DEPARTMENT OF CONSERVATIVE & ENDODONTICS
DETERMINATION OF WORKING LENGTH IN ENDODONTICS
Seminar Presented By
Dr. Krishna Rao Kilaru Post Graduate Student
S.D.M. COLLEGE OF DENTAL SCIENCES & HOSPITAL, DHARWAD, KARNATAKA, INDIA
DETERMINATION OF WORKING LENGTH IN ENDODONTICS. 1) INTRODUCTION. 2) SIGNIFICANCES OF WORKING LENGTH. 3) ANATOMICAL CONSIDERATIONS AND TERMINOLOGY. 4) USE OF REFERENCE POINTS. 5) HISTORICAL PERSPECTIVES. 6) METHODS OF DETERMINATION OF WORKING LENGTH. A. RADIOGRAPHIC METHODS. B. ELECTRONIC METHODS. C. AUDIOMETRIC METHOD. D. DIGITAL TACTILE SENSE METHOD. E. PAPER POINT MEASUREMENT. F. PATIENT RESPONSE. 7) CLINICAL SIGNIFICANCES. 8) SUMMARY AND CONCLUSION. 9) REVIEW OF LITERATURE. 2
1) INTRODUCTION: The determination of an accurate working length is one of the most critical steps of endodontic therapy. The cleaning, shaping and obturation of the root canal system cannot be accomplished accurately unless the working length is determined precisely. 2) THE SIGNIFICANCES OF WORKING LENGTH ARE. 1. The working length determines where the instruments are placed in canal and removal debris, metabolities, end products, & other unwanted items form the canal. 2. It will limit the depth to which the canal filling is placed. 3. It will affect the degree of pain and discomfort that the patient will feel following the appointment. 4. If calculated properly, it will play an important role in success of the treatment and if calculated incorrectly result in treatment failure. 3) ANATOMICAL CONSIDERATIONS AND TERMINOLOGY Simon has stressed the use of terms related to working length determination. WORKING LENGTH: - DEFINITION: - “The distance from a coronal reference point to the point at which canal preparation and obturation should terminate”. The ideal apical reference point in the canal is “apical stop”. ANATOMIC APEX: - Is the tip (or) the end of the root determined morphologically.
RADIOGRAPHIC APEX: -Is the tip (or) the end of root determined radiographically. APICAL FORAMEN: - Is the region where the canal leaves the root surface next to the periodontal ligament. (American association of Endodontists 1984), it is the main apical opening of the root canal. It is frequently eccentrically located away from the anatomic (or) radiographic apex. Kuttlerâ€™s investigation showed 68 to 80% of teeth are deviated. The anatomy of apical foramen changes with age. (a) The concept of the apex (b) The apex of a younger person
(c) changing apex due to hard tissue
ACCESSORY FORAMEN: - Is an orifice on the surface of the root communicating with a lateral (or) accessory canal. They may exist as a single foramen (or) as multiple foramina. APICAL CONSTRICTION: - (Minor diameter) is the apical portion of the root canal having the narrowest diameter. The minor diameter widens apically to the foramen (major diameter) and assumes a funnel shape. The difference in length between the major and minor diameter will increase with age. The facts that point out that the longitudinal view of the canal, as a tapering funnel to the tip of the root is incorrect. The funnel tapers to a distance short of the site of exiting and widens again. Because the adjacent walls of cementum are slightly convex (or) hyperbolic when viewed in long section the configuration of the area between the major and minor diameter resembles that of a morning glory flower. â€œThe morning glory flower configurationâ€? is clearly visualized in an obturated radiograph when sealer is slightly extrudes past the apical constriction.
Although the apical constriction often is thought of as a simple constriction in the dentin. Dummer et, al (1984) classified the apical constriction into four distinct types. The tapering constriction would lead to under preparation and parallel constriction would lead to over preparation.
THE CEMENTODENTINAL JUNCTION (CDJ):- Is the region where the dentin and cementum are united, the point at which the cemental surface terminates at (or) near the apex of a tooth. The CDJ is a histological landmark and cannot be located radio graphically (or) clinically. Langeland reported that the CDJ does not always coincide with the apical constriction. Location of CDJ is 0.5 to 3.0mm short of the anatomic apex. The apical constriction is located 0.5 to 1.0mm short of the radiographic apex, Due to variations; the problem exists in locating apical landmarks and in interpreting their positions on radiographs. ENDOMETRY: The term endometry refers to the accurate determination of the working length, which decides the apical termination part for all inter canal procedures from a reference point. Levy & Glatt demonstrated that the apical foramen deviates from the root tip in atleast 2/3 rd of all teeth. This deviation occurs towards the buccal or 6
lingual aspect twice often as it does towards the mesial or distal aspect. They advised use of taking angled radiograph in addition to the normal view for further information. 4) USE OF REFERENCE POINTS In anterior teeth the reference point is usually the incisal edge, but broken down teeth may be measured from adjustment teeth (or) from some projecting portion of the remaining tooth structure
In bicanal bicuspid the buccal canal is generally measured to the buccal cusp tip, but the palatal canal may use either cusp tip as reference. There may be a variation of at least 1mm in length, depending on which reference point is used in measuring. In mandibular molars especially in mesial canals crossing of files frequently occurs. Mesio buccal (MB) canal reference point may be mesio lingual (ML) cusp tip & ML canal reference
point may be MB cusp tip. Similar mechanism some times used for maxillary molars also.
Stop attachments made up of metal, silicone rubber and plastic are available. Tear drop silicone â€“ rubber stops have an added advantage because they do not have to be removed form the instrument during sterilization at 4500 F and tear drop tip can be positioned to indicate instrumental curvature. The stop attachments should be perpendicular and not oblique to the shaft of the instrument Length adjustments can be made against the edge of a sterile metric ruler Rubber stops instruments have certain disadvantages like movement of up (or) down the shaft, leading to short (or) past the apical constriction and time consuming.
5) HISTORICAL PERSPECTIVES. In the early days of endodontic treatment, at the end of the 19th century radiographs had not yet been applied to dentistry, and working length was usually calculated to the site where the patient experienced feeling for an instrument placed into the canal. This led to multiplicity of errors. If vital tissue were left in the canal unextirpated, the resulting 8
calculation would be too short. If a periapical lesion were present, the calculation could be much too long. Teeth with more than one canal in a root could also give inaccurate information. Then, with the advent of application of X-ray to dentistry by Kells in 1899, teeth treated without the benefit of radiographs, but evaluated by dental films, indicated these miscalculations, However the introduction of a calculated working length, even though it still was in error at that time, was also a significant step in the acceptance of endodontic treatment in the early twentieth century. In early 1900s, the popular opinion was that the dental pulp extended through the tooth, past the apical foramen into the periapical tissue, and that the narrowest diameter of the apical portion of the root canal was precisely at the site where the canal exists the tooth at the extreme apex. These views fostered then the prevailing technique to calculate to the tip of the root on the radiograph the radiographic apex – as the correct site to terminate canal preparation and till the canal. Thus the radiograph apex replaced the feeling of the patient as the apical position for the calculation of working length. In the 1920’s -Grove concluded that pulp tissue could not extend beyond the CDJ because the cell unique to the dental pulp, the odontoblast, was not found past the CDJ. Hatton and grove – advised that preparation beyond the CDJ would result in injury to periapical tissue. Blayney and Coolidge – Histological evaluations indicating that filling short of the root tip gave the best results. In 1955 Kuttler - Studied the microscopic anatomy of root tip, and decided that filing to the radiographic apex was an unwise clinical procedure, contributing to post operative pain and lowering the production of successful 9
cases. Hence many decided to file specific distances away from the root tip in an effort to stop filing into the periapical tissues. Some aspects of Kuttlerâ€™s study have been questioned. The teeth that he studied had no caries, either no restorations or no periapical lesions. These are hardly the type of teeth that are treated endodontically. However many authors verified his anatomic descriptions of the root tip and agreed with his statistics. 6) METHODS OF DETERMINING WORKING LENGTH: The requirements of an ideal method for determining working length include rapid location of the apical constriction in all pulpal conditions and all canal contents; easy measurement, even when the relationship between the apical constriction and the radiographic apex is unusual; rapid periodic monitoring and confirmation; patient and clinician comfort; minimal radiation to the patient; ease of use in special patients such as those with severe gag reflex, reduced mouth opening, pregnancy etc, and cost effectiveness. To achieve the highest degree of accuracy in working length determination, a combination of several methods should be used. This is important in canals for which working length determination is difficult.
