows: frequency of 5 Hz and power of 260 mJ; frequency of 10 Hz and power of 310 mJ; frequency of 30 Hz and power of 300 mJ. The results indicated that the antibacterial effect of the Nd: YAP laser depended on the frequency. Only a frequency of 30 Hz of the Nd: YAP laser inhibited the growth of Streptococcus mitis ATCC 333999. Thermal effects and antibacterial properties of an Nd: YAG laser was studied by. Ramskold, L.O., Fong, C.D., Stromberg, T. (1997) 89 to establish clinically safe levels of energy to deliver into the root canal and to determine the energy level needed to sterilize infected root canals. The results indicated that lasing cycles of 3 J-s for 15 s followed by a 15-s recovery interval can be continued for prolonged periods without risk of thermal damage to surrounding tissues. A study on the antibacterial effectiveness of the Nd: YAG, the Ho: YAG, and the Er: YAG laser in infected root canals was carried out by Moritz, A., Schoop, U., Goharkhay, K., et al 199978. The study highlights that all three lasers substantially decreased the bacterial population with only minimal differences in their microbicidal efficacy. At 1.5 W, the best results were obtained by the Er: YAG laser achieving a mean bacterial elimination of 99.64%, followed by the Nd: YAG laser (99.16%), and the Ho: YAG laser (99.05%).

The findings indicated that all three lasers act as strongly effective microbicides

30 without causing unfavorable temperature rises at the settings used. They can thus be considered a valuable tool for root canal treatment. The bactericidal action of the CO2 laser on animal teeth infected with an endodontic bacterial species (Actinomyces odontolyticus ) was evaluated by Le_Goff, A., Dautel_Morazin, A., et al (1999) 58 .

Incisors were separated into three groups: group 1--untreated control teeth; group 2-teeth treated with 3% NaOCl; and group 3--teeth lased with a CO 2 laser at 5 W using three successive 9.9 s irradiation periods with 10 s between treatments. The results of the study indicated an average 85% decrease in the colony-forming units in the lasertreated group, compared with the control group. However the NaOCl treatment was statistically superior to the CO 2 laser treatment. Mehl, A., Folwaczny, M. et al (1999) 72 investigated the antimicrobial properties of Er:YAG-laser radiation in dental root canals. The root canals were inoculated with Escherichia coli or Staphylococcus aureus for 2 h. The laser treatment groups were exposed for either 15 or 60 s to Er:YAG-laser radiation (pulse energy: 50 mJ; 15 pps). After irradiation or irrigation, the number of bacteria was evaluated using the surface spread plate technique. In the case of S. aureus, the primary bacterial load (control group) of the root canals was reduced to 0.15% after 15 s and 0.06% after 60 s of laser treatment. In the E. coli group, the number of bacteria was diminished to 0.13%, with the shorter radiation time and to 0.034% after 60 s of radiation. Irrigating the root canals with NaOCl, a reduction of the number of bacteria to 0.033% for S. aureus and to 0.020% for E. coli could be obtained.

As the results confirm, Er: YAG-laser radiation exerts very effective antimicrobial properties in dental root canals, depending on the time of radiation. The antibacterial effects of the Nd:V YAG laser on contaminated root canals and dentinal tubules were observed by Berkiten, M., Berkiten, R., Okar, I. (2000) 11. The samples were inoculated with Streptococcus sanguis (NCTC 7853) and Prevotella inter media (NCTC 93336), and the effects of Nd: YAG laser was tested on these teeth. The specimens were lased with 1.8 W and 2.4 W Nd: YAG laser for 30 s, and the presence of bacteria in tubules was observed under light microscopy. The 1.8 W lasers sterilized the tubules in 86.3% of sections inoculated with S. sanguis, whereas 2.4 W lasers sterilized in 98.5% of the sections. Both laser powers sterilized all samples inoculated with P. inter media. The scanning electron microscopic observations supported the light microscopic findings.

Strengthening And Sterilization Of The Root Canal Wall Using A Silver Ammonium Solution And The Laser: Silver ammonium solution has been used in iontophoresis of infected root canals and in caries prevention by application to the primary caries. The author attempted laser treatment using various lasers in the root canal for the purpose of sterilizing and strengthening the root canal wall, and useful results were obtained. The indications for this treatment are not explained here. This treatment is useful for application in infected root canals preparation. The pulsed Nd: YAG, CO2, semiconductor diode, and argon lasers are recommended as laser devices for this treatment. To prevent leakage of the 38% silver ammonium solution into the root canals and irradiated the canals using the pulsed Nd: YAG laser at 2 W and 20 pps for 5 seconds; 5.25% sodium chloride or 14% EDTA also has been used. Rooney et al reported sterilization rates of 80% to 90%, whereas others have reported rates of 60%, depending on the condition of the root canals, the type of laser device, the application parameters, and the techniques. There has been no report on the morphological or atomic analytical changes of the effect of Ag (NH3) 2F solution and CO 2 laser on root canal walls. Eto, J.N., Niu, W. et al (1999) in their study on the morphological and atomic analytical changes of the root canal wall dentin, treated with 38% diamine silver fluoride [Ag(NH3)2F] solution and irradiated by carbon dioxide (CO2) laser at the

31 continuous wave mode evaluated in vitro. There has been no report on the morphological or atomic analytical changes of the effect of Ag (NH3) 2F solution and CO2 laser on root canal walls. The teeth in-group 1 were either treated with Ag (NH3) 2F solution nor lased. Laser at the parameters of 1, 2, and 3 W irradiated groups 2, 3, and 4 for 10 seconds, respectively. Group 5 was treated with Ag (NH3) 2F solution only. The other 3 groups were treated with Ag (NH3) 2F solution and then lased by the same method as groups 2, 3, and 4. Results of this study showed that the smear layer and debris of the control and lased specimens were not completely removed, but the areas of carbonization of evaporation of smear layer and open dentinal tubules were observed on the specimens treated with Ag (NH3) 2F and lased at 1 W (group 6). After laser irradiation, the amount of silver on the root canal surfaces was significantly reduced to approximately one-third level on the measurement of SEM-EDX (p < 0.01).

These results suggest that CO2 laser is an effective method to remove or melt smear layer of root canal walls after treatment with 38% Ag (NH3) 2F solution if an appropriate parameter is selected. There have not been any reports of penetration and hardness following the application of Ag (NH3) 2F solution together with laser or iontophoresis. Yokoyama, K., Matsumoto, K. et al (2000) 126 used SEM-EDX and the Vickers hardness test to compare the penetration and hardness of silver resulting from use of either (i) pulsed Nd:YAG laser or (ii) iontophoresis, after root canal wall shaping using the standard method of coating with 38% Ag (NH3) 2F solution. Extracted human single-rooted teeth randomly divided into three groups. Group 1 was coated with Ag (NH3) 2F, Group 2 was irradiated with a Nd: YAG laser after coating with Ag (NH3) 2F solution, and Group 3 was iontophoresised after coating. The results showed that iontophoresis after coating with Ag (NH3) 2F solution (Group 3) resulted in the greatest and deepest penetration of silver into the root canal wall. There was no significant difference between teeth in Groups 1 and 2. For the hardness test, the results showed that Group 2 (laser treatment) teeth were the hardest. The authors therefore proposed that root canals should be treated using irradiation with an Nd: YAG laser that has been coated with Ag (NH3) 2F solution and that this method provides better results than either iontophoresis after coating, or coating alone.

Closure Of Apical Foramina Of Root Canals By Laser If apical foramina of root canals are completely closed temporarily by laser beams, the endodontic treatment is changed surprisingly. Anic et al have attempted this method, but no researchers have resolved all of the problems involved with its application. The author will continue to investigate the application of this technique. Preliminary studies performed by the author revealed that closing small apical foramina was possible using the pulsed Nd: YAG laser. By combining light-curable composite resin and argon laser or combining sectioned gutta-percha points and a pulsed Nd: YAG laser, however, the author found that it was relatively easy to close the apical root canal.

Laser Treatment Under A Stereomicroscope And A Fiberscope Laser treatment under a fiberscope has been performed for some time in stomach surgery. In the field of endodontics, treatments under a stereomicroscope have been put into practice in Japan as well as the United States. Laser treatment under a fiberscope also is under development and is likely to be put into practice soon. By combining these instruments, and root canal wall, apical seal, Dentin Bridge, and size and location of perforations is easy using this method. The pulsed Nd: YAG laser is used for these purposes.

32 Sedative And Anti-Inflammatory Treatment Of Trigeminal Neuralgia By Laser Trigeminal neuralgia is induced by many causes. The pain associated with pulpitis and apical periodontitis is one kind of trigeminal neuralgia. Some clinical cases have continued for a long time, even though standard endodontic treatment was conducted.

The application for laser sedative and anti-inflammatory treatments was examined for such problem cases, and interesting results were obtained. This method expected to be put into practice soon. The pulsed Nd: YAG and CO 2 lasers are recommended for this therapy. In the authorâ&#x20AC;&#x2122;s experience, the pulsed Nd: YAG laser used in combination with black is better than the CO2 laser. The laser power is 2 W and 20 pps, and exposure time depends in the pain reported by the patient. Usually, two laser exposures are performed under air-cooling. The mechanism of sedation is thought to be the same as that for the reduction of hypersensitive dentin. The mechanism of anti-inflammatory effects is thought to be the inflamed tissue and the decomposition of certain kinds of pain-producing substances and inflammatory factors as well as pain reduction at the central neurons by laser stimulation.

Prevention Of Tooth Fracture By Laser Although techniques for repairing root fracture have been proposed, the prognosis is generally poor. If the fusion of a root fracture by laser is possible, it will offer an alternative to extraction. Pulpless teeth have a tendency to fracture. Many dentists encounter at least one case in which they are obliged to extract a tooth because of fracture despite finishing the endodontic treatment.

To prevent such cases, new laser techniques are being developed. Teeth lased with 38% silver ammonium solution became difficult to fracture. Pulpless teeth are indicated for this treatment. Pulsed Nd: YAG, CO 2, and argon lasers can be used for this treatment.

The laser irradiation is performed in combination with 38% silver ammonium solution until the tooth surface becomes silver and mirror-like under air-cooling at 2 or 3 W and for about 20 seconds.Using a neodymium: yttrium-aluminum-garnet laser beam to seal vertical root fracture lines with tricalcium phosphate paste represents an alternative treatment for cracked teeth with noted clinical results. Levy, G.C., Koubi, G.F.(1993) 62 studied the permeability of molten crystals of hydroxyapatite in the dentin of a cracked root after crack lines have been filled with a preparation of tricalcium phosphate melted by a neodymium: yttrium-aluminum-garnet laser beam. The morphology of the sealed cracks was analyzed under a scanning electron microscope that showed a deep fusion of tricalcium phosphate along crack lines. Arakawa, S., Cobb, C.M., et al (1996) 5 in their in vitro study used scanning electron microscopy and polarized light microscopy to evaluate the feasibility of using either the CO2 laser or an Nd: YAG laser in combination with air/water surface cooling to effect fusion of fractured tooth roots.

Laser treatment consisted of multiple passes along the line of fracture, which was inspected using a dissecting microscope after each pass until a visual indication of fusion or irreparable damage resulted Scanning electron microscopy evaluation of the treated lines revealed heat-induced fissures and cracks, areas of cementum meltdown and re-solidification, crater formation, and separation of cementum from underlying dentin. The authors concluded that in no instance-regardless of re-approximation technique, laser type, energy, and other parameters-did the treatment effect fusion of the fractured root halves.Lin, C.P., Lin, F.H., et al (2000) 64 tried to use a developed DPbioactive glass paste to fuse or bridge the tooth crack line by a medium energy continuous-wave CO2 laser. Their study was divided into three parts: (1) The compositional and structure changes in tooth enamel and dentin after laser treatment; (2) The phase transformation and re-crystallization of DP-bioactive paste during exposure to the CO2 laser; (3) The thermal interactions and bridge mechanism between

33 DP-bioactive glass paste and enamel/dentin when they are subjected to CO 2 laser. They examined the changes of laser-exposed DP-bioactive glass paste by means of X-ray diffractometer (XRD), Fourier transforming infrared spectroscopy (FTIR), differential thermal analysis/thermo gravimetric analysis (DTA/TGA), and scanning electron microscopy (SEM). From the study, they found that the temperature increase due to laser irradiation was greater than 900 degrees C and that the DP-bioactive glass paste could be melted in a short period of time after irradiation. In the study, they successfully developed a DP-bioactive glass paste, which could form a melting glass within seconds after exposure to a medium energy density continuous-wave CO 2 laser.

The paste will be used in the near future to bridge the enamel or dentin surface crack by the continuous-wave CO2 laser.Lin, C.P., Lee, B.S. et al (2001)63 attempted to use lasers to fuse a low melting-point bioactive glass to fractured dentin. This report is focused on the phase, compositional, and morphological changes observed by means of X-ray diffractometer, Fourier transforming infrared spectroscopy, and scanning electron microscopy-energy depressive X-ray spectroscopy in human dentin after exposure to Nd: YAG laser. The irradiation energies were from 150 mJ/ pulse-10 pps-4 s to 150 mJ/pulse-30 pps-4 s. Based on the results the irradiation energy of Nd: YAG laser used to fuse a low melting-point bioactive glass to dentin is 150 mJ/ pulse-10 pps-4 s.

