0099-2399/91/1711-0567/$03.00/0 JOURNAL OE ENDODONTICS Copyright 9 1991 by The American Association of Endodontists
Printed in U.S.A. VOL. 17, NO. 11, NOVEMBER1991
Clinical Evaluation of the Accuracy of the Evident RCM Mark II Apex Locator Olivier Ricard, DDS, Dominique Roux, DDS, PhD, Leopold Bourdeau, DDS, MSD, and Alain Woda, DDS, PhD
The accuracy of the Evident RCM Mark II in locating the apical foramen was evaluated in 37 human teeth scheduled for extraction. After extraction, the difference between the position of the apical foramen determined electronically and its real anatomical location was measured under a binocular microscope, using a micrometer mobile in x, y, and z coordinates. The results show that in 86% (n = 37) of the cases, an accurate location __ 0.5 mm of the apical foramen was obtained.
1.9 mm. This device has been clinically tested only by Ricci et al. (19) who compared the electronic measurements with radiographic determinations made during endodontic treatments. They found that more than 90% of the measurements were accurate. In order to further evaluate the accuracy of the RCM, the difference between the position of the apical foramen determined electronically (0 on the RCM) and its real anatomical location were measured on extracted teeth. MATERIALS AND METHODS The study was carried out on informed and consenting patients treated at the dental clinic of the Faculty of Dentistry, Clermont-Ferrand, France. The experiment was performed on 37 root canals in 37 teeth scheduled for extraction made up of 22 anterior and 15 posterior teeth. The 28 patients were between 15 and 74 yr old. Of the selected teeth, 2 presented canals previously obturated, 24 had vital pulps, and 11 had necrotic pulps with periapical pathosis. In the case of multirooted teeth, only one canal per tooth was investigated. During the measuring of the 37 root canals, no significant hemorrhage was noted and only HPU 15 (SPAD, Quetigny, France) (similar to RC Prep; Premier Dental Products, Norristown, PA) was used as irrigant solution. Each tooth was anesthetized, isolated with a rubber dam, and a standard endodontic access opening was made. The pulp chamber was washed, dried with cotton pellets, and a first operator then applied the apex locator according to the manufacturer's instructions. This device required no calibration. The lip electrode was placed under the tongue without contact with metallic restorations. An endodontic file was inserted into the canal and controlled by reading the RCM until simultaneously the digital 0 appeared, the previously intermittent tone became continuous, and the luminous signal turned green, indicating that the foramen had been reached. The file was then locked in place with a self-curing composite resin (Concise; 3M Dental Products, St. Paul, MN) and its position was checked again with the RCM. In 7 of 37 cases, this second measurement indicated a shift of the file, from 0.1 to 0.3 mm, in relation to the initial 0. In these cases only the second position was considered. After extraction, the teeth were carefully examined. Thirtyfive teeth originally investigated were not included in the experiment because of a fracture, a crack in the root, or a
The generally accepted method for root canal length determination is still radiographic interpretation of an instrument placed in the canal. Most authors agree to fix the apical limit of endodontic preparations between 0.5 and 1.0 m m short of the radiographic apex. This is supposed to take into account the variations in the shape of the apical endodontic zone and the position of the foramen in relation to the central axis of the tooth (1, 2). However, this deduction of 0.5 to 1.0 mm corresponds only roughly to the real difference between the apical constriction and the apical foramen (3, 4). In fact, the imprecision of this method results from the difficulty of determining radiographically the location of the apical constriction in relation to the foramen (4-6). Consequently, Suzuki (7) in 1942 and then Sunada (8) in 1962 proposed an electronic method to detect the apical foramen. Since then, different apex locators have been developed commercially and, for most of them, the clinical accuracy of their electronic root canal measurement was evaluated either by radiographic controls (5, 9-13) or on extracted teeth (14-18). The values for accuracy have varied from a low of 15% (17) to a high of 94% (16). The disparity in the results obtained has shown the necessity for rigorous testing of each of these devices before recommending their use. The present study was undertaken to test the reliability of the Evident RCM Mark II (Evident Dental, London, Eng/and) apex locator in determining the position of the apical foramen. The RCM II has an analog meter, an audible indicator, and a luminous signal for determining when the desired point in the canal has been reached. Its digital readout has the claimed ability to indicate the distance in tenths of a millimeter from the tip of the probe to the apical foramen, providing the distance does not exceed
567
568
Journal of Endodontics -
Ricard et al.
