Nonionizing method of locating the apical constriction (minor foramen) in root canals

Nonionizing method of locating the apical constriction (minor foramen) in root canals Thomas John Stein, MEd, DiUD, MSa and John F. Corcoran, DDS, MS,b Allen Park and Ann Arbor, Mch. VETERANS

ADMINISTRATION

MEDICAL

CENTER

AND

UNIVERSITY

OF MICHIGAN

The electronic method was evaluated as to its accuracy when used to determine the position of the apical constriction (minor foramen) in root canals. There were 39 vital and 8 nonvital teeth for a total of 47 specimens from 22 patients. The specimens were prepared with a Buehler tsomet bone saw to a thickness of 500 pm. Distances were measured and recorded with the use of a Bioquant II image analysis system. The electronic method appeared to measure a mean value of 0.2 mm coronal to the cementudentinal junction in 47 canals where the apex locator was set at a reference setting of 40. When a frequency curve was plotted, it showed that the probability of being within 0.76 mm (1 SD) of the cementodentinal junction was 68%. This appears to correlate to where Kuttler indicated the minor constriction to be located. These devices seem to offer a unique method to locate the apical constriction and thus to ensure proper working length while reducing ionizing radiation. (ORAL SURC ORAL MED ORAL PATHOL 1991;71:96-9)

T he establishment of an accurate working length is one of the most important phases of endodontic treatment. The debridement, shaping, and obturation of the root canal system cannot be accomplished properly unless the working length is correct.‘-’ The most apical portion of the root canal system narrows from the opening of the foramen on the root surface (major foramen) to a constriction (minor foramen) within the canal slightly coronal to the cementodentinal junction. This hourglass-shaped portion of the canal dictates that the seal be made at the narrowest aspect. 4-7 Grove8 suggested that the tissue beyond the cementodentinal junction was not pulpal, and by not invading this space the cementum would close the canals. Kuttlerg studied the average distance between the major and minor diameters of the apical foramina in 268 teeth. He found the average distance to be 0.507 mm in patients 18 to 25 years old, and 0.784 mm in patients more than 55 years old. Working length in endodontic treatment has usually been estimated by placing a file at a predeter-

aEndodontist, Veterans Administration Park. bchairman, Department of Endodontics, versity of Michigan, Ann Arbor. 7/1$/16977

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mined “trial length”‘O in the canal space, and a radiograph is taken to verify the file’s relative location to the apical vertex. This value is subject to error since the major foramen may be eccentrically located on the anatomic root apex.g Measurements based on radiographs are on the average 1.6 mm longer than the actual tooth.‘O This change was due to magnification caused by film-object distance. Custer” in 1918 was the first to develop the idea that root canal length could be estimated by the use of an electrical current. Little was done with this idea until 1942, when Suzuki12 described a device that measured the electrical resistance between the periodontal ligament and oral mucosa. Inoue13 later developed a sonic readout system based on the electrical method. He found 92% agreement between his Sono-Explorer (Electra-Dent Inc., Cherry Hill, N.J.) and actual tooth lengths. Sunada and O’Neill14 found the Sono-Explorer measurements were identical to direct measurement of the extracted teeth in 83% of the cases. The Endometer (Dent-o-Tronics, San Antonio, Texas) and the Sono-Explorer were evaluated by Blank and coworkers15 in 55 human teeth in which 103 canals were used. Both devices were approximately 87% accurate. Plant and Newman16 also showed that the Sam-Explorer measurements were the same as the direct measurement in 30 of 32 canals (93.8%).

Volume Number

Locating

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apical

constriction

PROBE CEMENTODENTINAL FORAMEN OPEN,NG JUNCTION (C.D.J.)

TIP

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(P.T.)

(F o ) . . APICAL

Fig.