Prevention Of Microleakage Of Retrograde Root Canal Filling Micro leakage of retrograde root canal fillings is one cause of failure of apicoectomies. Although the improvement of canal sealers, root canal filling techniques, and application of calcium hydroxide paste as root canal medication are recommended to prevent microleakage, there is still no ideal method. The author and coworkers have been studying ways to solve these problems using lasers, and a decrease of microleakage at apicoectomy was confirmed in vitro. The closure of exposed dentinal tubules on the cut surface at the root end was observed by scanning electron microscopy. Pulsed Nd: YAG and CO 2 lasers are recommended at 1 to 2 W under air-cooling in combination with 38% silver ammonium solution. The root end cavity must be filled using cement or resin after thorough cleaning. The application of Nd: YAG laser to tooth surface can change its surface permeability. The purpose of a study by Stabholz, A., Khayat, A., et al (1992)102 was to investigate the effects of Nd: YAG laser on the permeability of dentin following apicoectomy and retrofill. The amount of dye penetration was significantly lower in lased roots than in non-lased ones (p < 0.05). Based on their results, it appears that application of Nd: YAG laser reduces the permeability of resected roots.An in- vitro study was done to compare the apical seals achieved using retrograde amalgam fillings or the Nd: YAG laser by Wong, W.S., Rosenberg, P.A., et al (1994) 120. They concluded that no statistically significant difference was found in bacterial leakage between the laser-treated group and the retrograde amalgam group. Sealing the root apex during apical surgery is important for a successful outcome. The effect of XeCl-308 nm excimer laser irradiation on the fusion and seal of hydroxyapatite to the root apex was tested in extracted human teeth by Mor, C., Stabholz, A., et al (1995) 76.Twenty-four roots of intact single-rooted premolars were instrumented to size 30 K-file at the apex leaving a patent apical foramen. The apex of each tooth was covered with a freshly prepared paste of hydroxyapatite powder mixed with saline. The samples were then divided into two groups. In 12 teeth, the apical area was irradiated with XeCl-308 nm excimer laser at a fluence of 0.7 J/cm2 for 5 s with pulse repetition rate of 25 Hz and a spot size of 0.13 cm2 immediately after the hydroxyapatite application. In the other 12 teeth, no laser treatment was performed after the hydroxyapatite application. The roots were mounted on a model for the detection of radicular leakage of hydrogen peroxide.

34 The results showed that the difference between the groups was not statistically significant. There has been no report of laser effect on apical leakage after laser treatment and obturation.Yamazaki, R., Goya, C., Tomita, Y. (1999) 125 performed a study to compare the apical leakage degree after laser treatment and obturation with that without laser treatment, and to evaluate the efficiency of argon laser irradiation in removing debris and smear layer from the prepared root canal walls in vitro. Argon laser at the wavelength of 470 nm and at the output of 0.3 W was irradiated at apical stop for 1, 2, or 3 seconds at the continuous mode. The apical leakage degree after laser treatment and obturation was reduced compared to that in the control (unlased teeth), but not significantly (p > 0.05). However, debris and smear layer in the laser-treated groups were removed from apical stop even at low energy density. These results suggest that apical leakage after argon laser treatment is not reduced significantly, but that argon laser is useful for removing debris and smear layer from root canals.The efficacy of XeCl excimer laser irradiation in reducing dye penetration through human coronal dentinal tubules was studied by Stabholz, A., Rotstein, L. 1995). The teeth were irradiated with XeCl 308-nm excimer laser at a fluence of 0.7 J/cm2 to form an elliptical lased area. The results showed that the mean total areas (mm2) measured in the lased specimens were significantly smaller than those in the controls (non-lased teeth).

Retrograde Endodontic Apicoectomy, Apical Cavity Preparation, And Periapical Curettage By Laser CO2 and Nd: YAG lasers have been investigated for apicoectomy, retrograde endodontic apical preparation, and periapical curettage. A new laser device for tissue treatment was developed in the United States. This Er, Cr: YSGG laser is applicable for the treatment of soft and hard tissues. Apicoectomy, retrograde endodontic apical root end cavity preparation, and periapical curettage can be performed using this one laser device. Cases with continuing clinical symptoms, root canals with fractured instruments, and sinus tracts in which pus drainage cannot be stopped by the standard endodontic treatment are included among the indications for this treatment, but the cutting ability of the hard tissue by Er: YAG laser appears to be inferior to that of the Er, Cr: YSGG laser. The laser parameters should be determined based on the size and length of the root apex that is to be cut. The potential advantages of CO2 laser in apical surgery have not been established histologically. Therefore, the long-term effects of CO2 laser on the apical and periapical tissues were examined histologically in dogs 6 months after apical surgery by Friedman, S., Rotstein, I., Bab, I.(1992)29. Lased specimens and unlased controls showed periapical inflammatory and osteogenic reactions. Lased root surfaces revealed craters with a superficial charred layer closely associated with new cementum-like matrix. The subjacent dentin appeared tubule-free and eosinophilic. Lased bone trabeculae showed a charred layer with a deeper osteocyte-free zone. The charred layer was covered by new bone. Detached charred segments in the marrow space and periapical inflammatory infiltrate were intimately associated with multinucleated giant cells, some containing minute char particles. Such cells were absent from the root and trabecular char linings. In addition, the charred surfaces were free of hard tissue resorption. These results suggest that CO 2 laser does not hinder healing when applied in apical surgery.Root resection was performed by Paghdiwala, A.F (1993)86 on endodontically treated extracted human teeth exposed to pulsed erbium: YAG laser radiation at energy levels between 50 and 90 mJ/pulse in wet and dry fields. The lased surfaces were examined by optical and scanning electron microscopy. The smooth, clean resected root surfaces, devoid of charring (in wet fields), indicated that the erbium: YAG laser has a potential application

35 in endodontic periapical procedures. In addition, researchers have shown that the zone of thermal damage and carbonization following erbium laser exposure on soft tissues and bone is appreciably less compared with other lasers, and therefore its use may result in improved healing and diminished postoperative discomfort.

Root Canal Filing Using Gutta-Percha Or Resin And Laser Gutta-percha is thought to be melted by laser heat energy. Anic and Matsumoto attempted to investigate whether it is possible to perform the root canal filing using sectioned gutta-percha segments and a pulsed Nd: YAG laser. This was shown to be possible by the vertical condensation method, but the technique required too much time. At present, this technique is not practical. Although a method combining an argon laser and lightcurable resin is in the literature, proper application of this method requires further research.

Removal Of Temporary Cavity Sealing Materials, Root Canal Sealing Materials, And Fractured Instruments In Root Canals Several methods have been used to remove temporary cavity sealing materials, root canal sealing materials, and fractures instruments in root canals, but there are no ideal methods. Lasers are soon to be applied for these purposes. According to experimental results, it was easy to remove temporary cavity sealing materials made of zinc oxide, eugenol, or gutta-percha by pulsed Nd: YAG and Er: YAG lasers; and fractured reamers or files in slightly curved and wide root canals. In fine and strongly curved root canals, however, there were many cases in which the laser tips perforated the root canal wall. The study by Yu, D.G., Kimura, Y., Tomita, Y., et al (2000)129 was to investigate the capability of removing the filling materials or broken files from root canals with pulsed Nd:YAG laser irradiation at three parameters, and to evaluate the temperature rises on root surfaces and morphological changes of root canal walls in vitro. The results showed that in more than 70% of the teeth, the obturated materials were completely removed by laser, and in more than 55% of the teeth, the broken files were successfully removed. Temperature rises ranging from 17 degrees C to 27 degrees C were measured from 6 to 11 repeated times. These results demonstrated that a pulsed Nd: YAG laser irradiation has the capability of removing the obturated materials in root canals and is useful for removing the broken files in same if the counter-measure reducing the temperature rise is performed.

Laser Treatment Of Periapical Lesions Of Sinus Tract Although sinus tracts almost always can be closed by standard endodontic treatment, a few cases require special treatment. For these cases, some special techniques are used to accelerate the wound healing. Laser therapy is recommended for such occasions. Cases for which apicoectomy or periapical curettage cannot be performed or for which standard endodontic treatment cannot be performed because of a deep post in the root canal are indications for this treatment. This treatment may be performed to accelerate wound healing in combination with endodontic or surgical treatment. Pulsed Nd: YAG and CO2 laser are recommended for these treatments. For the pulsed Nd: YAG laser, 2 W and 20 pps are the recommended parameters and the fiber tip must be inserted into the tract and drawn slowly from the root apex to the exit through the sinus tract. This treatment generally is performed three or four times during one visit. When using the CO2 laser, the exit of the drainage must be ablated as deeply as possible at 1 or 2 W and under air-cooling or local anesthesia. The aforementioned laser treatments are performed once or twice a week until the sinus tract disappears.

36 Root Canal Drying By Laser Infrared lasers have been used for debridement and sterilization of both soft and hard tissues. A laboratory study by Walsh, L.T., Walsh, L.J. examined the feasibility of using pulsed infrared laser radiation to remove moisture from root canals (with an adjunctive sterilizing effect). With the CO2 laser, long pulse durations were effective at dehydrating the canals, but elicited deleterious thermal changes both locally within the canal as well as on the root surface. With Nd: YAG laser treatment, large temperature increases on the root surface occurred even with low powers and low pulse frequencies, and extended times were necessary for dehydration.

With higher powers and pulse frequencies, complete dehydration could be achieved in less than 60 seconds, however root surface temperatures increased approximately 25 degrees, and the radicular dentine was damaged by the production of plasma.

Dehydration of root canals could not be achieved safely with these two infrared lasers, and damage to both radicular dentine and the periodontal ligament would occur if these techniques were to be applied clinically. Alternative methods, which do not exert significant thermal effects, should be investigated.

Laser In Treatment Of Root-Caries With the aging of the population and the endemic problem of gingival recession, patients will inevitably suffer from greater exposure of root surfaces and therefore will be more likely to develop root caries. The treatment of root caries is often frustrating. Traditional biomaterials used for the restoration of enamel caries have been less than satisfactory when margins of a cavity are adjacent to cementum. Although topical fluoride gels, toothpastes, and rinses have been used to prevent or to inhibit the development of root caries, there is a problem of access to the proximal surfaces. Consequently, the development of better methods to facilitate the prevention of root caries has become an important issue in dentistry. Lee, C.Q., Lemire, D.H., Cobb, C.M. advocate the use of CO2 laser irradiation on tooth-root cementum.

Effect Of Laser On Post-Operative Symptoms The effects of pulsed Nd: YAG laser irradiation for the treatment of root canals immediately after pulpectomy and shaping with regard to improvement of symptoms were evaluated clinically by Koba, K., Kimura, Y., Matsumoto, K. et al (1999)52. After extirpation of pulp and shaping using a step-back technique and cleansing with 5% sodium hypochlorite (NaOCl) and 3% hydrogen peroxide (H2O2), laser irradiation was applied at 1 W and 15 pps for 1 second in 23 teeth (laser-treated group). Root canals were then obturated. The control teeth were treated in the same way, but without laser irradiation. Occurrence of spontaneous pain was recorded 1 day after treatment and occurrence of percussion pain was recorded 1, 2, and 3 weeks after treatment. RESULTS: Effective ratio, which was the ratio of the number of "none" teeth to total teeth number in the laser-treated group, was higher than that in the control group, but there was no significant difference between 2 groups with regard to spontaneous and percussion pain (p > 0.05). These results suggest that the clinical application of pulsed Nd: YAG laser might be advantageous for the one-visit treatment of root canals immediately after pulpectomy shaping and to reduce postoperative pain. Koba, K., Kimura, Y., Matsumoto, K., et al (1999) 51, in a study examined post-operative symptoms and healing after endodontic treatment on patients diagnosed with chronic apical periodontitis. The canal terminus was irradiated with pulsed Nd: YAG laser (1 W, 15 pps, 1 s), before obturating procedure was carried out. Percussion pain was significantly less (P < 0.05) in the laser-treated group, both 1 week and 3 months after treatment. These results suggested that the clinical application

37 of pulsed Nd: YAG laser might be advantageous for the treatment of infected root canals.

Hazards Of Laser Smoke During Endodontic Therapy: The purpose of McKinley, I.B., Ludlow, M.O.(1994)71â&#x20AC;&#x2122;s study was to evaluate the potential for spreading bacterial contamination from the root canal to the patient and the dental team via the smoke produced by the laser. Five extracted teeth were deliberately inoculated with a specific strain of Escherichia coli. The canals were subjected to an agron laser. The smoke plume was captured and cultured. All of the cultures were positive for growth of the E. coli used. The authors concluded that the laser smoke does present a hazard of bacterial dissemination and that precautions must be taken to protect against spreading infections when using lasers in the root canal.

LASERS IN COSMETIC DENTISTRY Dental lasers were introduced and recognized as a tool for better patient care in the early 1990s. In the ensuing years, clinicians have found that practicing cosmetic dentistry can be more exciting and rewarding by using laser technology for accomplishing general and cosmetic tasks. Clinicians in this specialized area seek to provide the highest caliber of care, while enhancing the esthetics of the smile. When considering a smileâ&#x20AC;&#x2122;s components, cosmetic dentists focus on improvements related to the color, shape, alignment, and function of the teeth as well as the quality of the gingival architecture.

38 Argon Lasers The 488-nm wavelength of the argon laser has been used effectively to polymerize composite resins because it enhances the physical properties of the restorative material compared with conventional visible light curing. Argon curing of dentin bonding also has improved adhesion compared with conventional visible light curing. Argon curing of sealants improves the attachment to the enamel surface and reduces microleakage significantly compared with conventional light curing. The benefits of this procedure allow for enhanced physical properties, improved adhesion, and reduced microleakage, all accomplished in less curing time with argon lasers in 10second cycles compared with a conventional curing light administered in the 40-second cycles. The 488-nm working with composite resins (the selection of the composites should be compatible with specific wavelengths). Another breakthrough accomplishment achieved by using the 488-nm blue light argon laser is tooth whitening, which is discussed in more detail subsequently. The 514.5-nm green light argon is used to perform soft tissue procedures. Gingivoplasty, gingivectomy, crown lengthening, and troughing are among the services that can be carried out beautifully because of the intrinsic characteristic of the laser wavelength as it specifically targets hemoglobin. Coagulation and hemostasis are expected photo thermal interactions that can be used to advantage with the 514.5-nm wavelength. The argon lasers currently available on the market are the HGM dental 200, 300,400 series (HGM Medical Laser System, Salt City, UT). These models are offered in 488-nm and 514.5-nm wavelengths. The following argon lasers are available only in 488-nm wavelengths for curing and tooth whitening purposes: AccuCure 3000 (Lasermed, Salt City, UT), Arago (Premier Laser Systems, Irvine, CA), and Cure Star (Lares, Chico, CA).

