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Chapter 2
Diode laser overview: how it is done and how to manage it
transmission system. These systems must meet three basic needs: Ä preserve, at the point of application, a radiant power as close as possible to that of the emission source; Ä be manageable; Ä be replaceable and interchangeable. In odontostomatology the handling and practicality of the means of conduction of the laser beam are fundamental.4 The different branches of the dental discipline require different and customized instruments; it is therefore essential for the clinician to have access to specific inserts, handpieces and tips. The operator must, therefore, be able to change the means of conduction in relation to specific clinical needs. The ideal and most widespread instrument for laser transmission is, to date, the optical fiber. The optical fibers are of different types and shapes, responding to specific characteristics and requirements. Not all wavelengths cover this medium in an optimal manner.5 There are different construction materials, among which the most suitable for carrying the wavelengths of the diode are silica fibers.6 Then there are fluoride fibers, which are well suited to conveying the wavelengths typical of the erbium laser. The polycrystalline fibers are used to carry high frequency electromagnetic waves such as those of the CO2 laser. The diameter of the fibers is of particular importance: decreasing the diameter, there is an increase in the intensity of energy due to the greater concentration of the beam, a useful feature for surgery.5,7 For whitening or biostimulation, for example, larger diameters and, generally unfocused are preferred. There are also transmission tools currently in use (for CO2 erbium lasers), such as articulated arms equipped with mirrors and joints, which allow the various components to rotate so that the handpiece can be handled as freely as possible. Finally, there are the most modern systems for transporting radiant energy consisting of hollow fibers (alternatives to optical fiber, but with the disadvantage of having higher production costs and being more perishable). Photons bounce off the hollow mirrored surface of the fibers.5 Optical fibers can be reduced to simple tips, similar in size to ultrasonic inserts. The use of disposable tips and interchangeable inserts offers undoubted advantages in terms of ease of use and safety for the patient. The adoption of specific handpieces, capable of hosting pre-
cision inserts of crystalline sapphire has recently been proposed. In these newly introduced instruments, the distal end is connected to the main system by optical fibers. The use of sapphire tips would entail significant ergonomic and clinical advantages both for the clinician and the patient.
Optical fibers In medical procedures, laser energy is transmitted through a group of optical fibers. The use of optical fibers represents an advantage both for patients and clinicians: the fiber, being thin and flexible, can be suitably bent and adapted; the insertion of a fiber inside the tissues therefore requires only a small incision and the energy can be concentrated on the target without damaging the surrounding tissue. Therefore, medical procedures that use optical fibers are minimally invasive and, consequently, result in less traumatic experiences for patients. The optical fibers consist of a silicate core covered with a protective sheath with a low reflectance index. Light travels inside the core and can travel long distances. There are single-mode and multi-mode optical fibers. The former are widely used in the telecommunications world, generally for long-distance data transport; the latter, used for short-distance data transport, are frequently used in the medical field.3 Single-mode fibers generally have a diameter of less than 20 µm. Multimode fibers instead exceed 50 µm. While both the type of laser source and the conditions of activation of the optical fibers affect the laser power performance, other critical aspects are: proper fiber design, fiber termination, and end surface preparation. Typical lasers used in these medical procedures are Nd:YAG lasers (1064 nm), dual frequency Nd:YAG lasers (532 nm), diode lasers (800 nm ~850 nm ~980 nm) and Ho:YAG lasers (2.1 μm). For these common lasers, index hopping multimode optical fibers with pure silicon core can be a good solution for laser energy transmission, as they transmit light well in the visible range and at IR lengths of up to 2.1 μm. The CO2 laser (10.6 μm) and Er:YAG (2.9 μm) are establishing themselves in the medical field, but traditional optical fibers with silicon core do not work very well due to the high attenuation. As a replacement, it is possible to use hollow silica-based waveguides (silicon dioxide) optimized for these wavelengths.