(A.&)

1. Microscopic anatomy of root apex.

The purpose of this study was to evaluate the accuracy of the electronic method when used to determine the position of the apical constriction (minor foramen). MATERIAL

VERTEX

AND METHODS

Many of the newer types of apex finders are of the electronic type of which the Neosono-D is a typical example. The Neosono-D (Amadent Medical and Dental Corp., Cherry Hill, N.J.) has both an analog meter as represented by a light-emitting diode (LED) readout measuring distance in 0.1 mm increments, and an audible indicator. Twenty-two patients who were selected for the study were undergoing dental treatment at the Veterans Administration Medical Center at Allen Park, Mich. The 47 teeth removed were nonsalvageable and scheduled for extraction in the oral surgery clinic at the center. Consent forms were obtained under the guidelines of the Wayne State University Human and Animal Investigation Committee and the Research and Development Committee at the Veterans Administration Medical Center in Allen Park. The informed consent of all human subjects who participated in the experimental investigation reported or described in this article was obtained after the nature of the procedures and possible discomforts and risks had been fully explained. Before access opening, a pretreatment radiograph was taken. Access without rubber dam was made with a No. 6 bur with a high-speed handpiece and sterile irrigation. The pulp was removed and the canal space was irrigated with sterile water and dried with paper points. The method used to operate the Neosono-D was Method 1 in the instruction manual.t7 The Neosono-D lip clip was affixed to the patient. The probe was attached to an appropriate style B, K-flex file (Kerr/Sybron Corp., Romulus, Mich.). A rubber stop was placed on the file to mark the length. As the file was moved into the root canal, the digits on the readout screen decreased as the tip approached the apical foramen. With the reference dial set at 40, the distance from the apical foramen was supposed to be 0.5 mm from the major foramen when the LED read-

I. Microscopic evaluation of probe tip position (in millimeters)

Table

CDJ Mean SE Median SD Skew Range Minimum Maximum

to PT

-0.24 +0.11 -0.09 +0.76 -0.72 +3.18 -2.11 +1.07

FO

to PT

-0.9 1 +0.13 -0.75 +0.88 -0.65 t3.82 -3.15 to.67

-, Position was coronal to reference point; +, position was apical to reference point; CDJ, cementodentinal junction; FO, foramen opening; PT. probe tip.

out was 0.0. When the instrument LED readout showed 0.0, a radiograph was taken and the length was noted on the patient’s flow sheet. The tooth was then extracted in oral surgery and placed in a coded specimen cup filled with a solution of 10% formalin. The same distance file with a rubber stop was reinserted into the tooth to length and fixed with composite (Prisma, Johnson & Johnson Dental Co., East Windsor, N.J.) to ensure a good bond. The tooth was replaced back in the formalin for transfer to the lab. Sectioning of the teeth was done with the use of a low-speed bone saw. The Buehler Isomet (Buehler, Ltd., Lake Bluff, Ill.) uses a precision diamond wafering blade that eliminates the need for decalcification. The teeth were prepared by means of a modified Spurr’s low-viscosity embedding plastic (Buehler, Ltd.) according to methods developed by Weaker and Richardson.‘* After processing, the blocked teeth were placed in the saw chuck so that the cuts were made parallel to the long axis of the teeth in a mesialdistal direction. The first section was made as close as possible to the file. Then multiple sections were cut along this face. The unstained 500 pm sections were labeled and mounted on standard microscope slides. A Bioquant II (Bioquant, R&M Biometrics, Inc., Nashville, Tenn.) microcomputer system was used to measure and analyze the cut specimens. An Apple II Plus (Apple Computer, Cupertino, Calif.) computer

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greater than 1.0 mm. Measuring from the cementodentinal junction to probe tip, 20 of the 47 canals were overextended. Of the 20 that were overextended, 14 were less than 0.5 mm, 5 were greater than 0.5 mm, and 1 was greater than 1.0 mm. The remaining 27 probes were short of the cementodentinal junction. Of the 27 that were short, 12 were less than 0.5 mm, 8 were greater than 0.5 mm, and 7 were greater than 1 .O mm. The estimation of error of the measurements with the use of the Bioquant system was determined by using the Bausch & Lomb stage micrometer at a fixed range of 1.00 mm over 27 trials. The error was estimated to be 3.9%, or approximately 4%.