Nd: YAG Lasers The Nd: YAG laser (yttrium-aluminum-garnet solid doped with neodymium) generates a wavelength at 1064 nm and is well absorbed by the pigmented tissues, hemoglobin, and hemosiderin, which are found in abundance in the gingival tissues. The pulsed Nd: YAG laser features an optic fiber delivery system which is ideal for soft tissues procedures, including gingivoplasty, soft tissue crown lengthening, gingivectomy, with no intraoperative or postoperative discomfort; it also offers a clean working site with minimal bleeding. Postoperative sutures or dressings are unnecessary.

The need for drug administration and prescription is decreased because of the analgesic effect of the Nd: YAG laser, the potential for infection is reduced because of the bactericidal effect of the pulsed Nd: YAG laser.The pulsed Nd: YAG laser has been used to treat periodontal disease by eliminating the diseased pocket lining, harmful microbes, and enzymes. The optic fibers are inserted into the periodontal pocket and transmit the appropriate amount of energy necessary to create of a beautiful smile. The pulsed Nd: YAG is the most popular dental surgical laser, with a long research history.

They are available through the following sources: Pulsemaster 600 1Q (American Dental Technologies, Southfield, MI) and PerioLase (Lares).

39 CO2 Lasers The carbon dioxide (CO2) laser generates a mid-infrared wavelength at 10,600 nm, which is well absorbed by the water component of soft and hard tissues.

The delivery systems use articulated arms or wave-guides, not optical fibers. The primary dental applications for the CO2 laser are soft tissue procedures, such as gingivectomy, gingivoplasty, frenectomy, and biopsy. The thermal necrosis zone is shallow (usually 100 to 300 Âľm deep). The laser can vaporize soft tissue precisely and quickly in a no contact mode and is especially good at cutting dense fibers tissues or debulking substantial soft tissues masses. The available CO2 lasers are the LX-20 (continuous-wave output, 20 W) and Nova-Pulse (superpulsing capability) by ESC Medical Systems (Bothwell, WA).

Diode Lasers Diode lasers are semiconductor lasers used for all soft tissue procedures.

The Aurora HL and Aurora SL (Premier Laser System) provide 1.5 to 6 W of 800 to 830 nm continuous-wave power for soft tissue surgeries and treating periodontal problems. The Ceralas D15 (Ceramoptec, Longmeadow, MA) is a 980-nm GaA1As (Gallium-aluminum-Arsenide) diode for soft tissue, periodontal, and bleach procedures.

The Diolase ST 6.0 W (ADT, Corpus Christi, TX) and the LD-15 Soft Tissue (Biolase Technology Inc., San Clemente, CA) also are 800-to 830-nm lasers suitable for all tissue and periodontal and periodontal procedures.

Erbium Laser The 2940-nm wavelengths are well absorbed by water and hydroxyapatite. Both wavelengths are used for decontaminating cavity sites throughout preparation and removal of decay. There is no report of pain, vibration, or high-pitched noise experienced during the procedure. This is a true benefit from the patientâ&#x20AC;&#x2122;s perspective. The low power settings featured in erbium laser usage are a boon when used in an etching technique in conjunction with a traditional acid-etch technique, resulting in increased surface bond strength. Available erbium lasers are Centauri Er: YAG (Premier Laser Systems), 290 nm for hard tissue and some soft tissue procedures; Delete (Continuum Biomedical, Dublin, CA), for hard tissues and some soft tissues procedures; and Millennium Hydrokinetic (Biolase Technology, Inc), 2780 nm Er, Cr: YSGG (Erbium, Chromium, yttrium-scandium-gallium-garnet), laser for hard tissue and some soft tissue procedures.

1. Laser Bleaching: The objective of laser bleaching is to achieve the ultimate power bleaching process using the most efficient energy source, while avoiding any adverse effects. Using the 488-nm argon laser as an energy source to excite the hydrogen peroxide molecule offers more advantages than other heating instruments. Argon lasers emit fairly short wavelengths (488 nm) with higher energy photons; conversely, plasma-arc lamps, halogen lamps, and other heat lamps emit short wavelengths as well as longer invisible infrared thermal wavelengths (750 nm to 1 nm) with lower-energy photons and predictable high thermal character. This high thermal energy can create unfavorable pulpal responses.The argon laser rapidly excites the already unstable and reactive hydrogen peroxide molecule; the energy then is absorbed into all intermolecular and intermolecular bonds and reaches eigenstate vibrations. The hydrogen peroxide molecule falls apart into different, extremely reactive ionic molecules, altering them and producing simpler chemical chains. The result is a visually whitened tooth surface.

2. History of Bleaching: The desire to have whiter teeth and the bleaching technique have been documented since the mid-nineteenth century. Methods for bleaching

40 nonvital teeth include combinations of chloride of lime, calcium hydrochloride, and acetic acid; oxalic acid, 25% ether peroxide, hydrogen dioxide and hydrogen peroxide, and pure chlorine have been used as bleaching agents for vital teeth. In the early twentieth century, the use of 35% hydrogen peroxide was recognized as the most effective bleaching agent. In 1950, Pearson administered heat and hydrogen peroxide for nonvital teeth bleaching. In 1976, Nutting and Poe introduced the walking bleach technique, which uses 35% hydrogen peroxide and sodium perborate for nonvital teeth bleaching.For vital teeth bleaching, in 1918, Abbot used high-intensity light, raising the temperature of the hydrogen peroxide rapidly to accelerate the chemical process of bleaching. In the late 1960s, a successful technique for home bleaching was introduced

by Klusmier, at which time he discovered that 10% carbamide peroxide loaded in a mouth guard with the intent to improve the gingival condition also resulted in a bleaching effect. By March 1989, Haywood and Heymann introduced and published this technique; in the 1990s, this procedure has been used widely by the dental community.Some patients cannot complete the home bleaching process for various reasons, such as the high time investment required, discomfort or irritation from wearing the trays, or the unpleasant taste and gingival or stomach irritation from the bleaching gel. For such patients, power bleaching or in-office bleaching produces the whitening results quickly, without the long-term commitment of wearing trays; the patient’s visits once to have this procedure performed. It has grown more popular since bleaching became a basic dental cosmetic service.The history of power bleaching goes back to Abbot’s use of high-intensity light to raise the temperature of hydrogen peroxide, accelerating the chemical process of bleaching. Since the early 1980s, the heat lamp and heated spatula have been used as a heat source to accelerate the bleaching process of the concentrated hydrogen peroxide; this has been shown effective but also creates irritation to the pulp. The process of controlling the caustic 35% hydrogen peroxide liquid has been challenging. The latest development of power bleaching has offered easy-to-use bleaching agents, essentially using highly concentrated hydrogen peroxide mixed with thickening agents or additional buffering agents, catalysts, or coloring agents. The energy source can be derived from bluecolored halogen curing lamps, infrared CO2 lasers, and blue-colored plasma arc lamps as well as the cool blue argon laser and 980-nm GaA1As lasers.The goal of power bleaching is to whiten with efficiency, by obtaining controlled temperature elevation of the hydrogen peroxide on the tooth surface or by dumping high-energy photons to pump the hydrogen peroxide molecules up to the high vibrational eigenstate of the bleaching agents. The latter accelerates the chemical redox (reduction and oxidation processes occur simultaneously) actions of the bleaching process applied to the tooth surface but with no adverse pulpal effects.

Pulpal Responses: The heat element is favorable to accelerate the rate of reaction but unfavorable for maintaining pulpal health. Zach and Cohen showed that intrapulpal temperature increases of 10°F, 20°F, and 30°F cause 15%, 60%, and 100% irreversible pulpal damage in monkeys. In another study, Cohen attempted to measure incidental discomfort relative to vital bleaching procedures and to identify pulpal changes that would explain the sensitivity and pain phenomenon. He theorized that the heat builds up intrapulpal pressure, leading to the sensation of pain.The in vitro study of Zwahten et al proved that teeth treated with bleaching agents showed increased absorbance and less rising pulpal temperatures during laser or visible light curing exposure than teeth not treated with bleaching agents. In this study, 377-, 488-, 1064- and 2100-nm wavelengths were used, and various bleaching agents, such as Opalescence X

41 (Ultradent Products, South Jordan, UT), Shofu Hi-Lite (Shofu Dental Corp., Menlo Park CA), and Quasar Brite (Interdent, Los Angeles, CA), were implemented.

Combined use of the 488-nm wavelength with Shofu Hi-Lite elicited a raised minimum surface and pulp chamber temperature. The blue 488-nm wavelength coupled with a matching blue bleaching agent produce the minimally raised surface and pulp chamber temperature, establishing the ideal effect in patient pulpal comfort. Conversely, coupling the 488-nm blue light with a red bleaching material elicited a considerable increase in surface and pulpal temperature. The bleaching agent that absorbs the most energy should come in the complementary color to the wavelength used. Determining, the most favorable protocol for power bleaching regarding exact energy settings, activation time span, exact concentration of the components, and color of the bleaching agents requires further research. Shin and White presented a study of tooth surface and pulpal temperature changes caused by visible light cure units, which concluded that high-intensity curing lights achieve surface temperatures that are greater than lowintensity curing lights in much less time. This higher surface temperature may achieve similar or superior bleaching in less time.There is no apparent safety concern for pulpal temperature effects from the tested high-intensity curing light when exposure time is limited to 10 seconds or less per tooth. The present protocol works when high-intensity curing lights (plasma-arc lamp) are kept to 10-second exposure times to control the pulpal temperature. The ability of hydrogen peroxide to penetrate through enamel and dentin as a result of the relatively low molecular weight of the peroxide molecule (30 g/mol), may be accountable for the transient pulpal sensitivity occasionally experienced by some bleaching patients.Bowles and Thompson have shown that some pulpal enzymes are sensitive to the combination of hydrogen peroxide and heat, Calculations made from their data, however, show that the quantity of hydrogen peroxide that produced inhibition was relatively large (in range of 50 mg), whereas the present study reveals that only microgram quantities of hydrogen peroxide diffuse into the pulp. The quantitative difference explains why there is limited pulpal damage in clinical situations. More than 8 decades of conventional in-office vital teeth bleaching using a more concentrated (35%) hydrogen peroxide solution with heat or light has not resulted in pulpal necrosis except when tooth was overheated or traumatized.

3. Mechanism of Bleaching All dental bleaching agents- carbamide peroxide in concentration of 10%, 15%, 16%, 20%, and 22% used in tray bleaching techniques or 35% to 50% hydrogen peroxide-based power bleaching agents-ionize and decompose to initiate the redox chemical reaction bleaching process. Do all bleaching agents decompose the same way? Do all bleaching processes have the same end constituents?

The answers to both of these questions is probably no, and complex exploration is required when seeking answers to the mystery of ionization of hydrogen peroxide (HOOH). The entire chemical bleaching process could produce different ions and proceed in different ways as follows: The ionization of HOOH produces the hydroxyl (OH ˉ) because of breakage of the weakest bond between the two oxygen atoms in the hydrogen peroxide molecule. (see Eq.3). The ionization of HOOH produces the per hydroxyl ions (HOOˉ), considered to be a stronger free radical, and hydrogen ion (H+).

(See Eq 4). The ionization of HOOH produces water (H2O) molecules and oxygen ions (Oˉ ²), a weaker free radical. (See Eq.5). The ionization of HOOH produces water and oxygen molecules in the presence of salivary peroxidase enzymes. (See Eq.2).

Equations Equation of carbamide peroxide (urea peroxide) decomposing to hydrogen peroxide and urea:

42 CO (NH2)2•H2O2→ H2O2 + CO (NH2)2

(Eq. 1)

Equation of hydrogen peroxide dissociated into water and oxygen molecules: 2 H2O2→ H2O + O2

(Eq.2)

Equation of hydrogen peroxide decomposed to hydrogen ions: HOOH→ HO• + •OH

(Eq.3)

Equation of hydrogen peroxide decomposed to perhydroxide ions and hydrogen ions: HOOH→ HOOH ˉ + H +

(Eq.4)

Equation of hydrogen peroxide decomposing to water molecule and oxygen ions: HOOH→ HOH + O ˉ ²

(Eq.5)

Rate of Reaction: The expeditious rate in reaction in laser bleaching makes one major beneficial difference when compared with other methods of bleaching. Because bleaching has a short history of research and study, a calculated, hard definition of how the chemical rate of reaction operates is in its infancy. Enough research has been concluded to assure clinicians that laser bleaching using argon laser as an energy source in the tooth-whitening process. These two components-the ideal energy source and high concentration of the bleaching gel-meet all the criteria required for achieving the ultimate rate of reaction. The bleaching process is a chemical reaction composed of different factors that determine the rate of the chemical reaction. The increase of the temperature, concentration of the reactants, and intensity of the light in a photochemical reaction are all proportional to the rate of the chemical reaction of the tooth whitening.

The Ph value plays an important role in the rate of reaction in the bleaching process as well. Ionization of buffered hydrogen peroxide in the pH range of 9.5 to 10.8 produces more perhydroxyl HO‾2 free radicals. The result is a 50% greater bleaching effect in the same time allotment as other pH levels. The average pH value found in various strengths of hydrogen peroxide is approximately 4. The acidity allows the hydrogen peroxide to have a longer shelf life; however, to achieve efficiency standards, it should be buffered to a much higher pH value with the salt of an alkaline base before being used as an agent for tooth whitening. A thickening agent is added for ease of control and handling.

Carbamide Peroxide Versus Hydrogen Peroxide As A Bleaching Agent: Carbamide peroxide is synonymous with urea peroxide, hydrogen peroxide carbamide, and perhydrol urea. Typically, these products contain carbopol (Carbopal 940, BF Goodrich Co., Charlotte, NC) or carboxypolymethylene polymer as thickening agents to improve the texture for ease of handling and better tissue adhesion in addition to their use as bleaching agents in tray bleaching methods. Carbamide peroxide is unstable and immediately dissociates into its constituents parts on contact with tissue, saliva, or moisture. The usual tray bleaching method uses 10% to 15% strength carbamide peroxide decomposing to 3% to 5% hydrogen peroxide and 7% to 10% urea (See Eq.1) once the solution comes into contact with moisture. Hydrogen peroxide is the active ingredient contained within the bleaching agent. It then continues decomposing into

43 smaller constituent molecules or atoms. Urea continues to decompose into CO2 and ammonia. Ammonia is a strong base, which then offers an elevated pH environment, one that is more favorable for bleaching and simultaneously controls the acidity associated with plague retention. In the presence of salivary peroxidase enzymes, the hydrogen peroxide decomposes to the safer constituents of water and oxygen molecules as part of an inherent self-defense mechanism (see Eq.2). Because if its unstable nature, hydrogen peroxide decomposes instantly to produce various free radical ions (see Eq.35). These ions react with the long-chained, dark-colored chromophile molecules, breaking into smaller, lighter colored structures. It also could be the phenomenon of altering the optical structure of the chromophile molecule, rendering the stain invisible.