THE MOST COMMON METHODS ARE. i. RADIOGRAPHIC METHODS. ii. ELECTRONIC METHODS. iii. AUDIOMETRIC METHOD. iv. DIGITAL TACTILE SENSE METHOD. v. PAPER POINT MEASUREMENT. vi. PATIENT RESPONSE. RADIOGRAPHIC METHODS ARE GROSSMAN‘s method. INGLE‘s technique. WEINE’s modification. CURVED canals. OTHER METHODS, BEST METHOD. BREGMEN METHOD. BRAMANTE METHOD. EVERETT AND FIXOT GRID SYSTEM. EUCLIDEAN ENDOMETRY. RECENT ADVANCES IN RADIOGRAPHIC METHODS, RADIOVISIO GRAPHY. (RVG) XERORADIO GRAPHY. DIGITAL IMAGE PROCESSING. LASER OPTICAL DISK STORAGE.
A) RADIOGRAPHIC METHOD: Originally radiographic method was based on the tactile method. A file is introduced into the canal until the practitioner believes that the narrowest part of the root canal has been reached. The tooth is then radiographed. After processing, the relation between the tip of the instrument and the root apex is determined and the position of the file is changed accordingly. A new radiograph is taken if there is a significant difference. GROSSMANâ€™s METHOD. According to Grossman, an instrument extending to the apical constriction is placed in the root canal is determined by digital tactile sense and a radiograph is taken. A mark (or) stopper is placed at the occlusal (or) incisal reference point which will also be detectable on the radiograph. By measuring the length of radiographic images of both the tooth and measuring instrument as well as the actual length of the instrument the clinician can determine the actual length of the tooth by a mathematical formula. Actual length of x Instrument
Radiographic Length of tooth
Actual length of tooth = Radiographic length of instrument.
The disadvantage of this method is that a small error will be multiplied.
INGLEâ€™ TECHNIQUE:This method recommended by Ingle and reviewed by Bramante and Berbert reported that this method is superior to other methods. Materials and conditions: The following items are essential to perform this procedure. 1. Good, undistorted, preoperative radiographs showing the total length and all roots of the involved tooth 2. Adequate coronal access to all canals. 3. An endodontic millimeter ruler. 4. Working knowledge of the average length of all of the teeth. 5. A definite, repeatable plane of references / anatomic landmark on the tooth, should be noted on the patientâ€™s record. For intact (or) well restored teeth, the most common site for reference is the incisal edge of anterior teeth and the cusp height of posterior teeth. Teeth with fractured cusps (or) cusps severely weakened by caries restoration should be reduced to a flattened surface, supported by dentin. Failures to do so may result in weak cusps (or) weak enamel walls which can be fracture between appointments. Thus if the original site of references is lost and left unobserved, there is the probability of over instrumentation and overfilling. In order to establish the length of the tooth, a stainless steel reamer (or) file with an instrument stop on the shaft is needed. The exploring instrument size must be small enough to negotiate the total length of the canal but large enough not to be loose in the canal. A loose instrument which may move in (or) out of the canal after the radiograph has been taken can cause serious 13
error in determining the length of the tooth. In curved canals, pre curved instrument (or) nickel-titanium instruments are preferred.
Method: 1. Initial measurement: The tooth length is measured on a good preoperative radiograph. Example: The length is 23mm. 2. Tentative working length: As a safety factor, allowing for image distortion (or) magnification subtract at least 1mm from the initial measurement for a tentative working length of 22mm. The instrument is set with a stop at this length. 3. Final working length: The instrument is inserted into the tooth to this length and a radiograph is taken. Radiograph shows that the image of the instrument appears to be 1.5mm from the radiographic end of the root. This is added to the tentative working length giving a total length or 23.5mm form this subtract 1.0mm is adjustment for apical termination short of the cemento dentinal junction (CDJ). The final working length is 22.5mm. 4. Setting instruments: The final working length 22.5mm is used to set stops on instruments used to enlarge the root canal. Example: Initial measurement – 23mm Tentative working length –22mm Difference between end of instrument + end of root – 1.5mm 22 + 1.5mm = 23.5mm Adjustments for apical termination Short of CDJ 23.5 –1 = 22.5mm Final working length = 22.5mm
The 0.5mm which is reduced from the final measurement helps in corresponding the tip of the instrument to the apical constriction. The Ingle method produced the smallest variability in the determination of tooth length and the greatest percentage of successful measurements. However, there are many reports showing variations in the position of the apical foramen. When the two canals of a maxillary first premolar appear to be super imposed. Then the preferable method is to expose the radiograph from a mesial horizontal angle when the x-ray beam is directed from the mesial, the buccal canal is projected toward the distal on the film/ and palatal canal on mesial side on the film. Same with lower molar mesial canals (this is called SLOB rule (or) Clarkâ€™s rule).
Accuracy: How accurate is the radiographic method depends upon the radiographic technique used. Forsberg â€“ demonstrated that paralleling technique was more reliable than the bisecting angle technique. Olso et al â€“ 1 pointed out 82-89% accuracy not 100% - Hence they recommended such
others like tactile feel (or) electronic apex locators
A British group recommended the use of radiovisiography with image enhancement to improve the quality of length of tooth radiographs.
WEINE’s modification: Weine’s recommendations for determining working length based on radiographic evidence of root / bone resorption. 1. If no root (or) bone resorption is evident preparation should terminate 1.0mm from the apical foramen. 2. If bone resorption is apparent but there is no root resorption shorten the length by 1.5mm 3. If both root and bone resorption is apparent shorten the length by 2.0mm.
CURVED canals:Even though accurately determined and confirmed, the final working length may shorten as curved canals are enlarged. Since “a straight line is the shortest distance between two points” the final working length may shorten by as much as 1mm as the curved canal is straightened out by instrumentation. So the length should be reconfirmed after instrumentation is completed. The use of pre-curved files and Nickel Titanium files in curved canals are the best method to complete the endodontic treatment.
OTHER METHODS Various methods have been suggested to determine working length. They differ only as regards technique and complexity, with the result some off them are used more then others. Among the methods commonly employed in endodontics, those of Best, Bregmen and Bramante are the used methods. What are the advantages presented by these methods? And which is more precise? These questions have not been answered in the literature. Each author has proclaimed his technique to be the best. BEST METHOD In this method, as described by Best: A 10mm steel pin was fixed to the labial surface of the tooth with utility wax in a position parallel to its long axis before radiograph obtained. The radiograph so obtained was carried to the BW gauge which indicates the tooth length. Best attained little success, generally resulting in lengths greater than the real length of the teeth.
BREGMAN METHOD In this method flat probes, 25mm. in length, were prepared. Each had a steel blade fixed with acrylic resin as a stop, leaving a free segment of 10mm for placement into the root canal. This probe was placed in the tooth until the metallic end touched the incisal edge (or) cusp tip of the tooth. Then a radiograph was taken. In the radiographic image the following factors were measured:
CAD = Apparent tooth length, seen in the radiograph. CRI = Real instrument length. CAI = Apparent instrument length, seen in the radiograph. To these factors the following formula was applied: The real tooth length is CRD CRI X CAD CRD = CAI In this method Bregman did not indicate the point to be taken as reference for measurements in the coronal portion. Not only the incisal edge or the 19
cusp tip but also the visible mark of the probe appears radio graphically in different planes. In molar teeth the superimpositions of the radiographic images of the cusps, it is difficult and impossible to make measurement precisely. The percentage of success obtained with this method is low because of its high variability which showed the length sometimes to be greater and some times smaller. BRAMANTE METHOD Bramante, in 1970, presented a method to determine the tooth length, employing stainless steel probes of various calibers and lengths. These were bent at one end, forming a right angle, and this bend was inserted partially in acrylic resin, in such manner that its internal face was flush with the resin surface contacting the tooth surface. The probe was introduced into the root canal so that the resin touched the incisal edge or cusp tip, taking care to see that the bent segment of the probe would be parallel to the mesiodistal diameter of the tooth crown, thus making it possible to visualize it on the radiograph. Then the tooth was radiographed. In this radiograph, the reference points are as follows: A = Internal angle of intersection of the incisal and radicular probe segments. B = Apical end of the probe. C = Tooth apex.
The tooth length was calculated in two different ways. 1. Measuring the radiographic image length of the probe A to B; measuring the radiographic image length of the tooth from A to C; measuring the real length of the probe. To these data, the following equation may be applied: CRS x CAD CRD = CAS Where CRD = Real tooth length CRS = Real probe length CAD = Tooth length in the radiograph CAS = Probe length in the radiograph.