1 5 1 2
9
A
-F
6
3
0
o
I
04
o
o
m - - - o . o 8 .* (s.d.) O . 3 5 m m n=
06
9
mm
!
X
37
FIG 2. Histogram showing the distribution of the differences measured between the tip of the endodontic instrument and the apical foramen (X), given in blocks of 0.1 ram.
B
FIG 1. a, cervical edge of the apical foramen; b, apical edge of the apical foramen; F, apical foramen. A, X: distance between the tip of the endodontic instrument and the apical edge of the apical foramen. B, X: distance between the tip of the endoOontJcinstrument and the cervical edge of the apical foramen.
breaking of the composite seal, leaving 37 to constitute the reported sample. Each tooth was fixed horizontally to a Horsley-Clarke-type stereotaxic frame (Unimecanique, Epinay sur Seine, France) supporting a micromanipulator, mobile in the three orthogonal directions and graduated in 1/ 100 mm. This micromanipulator held a glass microelectrode filled with a dark dye. The microelectrode tip positions were thus easily observed under a binocular microscope (magnification • allowing an accurate measurement to be taken by a second operator of the distance between the apical foramen and the tip of the endodontic instrument. The only problem was then to decide on the precise site of the foramen to be considered for the measurement. Three cases were possible: (a) When the tip of the file was flush with the most cervical edge (a in Fig. 1), we considered that no difference existed between the anatomical foramen and its electronical localization. (b) When the file extended beyond the apical foramen, the measurement was taken between its most cervical edge and the tip of the instrument (Fig. 1B). (c) When the file remained short of the apex, the dental tissue was ground in a coronal direction from the cervical edge of the foramen with a diamond bur under a binocular microscope to expose the tip of the instrument, while preserving the most apical edge (b in Fig. 1) of the foramen. The measurement
TABLE 1. Distribution of distances from apical foramen to the tip of the file in vital, nonvital, and overall teeth*
Distance from Apical Foramen (ram)
Vital Teeth (n = 24)
Necrotic Teeth (n = 11)
Overall (n = 37)
-0.6 to -1.0 -0.1 to -0.5 0 +0.1 to 0.5 +0.6 to 0.7 -+0.5
2 (8.5%) 8 (33.5%) 10 (41.5%) 3 (12.5%) 1 (4%) 21 (87.5%)
1 (9%) 2 (18%) 6 (55%) 1 (9%) 1 (9%) 9 (82%)
3 (8%) 10 (27%) 17 (46%) 5 (13.5%) 2 (5.5%) 32 (86.5%)
* In the two cases of previously obturated canals, one measurement was exactly at the apical foramen and the other was 0.2 mm beyond it.
was then taken between this latter and the tip of the instrument (Fig. 1A).
RESULTS The results (Fig. 2) showed that the tip of the file was situated between 0. I and I m m short of the anatomical foramen in 35% of the cases, coincided with it in 46% of the cases, and was located between 0.1 and 0.7 m m beyond it in 19% of the cases. This means that in 86.5% of the cases, the error margin was equal to or less than -+0.5 mm. The average distance between the anatomical foramen and the tip of the file was 0.08 ___ 0.35 m m (SD). The results varied slightly depending on whether the pulp was necrotic or vital (Table 1). The electronic foramen was located 0.1 to 1 m m short of the anatomical foramen in 27% of the necrotic cases and in 42% of the vital cases. It coincided with the anatomical foramen in 55% of the necrotic cases and in 41.5% of the vital cases, and was located 0.1 to 0.7 mm beyond it in 18% of the necrotic cases and in 16.5% of the vital cases. The error margin was ~< -+0.5 m m in 82% of the cases with a necrotic pulp and in 87.5% with a vital pulp. The difference between vital and necrotic cases was not statistically significant at the p 0.05 level, using the chi-square test.