The in-office power bleaching method most often uses 35% hydrogen peroxide, although some methods use 50% hydrogen peroxide, a strength 7 to 16 times higher than that used in at-home bleaching techniques. Some clinicians use 35% hydrogen peroxide solution without adding any salt of an alkaline base or buffering agent; instead, solution-saturated cotton or gauze is placed on the teeth. The isolation approach for this method of treatment includes a rubber dam that has been tightly ligated to the teeth with floss and, underneath the dam, a layer of protective material, such as Oraseal (Ultradent Products), applied to the gingival tissue. This bleaching method requires a close examination of the isolation technique to ensure that the causation solution cannot leak through the rubber dam. Other hydrogen peroxide agents used in the power bleaching method can be incorporated with silica powder to create a paste form for easy handling. This paste could eliminate the need for a rubber dam.

Requiring only the isolation and protection of the gingival tissue with paint or liquid dam or composite as a gingival barrier, and a weak base, such as sodium hydroxide, as a buffering agent to raise the pH value for more efficient bleaching. Various proprietary powders, sodium perborate (waterless hydrogen peroxide), or dyes could be formulate into the clinicianâ&#x20AC;&#x2122;s preferred bleaching agents. Experienced clinicians can determine the appropriate bleaching agent depending on their own working style and knowledge.

Beginners should follow the protocol the manufacturer has recommended for their particular equipment.

Choosing a Laser for Bleaching: Three dental wavelengths have been cleared by the Food and Drug Administration (FDA) for tooth whitening: argon, CO 2, and the most recent 980-nm GaA1As diode. In February 1996, Ion Laser Technology (ILT, Salt Lake City, UT) gained FDA clearance for ILT argon (approximately 480 nm) and ILT Genesis 2000 CO2 laser (10,600 nm) with a patented bleaching gel and chemicals for laser tooth whitening. The laser method originally was patented by Yarborough, a dentist and inventor widely credited with introducing some of the presently used toothwhitening methods to the dental community. Yarborough founded Brite Smile (Birmingham, AL) to commercialize laser tooth whitening; Brite Smile was then acquired by ILT. In 1998, ILT changed the process of laser manufacturing, and the company underwent reorganization. The Brite Smile Co (Walnut Creek, CA) changed its protocol in 1999 and currently uses the plasma-arc lamp as an energy source for teeth whitening in their Brite Smile Centers. Yarboroughâ&#x20AC;&#x2122;s treatment concept for laser bleaching involves the mixture of 50% hydrogen peroxide in a sodium peborate, proprietary powder base. Argon laser energy is used first to remove deep-colored stains, followed by a CO2 laser, which emits the mid-infrared thermal energy that is absorbed rapidly by water and the moist bleaching paste. The bleaching paste is applied several times; the teeth are then cleaned, followed by a final coating of fluoride gel. The CO2 laser then is activated to promote the re-mineralization of the tooth surface.

44 Caution should be exercised when using the CO2 laser because the characteristic of this wavelength is thermal and well absorbed into water and hydroxyapatite, which are the primary components of enamel.There is a need for research efforts in laser bleaching (defined by the author as a dentist-controlled, in-office procedure using a high concentration of hydrogen peroxide and an added energy source to accelerate the process of tooth whitening). The preferred energy source is argon laser energy. The visible blue light emits a high-energy photon that efficiently excites the hydrogen peroxide molecules to an eigenstate molecular vibration without any thermal effect.

The thermal effect from the CO2 is favorable for its rate of reaction, but the potentially adverse pulpal responses are a valid concern. The author does not have sufficient experience with the new 980-nm GaA1As laser to comment on its efficacy in this procedure. Should clinicians consider the plasma-arc lamp as an energy source for tooth whitening? To date, the research has focused on its application as a curing source for photoinitiating a camphoroquinone-tertiary amine-type composite system. Similar to the argon laser, the plasma-arc lamp can provide the high (< 1000 Mw/cm²) to medium (< 500 Mw/cm²) intensity of light needed to reduce curing time and ensure the full polymerization of the composite to gain its proper physical properties. Millar and Lauca noted that the Apollo plasma-arc lamp emits a high intensity (>1000 mW/cm²) for 3-second curing cycles; for bleaching cycles, at 820 mW/cm²-similar to and slightly higher than the halogen curing lamp. Measurement of temperature rise at the fiberoptic tip on the 3-second curing cycle is approximately 20ºC; one bleaching cycle is approximately 12ºC, which is higher than the controlled halogen lamp at 6ºC. Duret emphasized that using the halogen lamps for 30 to 60 seconds potentially can raise the pulpal temperature from 4ºC to 14ºC, and when using the Apollo plasma-arc lamp for a 4-second bleaching cycle, the pulpal temperature can increase 2.2ºC. Before using plasma-arc lamps as an energy source for teeth whitening, clinicians must know the proper protocol and be aware of the existence of the infrared and thermal energy.

4. Safety Issues in Laser Bleaching There are no compromises when it comes to safety; responsible clinicians must recognize the operational parameters of the energy source selected. The argon-curing laser falls in the class III laser classification; this requires special training for operating the equipment and use of special eye protection with orange-colored lenses. The eyes are sensitive photoreceptors-everyone in the operatory area must wear these glasses. The intensity of the light used for bleaching must be blocked out with glasses with the proper optical density for specific wavelengths.One must handle the caustic hydrogen peroxide with extreme caution. The patient should be acquainted fully with the procedure and well protected with a good isolation technique. There are different techniques for isolating the bleaching site, such as the well-ligated traditional rubber dam, painting a gingival barrier, or merely working with lip and cheek retractors. Whatever method the clinician feels the most confident with (this includes familiarity with each step pf procedure) is acceptable.A first-aid kit should contain antioxidants such as Vitamin E in liquid or capsule form and aloe vera gel. Even with all isolation techniques in place, a single spilled droplet of hydrogen peroxide or bleaching compound, within seconds, blanches and burns gingival tissue. The patient may express discomfort with body language because the isolation techniques in place may make verbal communication impossible. The clinician should remain calm and apply the vitamin E oil quickly; the symptoms subside within 1 minute.The clinician must follow the protocol regarding the length of exposure time for the selected energy source, which depends on the intensity of the light (mW/cm²) and the particular wavelength. The shorter the wavelength, the higher

45 the energy of the photon. Conversely, longer wavelengths carry lower energy with more of the thermal effect of the photon. The general rule for avoiding unfavorable pulpal responses is 30 seconds per tooth because its thermal energy is at a higher energy output. Usually, there is a recommended time period for chemical oxidation followed by the light oxidation (5 minutes for argon laser and 10 minutes for plasmaarc lamp). Some bleaching compounds (Power gel [DMD, Westlake,CA], and Hi-Lite [Shofu, Menlo Park,CA]) give color indication when the redox process had been completed. Toxicologic considerations, such as cytotoxity or acute systemic toxicity, are much less of a problem with in -office powder bleaching than with the at-home tray bleaching because there is no chance for the patient to consume any bleaching gel or have long-term contact or exposure.

5. General Protocol In Laser Bleaching Evaluate the Dental condition: Review the patient’s oral habit and health history, lifestyle, and expectations. Identify the type of stain and confirm the shade with the patient by using the Vita shade guide arranged by the value as: B1/A1/B2/D2/A2/C1/D4/A3/D3/B3/A3.5/B4/C3/A4/C4.

Discuss existing restoration and condition (limitations). Take a photographic record (and study models for take-home bleaching trays). Discuss possible treatment sensitivity and other treatment options. Discuss the combination of office bleaching and home maintenance bleaching. Set-up: First-aid kit must contain antioxidants, such as Vitamin E and aloe vera, and anti-inflammatories, such as zinc oxide and propylene glycol (Preparation H) in addition to an eye wash bottle.

Assemble protection gear: Laser safety eye goggles, Large bibs 2” x 2”, 3 x 3” gauze, cotton rolls, cheek retractor Rubber dam or paint-on dam (Powerblock [Kreative]or Opaldam [Ultradent]) Assemble preparation Prep kit: Plain pumice paste mixed with 3% hydrogen peroxide and rubber cup Floss, interproximal strip, Brushes, water in a cup, Etching gel (phosphoric acid 37.5%) Fluoride gel or rinse Extra-fine soflex disks or Shofy polishing disks Bleaching Kit: 35% to 50% hydrogen peroxide bleaching gel or paste, such as Power gel. Hi-lite, Opalescence Xtra (Ultradent, South Jordan, UT), and Apollo Secret gel.

Brushes Mixing pad, spatula Bleaching procedure Begin coronal cleansing with pumice, Etch enamel for 5 to 1seconds, Wipe off, and rinse clean., Perform isolation.Brush the prepared bleaching medium carefully on the enamel area. Activate laser light. Use the following settings: 0.35 W 10-second duration for HGM Dental 200, 250 Mw for LaserMed Accucure 3000 or similar argon laser.Expose each tooth for 10 seconds, then repeat. Each tooth can receive 30 to 60 Seconds lasing per application or until the color of the bleaching gel changes (Hi-Lite, blue to white: Power gel, red to clear; Apollo Secret, yellow to clear).Wipe off the used bleaching medium with wet gauze or cotton pellets or brush For interproximal area. Do not rinse with water.Continue to paint on the fresh bleaching medium and activate until done.Wipe off and repeat with the third application. When the third application is done, wipe off the gel, irrigate with water, remove Isolation

46 gear, and rinse well for 1 minute with fluoride rinse. Polish the tooth surface with extrafine polishing disks.Express satisfaction and delight showing the after result, and confirm with the Shade guide.Give postoperative care instructions.Take a second photographic record. Provide home bleaching kit (optional when applicable) Additional Considerations. Consider covering bicuspid-to-bicuspid area, upper and lower arch. It varies in each individual situation; a single dark tooth or an unevenly colored area will need more applications. Have a team assistant hold another light unit, such as a plasma-arc lamp, to expose only 10 seconds per tooth. This speeds the process. Keep the bleaching compound 0.5 mm away from the gingival or root surface.

Difficult cases (e.g., tetracycline stains) can take five applications, or schedule the patient for an additional bleaching appointment as well as continued treatment wit the home bleaching method. The combination of one visit of power bleaching and shortterm home bleaching is an effective approach to tooth whitening.Larger teeth with thicker enamel respond more favorably with better results. Small teeth with thinner enamel have less bleaching effect with a higher chance of unfavorable pulpal response.

Patients with prior bleaching experience respond to the laser bleaching quickly and favorably.

LASERS IN OPERATIVE DENTISTRY

47 a. Caries detection and prevention with laser energy: Because of the difficulties associated with the diagnosis of occlusal caries, many clinicians have adopted the philosophy of "watch and wait". The decision to treat, be it by sealing or cavity preparation, is often made after the caries process is well established, and either bonding techniques fail, or unnecessary sound tooth structure is lost. The current diagnostic model of visual, probe, and radiographic examination is qualitative, subject to operator interpretation, and consequently can produce varied diagnoses from dentists examining the same patient. Recent advances in caries diagnosis and an understanding of the caries process, fissure morphology, and bonding principles allow early intervention. Mirror and probe examination is only 25 percent accurate in detecting early occlusal caries. The use of caries detection dye and laser caries diagnosis raises diagnostic accuracy beyond 90 percent. Hidden caries is now an historic phrase. Early and accurate diagnosis of occlusal caries enables successful prevention and minimal intervention restorative techniques, ending the common evolution from occlusal restorations through to cusp restorations, crowns, and endodontics.A new era has begun in the use of lasers in dentistry, especially in regard to the hard tissue of the teeth. Early caries detection methods such as fluorescence are already in use in Europe, and optical coherence tomography, electric impedance, and ultrasound are likely to become available for use by clinicians in the near future. These methods can be used in two opposing fashions. First, clinicians with traditional training are likely to use them to intervene physically with developing carious lesions at an earlier stage, drilling and filling and placing so-called restorations unnecessarily. This would be a disastrous outcome many more restorations than necessary would be placed, the tooth structure would be weakened, and the bodyâ&#x20AC;&#x2122;s natural protective mechanisms of inhibition of demineralization and enhancement of remineralization through saliva would be exploited. Alternatively, early detection of caries can be dramatically exploited in conjunction with innovative methods for early caries intervention, which in many cases would obviate the need for restorations, preserving the tooth structure and preventing further progression of dental caries or even reversing the process. Among these innovative methods is the prevention of progression of caries by laser treatment of the susceptible sites of the teeth.

Caries detection using laser light:

48 Fluorescence Fluorescence is a well-known phenomenon in science and technology. In simple terms, light at one wavelength (excitation wavelength) is absorbed by the tissue and emitted at a second longer wavelength (emission wavelength). The phenomenon occurs only when there is specific substance that is excited by a specific wavelength of light. Stubel was the first to report fluorescence of teeth using UV excitation, and Eisenberg reported fluorescence by blue light. In 1980, Alfano and Yao reported a systematic investigation of fluorescence from visible light excitation of teeth. They used human teeth with and without caries and observed emission peaks at 427 µm, 480 µm, and 580 µm after radiating by 350, 410, and 530 nm from a tungsten source. The emission spectrum of the carious lesions was shifted to the red portion of the spectrum.

Later, Alfano and Yao looked at excitation from 400 to 700 nm and found differences between sound and carious tissue. Meanwhile, work in Sweden by Sundstrom et al used light of 337, 488, 515, and 633 nm and investigated sound and carious tissue. They reported that no fluorescence from the 633-nm excitation was observed in the visible region but did not look for longer wavelengths. After these studies, considerable effort was put into fluorescence using blue laser light at 488 nm under the term quantitative laser fluorescence (QLF) and by different workers using red light at 633 nm or beyond.

These two areas of study have led to clinically useful instrumentation.