This method is a variation that follows the principles of the Bregmen method. 2. Measuring the distance between the apical end of the probe (B) and the tooth apex (C) in the radiograph, adding or diminishing this measurement of the real length of the probe, in this way obtaining the tooth length. This method is a variation that follows the principles of the Ingle method. GRID SYSTEM: Everett and Fixot (1963) designed an x-ray grid system for determining the length of the tooth. The diagnostic x-ray designed consists of lines 1mm a part running length wise and cross wise, every fifth mm is accentuated by a heavier line to make reading easier on the radiograph. Enameled copper wire is placed into Plexiglas and fixed to regular periapical film. The grid is taped to the film to lie between the tooth and film during exposure so that the pattern becomes incorporated in the finished film. The tooth length determined by this method is more accurate than by other methods.
EUCLIDEAN ENDOMETRY: An extra canal length determination method called Euclidean endometry was developed. This uses two geometrically distorted radiographs in determining the real length of the tooth. The two radiographs are taken with a cone fitted with an “Updegraves XCP” (Extension cone paralleling method) device at two different vertical angulations. The actual tooth length is calculated by geometrical principles from the length of the tooth in the two radiographs and the known verticular angular differences. Disadvantages of radiographic methods 1. Anatomic structures and radiopaque materials may be super imposed on the image of the root. 2. The biologic risk of radiation. 3. The procedure is time consuming. 4. Radiograph is a two dimensional representation of a three dimensional object. 5. The apical foramen could not be correctly identified because it frequently deviated from the anatomic apex. Chunn et al. – Found that a file introduced into a root canal that was diagnosed extended the root tip in 33% of the cases with the bisecting angle technique and over extended. the root tips in 20% using a paralleling technique. 6. Patient with gag reflex (or) limited mouth opening may inhibit taking radiographs. Recent investigations tend to show that the radiograph technique of tooth length determination is less accurate than was previously believed.
RECENT ADVANCES IN RADIOGRAPHIC METHODS, 1. RADIO VISIO GRAPHY. (RVG) 2. XERORADIO GRAPHY. 3. DIGITAL IMAGE PROCESSING. 4. LASER OPTICAL DISK STORAGE. 1. RADIO VISIO GRAPHY. (RVG) â€“ (000-1989: 238-42) Introduced to dentistry by Francis Mouyen. The radiographs have become an essential part of dental practice. The silver halide based film emulsions have two major disadvantages. 1. Fairly high radiation dose is needed. 2. Film processing interrupts treatment.
A new system called RADIO VISIO GRAPHY (RVG; France) claims to minimize these problems. By means of a solid-state radiation detector more sensitive than conventional silver halide films, the system presents intra oral radiographic images immediately after exposures. 24
As the name suggests, the RVG device is composed of three major components. 1. The ‘RADIO’ 2. The ‘VISIO’ 3. The ‘GRAPHY’. 1. The ‘RADIO’ part consists of a conventional x-ray generator connected to a highly precise microprocessor timer for very short exposure times and an anatomically adopted sensor with rounded edges and angles. The sensor has a sensitive area of 17 X 26mm 2 consisting of an exchangeable scintillation screen, a fiber optic, and a miniature charged coupled device imaging system. 2. The ‘VISIO’ part of the RVG unit stores the incoming signals during exposure and then converts them point by point into one of 256 discrete grey levels. In real time the RVG is visualized four times larger than when compared to normal radiograph. Image can be stored point by point. In the zoom mode only apical portion can be seen. 3. The ‘GRAPHY’ part of the RVG unit consists of a digital mass storage unit that can be connected to various video print out (or) direct photographs of the screen may be made to provide an opportunity to access the radiographic information further. Radiation doses can be reduced to 75% lower than normal radiography. Although the resolution decreases with increasing zoom, the ability of the unit to provide magnification is especially useful in endodontics because it allows good visualization.
2) XERORADIOGRAPHY Xero means â€“ dry with in 30 seconds. Is a completely dry, nonchemical process, which makes use of electrostatic process as in Xerox machines Invented by Chester F. Carlson in 1937 Xeroradiography makes use of an aluminum plate that is coated with a layer of vitreous selenium. The selenium particles are given a uniform electrostatic charge. The charged plate is placed in a light proof, airtight cassette. When the film is exposed, it causes a selective discharge of the selenium depending upon the amount of radiation used and relative density of the object. The pattern of electric discharge on the plate is called latent image. The latent image is then converted into a visible image by a process called processor. The plate is exposed to charged particles called toner. These particles adhere to the charged areas in amounts proportional to the quantity of charge present. This image is now transferred to a special kind of paper called Xerox opaque paper. The unique feature of Xeroradiography is that it is possible to have both positive and negative image. Once the latent image is converted to a real image on to a paper the selenium plate can be discharged, cleaned and used again. It can be reused as many as 1000 times. Xeroradiographic image differ from conventional radiograph. 1)
It exhibits high edge contrast due to phenomenon called edge enhancement. This facilitates perception of anatomic details.
The image is on paper and is viewed in reflected light.
Choice of positive and negative image is possible
Advantages of Xeroradiography are. 1 Reduction in exposure time. 2 Ease in manipulation. 3 Ease of viewing. 4 Edge enhancement. (Boundary between structures is clear). 3) DIGITAL IMAGE PROCESSING This types of image analysis the radiographs to be digitalized and manipulated electronically. A high quality video camera with a resolution of 525 lines pairs per frame, an analog to digital converter paired to a digital frame buffer and a computer form the basis of the hardware needed for this type of image. Radiographs are taken using conventional techniques and processing. They are then back lit and digitalized, digitalized image areas (or) pixels are converted to 256 gray levels. The gray level of each pixel is balanced to the average optical density in the related areas in the radiograph. Traditionally, additional radiographs taken over are digitalized in the same manner as described â€“ A gray level value of 32 is added to the subsequent image to give the subtraction image a gray level value in the middle of the dynamic range. This process is done for each succeeding radiograph and its digitalized image is substracted from the original (or) reference image. The object of digital substraction radiograph is to duplicate diagnostic information without background noise (or) those structures with no diagnostic significance (structured noise). An advantage of digital substraction radiography is that it reduces the sources of error inherent in photographic substraction by minimizing (or) eliminating the irrelevant differences& processing variations. Because the subtraction image can be manipulated electronically, it is possible to remove bone trabeculae and 27
enhance the remaining image, typically tooth. This enables the clinician to visualize tooth anatomy that would be difficult to capture by conventional radiographic means. Another advantage is that diagnostic and working films can be manipulated by this system and then stored electronically for immediate recall. This technique is superior to conventional radiography for detecting cancellous and cortical bone changes, as well as being able to detect these changes sooner in both types of bone. 4) LASER OPTICAL DISK STORAGE. Laser optical disks are a useful medium to store radiographic images. An 8-inch optical disk is capable of storing up to 10,000 images with a 0.5 sec retrieval & display time. The image is recorded by a focused laser beam heating a thin film of tellurium sub oxide at specific points on the optical disk. (The heating process changes the reflectivity on of the tellurium oxide to a higher reflective value, which institute data storage. The recovery of image from the optical disk is accomplished by the detection of reflected light from the disk surface at the points with the higher reflective value). When compared with normal radiographs, this method has been shown to produce images that are equal to and in some circumstances of superior diagnostic merit.
DETERMINATION OF WORKING LENGTH BY ELECTRONICS 1. INTRODUCTION 2. HISTORY 3. BASIC FUNCTION OF ELECTRONIC APEX LOCATORS (EAL) 4. CLASSIFICATIONS OF ELECTRONIC APEX LOCATORS A. THE FIRST GENERATION (OR) RESISTANCE TYPE. B. THE SECOND GENERATION (OR) IMPEDENCE TYPE. C. THE THIRD GENERATION (OR) FREQUENCY DEPENDENT TYPE. D. THE FOURTH GENERATION. 5. COMBINATION OF APEX LOCATOR & ENDONTIC HANDPIECE 6. ELEMENT DIAGNOSTIC UNIT & APEX LOCATOR. 7. ADVANTAGES 8. DISADVANTAGES 9. HOW THE APEX LOCATORS SHOULD BE USED? 10.OTHER USES OF APEX LOCATORS 11.CONTRAINDICATIONS 12.CLINICAL SUGGESTIONS 13.CLINICAL ACCEPTANCE 14.COMMON PROBLEM SOLVING 15.THE FUTURE FOR ELECTRONIC APEX LOCATORS.