Vol. 17, No. 11, November 1991
DISCUSSION In this study, several guidelines were followed: (a) the measurement made in vivo was verified after the endodontic instrument was sealed in place, (b) the teeth were extracted enabling the actual localization of the apical foramen, and (c) an accurate method of measurement was used. Moreover, the range of values shown in Fig. 2 was slightly overestimated because of our method of measurement since in our direct measurement on extracted teeth the greatest distance between the tip of the file and the foramen edge (Fig. 1) was measured, thus putting the RCM Mark II at a disadvantage. In light of these considerations, the reliability of the RCM device could be considered acceptable since an accurate location within +0.5 m m of the anatomical apical foramen defined as being the base of the cemental cone ( F in Fig. 1) was obtained in more than 86% of all cases. These results were similar to those obtained with the Sono-Explorer (Mark II and Mark III) by Inoue and Skinner (11), Trope et al. (12), Kaufman et al. (13), O'Neill (14), Blank et al. (15), Plant and Newman (16), or with the Neosono D by Berman and Fleischman (18), the reported accuracy of which ranged from 83 to 94%. These results were obtained using two basic methods. In one method, the evaluation was based, as in our experiment, on the measurement of the real distance between the tip of the file and the apical foramen, after extraction of the tooth. However, most of these studies did not mention which anatomical reference points on the apical foramen were used for the direct measurements. In the other method, a visual examination of a radiograph was used. We believe that this method is misleading since the radiograph which serves as reference displays considerable dimensional distorsions itself. Chunn el al. (17) reported that 43% of the files, which were taken as being short of the apex on the radiographs, actually extended past the foramen opening. These findings indicate that radiographic methods for determining the root canal length or for evaluating the reliability of electronic apex locators are inaccurate (6). In this study, in 14% of the cases, the tip of the file was located 0.5 mm to 1.0 m m short of or beyond the foramen. This relative inaccuracy is probably related to what the apex locator recognizes as the foramen. Indeed, it would be surprising if there were a sudden change in the electrical properties at any specific level of the apex, e.g. at level F as shown in Fig. 1. Many factors can modify the electrical properties of the apical tissues. For example, Huang (20) has demonstrated that the moisture content in the root canal or the diameter of the apical foramen, especially in the case of a necrotic pulp with periapical pathosis which may widen the foramen opening, could influence the accuracy of the electronic root canal
RCM Apex Locator Evaluation
569
measurement. However, and in agreement with the findings of other authors (9, 10) using different electronic devices, this study showed no statistically significant difference between the results obtained in vital pulps and necrotic pulps. Finally, it should be noted that only the apical foramen can be detected by apex locators (17). The authors wish to thank S. Millien and A. M. Moins-Gaydier for assistance with the manuscript preparation, M. Leroux for the photography, and J. Cane for the English translation. Drs. Ricard, Roux, Bourdeau, and Woda are affiliated with the Laboratoire de Physiologie Orofaciale, Facult6 de Chirurgie Dentaire, Clermont-Ferrand, France. Address requests for reprints to Dr. Alain Woda, Laboratoire de Physiologie Orofaciale, Facult~ Chirurgie Dentaire, 11, Bd Charles de Gaulle, 63000 Clermont-Ferrand, France.
References 1. Kuttler Y. Microscopic investigation of root apices. J Am Dent Assoc 1955;50:544-52. 2. Vertucci J. Root canal anatomy of the human permanent teeth. Oral Surg 1984;58:589-99. 3. Burch JG, Hulen S. The relationship of the apical foramen to the anatomic apex of the tooth root. Oral Surg 1972;34:262-8. 4. Dummer Paul MH, Mc Ginn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. Int Ended J 1984; 17:192-8. 5. Tidmarsh BG, Sherson W, Stalker NL. Establishing endodontic working length: a comparison of radiographic and electronic methods. NZ Dent J 1985;81:93-6. 6. Levy AB, Glatt L. Deviation of the apical foramen from the radiographic apex. JNJ State Dent Soc 1970;41:12-3. 7. Suzuki K. Experimental study on ionophoresis. J Jpn Stomatol 1942;16:411-7. 8. Sunada I. New method for measuring the length of the root canal. J Dent Res 1962;41:375-87. 9. Busch LR, Chiat LR, Goldstein LG, Held SA, Rosenberg PA. Determination of the accuracy of the Sono-Explorer for establishing endodontic measurement control. J Endodon 1976;2:295-7. 10. Cohen HP. A clinical evaluation of the Neosono M electronic apex locater. J Conn State Dent Assoc 1984;58:151-5. 11. Inoue N, Skinner DH. A simple and accurate way of measuring root canal length. J Endodon 1985;11:421-7. 12. Trope M, Rabie G, Tronstad L. Accuracy of an electronic apex locater under controlled clinical conditions. Ended Dent Traumato11985;1:142-5. 13. Kaufman AY, Szajkis S, Niv N. The efficiency and reliability of the dentometer for detecting root canal length. Oral Surg 1989;67:573-7. 14. O'Neill LJ. A clinical evaluation of electronic root canal measurement. Oral Surg 1974;38:469-73. 15. Blank LW, Tenca JI, Pelleu GB_ Reliability of electronic measuring devices in endodontic therapy. J Endodon 1975;1:141-4. 16. Plant JJ, Newman RF. Clinical evaluation of the Sono-Explorer. J Endodon 1976;2:215-6. 17. Chunn CB, Zardiackas LD, Menke RA. In vivo root canal length determination using the forameter. J Endodon 1981 ;7:515-20. 18. Berman LH, Fleischman SB. Evaluation of the accuracy of the Neosono D electronic apex locater. J Endodon 1984;10:164-7. 19. Ricci C, Dupont AM, Laurichesse JM. Etude clinique de I'efficacit~ des appareils de mesure ~lectronique de la Iongueur de travail. Rev Fr Ended 1986;5:13-26. 20. Huang L. An experimental study of the principle of electronic root canal measurement. J Endodon 1987;13:60-4.
