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Working Length Determination

Working Length Determination. Dr. hadil abdallah altilbani. The objective is to establish the length (distance from the apex) at which canal preparation and subsequent obturation are to be completed. Of course, lengths will vary according to many factors; these ideals are not always attainable.

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Working Length Determination

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  1. Working Length Determination Dr. hadilabdallahaltilbani

  2. The objective is to establish the length (distance from the apex) at which canal preparation and subsequent obturation are to be completed. Of course, lengths will vary according to many factors; these ideals are not always attainable.

  3. REFERENCE POINT The reference point is the site on the occlusal or incisal surface from which measurements are made. This point is used throughout canal preparation and obturation.

  4. Selection A reference point is chosen that is stable and easily visualized during preparation. Usually this is the highest point on the incisal edge on anterior teeth and a buccal cusp tip on posterior teeth. The same reference point is best used for all canals in multirooted teeth. The mesiobuccal cusp tip is preferred in molars.

  5. Stability A reference point that will not change during or between appointments is selected. If it is necessary to use an undermined cusp, it should be reduced considerably before access preparation. Areas other than cusp tips, such as marginal ridges or the floor of the chamber, are unreliable or difficult to visualize.

  6. A, Do not use weakened enamel walls or diagonal lines of fracture as a reference site for length-of-tooth measurement. B, Weakened cusps or incisal edges are reduced to a well-supported tooth structure. Diagonal surfaces should be flattened to give an accurate site of reference.

  7. TECHNIQUE FOR DETERMINATION Different techniques have been used, studied, and advocated for determining working length, including radiographic (conventional or digital), electronic, and tactile methods; none are totally accurate or infallible . Radiographs are usually made to determine the working length.

  8. Determination of Working Length by Radiographic Methods Good, undistorted, preoperative radiographs showing the total length and all roots of the involved tooth. Adequate coronal access to all canals. An endodontic millimeter ruler. Working knowledge of the average length of all of the teeth. A definite, repeatable plane of reference to an anatomic landmark on the tooth, a fact that should be noted on the patient’s record.

  9. Estimated Working Length 1. The diagnostic film, which is made using a paralleling technique, is measured from the reference point to the apex with a millimeter endodontic ruler.

  10. A, Initial measurement. The tooth is measured on a good preoperative radiograph using the long cone technique. In this case, the tooth appears to be 23 mm long on the radiograph. 2. Subtract at least” 1.0 mm “safety allowance” for possible image distortion or magnification.

  11. 3. Set the endodontic ruler at this tentative working length and adjust the stop on the instrument at that level B, Tentative working length. As a safety factor, allowing for image distortion or magnification, subtract at least 1 mm from the initial measurement for a tentative working length of 22 mm.

  12. 4. Place the instrument in the canal until the stop is at the plane of reference , the instrument is left at that level and the rubber stop readjusted to this new point of reference. 5. Expose, develop, and clear the radiograph.

  13. C, 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 1.5 mm from the radiographic end of the root. This is added to the tentative working length,giving a total length of 23.5 mm. From this, subtract 1.0 mm as adjustment for apical termination short of the cementodentinal junction. The final working length is 22.5 mm.

  14. 6. On the radiograph, measure the difference between the end of the instrument and the end of the root and add this amount to the original measured length the instrument extended into the tooth If, through some oversight, the exploring instrument has gone beyond the apex, subtract this difference.

  15. 7. From this adjusted length of tooth, subtract a 1.0 mm “safety factor” to conform with the apical termination of the root canal at the apical constriction. If there is root resorption, the apical constriction is probably destroyed—hence the shorter move back up the canal. 8. Set the endodontic ruler at this new corrected length and readjust the stop on the exploring instrument

  16. D, Setting instruments. The final working length of 22.5 mm is used to set stops on instruments used to enlarge the root canal.

  17. 9. Because of the possibility of radiographic distortion, sharply curving roots, and operator measuring error, a confirmatory radiograph of the adjusted length is highly desirable. 10. When the length of the tooth has been accurately confirmed, reset the endodontic ruler at this measurement.

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  19. 11. Record this final working length and the coronal point of reference on the patient’s record. 12. Once again, it is important to emphasize that the final working length may shorten by as much as 1 mm as a curved canal is straightened out by instrumentation. It is therefore recommended that the “length of the tooth” in a curved canal be reconfirmed after instrumentation is completed.

  20. STANDARDIZATION OF ENDODONTIC INSTRUMENTS The diameter of the tip of the instrument at the first rake angle. This diameter is termed “D1”. The diameter at the end of the cutting edge is termed “D16”. In all instruments, the difference of the diameters D1 and D16 is always a constant 0.32 mm. This confers a consistent taper to instruments of whatever size (taper .02: the increment in diameter is 0.02 mm x each millimeter of length).

  21. The D1/D16 distance is also constant (16 mm), so that the working portion of the instruments is always the same, despite the variability of the lengths of the available instruments: short (21 mm) for the molars of patients with small mouths, standard (25 mm), and long (31 mm) for the canines and any particularly long roots. D1 16 mm D16

  22. The colors have also been standardized. They are repeated every six instruments, with the exception of the first three of the series. In accordance with this standardization, therefore, the increase in D1 from one instrument to another is 0.02, 0.05, or 0.1 mm. From # 06 to # 10, each instrument increases by 0.02 mm; from # 10 to # 60, by 0.05 mm; and from # 60 to # 140, by 0.1 mm

  23. The dimensions of endodontic instruments arranged according to the recommendations of the International Standard Organization ISO standardization Color coding permits rapid visual identification of the diameter. After the three smallest sizes #6 pink, #8 gray, #10 violet, the sequence white-yeIlow-red-blue-green-black is repeated three times. The cutting section is, in accordance with the ISO standard, 16 mm long (1 1 ). Three diameters are specified: d1 at the tip, d 2 at the end of the cutting portion 1 6 mm from the tip, and d3 3 mm from the tip.

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