INTRODUCTION In this era of electronically inspired calculators and computers, it was only a matter of time before a device would be developed that indicated an objective determination for this information The result is the Electronic apex locator. Although the term “apex locator” is commonly used and has become accepted terminology, it is a misnomer. Some authors have used other terms to be more precise. These devices all attempt to locate the apical constriction, the cemento dentinal junction, and the apical foramen. They are not capable of routinely locating the radiographic apex. Electronic apex locator has attracted a great deal of attention because they operate on the principles of electricity rather than biologic properties of tissue involved. EAL are useful when the apical portion of the canal is obscured by certain anatomic structures such as impacted teeth, tori, zygomatic arch, excessive bone dentisty, overlapping roots (or) shallow palatal vaults. EAL’s currently are being used to determine the working length as an important adjunct to radiographs.EAL help to reduce the treatment time and radiation dose. HISTORY In 1918, CUSTER was the first to report the use of electric current to determine working length In 1942, SUZUKI, reported his study on iontophoresis of ammoniated silver nitrate in the teeth of dogs. The silver solution was placed in the root canals 30
and then totally dispersed by a negative electrode in contract with the oral mucous membrane. The conclusion of this experiment was that the electrical resistance between the root canal instrument inserted into a root canal and an electrode applied to the oral mucous membrane registered a consistent value of approximately 6.5 kilo ohms (kW). In 1960 GORDON, was the second to report the use of clinical device for electrical measurement of root canals. In 1962 SUNADA, adopted the principle reported by Suzuki and was the first to describe the detail of a simple device to measure working length in patients. He used a simple direct current ohm meter to measure a constant resistance of 6.5 (kW) between oral mucous membrane and periodontal ligament regardless of age of the patient or the shape and type of the teeth. He measured with a direct current. The polarization of the reamer disturbed the measurement, and frequent polishing of reamer tip was needed. Because electronic measurements with a direct current was unstable. This device used by Sunada in his research became the basis for most apex locators.
In 1987, HUANG, reported that this principle is not a biologic characteristic, but rather a physical principles of electricity alone.
BASIC FUNCTIONS OF EAL’S All apex locator’s function by using the human body to complete an electrical circuit one side of the apex locator’s circuitry is connected to an endodontic instrument. The other side is connected to the patient’s body; either by a contact to the patient’s lip (or) by an electrode in the patients hand. The electrical circuit is complete when the endodontic instrument is advanced apically inside the root canal touches the PDL.the display on the apex locator indicates that the apical area has been reached.
CLASSIFICATIONS OF ELECTRONIC APEX LOCATORS Presented by Mc Donald. This classification on the type of current flow and the opposition to the current flow, as well as the number of frequencies involved. FIRST GENERATION. 1st Generation apex locators, also known as RESISTANCE apex locators. Principles: measures opposition to the flow of direct current (or) resistance. When the file of the reamer reaches the apex in the canal, the resistance value is 6.5 kW (current 40ma). Examples: The root canal meter(1969) – in this 150 HZ current is used. Pain was often due to high current. So improvements were made and released as Endodontic meter and Endodontic meter S II
which used a current of
less than 5µA. Inoue reported a modification that incorporated the use of an audiometric component that permitted the device to relate the canal depths to the operator via low frequency audible sounds. One of the most widely used apex locators in 1970’s & 80’s the “Sono- Explorer” was developed using this modification. In 1975 Neosono
and many other resistance type apex locators became
popular. They have improved circuitry, are more compacted and are easy to operate. Other devices in 1st generation are Dentometer and Endo Radar 33
These devices were unreliable when compared to radiographs, with many of the readings longer (or) shorter than the accepted working length. Moreover the resistance type EAL’S yield inaccurate results when electrolytes, excessive moisture, vital pulp tissue, exudates and excessive hemorrhage are present in the canals. Today’s most first generation apex location devices are off the market. THE SECOND GENERATION; 2nd second generation apex locators, also known as IMPEDANCE apex locators. Principle: Measures opposition to the flow of alternating current (or) impedance. DEFINITION of IMPEDANCE: An apparent increase of resistance to an alternating current owing to induction in a circuit. Developed in 1980’s to improve the resistance type apex locators. These uses the electronic mechanism that the highest impedance is at the apical constriction, which is the narrowest portion of the canal where impedance changes drastically(Impendence systems are based on the theory that the root canal ,a long. hollow tube, develops an electrical impedance, caused by transparent dentin deposition, which exhibits a sharp decrease at CDJ. This sudden drop can be measured electrically). The property is utilized to measure distance in different canal conditions by using different frequencies. Examples: The change in frequency method of measuring was developed by Inoue in 1971 as “Sono –Explorer is calibrated at the periodontal pocket of each tooth and measured by the feedback of the oscillator loop. The beeping 34
of the device indicated when the apex was reached. A later model, the Sonoexplorer MK III uses a meter to indicate distance to apex. This device operates on a current of single low frequency. The Endocator was an example of impedance type apex locator where it can be used in presence of electro conductive fluids. Here a high frequency (400 KHZ) current used. With an electrode connected to the dental chair and a Teflon sheath over the probe it was able to make measurements in canals even with conductive fluids present. The Teflon sheath coated file was difficult use in narrow canals and was affected by autoclaving. Patient was uncomfortable due to high current used. Ushiyamaâ€™s method (1983) voltage gradient method. Measure canal length in presence of strong electrolytes. This method uses a concentric bipolar electrode. That measures the current density evolved in a very limited area of the canal with the use of 400 HZ current. Bipolar electrode is located at the apical constriction, because the current density is maximum at the apical constriction. Drawbacks are â€“ It will not fit into a narrow canal, because this method detects a constriction of the canal, the meter identifies any constriction in the middle of the canal as an apical constriction. If the canal has no constriction the meter cannot indicate anything at all. THE APEX FINDER: -
Has a visual digital LED indicator and pulp
tester. THE ENDO ANALYZER:- Is a combined apex locator and pulp tester. DIGIPEX:-Has a visual LED digital indicator and an audible indicator. It requires calibration. 35
DIGIPEX II: - Is a combination of apex locator and pulp tester EXACT – A – PEX: - Has an LED bar graph display and audio indicator. FORMATRON:-Has a flashing LED light and a digital LED display and does not require calibration. This device is small, light weight and inexpensive. THE PIO: - Apex locator has an analog meter display and an
indicator. It has an adjusting knob for calibration. DISADVANTAGES:Root canal has to be reasonably free of electro conductive materials to obtain accurate readings, leading to inaccurate, usually shorter measurements. This created a “catch- 22” situation. Should canals be cleaned and dried to measure working length (or) should working length be measured to clean and dry canals. There is another issue:- not all apex locators incorporated the same degree of sophistication in electronic circuitry that adjusts its sensitivity to compensate for the intra canal environment (or) indicates on its display that it should be switched from a wet to a dry made (or) vice versa. THE THIRD GENERATION (OR) FREQUENCY DEPENDENT TYPE APEX LOCATORS. The 3rd generation apex locators are similar to 2nd generation except that they use multiple frequencies to determine the distance from the end of the canal. In biologic settings, the reactive component facilitates the flow of alternating current, more for higher than for lower frequencies. Thus a tissue through which two alternating currents of different frequencies are flowing 36
will impede the lower frequency current more than the higher – frequency current. The reactive component of the circuit may changes in a canal. When this occurs, the impedances offered by the circuit to currents of differing frequencies will change relative to each other. This is the principle on which the operation of the third generation apex locators is based. Since the impedance of a given circuit may be substantially influenced by the frequency of the current flow, these devices are called frequency dependent. Since it is impedance, not frequency, that is measured by these devices, and since the relative magnitude of the impedances is converted into “length” information, the term “comparative impedance” is more appropriate. Examples :1. ENDEX: (or) APIT – Described by Yamaoka et al. uses a very low alternating current. The signals of two frequencies (5 &1 KHZ) are applied as a composite wave form of both frequencies. As the attached endodontic reamer enters the coronal part of the canal, the difference in the impedances at the two frequencies is small. As the instrument is advanced apically, the difference in impedance values begins to change. As the apical constriction is reached, the impedance values are at their maximum differences and these difference are indicated on the analog meter and audio alarm. This impedance difference is the basis of the “difference method”. The unit must then be reset for each canal. The major advantage of this device is that it works well regardless of the presence of pus (or) electro conductive environments in the canal. However a disadvantage is that a calibration needs to be done each time.