Quantitative Laser Fluorescence Groups in Netherlands and Sweden worked on QLF during the late 1980’s and throughout the 1990s with collaborators in the United States.

A hardware and software system was developed that collects images of lesions based on excitation at 488 nm with argon laser. A filtered blue light source has been developed successfully that works equally well and is still termed QLF (quantitative laser-induced fluorescence). This technique is used for smooth surface lesions but as yet has not been proved in occlusal lesions. The blue light is used to irradiate the surface of the tooth by a specially constructed hand-piece, and the fluorescent image is captured by computer. A filter is used to eliminate the excitation wavelengths from the emitted light so that only the fluorescent is detected. The lesions appear as shadowy images against the bright fluorescent background of the sound enamel. It is not known at this time what causes this fluorescence and why the carious lesion does not. The shadow may be primarily due to increased scattering in the lesion. The image can be stored, measured, and quantified in terms of shape and area. Images at subsequent times can be taken similarly be taken, and by subtraction the clinician can decide on lesion reversal or progression. The technique is in use for clinical trials in several sites. The reproducibility of the method is high and shows great promise for the limited types of lesions that can be detected by it. There have been problems of stain confounding the signal. It remains to be seen whether this technique will be useful as a general clinical tool for the practicing dentist.

Fluorescence Resulting From Red Light Excitation Of Occlusal Surfaces During the 1990s, investigators proceeded from the earlier observations that red light could be used and found that fluorescence occurred in the near-infrared region. Hibst and Gall systematically studied this phenomenon and used a 655-nm laser as the excitation source, with filters at 680 nm, and measured the fluorescent signal at higher wavelengths. Several other groups rapidly progressed with their studies. This work cumulated in the development of a commercial device (Diagnodent, KaVo, Biberach, Germany) in Germany that is in use in several European countries, Brazil, and, since April 2000, in the US. The red laser diode light is directed toward the occlusal surface by a specially designed probe tip, and the fluorescent signal is filtered form the incident

49 light and fed back to the detector through the same device. The signal comes out as a number on the instrument on a scale of 0 to 99.The higher the number, the more caries below. Although this approach does not give a two-dimensional or three-dimensional image, it is a big step forward with current visual or tactile examinations used in the US.Limited clinical and histologic studies to date have shown that a low signal signifies sound tissue below with greater than 80 % accuracy. Most importantly, as the signal increases, it indicates caries below that needs chemical or physical intervention. The management of these occlusal lesions can be followed non-invasively with time to assess the success or otherwise of intervention regimes, such as anti-bacterial or fluoride therapy. The component of the fluoresces in not yet established fully, but it is a bacterial by-product. Other extrinsic staining can interfere with the signal, and this is a problem yet to be solved. As yet there are limitations to the accuracy of the device, but as a functional tool to be used with care, it shows great promise. The device cannot detect secondary caries adjacent to restorations, and it does not appear technically possible to use it for that purpose. Studies by Forgie et al indicate that the device may be useful for inter-proximal lesions, but this has yet to be established in clinical studies.

Optical Coherence Tomography Optical coherence tomography is an imaging technique that is capable of two-dimensional or three-dimensional images of subsurface tissue. The difference in scattering or polarization between sound and carious enamel can be exploited. Laser light of a wavelength that enamel is rapidly transparent to is used, such as 1310 nm. It passes into the tissue, and the emerging light is detected in relation to its phase, which is a measure of the distance that it has traveled. Laboratory investigations using polarization-sensitive Optical coherence tomography have been reported to be able to detect carious lesions in the enamel and to produce an image that shows the extent and severity of the lesion. As yet, the technique is far from clinical use, but it shows considerable promise for the detection of lesions without ionizing radiation and of hidden lesions in occlusal surfaces. b. CARIES PREVENTION USING LASER ENERGY The U.S. Food And Drug Administration approved the use of an Er: YAG laser for caries removal and cavity preparation in teeth. This was the first approval in the U.S for laser use on dental hard tissues. A second Er: YAG laser and an Er: YSGG laser have been cleared for similar hard tissue use. Other hard tissue uses are likely to be approved in the near future, including the use of lasers for the inhibition of progression of dental caries. Early studies showed that the acid reactivity of dental enamel could be altered by treatment with laser irradiation. Yamamoto et al used Nd: YAG laser (1064 nm) and showed the potential to fuse enamel and make it resistant to acid, but enormous irradiation intensities were required to do this (1 GW/cm²). In the early 1980s, Featherstone et al, proposed that the appropriate laser for caries prevention would be those that overlapped with the major absorption bands of the tissue. Featherstone et al, have measured thermal effects, ablation, vaporization, and thermal modeling, all at numerous wavelengths. This work has led to laboratory studies so as to establish scientific basis for the choice of laser conditions that can be used clinically for the prevention, removal, or treatment of caries lesions. The underlying hypothesis for caries prevention that has now been proved is two-fold:

ď&#x20AC;´

There are specific sets of irradiation conditions for laser light that interact most effectively with dental hard tissues.

50 

Efficient conversion of light to heat as the laser light is absorbed results in increased resistance of tooth mineral to dissolution by acid.

Laboratory Studies Showing Caries Inhibition After Laser Irradiation Studies have shown that CO2 laser treatment of dental enamel can inhibit subsequent caries-like progression in the laboratory by up to 85%. The studies were conducted using well-established pH-cycling models that were developed on the basis of studies in the mouths of orthodontic patients. The degree of protection against caries progression provided by the one-time initial laser treatment in this model was comparable to daily fluoride treatment by a fluoride dentifrice in the same model.

Mechanism of Inhibition of Caries Progression and Optimal Laser Parameters Carbonate is lost from the carbonated apatite mineral of the tooth during specific laser irradiation. Pulsed CO2 laser irradiation interacts with the phosphate groups in the dental mineral, is preferentially absorbed, is transformed efficiently to heat, can raise the temperature to levels that drive off the carbonate using low energies with pulses of 100 µs or less. The effects depend on wavelength and pulse characteristics. By adjusting the characteristics of the laser, the optimal heating at the surface can be obtained, while maintaining the temperature rise in the pulp at a safe level of less than 4ºC. Mechanically, what occurs is that the carbonated hydroxyapatite in the surface and immediate subsurface of the enamel is heated to temperatures greater than 400ºC, decomposing the carbonate and leaving behind a hydroxyapatite-like mineral that is much less soluble than the original mineral, as described earlier. It has been shown that variety of conditions can be used to produce this effect. The optimal wavelength in the experiments is 9.3 to 9.6 µm, with pulse durations of 100 µs or less and fluences (energy per surface area, per pulse) of less than 4J/cm². Current studies are concentrating on optimizing the laser parameters. There is no commercial laser currently available that can produce these conditions.

51 Clinical Application of Caries Prevention by Laser Irradiation Although it has been shown in the laboratory, using pH-cycling models, that as few as 20 pulses of 100-Âľs duration each can produce a similar preventive effect to daily fluoride dentifrice use, these promising results have not been tested in human mouths. It is also necessary to conduct human safety studies to confirm that the laboratory assessments regarding pulp temperature changes translate to no damage in the human mouths.

Combination of Ablation and Caries Prevention It would be desirable to develop a laser that can remove carious tissue initially and treat subsequently the walls of the area where carious tissue is removed to make them resistant to subsequent caries challenge.

Fried et al have reported a CO2 laser that removes carious tissue efficiently and can inhibit caries progression. The fluences used for caries removal are higher than those necessary for caries prevention, but the residual energy may be sufficient to provide caries inhibition in the cavity preparation walls. The laser treatment would be followed by placement of a composite resin and inhibit subsequent caries around that restoration.

Conclusion Irradiation of dental enamel by specific wavelengths and fluences of CO2 laser light beneficially alters the chemical composition of the crystals, decomposing the carbonate component, markedly reducing the acid reactivity of the mineral. Efficient conversion of light to heat in the outer few micrometers of enamel increases the resistance of the mineral to acid if a critical threshold temperature is reached. This surface alteration has marked effect in inhibition of subsurface caries progression. The authorâ&#x20AC;&#x2122;s group has proved their initial hypothesis that specific wavelength irradiation is absorbed by the mineral and converted efficiently to heat at the surface, causing thermal composition of the enamel crystals to a less soluble form.

c. HARD TISSUE LASER PROCEDURES & ITâ&#x20AC;&#x2122;S BIO-PHYSICS With more than 170 million restorations placed each year worldwide, many of which could be treated using a laser, an increasing need exists for understanding hard tissue laser procedures. A more conservative, less invasive treatment of the carious lesion has intrigued researches and clinicians for decades.

52 Historical review Investigational research into laser drilling of teeth followed a few years after the investigation of the ruby laser. Goldman et al and Stern and Sognnaes carried out the original research in the 1960s. Hard tissue treatment included caries therapy and cavity preparation. This research was followed by studies of the neodymium (Nd) and carbon dioxide (C02) lasers on hard tissue in the 1970s.

Conventional mechanical preparation with the dental drill has been associated with fear and pain. This association may be due to the fear of the needle or the noise and vibration with the dental hand piece.Vahl, using a ruby laser, reported extensive deep destruction of carious areas along with crater formation and melting of dentin. Kantola experimented with CO2 laser. Cracking and disruption of enamel rods, incineration of dentinal tubule organic contents, and loss of tooth structure occurred. There was evidence of carbonization and fissuring along with increased minerlization caused by removal of organic contents. Wigdor et al reported loss of the odontoblastic cellular layer with the use of the CO2 laser. Experimental with the Nd: yttrium-aluminumgarnet (YAG) laser, Lenz et al found that the tooth surfaces were sealed, and incipient caries-like lesions were inhibited. They found that an increased pulpal temperature might pulpal damage if the dosimetries are not precisely controlled. Because of the affinity if this wavelength to pigmented tissue, topical pigmented initiator was required to ablate sound dentin. Likewise, Wigdor et al showed major destruction of the odontoblastic cell layer with melting of the intertubular dentin. Inflammatory cell infiltration debris and carbonization resulted alongside with areas of necrosis and micro cracks. In 1974, Stern concluded that unless heat-related structural changes and damage to dentinal tissues could be reduced, laser technology could not replace the conventional dental drill. High-powered photo thermal lasers are not ideal for hard tissue interactions. They compromise tooth structure and create a pathologic condition that is unfavorable. Further advances in laser technology have led to favorable biologic interactions. In 1988, Paghdiwala in the United States tested for the first time the ability of the erbium (Er): YAG laser to ablate dental hard tissues. He successfully prepared holes in the enamel and dentin with low energy. Without water-cooling, the prepared cavities showed no cracks and little or no charring, whereas the mean rise in temperature in the pulpal cavity was 43º C.It was shown by Hibst et al and by Kellar et al that the Er: YAG laser was capable of ablating caries with negligible effects on adjacent hard and soft tissues. Kellar et al in a prospective study showed that when the Er: YAG laser was used in conjunction with an adequate water spray for cooling during cavity preparation; it was comfortable alternative to conventional mechanical preparation. Relatively little pain was felt, and the procedure was thought to be efficacious and safe. Pulpal integrity was maintained. Preparation time, however, was approximately twice that of the dental hand piece. The ablation efficiency was about one order of magnitude lower than soft tissue and about a factor of 2 to 4 lower than for bone. Ablation rated in enamel was 20 to 50 µ per pulse.In May 1997, the Er: YAG (2.94 µm) laser was cleared for marketing by the U.S Food And Drug Administration (FDA) after extensive scientific and clinical studies. Precise ablation of sound and carious enamel and dentine with a shallow thermal penetration depth is a quality of this laser wavelength. Likewise, a similar photo acoustic laser, erbium, chromium (Er, Cr): yttrium-scandium-gallium-garnet (YSGG) at 2.79 µm, has the same properties. Pulpal temperature is not increased above the threshold limit for irreversible pulpal inflammation to occur, and no charring or topical initiator is required. Glockner et al reported that during cavity preparation with the laser, there was a temperature change after a few seconds from 37º C to 25º C to 30º C as a result of cooling with water and air. Even with trephination, there was an increase in temperature in the pulp only when

53 the temperature-measuring probe was hit directly by the laser beam. Frentzen et al reported that the surface morphology of enamel remained rough after Er: YAG preparation. The laser treatment allowed additional etching, resulting in a micro retentive pattern. The dentinal tubules beneath the preparation zone showed no morphological change.

Hard Tissue Laser Biophysics Many factors must be considered when determining the biologic effects of laser light energy on dental tissue. The biophysics of hard tissue laser include the wavelength, energy density, and pulse duration of the laser radiation and the properties of the tissue, such as absorption, reflection, transmission and scattering. Absorption and transmission of laser light is primarily wavelength dependent. In the mid-infrared region of the light spectrum, the absorption properties in water and hydroxyapatite vary depending on the wavelength. Low absorption occurs at 2 µm as compared with high absorption at 3 µm and 10 µm. Adsorption in water and hydroxyapatite at 1 µm is approximately 10,000 times less than at 3 µm. The lasers cleared for marketing by the FDA (Er: YAG, Er, Cr: YSGG) can be categorized as having photomechanical effects. Laser light that is highly energetic and is short pulsed causes fast heating of dental tissue in a small area.

A fast shock wave is created when the energy dissipates explosively as a volumetric expansion of the water in the hard tissue occurs. This process is called Cavitation. All dental hard tissue contains various amounts of water. Water molecules in the target tooth are superheated, explode, and, in turn, ablate tooth structure and caries. A bactericidal effect, typical of laser-tissue interaction, occurs as well. The mechanical shock waves that occur are due to a rapid photo vaporization of water, producing a volumetric change of state of the liquid water within the tooth. This change creates high pressures, removing and destroying selective areas of adjacent tissue. The photo acoustic effect that develops is characteristic of a short inter action time (100 µs) and a high laser density. The incident laser energy is absorbed in a thin surface layer. Water, hydroxyapatite, and collagen have an affinity for this laser energy. The water spray of the laser hand piece accelerates this effect. Water –mediated explosive tissue removal has been shown to be most efficient way of removing tissue, while transferring minimal heat to the remaining tooth. Structural morphology of the tooth shows no evidence of cracking, fissuring, or charring. The dentin shows open tubules. Organic material is ablated, leaving inorganic components of the tooth untouched. Greater tooth surface area for enhanced bond strength is created. The depth of penetration in hard tissue is 5 µ using a 300-µs-pulse width.