8

2

DISCUSSION 0

-2.3

-1.7

-1.1 -.5 3 Distance (mm)

.9

1.5

Fig. 2. Frequency distribution showing percentage of cases(68%) that are within 1 SD (0.763 mm) of cementodentinal junction.

and HIPAD digitizing tablet (Bioquant, R&M Biometrics, Inc., Nashville, Tenn.) were interfaced with a television camera and a Leitz microscope (Wild Leitz GMBH, F.R.G.). The video camera’s image of a specimen was displayed with the cursor crosshairs overlaying it which measured individual distances between points. A Bausch & Lomb stage micrometer (Bausch & Lomb Optical Co., Rochester, N.Y.) graduated in 0.01 mm units was used to calibrate the instrument. This compensated for video magnification over and above the microscopic magnification. Results were placed in individual arrays and printed on a dot matrix printer. All statistics were done with an SPSS Statistical Program (Eastern Michigan University, Ypsilanti, Mich.) on the main frame computer of Eastern Michigan University. RESULTS

There were 39 vital and 8 nonvital teeth for a total of 47 specimens from.22 patients. In 38 of 47 specimens, blood was found in the canals. Two cases had a clear fluid. Three cases had nothing in the canals. Exudate was found in four of the cases. The mean age of the patients was 48.9 years. The range was 45 years with a maximum of 71 years and a minimum of 26 years. Fig. 1 represents the microscopic anatomy of the root apex. Table I presents the microscopic distance of the probe tips. Measuring from the foramen opening to the probe tip, 3 of the 47 canals were overextended. Of the 3 that are overextended, 2 were less than 0.5 mm, 1 greater than 0.5 mm, and none was

The purpose of this study was to evaluate the accuracy of the electronic method when used to determine the position of the apical constriction (minor foramen). The electronic apex finders seemed to consistently measure (68% to 73%) a point that is near the apical constriction. Table I lists the distances microscopically from the probe tip to the cementodentinal junction, and the foramen opening. Measuring from the foramen opening to the probe tip, 3 of the 47 canals (6%) were extended past the foramen opening with a range of 0.07 mm to 0.67 mm. The remaining 44 probes (94%) were short of the foramen opening. Measuring the cementodentinal junction to probe tip, 20 of the 47 canals (42%) were extended past the cementodentinal junction within a range of 0.05 to 1.07 mm. Twenty-seven probes (58%) were short of the cementodentinal junction within a range of 2.39 to 0.05 mm. The mean microscopic distance measured was 0.24 mm (SD 0.76 mm) coronal to the cementodentinal junction. Taking the 47 individual points along a range of 1.07 to 2.11 mm (1 SD) and graphing them (Fig. 2), it can be seen that there is a 68% probability that each measurement will lie within 1 SD of the cementodentinal junction. The apical constriction cannot be positively located unless cross sections are taken. This happens because the constriction may be out of the plane of section in longitudinal sections. In taking cross sections, the cementodentinal junction would be difficult to locate because the junction is an undulating line. Longitudinal sections seem to offer the best that can be hoped for when length measurements are needed. The study appears to show that on the average the Neosono-D is measuring a point where Kuttler9 placed the minor diameter (apical constriction), “found usually in the dentin just before the canal penetrates the cementum portion . . . a constriction . . . “. This is the location according to Grove8 where the pulpal tissue terminates and the periodontal tissue begins. The calibra-

Locating apical constriction

Volume 7 1 Number 1

tion of these devices according to Sunada relies on the conductability of the periodontal tissue.This biologic principle, however, may be incorrect. Huang” in a new theory suggests that the principle of electrical root canal measurements is not due to biologic differences of the tissues but to the physics of electricity. He postulates that it is the result of a constant surface contact between the oral tissue and the probe tip when the diameter of the opening was less than 0.4 mm and the surface area of contact of the probe tip was 2 square mm at 40 pk. However, both of these theories could be used to explain the results of the electronic apex locators used in this study. Electronic apex finders seem to offer a potential method to obtain working length determination with reduced radiation exposure and eliminate, to a certain extent, problems with anatomic variations obscuring visualization of the pararadicular area. CONCLUSIONS