2. The APEX FINDER. A.F.A (All fluids allowed). Is another type of frequency dependent EAL, which uses five different frequencies (0.5, 1,2,4,8 KHZ) & to read four amplitude ratio’s. The unit is self – calibrating and can measure with electrolyte present in the canal. 3. NEOSONO ULTIMA – EZ Apex locators. 4.
MARK V PLUS
JUSTWO (or) JUSTY II
ROOT ZX:A third generation apex locator that uses dual frequency and comparative
impedance principles was described by Kobayashi. The electronic method employed was the ratio method (or) division method. The Root ZX measures the two impedances at two frequencies (8 and 0.4 KHZ) inside the canal. A micro processor in the device calculates the ratio of the two frequencies. The quotient of the impedance is displayed on an LCD (Liquid Crystal Display) meter panel and represents the position of the Instrument tip inside the canal. The Root ZX is mainly based on detecting the change in electrical capacitance that occurs near the apical constriction. Advantages are 1. It requires no adjustment (or) calibration 2. Can be used when the canal is filled with strong electrolyte (or) when the canal is “empty” and moist 3. The meter is an easy to read LCD. Review: - A number of in vitro and in vivo studies on the accuracy and reliability of the Root ZX length been reported. Electronic working length determinations made with the root ZX length compared with direct anatomic working length measurements after extraction of the teeth in the study 38
1. McDonald et al. reported that the Root ZX demonstrated 95% accuracy in their study when the parameters were 0.5 to 0.0mm from the cemento dentinal junction. 2. Four studies indicated an accuracy for the Root ZX in the range of 82 to 100% (Âą Âą 0.5mm from the apical foramen). 7. PROPEX:Is a modern apex locator based on multi frequency enables to locate apical foramen with great precision in any canal condition.
facilitates the access to the exact file position. Propex audio signals combined with the screen information helps about 2-3mm before the apex. Propex warns when the file approaching the apical zone by emitting 2 beeps. 8. FORMATRON D-10. ( Parkell company) Monitors the impedance between the lip clip and the file, it does this by being sensitive to both the voltage applied and the current flowing in the patient circuit with current of multiple frequencies. The D-10 does not feature an LCD read out (cost containment factor) but is adorned by a string of colored lights that descend on the schematic of a stylized root. When for short of foramen, the tracking lights are Green. Cautionary yellow when the file tip approaches close to the foramen. Red light identifies the apical foramen. As file descends, indicated by orange light and the device starts beeping.
THE FOURTH GENERATION:The BINGO 1020 / RAY â€“ PEX 4. (Forum engineering technologies Israel). A fourth generation device and the unit use two separate frequencies 400 HZ and 8 KHZ similar to the 3 rd generation units. The manufacturers claim that the combination of using only one frequency at a time and basing measurements on the root mean square values of the signals increases the measurement accuracy and the reliability of the device. An in vitro study found Bingo 1020 is as reliable as the Root ZX and user friendly marketed by Dentsply as RAY - PEX 4.
COMBINATION OF APEX LOCATOR & ENDONTIC HANDPIECE The Tri Auto ZX is primarily a cordless automatic, endodontic handpiece with a built in Root ZX apex locator. The hand piece uses nickel titanium rotary instruments that rotates at 280 ± 50rpm. The position of the tip of the rotary instrument is monitored on the LED control panel of the handpiece during the shaping and cleaning of the canal. The Tri auto ZX has three automatic safety mechanisms. 1 Auto start-stop mechanism. The hand piece automatically starts rotation when the instrument enters the canal and stops when the instrument is removed. 2. Auto torque reverse mechanism. The handpiece automatically stops and reverses the rotation of the instrument when the torque threshold (30gms / centimeter) is exceeded. This mechanism developed to prevent instrument breakage 3. Auto – apical – reverse mechanism. The handpiece automatically stops and reverses rotation when the apical constriction that has been preset by the clinician. To prevent instrumentation beyond the apical constriction.
The Tri Auto ZX has four modes 1. In the Electrical measurement of root (EMR) mode. A lip clip, hand file and file holder are used with the apex locator in the handpiece to determine working length. The handpiece motor does not operate in this mode. 2. The low mode. The torque threshold is lower than in the high mode. The low mode is used with small to mid –sized instruments for shaping and cleaning the apical and mid –third sections of the root canal. All three automatic safety mechanisms are functional in this mode. 3. In High mode. The torque threshold is higher than the low mode but lower than the manual mode. The high mode is used with mid size to large instrument for shaping and cleaning in the mid third and coronal third sections of the root canal. All three automatic safety mechanisms are functional in this mode. 4. Manual Mode. Offers the highest threshold of torque. In manual mode, the auto start stop. & the auto – torque –reverses mechanisms do not function. The auto apical reverse mechanism does function. Manual mode is generally used with large instruments for coronal flaring. Review: - In vitro, the accuracy of the EMR mode of the Tri auto ZX to determine working length to the apical constriction has been reported at 0.02 + 0.06 mm. The accuracy was reported to have 95% acceptable measurements in a study that compared with direct anatomic working length with the electronic working length.
In a vivo study the canals were cleaned &shaped with the Tri auto ZX with the auto apical- reverse mechanism set at 1.0. In all cases, radiographs showed that the pre instrumentation working length was with in 0.5 mm of the final instrument working length & with out over extension of Gutta percha, instrument breakage or canal transportation. Other apex locating hand pieces:KOBAYASHI et al. Reported the development of a new ultrasonic root canal system called the SOLFY ZX, which uses the Root ZX to electronically monitor the location of the file tip during all instrumentation procedures .The device, minimizes the danger of over instrumentation. The ENDY 7000: (Europe). It is an endodontic hand piece connected to an Endy apex locator that reverses the rotation of the endodontic instrument when it reaches a point in the apical region present by the clinician. Recently the DENTAPORT ZX was introduced. It consists of two modules 1). The Root ZX module and 2).Tri auto ZX module. Both functions can be used by exchanging the back cover. In the Tri auto ZX module, it appears that the file was easily controlled when using the hand piece at 50 to 800rpm and a torque ranging from 30 to 500g\cm. One advantage Dent port ZX is it has an auto apical slow down function. When the rotary file reaches the apical constriction, the rpm slows down allowing for a careful sculpture of the apical portion. However further research is needed.
ELEMENT DIAGNOSTIC UNIT & APEX LOCATOR. A new unit to the market in 2003 is the elements diagnostic unit and apex locator. The device does not process the impedance information as a mathematical algorithm, but instead takes the resistance and capacitance measurements and compares them with a database to determine the distance to the apex of the root canal. It uses a composite waveform of two signals 0.5 and 4 KHZ compared to the Root Zx signals 8 and 0.4 KHZ. The signals go through a digital â€“ to - analogue converter to be converted into an analogue signal, which then goes through amplification and then to the patient circuit model which is assumed to be a resistor and capacitor in parallel. The feedback signal wave forms are then fed into a noise reduction circuit. The manufacturer claims that this allows less sampling error per measurement and more consistent readings. ADVANTAGES OF THE ELECTRONIC METHOD. 1. Only method that can measure length up to apical foramen, not to radiographic apex.. 2. Accurate 3. Easy and fast 4. Reduction of X-ray exposures 5. Artificial perforation can be recognized. DISADVANTAGES OF THE ELECTRONIC METHOD. 1. Requires special device 2. Accuracy is influenced by electrical condition of canal 3. Difficult in teeth with wide open apex. 44
4. Inconsistent results in cases of vital teeth (except newly developed devices). HOW THE APEX LOCATORS SHOULD BE USED? General Instructions: In electronic measurements a stable circuit should be build between the measured canal and the device. Electrical connection: At each electric contact point (File holder â€“ file, Lip clip mucous membrane) a firm electric connection is required. Cervical leakage: The cervical leakage of the measuring current is the greatest cause of the inaccurate measurements (high reading) in the electronic method. The causes of cervical leakage might be metal restorations, decay of the teeth, and electro conductive irrigants. Others Dry canals:-low readings (obtaining long working length) are apt to occur with extremely dry canals in the measurement involving conventional apex locators. Long Root:-It is reported that high readings (obtained a short working length) occurred in teeth with extremely long roots in the measurement involving conventional apex locators. Lateral canal:-If the tooth has a large lateral canal, the meter may indicate the apex in an early stage of the measurement when the file tip reaches an inner opening of the lateral canal.