Capabilities And Limitations The Er: YAG and Er, Cr: YSGG lasers are cleared by the FDA for class I through V cavity preparations, I mm from the pulp, in children and adults for firstdegree and second-degree caries removal. Laser enamel modification (etching) is characterized by the typical visible chalky appearance at the cavosurface margin and internally within the preparation. Shear bond strength when combined with acid etching is greater than conventional acid etching alone (combined 31 Mpa). The lasers have FDA clearance to do the following:  

Remove caries Remove enamel

54     

Remove dentin Remove cement Remove composite Remove glass ionomer Ablate soft tissue with no hemostasis

Lasers do no ablate the following:   

Amalgam Gold Porcelain

d. LASERS IN CARIES REMOVAL Recently, several infrared lasers have been introduced in the dental clinic to remove carious dental hard tissues in anticipation of replacing the high-speed dental drill. Among them, the Er: YAG laser has shown the most promise for hard tissue ablation. Recently, Er, Cr: YSGG laser has been introduced in dental clinics to remove carious dental hard tissues in anticipation of replacing the high-speed dental drill.An investigation was performed by Hossain, M., Nakamura, Y et al (1999)41, to determine quantitatively the ranges of ablation and to evaluate the morphological changes in human enamel and dentin irradiated by Er, Cr: YSGG laser with or without water spray. RESULTS: The irradiation with water spray significantly (p < 0.001) increased the ablation depths compared to those irradiated without water mist. CONCLUSIONS: These results suggest that during the Er, Cr: YSGG laser irradiation, water spray directed at the ablation sites increases the ablation depths and water plays an important role as an initiator of the ablation of dental hard tissues.The Er: YAG laser seems to be effective in the treatment of carious lesions and in cavity preparation in vitro according to a study by Armengol, V., Jean, A., et al (1999) 8. They treated carious lesions, sound dentin, and enamel either with conventional methods or with an Er: YAG laser and to compared the results. On laser-treated teeth, scaly, flaky, rough surfaces were seen: surfaces were clean with several morphological relief’s that may enhance bonding resin restoration. The Er: YAG laser beam can ablate carious dentin with an energy level of 250 mJ at 2 Hz. Sound dentin can be cut at 300 mJ and 2 Hz; for enamel, 350 mJ and 3 Hz are required. Yamada, Y., Hossain, M., Kawanaka, T., et al (2000) 121, did a study to investigate the removal effect of the Nd:YAG laser irradiation and Carisolv on carious dentin. DIAGNOdent carefully assessed the cavity. The results revealed that application of Carisolv followed by Nd: YAG laser irradiation at 4-6W pulse energy effectively removed dentin caries. From the SEM study, it was found that the cavity surface treated with the laser revealed various patterns of micro irregularity, often accompanied by microfissure propagation. There was also no smear layer. Therefore Nd: YAG laser and Carisolv could provide an alternative technique for caries removal instead of the conventional mechanical drilling and cutting. Effective ablation of dental hard tissues using Er: YAG laser has been reported and its application to caries removal has been expected. Yamada, Y., Hossain, M., Suzuki, N., et al (2001)122, investigated the effectiveness of caries removal by using an Er: YAG laser irradiation with and without Carisolv, in vitro. DIAGNOdent carefully assessed the cavity. Their results revealed that application of Carisolv followed by Er: YAG laser irradiation at 100-140 mJ pulse energy effectively removed dentin caries, it was found that the cavity surface treated with the laser revealed various patterns of micro irregularity, often accompanied

55 by microfissure propagation. There was also no smear layer. The study revealed that Er: YAG laser and Carisolv could provide an alternative technique for caries removal for conventional mechanical drilling and cutting.

e. LASERS IN CAVITY PREPARATION Laser Cavity Preparation Technique Different laser parameters or settings are required for ablation of enamel, dentin, and caries because of the greater water content, in increasing order, for enamel, dentin, and caries.

Wet Composition (Wt %) Enamel Inorganic

Dentin

96

70

Organic

1

20

Water

3

10

Recommended settings for the Er:YAG laser are as follows: Energy

Pulse per second

(mJ)

(Hz)

Caries

100-200

10

Enamel

200-250

15

Dentin

150-200

10

Etching

30-50

15

Because Er wavelength has an affinity for the water content of hard tissue, less energy is required to ablate caries than enamel or dentin as a result of its increased hydration.

The laser has dual feedback to the operator-tactile and auditory. Tactile feedback is due to the gentle touch of the contact tip against the tooth surface. Cutting radiation moves out only from the distal end of the tip. The water- air stream is directed on the cutting tip and onto the target tissue. The operator always should move the tip end to provide effective ablation and better tissue cooling. For wide cutting, the tip is moved constantly over the surface. The operator need not change the operating parameters during the cavity preparation. For example, using the laser parameters for ablating enamel, once in dentin the contact cutting tip can be repositioned in a non-contact relationship to the surface of the tooth to decrease the energy density. A non-contact mode is usually 1mm from the surface of the tooth. The decreased energy causes a slower ablation effect. There is a decreased requirement for anesthesia with the use of the hard tissue laser. If during the procedure the patient becomes uncomfortable, an

56 attempt should be made to decrease the hertz (pulse per second), decrease the energy, or move the cutting tip from the contact mode (directly touching the tissue) to a noncontact mode. For deeper cutting, the tip is moved up and down as in a pumping action. The operator can also detect different tooth structures by hearing the sound of ablation (popping sound), which is differentiated by tissue type. During inter-proximal tooth preparation, adjacent teeth can be isolated and protected with the use of a rubber dam or a metal matrix. Laser energy is delivered to the tissue using fiber optics or wave-guides. Disposable or reusable cutting tips of various diameters are coupled to the distal end of the delivery system. They are used in a contact or non-contact position on the tissue. A summary of instructions for hand piece application for cool cutting with a contact fiber tip follows:       

Always gently touch the target tissue with tip end.

Cutting radiation goes out only from the end of the fiber tip.

Direct water stream to the target tissue Always keep operation area wet.

Always keep tip moving to provide effective ablation and better cooling.

For wide cut, constantly move the tip over the surface.

For deep cut, constantly move tip up and down (pumping).

The laser is capable of ablating and preparing the cavity in an irregular fashion, which is ideal for placement of a composite or glass ionomer restoration. In contemporary dentistry, the emphasis is on conservation of tooth structure, in contrast to G.V. Black preparation. This improved precision results in a minimally invasive procedure, which compromises little non-carious healthy tooth structure. The strength of the tooth is maintained, and the bond strength of the restoration is enhanced. Similar to G.V. Black preparation, line angles and point angles can be placed in the preparation for greater mechanical retention of the restoration.Following the development of the ruby laser by Maiman in 1960, the Nd: YAG laser, the CO2 laser, the semiconductor laser, the He-Ne laser, excimer lasers, the argon laser, and finally the Er: YAG laser capable of cutting hard tissue easily were developed and have come to be applied clinically.The Er: YAG laser emitting at a wavelength of 2.94 microns developed by Luxar was used for the clinical preparation of class V cavities by Matsumoto, K., Nakamura, Y., et al (1996)69. Parameters of 8 Hz and approx. 250 mJ/pulse maximum output were used for irradiation. The Er: YAG laser used in this study was found to be a system suitable for clinical application. No adverse reaction was observed in any of the cases. Class V cavity preparation was performed without inducing any pain in 80% of the cases. No treatment-related clinical problems were observed during the followup period of approx. 30 days after cavity preparation and resin filling. Cavity preparation took between approx. 10 sec and 3 min and was related more or less to cavity size and depth. Overall clinical evaluation showed no safety problem with very good rating of 81.7%.In a study by Levy, G. Koubi, G.F.and Miserendino, L.J, (1998)60, the cutting ability of a newly developed dental laser was compared with a dental highspeed hand piece and rotary bur for removal of enamel. Measurements of the volume of tissue removed, energy emitted, and time of exposure were used to quantify the ablation rate (rate of tissue removal) for each test group and compared. The maximum average rate of tissue removal by the laser was 0.256 mm3/s at 8 W, compared with 0.945 mm3/s by the dental hand piece. Light microscopy and scanning electron micrograph examinations revealed a reduction in the amount of remaining debris and smear layer in the laser-prepared enamel surfaces, compared with the conventional method. Based on

57 the results of this study, the cutting efficiency of the high-speed hand piece and dental bur was 3.7 times greater than the laser over the range of powers tested, but the laser appeared to create a cleaner enamel surface with minimal thermal damage. Further modifications of the laser system are suggested for improvement of laser cutting efficiency.Khan, M.F., Yonaga, K., Kimura, Y., et al (1998)46, investigated microleakage at class I cavities filled with amalgam, composite resin, or glass-ionomer after preparation by Er: YAG laser and to compare the results with those by a conventional method using an air turbine. The results showed that there was no significant difference in microleakage between the cavities prepared by Er: YAG laser and those by air turbine (p > 0.05). SEM evaluation demonstrated good adaptation with most of the composite resin or glass-ionomer restorations, but amalgam restorations showed slightly poorer adaptation. The results suggest that Er: YAG laser is useful for class I cavity preparation from the viewpoint of microleakage.A study was done to investigate microleakage after composite resin filling to class V cavities prepared by Er: YAG laser and to compare the results with those obtained by a conventional method using an air turbine in vitro. The study was done by Niu, W., Eto, J.N., Kimura, Y., et al (1998). The results suggested that microleakage at the cavities prepared by Er: YAG laser is at the same level as for prepared by air turbine using dye penetration and SEM methods.A in vitro study by Armengol, V., Jean, A., Marion, D (2000) 7 compared temperature rises during cavity preparation with an Er: YAG laser, Nd: YAP laser, and a high-speed hand piece. The results showed that Nd: YAP laser induced significantly higher temperature rises than Er: YAG or hand piece. Temperature response to the Er: YAG laser and the hand piece seemed to be similar. f. LASERS IN PHOTOPOLYMERIZATION OF RESRORATIVE MATERIALS Background: The argon laser is a versatile multiwavelength laser with many proven and potential clinical applications in dentistry. Its seven wavelengths range from 457.9 nm to 514 nm, emitting a blue-green visible light with 476 nm, 488 nm, and 514 nm being the strongest wavelengths, allowing it to be used for polymerizing of lightactivated materials as well as cutting soft tissue. In 1989, Powell et al showed that 5 seconds of argon laser exposure created a composite with higher compressive strengths than 20 seconds of visible curing light. They showed that with 75% less time the argon laser could produce equal or better results than the conventional halogen light.Severin and Maquin reported the ability of the argon laser to increase the hardness of composite resin as compared with samples that had been cured with the halogen light. They also predicted the use of the argon laser for clinical applications if a minimum of 300 nW could be produced.Kelsey et al showed improved physical properties of 10-second cured argon samples versus visible curing light at 40 seconds. These properties included diametral tensile strengths, transverse flexural strengths, and compressive strengths. They reported significantly increased physical properties with less curing time At the 1989 International Association for Dental Research (IADR) meeting, Arai et al likewise showed the beneficial effects of the argon laser on the Knoop hardness number of composite resin, and at the 1991 IADR meeting, Burtscher reported on the positive effects of the argon laser on curing depth of composites. Blankenau et al showed that laser curing converted a greater amount of monomer to polymerized resin, leaving less unreactive monomer than that cured with a visible light, and Losche reported a greater conversion rate of camphoroquinone with the argon laser. The camphoroquinone photoactivated resins have their peak activity for conversion between 470 and 480 nm. The argon laser is effective and beneficial on polymerizing these

58 resins because the argon laser emits a blue-colored light that is visible and, as published data have indicated, highly effective in polymerizing light-activated restorative materials. In June 1991, the U.S Food and Drug Administration (FDA) cleared for marketing and clinical use the first argon laser for polymerizing of light-activated materials and soft tissue surgery. Since that time, the argon laser has received clearance in other countries as well, leading to expanded clinical use of the argon laser. The laser that can be used in conjunction with all clinical aspects of composite resin curing at approximately 250 nW of power. After acid etching, the laser is used to cure the bonding materials in 2 to 5 seconds before polymerizing and bonding the composite resin to the tooth, using a 10-second cure time. This approach provides a clinical result that is equivalent to visible light-cured resins with 40- to 60-second exposure but is accomplished in less time.

59 Clinical Application: The argon laser is useful in class 2 composite restorations, not only because of the decreased curing time needed, but also the small fiber size allows for easy access of the curing light to the inter proximal restoration. Kelly et al published data showing that optimal results can be accomplished with only 250 to 350 mW of argon laser power, and likewise, optimal results are achieved with only 10 to 12 seconds of curing time. Studies continue to support the ability of the argon laser to cure composite fact and effectively with Vargas et al reporting adequately polymerized composite resin in 30% to 50% less time and Christensen and Christensen reporting polymerization in 10 seconds or less for five different resins. Spot size of the argon laser has little or no bearing on the strength of the material. Aw and Nichols showed there was no significant difference in shrinkage of composites cured with an argon laser or halogen light, and Christensen and Christensen confirmed that short curing times with the laser did not affect shrinkage. Severin and Maquinâ&#x20AC;&#x2122;s predictions seem to have been substantiated through research.The results of work published in 1993 showed the safety of the argon laser in curing composites. Pulp temperature studies on extracted human and dog teeth indicate pulpal temperatures generated by 10 to 20 J/cm² of laser energy to be far below any level for potential damage; similar results were reported by Anic et al during curing of composite resin. Pulpal histologies from in vivo testing confirm that the argon laser at energy levels used in restorative dentistry created neither short-term nor long-term pulpal pathology. Tests by the authors research group have shown the effectiveness of the argon laser in polymerizing restorative materials other than composite. Light-activated cavity liners, such as Timeline (Dentsply/Caulk, Melford, DE), show significantly improved diametral tensile strengths with shorter cure times than the same material cured with halogen light. Likewise, all light activated glass ionomers tested by Blankenau et al showed significantly better diametral tensile strengths when cured with the argon laser. Additionally, the argon laser is effective clinically for applying pit-and fissure sealants. With a curing time of only 5 to 10 seconds, it is easier for the patient to remain as still as well as to control salivary contamination, providing a good clinical result. Laboratory tests have shown less microleakage of sealants cured with the argon laser versus those cured by the visible light source, in addition to only 10 seconds of curing time being needed. Diametral tensile strengths of the sealants cured with the laser were also significantly improved.