Printed in U.S.A. VOL. 17, NO. 11, NOVEMBER1991
Clinical Evaluation of the Accuracy of the Evident RCM Mark II Apex Locator Olivier Ricard, DDS, Dominique Roux, DDS, PhD, Leopold Bourdeau, DDS, MSD, and Alain Woda, DDS, PhD
The accuracy of the Evident RCM Mark II in locating the apical foramen was evaluated in 37 human teeth scheduled for extraction. After extraction, the difference between the position of the apical foramen determined electronically and its real anatomical location was measured under a binocular microscope, using a micrometer mobile in x, y, and z coordinates. The results show that in 86% (n = 37) of the cases, an accurate location __ 0.5 mm of the apical foramen was obtained.
1.9 mm. This device has been clinically tested only by Ricci et al. (19) who compared the electronic measurements with radiographic determinations made during endodontic treatments. They found that more than 90% of the measurements were accurate. In order to further evaluate the accuracy of the RCM, the difference between the position of the apical foramen determined electronically (0 on the RCM) and its real anatomical location were measured on extracted teeth. MATERIALS AND METHODS The study was carried out on informed and consenting patients treated at the dental clinic of the Faculty of Dentistry, Clermont-Ferrand, France. The experiment was performed on 37 root canals in 37 teeth scheduled for extraction made up of 22 anterior and 15 posterior teeth. The 28 patients were between 15 and 74 yr old. Of the selected teeth, 2 presented canals previously obturated, 24 had vital pulps, and 11 had necrotic pulps with periapical pathosis. In the case of multirooted teeth, only one canal per tooth was investigated. During the measuring of the 37 root canals, no significant hemorrhage was noted and only HPU 15 (SPAD, Quetigny, France) (similar to RC Prep; Premier Dental Products, Norristown, PA) was used as irrigant solution. Each tooth was anesthetized, isolated with a rubber dam, and a standard endodontic access opening was made. The pulp chamber was washed, dried with cotton pellets, and a first operator then applied the apex locator according to the manufacturer's instructions. This device required no calibration. The lip electrode was placed under the tongue without contact with metallic restorations. An endodontic file was inserted into the canal and controlled by reading the RCM until simultaneously the digital 0 appeared, the previously intermittent tone became continuous, and the luminous signal turned green, indicating that the foramen had been reached. The file was then locked in place with a self-curing composite resin (Concise; 3M Dental Products, St. Paul, MN) and its position was checked again with the RCM. In 7 of 37 cases, this second measurement indicated a shift of the file, from 0.1 to 0.3 mm, in relation to the initial 0. In these cases only the second position was considered. After extraction, the teeth were carefully examined. Thirtyfive teeth originally investigated were not included in the experiment because of a fracture, a crack in the root, or a
The generally accepted method for root canal length determination is still radiographic interpretation of an instrument placed in the canal. Most authors agree to fix the apical limit of endodontic preparations between 0.5 and 1.0 m m short of the radiographic apex. This is supposed to take into account the variations in the shape of the apical endodontic zone and the position of the foramen in relation to the central axis of the tooth (1, 2). However, this deduction of 0.5 to 1.0 mm corresponds only roughly to the real difference between the apical constriction and the apical foramen (3, 4). In fact, the imprecision of this method results from the difficulty of determining radiographically the location of the apical constriction in relation to the foramen (4-6). Consequently, Suzuki (7) in 1942 and then Sunada (8) in 1962 proposed an electronic method to detect the apical foramen. Since then, different apex locators have been developed commercially and, for most of them, the clinical accuracy of their electronic root canal measurement was evaluated either by radiographic controls (5, 9-13) or on extracted teeth (14-18). The values for accuracy have varied from a low of 15% (17) to a high of 94% (16). The disparity in the results obtained has shown the necessity for rigorous testing of each of these devices before recommending their use. The present study was undertaken to test the reliability of the Evident RCM Mark II (Evident Dental, London, Eng/and) apex locator in determining the position of the apical foramen. The RCM II has an analog meter, an audible indicator, and a luminous signal for determining when the desired point in the canal has been reached. Its digital readout has the claimed ability to indicate the distance in tenths of a millimeter from the tip of the probe to the apical foramen, providing the distance does not exceed
567
568
Journal of Endodontics -
Ricard et al.