Open apex: - If the tooth has a wide open apex, the electronic measurement is almost impossible. The radiographic method is recommended. OTHER USES OF APEX LOCATORS. 1. Detection root perforations: The 3rd generation apex locators are especially advantageous in this respect. Since they can function even in presence of blood. The early detection and immediate treatment of an iatrogenic perforation is most important for making a good prognosis. Radiographic detection often hinders the existence of the perforation, particularly when it occurs buccolingually. An in vitro study conducted by Kilaru et al in 2005 reported that the detection of root perforation by apex locator (FORMATRON D 10) was 85%. The file tip ended 0.06mm to 0.60mm short of the external outline of root surface. Therefore, the EAL can be used in detecting root perforations. 2. Accuracy in primary teeth: The location of the actual apical foramen in the primary teeth, which are in the process of physiologic resorption, provides a great challenge to clinicians. Katz et al reported that Root ZX had an accuracy that was similar to the actual length and the radiograph film and with a tendency of slightly underestimate the root canal length by 0.98 mm of the apex. The tooth, root canal type, status of the periapex and clinical conditions did not influence these results. 3. Effect of foramen size on the accuracy of EAL: In general, there is a consensus that the file size does not affect the accuracy of EALâ€™s Nguyen et al, conducted an in vitro study to observe the effect on the measurement of the relative diameters of the file and root canal 46
using Root ZX. The initial canal length was measured by using EAL by a size 10 file then the canal was enlarged to size 60 with rotary files and the final lengths were obtained using a size 10 file and a size 60 file. The position of the file tip was observed histomorphometrically after the apical 4mm of the canal was exposed by grinding the buccal aspect of the root. Differences the final length 10 to 60 and initial lengths were similar. 4. Effect of resorption on the accuracy of EAL’s: The use of EAL’s in apical resorption is under question because of the possible destruction of the apical constricture and the loss of periodontal tissue. Goldberg et al, reported that the accuracy of EAL in apical resorption may depend on the operators experience and could locate root end consistently even with the resorption lacunae. 5. Effect of different metal Types: The question whether which type of metal be used. Nekoofar et al, evaluated the accuracy of Neosono ultima EZ with nickel titanium and stainless steel files and accuracy of Ni - ti is 94% and stainless files is 92% there was no statistically significant difference. CONTRAINDICATIONS of EAL’s The use of apex locators other electrical devices such as pulp tester’s electrosurgical instruments, are contraindicated for patients who have cardiac pacemakers. Electrical stimulation to the pacemaker’s patient can interfere with pacemaker function. In special cases, an apex locator may be used on a patient with a pacemaker when it is done in close consultation with the patient’s cardiologist.
CLINICAL SUGGESTIONS 1. Conventional radiograph still is needed? Yes. The EALâ€™s only provide the electronic impedance and not the canal shape. To obtain anatomic information of the roots and canals, Medico legal record keeping requirements a radiograph is still mandatory in an endodontic procedure. 2. Working length is changing continuously. The working Length changes constantly throughout the root canal treatment. During the canal preparation procedure, the file in advertently may go beyond the apical foramen, breaking the apical constriction and creating an oval-shaped exit, which leaves a thin wall at the coronal part of dentin. As the file tip touches the most coronal margin of the oval exit, the unit will show an apex sign, there by measuring a shorter length than the initial working length. This may occur because the use of a rotary instrument is increasing in the endodontic practice. A straightening of the curved canal can be another cause. In order to avoid this problem care needs to be taken so as not to break the apical seat (or) the remaining thin dentin wall. A file size that fits snuggly inside the apical canal is recommended. CLINICAL ACCEPTANCE Use of electronic apex locators to determine working length has still not gained wider spread acceptance world wide. This may be due to early devices which suffered from poor accuracy, did not function in 48
presence of irrigants, cost of the instrument and exposure to the technology are the factors. A survey in New Zealand found apex locators use favored by younger practioners, and a reduced number of radiographs taken during root canal treatment of maxillary molars In Japan there is extensive use of apex locators. COMMON PROBLEM SOLVING The following one the some of the problems encountered by using EALâ€™s 1. Unstable electronic signal with rapid wandering signs. Occurs most frequently when the file touches the metallic restorations (or) cervical leak through the sub gingival caries. Solution: Removing the metallic restoration and blowing air onto the wet chamber solves the problem. 2. Sharp drop of the signal at the apical foramen. The normal operation of a EALâ€™s is demonstrated by the smooth & gentle movement of the signal from the orifice to the apical foramen. This occurs mostly with a dry canal. When the file tip is at the extremely dried point, there is little (or) no electric current, even at higher frequencies. As soon as it meets with the apical tissue, a sudden circuit breaks out, which brings the signal to the apex mark. Solution: Gentle irrigation of the canal will reiterate the normal operation of the unit. 3. Apex sign from the beginning severely bleeding (or) exudating canal. At times, the signal reaches the APEX mark before the file enters the foramen area. This is due to electrolyte in the canal. This phenomenon
occurs often with extreme bleeding and actively draining pus (or) exudates from the canal. Solution: - gentle irrigation with Naocl (or) saline until the drainage becomes controlled 4. Premature reading, open apex When there is open (or) blunderbuss â€“ type foramen, the meter tends to read short from the true apical foramen. Premature reading is probably due to the sharp drop in the gradient of the impedance ratio at the thin dentin walls. THE FUTURE FOR ELECTRONIC APEX LOCATORS. The future of apex locators is very bright, significant improvement in the reliability and accuracy of apex locators took place with the development of 3rd generation models. It is probable that more dentists will now use apex locators. In the management of endodontic cases. At this time, However, the conclusion of studies have not demonstrated that apex locators are clearly superior to radiographic techniques, nor can they routinely replace radiographs in working length determination. It has been demonstrated that they are at least equally accurate future apex locators should be able to determine working length in all electronic conditions of the root canal without calibration. The meter display on future apex locators should accurately indicate how many millimeters the endodontic tip is from the apical constriction.
DETERMINATION OF WORKINGLENGTH BY AUDIOMETRIC METHOD. This method is invented by Inoue in 1985. The audiometric method, a variation on the principal of electrical resistance of comparative tissue, uses low frequency oscillation sound to indicate when similarity to electric resistance has occurred by a similar sound response. By placing an instrument in the gingival sulcus and inducing an electric current until sound is produced, and then repeating this by placing an instrument through the root canal until the same sound is heard, one can determine the length of the tooth. This principal utilized in electronic measurements as an audible component. This method is nothing but modification of radiographic and electronic method uses low frequency oscillation sound to determine working length.
DETERMINATION OF WORKINGLENGTH BY DIGITAL TACTILE SENSE. Some experienced clinicians claim that it is possible to gauge the apical constriction of the root canal system by tactile sense. There are several problems with this claim. First, not all the teeth possess an apical constriction due to the presence of apical resorption. Second, the ability to gauge the apical constriction relies on the presence of a natural canal taper that has a minimal constriction only at the termination of the canal. Third, the tactile detection of the apical constriction relies upon the selection of a file size that will first bind only at the apical constriction. Given that the size 51
of the apical constriction varies considerably, the method is reliant upon several pre conditions as well as fortuitous selection of the correct instrument size. All clinicians should be aware that this method, by itself, is often inexact. It is ineffective in root canals with an immature apex and is highly inaccurate if the canal is constricted through out its entire length. This method should be considered as supplementary to high quality, carefully aligned, parallel, working length radiographs and apex locator. SEIDBERG et. al reported an accuracy of just 64% using digital tactile sense. Another study found the accuracy is only 25% by digital tactile sense. Even most experienced specialist would use two or more methods to determine accurate working length in every canal.
DETECTION OF WORKING LENGTH BY PAPER POINTS. In a root canal with an immature apex, the most reliable means of determining working length is to gently pass the blunt end of a paper point into the canal after profound anesthesia has been achieved. The moisture (or) blood on the portion on the portion of the paper point that passes beyond the apex may be an estimation of working length (or) the junction between the root apex and the bone. In cases in which the apical constriction has been lost owing to resorption (or) perforation, and in which there is no free bleeding (or) suppuration into the canal, the moisture (or) blood on the paper point is an estimate of the amount the preparation is overextended. This paper point measurement method is a supplementary one. A new dimension has recently been added to paper points by the addition of millimeter markings. These paper points have markings at 18, 19, 20, 22 and 24 mm from the tip and can be used to estimate the point at which the paper 52
point passes out of the apex. These paper points were designed to ensure that they be inserted fully to the apical constriction. The accuracy of these markings should be checked on a millimeter ruler.