The laser seems to provide a significantly improved pit-and-fissure sealant.Studies with the argon laser have shown that by replacing the visible cure halogen light with an argon laser, improved bond strengths could be achieved. Powell et al reported that the enamel bond strengths using Scotch Bond 2 (3 M Dental Products, St. Paul, MN) were equal to or slightly better than those achieved with the visible light but required only 5 seconds of curing time instead of 20 seconds. Blankenau et al also reported on significantly improved dentin bond strengths using the argon laser instead of the visible light. Shanthala and Munshi showed a 16% to 25% increase in enamel bond strengths through the use of argon laser for curing.Potts, T.V., Petrou, A (1990)88 exposed photo polymerizing resins to three different wavelengths of light emanating from the argon laser. It was determined that the most efficient wavelengths for photo-polymerization of camphoroquinone-activated resins were at 477 and 488 nm. The 514.5-nm wavelength was relatively ineffective in activating polymerization. Four camphoroquinoneactivated resins were placed in the root canals of teeth and tested for polymerization depth using a 488-nm wavelength laser beam coupled to an optical fiber 200 microns in diameter. The results indicate that an argon laser coupled to an optical fiber could become a useful modality in endodontic therapy.Because of the multiple wavelengths in the argon laser, it can be used for soft tissue surgery, such as removing fibromas,

60 hyperplastic gingival, and excess tissue around restorations and controlling bleeding around crown preparations as well as many other soft tissue surgical procedures. Its advantages are similar to other lasers: little or no bleeding, little swelling after surgery and minimal postoperative discomfort.

Clinical Case: A 19-year-old female student requested cosmetic correction of the large spaces between her lower anterior teeth. The teeth were radiographically and clinically sound. Using cotton roll isolation, the teeth were cleaned with flour of pumice and water using a slow-speed hand piece on a rubber cup. After cleaning, the teeth were rinsed with water and dried. Using a phosphoric acid gel, the inter proximal surfaces were etched for 10 seconds and rinsed with water and dried. Using a phosphoric acid gel, the inter proximal surfaces were etched for 10 seconds and rinsed with water. After rinsing, the excess water was removed using pledgets of cotton, but the teeth were not desiccated. Using a wet bonding agent (Prime and Bond 2.1, L.D.Caulk, Co), the bonding agent was applied to the acid-conditioned with a gentle stream of air, then laser cured for 5 seconds. TPH (Dentsply/Caulk, Melford, DE) was used as the restorative composite to achieve the desired shape. The material was light achieved with argon laser light at 230 mW of energy for 10 seconds per increment. After all areas were polymerized, the restorations were shaped and polished using conventional polishing techniques. Occlusion was adjusted, and home care instructions were given.

Postperative photographs are immediately postinsertion.

Summary: Research supports the use of argon laser in dentistry. Used at powers of 250 mW + 50 mW for 10 seconds per increment, the argon laser provides good curing of light-activated restorative materials in a shorter period of time with equal or better physical properties as compared to the conventional halogen curing light. When used at approximately 1.5 W, it is a good soft tissue surgical instrument that cuts with little or no bleeding and minimal postoperative pain. The future looks bright for the use of the argon laser on other areas, such as decay prevention or pulpal treatments for primary teeth as well as an adjunct to endodontic therapy. g. LASERS IN REMOVAL OF RESTORATIVE MATERIALS With new wavelengths that allow light transmission by optical fibers, the laser is now often used in endodontics either during treatment or re-treatment.

Blum, J.Y., Peli, J.F., Abadie, M.J.(2000) 12, in their study on â&#x20AC;&#x2DC;Effects of the Nd: YAP laser on coronal restorative materials: implications for endodontic retreatment, concluded that provided sufficient caution is used, the laser may be helpful in removing restorative materials ( such as silver amalgam, composite resins and other permanent cements ) during re-treatment. h.

MORPHOLOGICAL CHANGES IN ENAMEL AND DENTINE AFTER LASER IRRADIATION The effect of a CO2 laser on the structure and permeability of smear layercovered human dentin was evaluated in vitro by Pashley, E.L., Horner, J.A. et al (1992) . Three different energy levels were used (11, 113, and 566 J/cm2).

61 ď&#x20AC;´ ď&#x20AC;´

ď&#x20AC;´

The lowest exposure to the laser energy increased dentin permeability, due to partial loss of the superficial smear layer and smear plugs.

The intermediate energy level also increased dentin permeability by crater formation, making the dentin thinner. The lack of uniform glazing of the surface of the crater, leaving its surface porous and in communication with the underlying dentinal tubules also contributed to the increase in dentin permeability.

The highest laser energy produced complete glazing of the crater surfaces and sealed the dentinal tubules beneath the crater. However, it also completely removed the smear layer in a halo zone about 100-microns wide around each crater which increased the permeability of the pericrater dentin at the same time it decreased the permeability of the dentin within the crater.

The results suggest that the combined use of scanning electron microscopy and permeability measurements provides important complementary information that is essential in evaluating the effects of lasers on dentin.Stabholz, A., Neev, J. et al (1993)98 evaluated the effects of the ArF-193 nm excimer laser on the dentinal tubules of extracted human teeth under a scanning electron microscope. The ArF excimer laser was applied for 5 seconds on three of the quadrants with fluences that ranged from 0.2 J/cm2 to 15 J/cm2 and pulse repetition of 25 Hz. The effects of the ArF excimer laser irradiation varied. Laser fluences of 0.2, 0.5, and 1.0 J/cm2 had no effect. Although fluence of 15 J/cm2 caused significant removal of peritubular dentin, melting and resolidification of the dentinal smear layer was also observed under the scanning electron microscope with a laser fluence of 5 J/cm2.Round enamel and dentin surfaces of sound and carious extracted human teeth were irradiated by an ArF: excimer laser for up to 180 sec in a study by Arima, M., Matsumoto, K.(1993) 6. Thermographic measurements indicated that the temperature rise due to heat accumulation caused by laser irradiation on these enamel and dentin surfaces was up to 19 degrees C (10 HZ with 540 J/cm2), and the temperature returned to the preirradiation value within 10 sec after the irradiation was stopped. Under light microscopy, no carbonization was evident on these surfaces, and a simple recess was formed by abrasion or vaporization in the irradiated regions. In the secondary SEM, uniformly distributed fine pores and prism structures appeared slightly on the enamel surfaces. Between the peritubular and the intertubular dentin, there appeared a distinct difference in the dissolved area. The laser almost completely removed carious regions of the enamel and the dentin, and penetration extended beyond the carious regions. In the backscattered electron SEM, highly mineralized layers were observed on the enamel and dentin surfaces dissolved by the laser.The future use of lasers in endodontics is dependent upon predictable and consistent ablation of dentin. In a pilot study Stevens, B.H., et al (1994)103 used an Ho: YAG laser fiberoptic delivery system to apply laser energy to prepared tooth sections in vitro. At different energy levels Stevens et al observed changes in the dentin surface ranging from minute surface pitting to the formation of large craters. Increases in laser energy were compared with increases in surface area, depth, and volume of craters produced within the range of 150 to 1200 mJ. The Ho: YAG laser fiberoptic delivery system used in this study provides an effective means of ablating dentin. The effect of the XeCl-308nm excimer laser on the mineral content and surface morphology of cut dentin was examined by Dankner, E., Neev, J. et al (1997) 22. Each dentin specimen was lased for 4 s at a fluence of 1 J/cm2 and a frequency of 25 Hz.. Scanning electron microscopy and energy dispersive spectrometry revealed a significant decrease in the phosphorus levels following laser treatment. A decrease in calcium levels also occurred but was not statistically significant. Morphologically, the lased dentin showed an

62 apparently melted surface with partial obstruction of the dentin tubules as well as cracks along the lased surface. Therefore, it appeared that laser treatment may alter the chemical structure as well as the surface morphology of the dentin.

A study by Aniâ&#x20AC;Ą, I., Segoviâ&#x20AC;Ą, S. et al (1998) 4 compared morphological changes on the dentin surface induced by laser light delivered perpendicular or parallel to the dentin surface. The surface of the dentin slices and the root canal walls were lased with argon, CO2, and Nd: YAG lasers. When the laser beam was parallel to the dentin, the effects of the laser energy ranged from no effect to eroding and melting of the smear layer and dentin in the samples. When the laser beam was perpendicular to the surface, all three lasers produced well-shaped craters. From this, it was concluded that the angle of the laser beam in relation to the target surface can be a deciding factor of how much energy will be absorbed by the dentin and consequently of the morphological changes induced by the laser.An investigation was performed by Hossain, M., Nakamura, Y et al (1999)41, to determine quantitatively the ranges of ablation and to evaluate the morphological changes in human enamel and dentin irradiated by Er, Cr: YSGG laser with or without water spray.

RESULTS: The irradiation with water spray significantly (p < 0.001) increased the ablation depths compared to those irradiated without water mist. Morphological findings by SEM indicated that when irradiated without water spray, carbonization with brown or dark color was recognized in enamel or dentin, respectively. In addition, cavities with a molten lava-like appearance were produced and an irregular structure with many microholes was observed in dentin. Hossain, M., Nakamura, Y. et al(1999)39, performed an investigation to evaluate the effect of CO2 laser irradiation on the acquired acid resistance of dental hard tissues to artificial caries-like formation and the ultra structure of lased areas was morphologically investigated in vitro.

Results: The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, followed by 2 W, 1 W, and unlased samples. SEM observation showed that the lased areas were melting with solidification of the smear layer. Even after acid demineralization, the lased surfaces were almost unchanged.

Conclusions: The results of this study suggested that CO2 laser irradiation could sufficiently melt and solidify the enamel and dentin surfaces and thus enhance resistance to artificial caries-like formation.

A study to examine the effects of CO2 laser emitted at 9.3 microns on human sound and carious dental hard tissue ablation with a stereoscope, scanning electron microscope (SEM), and energy dispersive X-ray spectrometer (SEM-EDX) and to identify possible applications of this laser in clinical treatment.( Takahashi, K., Kimura, Y., Matsumoto, K. 1998)105.

Results: The lased sound enamel and dentin surfaces showed crater-like structures which had been produced by the high laser energy. On the other hand, some portions of carious hard tissues were evaported by the laser. A slight amount of carbonization was observed by stereoscopy. Calcium (Ca) and phosphorus (P) content of sound or carious hard tissues was increased significantly (p < 0.01) after laser irradiation, but the ratio of Ca to P after laser irradiation was significantly increased (p < 0.01) on sound hard tissue only.

63 Conclusion: These results suggest that the 9.3 microns CO 2 laser may be useful for the prevention or removal of caries in clinical situations.Lan, W.H., Chen, K.W. et al (2000)57 compared the morphological changes after Nd-YAG and CO2 laser irradiation on dentin surfaces with or without the smear layer. The parameters for the Nd-YAG laser were 50 mJ, 100 mJ, and 150 mJat 10 pps, 20 pps, and 30 pps, and for the CO2 laser were 2 W, 3 W, and 4 W at 5 ms x 20 pps, 10 ms x 10 pps, 20 ms x 20 pps, 50 ms x 2 pps, 100 ms x 2 pps, and 200 ms x 2 pps. The results showed that the Nd-YAG laser caused crater and melting of the dentin surface, especially in dentin specimens with smear layers. The CO2 laser produced extensive cracking lines on dentin surfaces with a smear layer, whereas surface erosion and crater formation were found on specimens without a smear layer. In conclusion, both the laser types and smear layer have a significant influence on the morphological changes of dentin surfaces irradiated by lasers.Turkmen, C., Gunday, M. et al (2000) 115 compared the effect of three laser systems: CO2 (10.600 nm), Nd:YAG (1.064 nm), and ArF excimer (193 nm) lasers on dentin hard tissue and on temperature increases of the pulp chamber.

The dentin surface was then lased for 30 s at the same settings (3 W, 2 mm spot size, 20 pps) with each laser. The average internal temperature increases were as follows: CO 2, 37 degrees C; Nd: YAG, 28 degrees C; and ArF excimer, 1 degrees C. Scanning electron microscopy of the dentin in the occlusal cavity revealed extensive carbonization, isolated balls of recrystallized material, and the presence of smear layer at some dentinal tubule orifices for the CO 2 and Nd: YAG lased teeth. Smear layer was also observed for the ArF excimer samples; however, they exhibited far less surface cavities than the others and seemed to undergo little morphological change on the dentin. Despite the high number of research projects concerned with digital applications of lasers, few studies have targeted the effects of Er: YAG laser irradiation on human enamel or dentin structures.Evaluation of the morphological changes in human enamel and dentin irradiated by Er: YAG laser with or without water mist was done by Hossain, M., Nakamura, Y.et al (1999)40. An Er: YAG laser was used to ablate human dental hard tissues using a pulse energy that ranged from 100 to 400 mJ at a frequency of 2 Hz for 5 seconds. Ablation rates with or without water mist at different pulse energies were measured, and the morphological changes on enamel and dentin were also investigated by stereomicroscopy and scanning electron microscopy (SEM).

The results of this study suggest that addition of a fine water mist directed at the ablation sites does not greatly decrease the ablation, and does not cause any carbonization and melting in the surrounding dental hard tissues.Tokonabe, H., Kouji, R. et al (1999)114 in a study investigated the morphological changes in human enamel and dentin structures irradiated with the use of an Er: YAG laser. The results showed that the Er: YAG laser beam produced defects without signs of serious thermal damage to enamel or dentin. Undesirable thermal effects such as surface cracking or carbonization were not observed. Histological examinations revealed the presence of a thin basophilic line at the bottom and along the walls of defects in the dentin. These morphological changes were evidence of minimal thermal damage to surrounding tissue. These findings suggest that it is possible to remove the enamel and dentin using Er: YAG laser irradiation with minimal thermal changes.