1. In 47 canals, 44 probes (94%) did not extend past the major foramen opening. Twenty-seven of the 47 probes (58%) were coronal to the cementodentinal junction. 2. With the use of microscopic measurements, the apex finder appeared to measure a mean value of 0.24 mm coronal to the cementodentinal junction in 47 specimens where the reference dial was set at 40. This appears to correlate to where Kuttler indicated the minor constriction to be located. 3. With the use of the 47 specimens and plotting a frequency curve of individual distances, 68% of the cases fell under the curve. That is, the probability of being within 1 SD (0.763 mm) of the cementodentinal junction was 68%. I expressmy appreciation to both Warren Williams,PhD, for statistical analysis,and to GeorgeHarrison for his excellent slidepreparation. I alsothank Ms. Nancy Bernat and Dr. Richard Plezia for their helpin collectingthe data. I personallythank the hospitaladministrationand staff of the VeteransAdministration in Allen Park, Mich., for allowing me to completemy graduate studies.I especially thank Dr. Harold Morris and Dr. Ralph Kendall for their help, patience,and flexibility in allowing meto pursuethis endeavor.I alsothank Dr. John Corcoran, my chairman, Dr. Richard Zillich, my thesischairman, and Dr. Jeffrey Ash for all their patienceand help.This thesiswassubmitted in partial fulfillment of the requirementsfor the degree of Master of Science in Endodonticsin the Horace H.

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Rackham School of Graduate Studies, the University of Michigan, Ann Arbor, Mich. The triad of patient care, education, and researchthat is the missionof the Veterans Administration hasallowedmany health providersan opportunity to help patientsand to strive to provide a better health delivery system. REFERENCES

1. moueN. A simpleand accurate way of measuring root canal length. J Endod 1985;11:421-7. 2. Bramante CM. A critical evaluation of some methods determiningtoothlength. ORAL SURG ORAL MED ORAL PATHOL 1974;37:463-73. 3.

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Seidberg BH. Clinical investigation of measuring working lengths of root canals with an electronic device and with digital tactile sense. J Am Dent Assoc 1975;90:379-87. Soltanoff W, Parris L. Controlled silver point filling technic for endodontically involved teeth. J Am Dent Assoc 1962;65: 301-10. Luks S. Gutta-percha versus silver points in the practice of endodontics. N Y State Dent J 1965;31:341-5. Sunada I. New method for measuring the length of the root canal. J Dent Res 1962;41:375-87. Palmer MJ, Weine FS, Healey HJ. Position of the apical foramen in relation to endodontic therapy. Can Dent Assoc J 1971;37:305-8. Grove CJ. A new simple standardized technique producing perfect fitting impermeable root canal fillings extended to the dento-cement0 junction. Dent Items of Interest 1928;50: 855-7.

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11. Custer LE. Exact methods of locating the apical foramen. J Nat1 Dent Assoc 1918;5:815-9. 12. Suzuki K. Experimental study on iontophoresis. J Jpn Stomato1 1942;16:41 l-7. 13. Inoue N. Dental “stethoscope” measures root canal. Dent Survey 1972;48:38-9. 14. O’Neill LJ. A clinical evaluation of electronic root canal measurement. ORAL SURG ORAL MED ORAL PATHOL 1974;38: 469-73.

15. Blank LW, Tenca JL, Pelleu GB. Reliability of electronic measuring devices in endodontic therapy. J Endod 1975;l: 141-5. 16. Plant JJ, Newman RF. Clinical evaluation of the SonoExplorer. J Endod 1976;2:215-6. 17. Amadent, Instruction Manual. Cherry Hill, NJ: American Medical & Dental Corp., 1984. 18. Weaker F, Richardson L. A modified processing and sectioning technique for hard tissues. Am J Med Technol 1978; 44:1030-2. 19. Huang L. An experimental study of the principle of electronic root canal measurement. J Endod 1987;13:60-4. Reprint

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Thomas John Stein, MEd, DMD, MS 32219 W. 14 Mile Rd. Farmington Hills, MI 48018