DETECTION OF WORKING LENGTH BY PATIENT RESPONSE. Another fallacious belief is that if the pulp is necrotic (or) if canal preparation is completer, an unanesthetized patient will detect the file tip when it reaches and contacts the vital tissue at the apical foramen. Supposedly the patient then signals this event with an â€œeye blinkâ€? (or) other pain response. There are problems with this approach also. First, the procedure is painful for the patient. second a necrotic pulp frequently contains vital inflamed tissue that extends several millimeters into the canal. This tissue may be very sensitive and respond to instrument contact short of the apex. Third, a patient feels pain after canal preparation is complete from hydraulic pressure even though instruments do not reach the apical region. The opposite of pain with instruments short of length is lack of pain response when instruments are beyond the apex. This has been observed in some situations when, in an unanesthetized, patient, and an instrument have passed several millimeter out of the apex without being defected.
7. CLINICAL SIGNIFICANCES Before determining working length the coronal access to the pulp chamber should be in a straight line with easy path of insertion and removal of endodontic instruments. (Files, reamers etc).
- It is very important to monitor the working length periodically since the working length may change as a carved canal is straightened. The loss may be related to the accumulation of dentinal and pulpal debris in the apical 2 to 3 mm of the canal. Other factors such as failing to maintain foramen patency, failing to irrigate apical one third adequately, ledge formation and blockage of canal. - Optimal length of canal preparation and the optimal level of canal obturation are controversial points. Most dentists agree that the desired end point is the apical constriction, which are not only the narrowest part of canal but also a morphologic landmark that can help to improve the apical seal when the canal is obturated. - Failure to determine working length and maintaining working length may result in the length being too long and may lead to perforation through the apical constriction. Destruction of the constriction may lead to over filling (on) over extension and increased incidence of postoperative pain, prolonged healing period, incomplete regeneration of cementum, PDL and alveolar bone. -
Failures to determine and maintain working length accurately may also lead to shaping and cleaning short of the apical constriction. Leading to persistent discomfort, incomplete apical seal, apical leakage supports the continued existence of viable bacteria and contributes to a continued periradicular lesion and lowers the rats of success.
- In this era of improved illumination and magnification, working length determination should be to the nearest one â€“ half millimeter.
An instrument for measuring root canal length and apex location. â€œA rapid techniqueâ€?. Apex finder: Is an instrument designed primarily for apex location and measuring of root canal length. This instrument consists of a fine, tapered shaft made of soft plastic, and a narrow, stainless steel tube which is beveled at one end (needle). The other end of the tube is surrounded by a plastic ring to facilitate its handing. The plastic shaft is inserted through the tube in one direction, some what similar to a piston in a syringe. The barbs are 1mm long and present at an acute angle to the long axis of the shaft. All the barbs are inclined in one direction away from the tip of the shaft.
Plastic shaft inside the tube
The apexfinder in position.
The plastic shaft protruding from the tooth after removal of
tube. Technique: The use is based on measuring the distance traveled by the plastic shaft from the cusp tip (or) incisal edge to the apical foramen. After removal of pulp tissue the outer tube is inserted into the cavity until it just touches the floor of the pulp chamber. This is necessary to place the beveled tip of the tube into the canal orifice in order to gain access to the root canal. The tube is intended primarily for carrying the plastic shaft through the canal orifice to the root canal. The shaft is inserted into the tube and directed toward the root. It is first introduces to within one third (or) less of the apex; then the tube is carefully removed from the mouth, leaving the shaft in its place in the root canal; protruding out of the cavity. Care should be taken that the plastic shaft be always pushed in one direction â€“ root ward â€“ whether inside the tube (or) the root canal. It should be pushed apically with utmost core. As it passes into the canals, the feel seems smooth and uninterrupted. When the operator feels that the apical foramen is reached, the shaft is advanced 56
for a short distance. 1mm and stopped. It should then be pulled gently for a short distance toward the crown. If it slides out smoothly, without resistance, it must be stopped and given another push to advance further apically. The process of pushing the instrument for a short distance followed by a gentle pull, to examine the resistance, may be repeated until an accurate sense of resistance is encountered. Inability to pulp the instrument easily from its place (resistance to with drawl) will inform the operator that the tip of the shaft is slightly past the apex and one of its teeth (barbs) has engaged the margin of the apical foramen. The side of the shaft at the outer end should then be marked for identification. This is done by making a mark on the shaft opposite to the incisal edge (on) cusp tip. A pull stroke is now used to remove the instrument from its place in the root canal. The force used to pull the shaft should be gentle, but firm enough to overcome the resistance in order to bend the barb (or) barbs which engaged the apical end of the root. The length is measured by distance between the mark on the side of the shaft and the nearest barb (tooth), showing a change in direction (bending ) and loss of its acute angle.
Apical terminus location of root canal treatment procedures. [000. 2000, 89:99-103]. by Min- kai wu 57
Canal instrumentation includes both cleaning and shaping. Cleaning is the significant reduction of tissue as well as micro-organisms and their byproducts from the pulp system]. With a vital pulp microorganisms would not be present in the apical part of the canal. In infected cases bacterial contamination may reach the most apical part of the canal and occasionally the periapex. The purpose of shaping is to create a canal configuration suitable for obturation. If termination is too short (or) too long, the outcome is negatively influenced. If the apical canal is not completely obturated, residual bacteria may survive and multiply; tissue fluids percolating into the canal may provide nutritive substrate. The apical 3mm of the root canal system has been considered to be a critical zone in the treatment of infected root canal. Obturation and restoration prevent the reinfection of the pulp space by micro-organisms from the oral cavity, to seal all portals of exit and to serve as a wound dressing against which healthy tissue can oppose. In 1994, Stabholz et. al. summarized the factors influencing the success and failure based on a series of mainly retrospective studies and concluded the prognosis is decreased with over fill and with significant under fill. Anatomy of the apical canal. The traditional classical concept of this anatomy is from Kuttler. The apical constriction is commonly advocated as the ideal termination for RCT, being a natural narrowing of the root canal and termination of the pulp. This is where an apical stop is formed against which the obturation materials are packed. Because this constriction is usually not present, the apical foramen may be a more useful landmark. The distance between the apical constriction and apical foramen ranges from 0.5 to 1.0mm for teeth of different ages. When the A.F is located, the position of the A.C canal is 58
estimated. If the A.C is not present, the preparation and obturation will usually be with in the confines of the root. In fact, it is difficult to locate either the A.C (or) the A.F clinically. Usually visible radiographically is the root apex. Although 0.5 to 1mm short of the radiographic apex is commonly used as the termination point, this is only an estimate. It is an attempt to debride and obturate close to the A.F but hopefully, not beyond. Obviously this will often not be the outcome. Termination point with a vital pulp. When an irreversible pulpitis (vital pulp), bacteria (if present) are usually limited to the chamber. Instrumentation apically is to remove the non infected tissue and to shape the canal. For these cases the favorable point to terminate instrumentation and to form an apical stop appears to be 2 to 3mm short of, rather than 0 to 2mm from, the apex. This principle (partial Pulpectomy) was originally proposed by Davis in 1922, he suggested preservation of vital pulp apically, often referred to as the apical pulp stump. Following this principal, a good success rate was obtained by kerekes and SJogren et al. Therefore for vital cases, the biologic and clinical evidence indicates it is unnecessary to terminate the procedures close to the apical foramen. When the apical pulp stumps remains extrusion of irritating filling materials into the periradicular tissues may be prevented, thereby favoring apical healing. Apparently, the reaction of the pulp stump to the filling materials will not negatively influence the health of periapical tissues. The concept that the apical periodontium should not be challenged with the extrusion of root canal filling materials beyond the end of the canal is supported by many authors. 59
Termination point for infected canals: Infected canals likely differ from teeth with vital pulps. In addition to removal of necrotic tissue and debris, an important goal is to reduce (or) eliminate bacteria. Because it is unknown how many bacteria remaining in the apical portion of the root canal can be managed by host defenses, instrumentation length should presumably not be shorter than the apical level of bacteria. Bacteria may remain sealed in the root filled canals of many radiographically successful cases. The best success for treatment of teeth with necrotic pulps has been recorded when RCT was terminated at (or) within 2mm of the radiographic apex (0 to 2mm) for infected canals with visible apical pathosis. During instrumentation, dentin debris, which may be infected, is produced and may remain within the apical canal. In the canal, this debris may reduce working length and may hinder repair. Recapitulation to the working length may maintain the working length but not remove the dentinal debris that have plugged the canal beyond the working length with the use of balanced force, canal master u, light speed and profile techniques, and frequent irrigation are found to be efficient in reducing accumulated dentinal debris in the apical canal. Another techniques to enlarge and clean the apical canal is ‘ apical cleaning’ Parris et al after step back filling, used successively larger files a few sizes larger than the master apical file with a remaining motion; this technique has less debris accumulation. Another technique is ‘ apical patency’ concept. This is using a very small size file 10 (or) 15 to 1mm longer than the final working length in an attempt to remove the dentinal debris from the very apical portion of 60
the canal. Considering the apical canal anatomy, this approach seems unreasonable, if the file extends beyond the radiographic apex it will damage the apical periodontium instead of removal. In addition the small file will likely not remove significant amount of debris. Hence apical potency concept remains untested. Termination point for Re-treatment. The apical constriction is the narrowest diameter of the blood supply. Apically, the canal widens and may have a richer blood supply that may allow better immune activities than in the pulp canal. However, bacteria may sometimes persist in the canal and survive beyond the apical constriction; a speculation is that these bacteria are related to RCT failures. Hence in retreatment cases it is preferable to clean the canal up to the apical foramen. In order to reduce the introduction of irritants into the periapex, first clean the coronal part of the root canal with step down (or) crown down sequence with copious irrigation. However, instrumentation extending beyond the radiographic apex, have its apical terminus beyond the apical foramen and found to hinder apical healing significantly. Although instrumentation to the apical foramen is suggested for some failure cases, usually the apical stop should be created 1 to 2mm short of the apical foramen to continue the instruments irrigants, and obturation to the canal space.