THE FUTURE OF LASERS IN DENTISTRY Laser technology is developing very quickly. New Lasers with a wide range of characteristics are available today and are being used in the various fields of dentistry. The search for new devices and technologies for dental procedures was always challenging and in the last two decades much experience and knowledge has been gained. Clinical lasers are of two

64 types; soft lasers are essentially an aid to healing with relatively few rigorous studies available to support their use. Surgical hard lasers, however, can cut both hard and soft tissues and replace the scalpel and drill in many areas. From initial experiments with the ruby laser most clinicians are using Argon, CO 2 and now Nd:YAG systems. The first dental laser based on a Nd: YAG engine provides hand pieces of similar size to conventional instrumentation and, being fed by a fibre-optic 'cable', has the flexibility for intra-oral use that the CO 2 lasers, widely used in oral surgery, lack. Furthermore, extensive clinical investigation has demonstrated their safety in clinical practice and the fact that procedures can usually be performed without a local anaesthetic is obviously seen as a considerable advantage by patients. Sterilizing as it cuts, the Nd: YAG laser promises to find uses not only in caries removal and soft tissue surgery, but also in endodontics and gingival curettage.Lasers will have a definitive place in dentistry in the future, but to be practical, one dental laser will have to be applicable to a number of therapeutic procedures. Due to its very favorable absorption on dental hard tissues, the CO2 laser will also undoubtedly be useful for many other procedures in dental practice.

A long â&#x20AC;&#x201C; needed characteristic of a laser has been the simultaneous delivery or blending of several wavelengths in the range of CO2, argon and Nd: YAG lasers that would offer the advantage of both cutting and coagulation. With Free Electron Laser, this application is theoretically possible using one machine with the same optical system.

The availability of new wavelength will also lead to the development of dyes less toxic than the ones now available. After Maimanâ&#x20AC;&#x2122;s invention of the ruby laser, researchers were able to create lasing with other solid-state substances as well as gases and liquids.

Although research laboratories around the world have experimented with the entire chart of the electromagnetic spectrum for lasing capabilities, certain wavelengths have become the standard for dental applications. The first of these wavelengths to be cleared to market by the U.S Food and Drug Administration (FDA) for intraoral use was the carbon dioxide (CO2) laser (CO2 Microsurgical Laser System 370, Metricon, Ltd, October 10, 1980, FDA 510 (K) Number K802034). The real interest for the use of lasers in dentistry occurred in the early 1990s with the introduction of the pulsed neodymium: yttrium-aluminum-garnet (Nd: YAG) laser (dLase 300, Sunrise Technologies, Sunnyvale, CA, May 3, 1990, K900539, which was followed shortly thereafter by the argon (various models, HGM Medical Laser Systems, Salt Lake City, UT, September 13, 1991, K912628) and various erbium (Er) (Centauri Er: YAG laser, Premier Laser Systems, Irvine, CA, May 5, 1997, K933841; Millennium Er: YSGG laser, Biolase Technology, San Clemente, CA, October 8, 1998, K980585) and diode wavelengths (Aurora Surgical Diode Laser, Premier Laser Systems, December 15, 1995, K954316; cereals Diode Model D15, CeramOptec, East Longmeadow, MA, October 21, 1998, K983058).As of this writing, the three best markets for dental lasers have been Germany, Japan, and the United States. Of total world sales, the United States market represents 40% to 50%; Japan 30% to 35%; and Germany 20% to 25% (unpublished data, The Institute for Advanced Dental Technologies [IADT]. The Unites States also has two to three times the number of dentists compared with Germany or Japan and represents the largest marketplace for laser sales. An estimate of the percentage of U.S dentists who have purchased a laser unit is 2.5% to 3.5% (unpublished data, IADT). That is roughly 3000 to 4000 units sold over a 10-year period. There is a huge growth potential for this technology in dentistry. This article explores that potential and examines factors that will help propel the future growth of lasers in dentistry.

65 1. FUTURE ADVANCES IN LASER TECHNOLOGY

Many dentists may use size and pricing as excuses for not purchasing lasers.

Most dentists do have a space problem (after all, how many large pieces of equipment can one place in an 8 foot by 10 foot treatment room) or a concern that pieces are still too high. The last 10 years have seen a sometimes-significant reduction in size (an 801b floor unit diode laser versus a less than 20-1b tabletop diode laser) and price (in 1991, an Nd: YAG cost $52,000 versus $24,000 in 1999).

Size: The trend in smaller sizes will continue in the future to the point of shrinking most lasers to small tabletop or hand-held instruments. The U.S military already has fabricated a hand-held laser coagulator for field use. The active medium used in this small military laser is s specific configuration of semi conducting wafers (diode bars).

It is diode technology- either used as the active medium itself or as a pumping mechanism to drive other solid-state lasers- that will help make future lasers more efficient and much smaller.Presently, dental diode lasers are commercially available in either 800-to 830-nm or 950-to 1010-nm wavelengths. This number will increase in the future; medical diodes are presently available in six different wavelengths. Diode lasers are efficient, converting 30% of input electric power into laser output power. This can be compared with about 1% to 2% electric efficiency for most lamp-pumped solid-state lasers. Thus was born the idea of replacing flash-lamps with appropriate wavelengths of diode lasers and creating diode-pumped solid-state lasers (DPSSLs). Because they are more efficient than their flash-lamp-pumped counterparts, DPSSLs require smaller power supplies and cooling mechanisms and can be manufactured at a reduced size and cost. Another benefit of using diode lasers to pump solid-state lasers is that possibility of using new and different active media that presently cannot be stimulated by flash or arc lamps, creating totally new laser wavelengths. Diode technology advancements will play a major role in the future of lasers in dentistry.

Price: It is a simple concept- prices decrease, and sales increase. Price will decrease over rime for three reasons:   

Increased use of diode technology Increase sales Competition

As already mentioned, diode use can increase laser efficiency, and that can lead to reduced manufacturer costs. As dental laser sales continue to increase, costs can drop because manufacturers can make better deals with their suppliers. As sales increase, so does competition, causing possible further-reductions in price. In addition to the obvious Psychologic benefit lower pricing would have on the dental market, the real advantage is that more lasers would be sold. As annual revenues increase, new markets could be developed overseas, which would increase sales and revenues further. This cycle is important for the future of lasers in dentistry because without increased revenues, manufacturers cannot fund research and development properly.A good case in point is the present delivery system for erbium dental lasers, which are marketed mainly for hard tissue use (e.g., cavity preparation). Because the erbium wavelength is greater than 2.5 µm, standard quartz fibers cannot be used to deliver the lasers energy.

Ideally, one would want a delivery system with the same characteristics found in those fibers (i.e., longitivity, flexibility, consistent beam, transmission). As of this writing, a

66 long-life, maintenance-free delivery system has not been developed, even though research into this area began in the mid-1980s. It may be that no one wanted to fund the necessary research and development required for such a system until now because in the past there was not a large enough market in medicine to allow a timely return on research and development expenditures. The dental laser market could stimulate a tremendous amount of research and development.Several FDA clearances accruing in the late 1990s sparked a renewal of interest within the dental community, and accordingly a notable increase in laser sales was noted. The trend may continue for the next several years, if not decades. The dental market has the ability to lead the way for increased expenditures in research and development, which, in turn, can develop more efficient lasers, discover new active media and delivery systems, and control prices.

2. ADVANCES IN LASER DENTISTRY

It has been said that the laser is an invention in search of an application. That was true in dentistry during the 1990s. When the first Nd: YAG dental laser appeared in the U.S market, claims were made for a myriad of applications concerning both hard and soft dental tissues. As more wavelengths appeared, more claims followed. It did not take long to discover that some of the stated claims were inaccurate or unsubstantiated (or both). Thanks to a tremendous amount of research, training, and education, clinicians now know which laser to use and when. But what about the future? What can dentists look forward to during the first couple of decades of the twenty-first century?

Restorative Dentistry Replacing the High-Speed Turbine: Ultimately, laser technology will replace the air turbine for composite restorations, G.V Black preparations, full crowns, inlays, onlays, finish lines, and old restorations. Scanning electron microscopic images of human enamel with various geometric shapes drilled into its surface showed to have sharp line and point angles, and their walls were parallel to one another. The instrument used to cut these shapes was a pulsed neodymium: yttrium-lanthanumfluoride (Nd: YLF) laser (1053 nm).

Caries Inhibition: In 1980 Yamamoto and Katsuhiko reported that Nd: YAG lasing could prevent dental caries in enamel. Although Powellâ&#x20AC;&#x2122;s group has investigated caries inhibition with the argon laser, Featherstoneâ&#x20AC;&#x2122;s work with the CO2 laser has shown the most promise in the area of research. To date, all of Featherstoneâ&#x20AC;&#x2122;s investigations had been in the vitro studies. Featherstone believes, however, that clinical studies could begin within a 2-to-3 year period (personal communication, February 1997) and that within the next 10 to 15 years a small inexpensive CO2 laser designed specifically for caries inhibition will be used by the hygienist as part of the standard treatment for caries prevention

67 Curing: During the 1990s, composite restorative materials have gained in popularity.

Their increased usage caused researchers to develop small, low-power argon lasers (488 nm) for curing composites. With the advances being made in diode technology, within the next 5 years a small hand-held blue diode laser will replace all current curing systems.

Detecting Caries: An alternative to using radiographs in dentistry may be an imaging technique known as terahertz pulsing imaging. Terahertz waves or millimeter waves are located just below the infrared band in the electromagnetic spectrum and are generated by lasing semiconductors with ultrafast pulses (femtoseconds) of visible laser light.

Although terahertz pulse imaging research is still in an early stage, researchers presently can shift contrast mechanisms to measure specific thickness or tooth enamel, peer inside the dentin for caries, or construct a movable three-dimensional image of the tooth on a computer screen. A different system being developed at the University of Strathclydeâ&#x20AC;&#x2122;s Institute of Photonics in Glascow, Scotland, uses a diode-pumped cronium: lithium-sulfer-argon-flourine (Cr: LiSAF) laser (850 nm) to take advantage of the toothâ&#x20AC;&#x2122;s natural ability to fluorine. The technology differs from the argon laserâ&#x20AC;&#x2122;s ability to excite fluorophores because in contrast to the argon, this unit can penetrate and give readings of the enamel greater than 0.5 mm deep. Optical coherence tomography (OCT) is another technology that may replace dental radiographs. Optical coherence tomography is similar to ultra-sound but uses light waves instead of acoustic waves to interact with the target tissue to create images. In contrast to ultrasound, optical coherence tomography does not require a conducting medium. Although all three systems are a few years from being seen in any dental office, they have major advantages over current x-ray technology in tat they do not use ionizing radiation and are much more sensitive in recording changes in demineralization of the tooth. In the future, one of these technologies plus the use of the CO 2 caries inhibition laser are to be powerful tools in caries management.

Selective Caries and Calculus Removal: To date, at least two wavelengths have capabilities to ablate selectively specific components of teeth, while not affecting adjacent tooth structures. The free-running pulsed Nd: YAG laser can remove enamel caries yet has virtually no effect on caries-free enamel (American Dental Technologies, Corpus Christi, TX), whereas the frequency-doubled alexandrite laser can remove calculus from root structure and not harm the surrounding cementum. Although both of these procedures have clinical significance, because of its cost factor the alexandrite laser may never be seen in the market place if more clinical applications cannot be found for this laser. The reason is purely economic in nature.

68 Endodontics: In the early 1990s xenon chloride excimer laser was used to clean and shape the root canal, eliminating the need for files and reamers. The goal of researchers and manufacturers has to be to identify a wavelength that would replace reamers and files, have other hard or soft tissue applications, be cost-effective, and be at least as effective as conventional root canal therapy. Although there has been a large amount of research in laser endodontics using various wavelengths, no system has been built to meet all the previously stated requirements. Even though many German dentists are using the free-running pulsed Nd: YAG and diode lasers for adjunctive root canal therapy, as of this writing, only a handful of lasers have FDA clearance in the United States. That clearance limits the laserâ&#x20AC;&#x2122;s use only to coronal pulp procedures; this expected to change, however.Once the needed FDA clearance for total laser endodontics is obtained the unit will probably be an infrared wavelength, and its delivery system will be use a small (50 to 200 Âľm) optic fiber that will have the ability to side-fire. It is predicted that gutta-percha will be replaced with flowable composite material that will be injected into the lased canal and cured with the small hand-held blue diode laser. A system as just described would save valuable clinical time by eliminating the shaping of the canal that is presently necessary to accommodate the gutta-percha cones. Most of the aforementioned components exist today; their safety and effectiveness need to be demonstrated.

Cosmetic Dentistry: Practically every dentist lecturing on cosmetic dentistry advocates the use of lasers to shape or contour the oral soft tissue because of (1) less bleeding, (2) better visualization of treatment site, (3) no postsurgical tissue shrinkage, (4) decrease in postsurgical discomfort, (5) the ability to make final impressions on the same day as laser surgery, and (6) decreased need for injections. AS lasers continue to be recommended for soft tissue manipulation, laser cosmetic surgery will become standard of care within the next 10 years. Lasers simple are better and have unique advantages for the patient and clinician over steel blades or electro surgery.Another area that is seen and becoming more diversified in usage is computer-aided design/computer-aided manufacturing (CAD/CAM) systems, which use lasers for measuring the internal and external shapes of the tooth. For the dentist using this technology in the office, the systems not only will have the capability of fabricating single units (inlays, onlays, and crowns) more precisely than with casting technology, but also preparing multiple fixed units. In the future, dental laboratories will use CAD/CAM technology to fabricate the framework for fixed or removable prostheses. (Presently, dental laboratories use special Nd: YAG lasers for welding purposes because of their advantages over conventional welding techniques).

Low-Level Laser Therapy: Low-level laser therapy (LLLT) is based on the concept that certain low-level doses of specific coherent wavelengths can turn on or off certain cellular components or functions. Practically speaking, dentists outside the United States (no FDA clearance yet for such devices) have been administering LLLT to their patients as an aid in healing, reducing pain and swelling, and controlling oral infections for atleast the past 3 decades. The research shows that LLLT works, but out of the thousands of studies that exist using LLLT, few represent good evidence-based research. The lasers that are used most commonly are the helium-neon (633 nm) or diode (820 or 940 nm) with power outputs well below 1W.