Systemic considerations: Concerns have recently been raised relative to the impact of oral conditions on systemic health. The impact may be by bacterial (or) 61
immunogenic seeding of distant organs (or) tissues via the vascular (blood (or) lymphatic) system. It has been demonstrated that a bacteria often is the result of over instrumentation of teeth with necrotic, bacterially colonized pulp spaces. Although no definitive evidence that introducing bacteria (or) antigens from infected canals into the blood stream causes systemic diseases, it would seem prudent to avoid this situation when possible.
8) SUMMARY AND CONCLUSION: No individual technique is truly satisfactory in determining endodontic working length. The CDJ is a practical and anatomic termination point for the preparation and obturation of the root canal and this cannot be determined radio graphically modern electronic apex locator’s can determine this position with accuracies of greater than 90% but still have some limitations. Knowledge of apical anatomy, prudent use of radiographs and the correct use of an electronic apex locator will assist practitioners to achieve predictable. In conclusion, based on biological principal and experimental evidence instrumentation (or) obturation should not extend beyond the apical foramen).
9) REVIEW OF LITERATURE. 1. Tooth Length determination: A review Alexander et. al, “000” 1991:72:238 242 62
Tooth length determination is a crucial step in endodontic treatment, until the late 1970â€™s tooth length determination was based mainly on radiographic interpretation. The advent of apex locatorâ€™s, which identify the difference in the electrical resistance between the root canal and the periodontal membrane, ushered in a new era for measuring tooth length. 2. A critical evaluation of some methods of determining tooth length. Bramante and Berbert et al 000. 1974; 37; 463-473 Two hundred twenty four teeth were used to compare the methods of Best, Bregmen, Ingle, and Sunada for determining tooth length. A statistical analysis of the data indicated that the Ingle method was superior to the others, although the Sunada method gave the most accurate results for the palatal roots of maxillary premolars and molars. 3. Presentation and physical evaluation of RVG Francis Mouyen et al 000.1989; 68: 238-42 A comparison of physical properties has been made between intra oral films and images made with R.VG system. The RVG system uses considerably reduced levels of radiation to produce an image immediately after exposure. 4. Review; Electrical apex locators. Gordon. et al, IEJ, 37, 425-437, 2004. Electronic apex locators reduce the number of radiographs require and assist where radiographic method create difficulty. This article reviewed the development, action use types of electronic apex locators.
5. Electronic canal length measurement Kobayashi et al. 000; 1995; 79: 226-31.
The most important advantage of the electric method is that it can measure the length of the root canal to the end of the apical foramen, not the radiographic apex. The most striking disadvantage of the electronic method is that if strong electrolytes are in the root canal, the meter shows a reading that is too high. Recently new devices have been developed that can measure accurately even in the presence of strong electrolytes. 6. New electronic canal measuring device based on the ratio method. Kobayashi et al . J.O.E; 1994: 20; 111-114. A new concept for electrically measuring the root canal length has been developed. The device simultaneously measures two impedances of the canal using current sources with the different frequencies. Then the radio between the two electric potentials proportional to impedance is calculated. 7. Determination of location of root perforations by EALâ€™s Kaufman et al 000; 82: 324-9 The aim of the study was to determine the location of root perforations by evaluating the accuracy of two electronic apex locators with differing function and by assessing the adequacy of radiographic identification and concluded that EALâ€™s determined the location of the perforations in an acceptable clinical range short of the root surface: Radio graphs were found to be less reliable in identification of perforation locations. 8. Methodological considerations in the determining of working length. Martinez et al I.E.J, 34, 371-376, 2001. The aim of this study was to evaluate the diagnostic efficacy of an electronic system for the determination of working length. In comparison with two radiological methods (conventional Film and digital radiography) and concluded that none of these techniques were satisfactory in establishing the 64
true working length. There were no differences between the techniques investigated. 9. Comparison of Radiographic and Electronic working lengths Mc Donald et al J.O.E, 22, 173-176, 1996. The working length of root canals in human cadaver teeth was determined by positioning an endodontic file at the apical termination point as indicated by an apex locator and these some teeth were radiopraphed at various angles with the file in place and concluded that the apical constriction for the apex locator was significantly less than that for the radiographic method, thus the method using radiographic method, thus the method using apex locator was more reliable. 10.An instrument for measuring root canal length and apex location. A rapid technique. Negm et al 000,53,405-409,1982. The invention of a new instrument (apex finder) for measuring the root length and apex location is reported. This instrument is an accurate and reliable tool for the apex determination. The application method is based on the insertion of a plastic, fine-tapered barbed shaft through a beveled tube into the root canal. When resistance to with drawl is felt, which indicates that one of the barbs has engaged the apical margin, the shaft is marked at the level of the cusp tip. The distance between the mark and the barbs which caused the resistance is measured. The barbs will show apical inclination. The practitioner can rely on this technique in the majority of cases provided that a full range of plastic shafts, with different dimensions, is available for use with the outer tube.
11. Clinical evaluation of a new method for determining tooth length with out radiograph. Negm et al 000,56,415-420,1983 A new instrument the (apex finder) for measuring tooth length was recently introduced for use in endodontics. The investigations showed that the new technique offers a direct method for measuring the distance between the coronal and apical ends of the tooth. Statistical analysis of the data indicated that the new method was superior to the others. The apex finder was accurate in 90% of the cases. when radiographs were used, the results were accurate in 75% of the cases, while the use of the radiograph and the tooth lengthformulagave60.4%accuracy.
10) REFERENCES 1) FRANKLIN.I. WEINE. – Endodontic therapy. 6th edition 2) GROSSMAN- Endodontic practice. 11th edition. 3) JOHN. I. INGLE. – Endodontics. 5th edition. 4) PARAMESWARAN- Current trends in endodontology. 5) STOCK. – Atlas of endodontics. 3 rd edition.. 6) ALEXANDER et. al, Tooth Length determination: A review; “000” 1991:72:238 242. 7) BRAMANTE & BERBERT et al, A critical evaluation of some methods of determining tooth length. 000. 1974; 37; 463-473. 8) FRANCIS MOUYEN. et al, Presentation and physical evaluation of R.V.G. 000; 1989; 68; 238-242. 9) GORDON et al, Review of electronic apex locator. I.E.J; 2004; 37, 425-437. 10) KAUFMAAN et al, Determination of location of root perforations by EAL’s 000; 1996; 82: 324-329.
11) KOBAYASHI et al, New electronic canal measuring device based on the ratio method. J.O.E; 1994: 20; 111-114. 12) KOBAYASHI et al, Electronic canal length measurement. 000; 1995; 79:226-31. 13) MARTINEZ et al, Methodological considerations in the determining of working length. I.E.J, 2001; 34, 371-376, 14) Mc Donald et. al, Comparison of radiographic and electrical working length . JOE, 1996; 22;173-176. 15) Negm et al, Clinical evaluation of a new method for determining tooth length with out radiograph. 000,56,415-420,1983 16) Min- kai wu et al, Apical terminus location of root canal treatment procedures. [000., 89:99-103. 2000].
Published on May 1, 2014
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