1 5 1 2
9
A
-F
6
3
0
o
I
04
o
o
m - - - o . o 8 .* (s.d.) O . 3 5 m m n=
06
9
mm
!
X
37
FIG 2. Histogram showing the distribution of the differences measured between the tip of the endodontic instrument and the apical foramen (X), given in blocks of 0.1 ram.
B
FIG 1. a, cervical edge of the apical foramen; b, apical edge of the apical foramen; F, apical foramen. A, X: distance between the tip of the endodontic instrument and the apical edge of the apical foramen. B, X: distance between the tip of the endoOontJcinstrument and the cervical edge of the apical foramen.
breaking of the composite seal, leaving 37 to constitute the reported sample. Each tooth was fixed horizontally to a Horsley-Clarke-type stereotaxic frame (Unimecanique, Epinay sur Seine, France) supporting a micromanipulator, mobile in the three orthogonal directions and graduated in 1/ 100 mm. This micromanipulator held a glass microelectrode filled with a dark dye. The microelectrode tip positions were thus easily observed under a binocular microscope (magnification • allowing an accurate measurement to be taken by a second operator of the distance between the apical foramen and the tip of the endodontic instrument. The only problem was then to decide on the precise site of the foramen to be considered for the measurement. Three cases were possible: (a) When the tip of the file was flush with the most cervical edge (a in Fig. 1), we considered that no difference existed between the anatomical foramen and its electronical localization. (b) When the file extended beyond the apical foramen, the measurement was taken between its most cervical edge and the tip of the instrument (Fig. 1B). (c) When the file remained short of the apex, the dental tissue was ground in a coronal direction from the cervical edge of the foramen with a diamond bur under a binocular microscope to expose the tip of the instrument, while preserving the most apical edge (b in Fig. 1) of the foramen. The measurement
TABLE 1. Distribution of distances from apical foramen to the tip of the file in vital, nonvital, and overall teeth*
Distance from Apical Foramen (ram)
Vital Teeth (n = 24)
Necrotic Teeth (n = 11)
Overall (n = 37)
-0.6 to -1.0 -0.1 to -0.5 0 +0.1 to 0.5 +0.6 to 0.7 -+0.5
2 (8.5%) 8 (33.5%) 10 (41.5%) 3 (12.5%) 1 (4%) 21 (87.5%)
1 (9%) 2 (18%) 6 (55%) 1 (9%) 1 (9%) 9 (82%)
3 (8%) 10 (27%) 17 (46%) 5 (13.5%) 2 (5.5%) 32 (86.5%)
* In the two cases of previously obturated canals, one measurement was exactly at the apical foramen and the other was 0.2 mm beyond it.
was then taken between this latter and the tip of the instrument (Fig. 1A).
RESULTS The results (Fig. 2) showed that the tip of the file was situated between 0. I and I m m short of the anatomical foramen in 35% of the cases, coincided with it in 46% of the cases, and was located between 0.1 and 0.7 m m beyond it in 19% of the cases. This means that in 86.5% of the cases, the error margin was equal to or less than -+0.5 mm. The average distance between the anatomical foramen and the tip of the file was 0.08 ___ 0.35 m m (SD). The results varied slightly depending on whether the pulp was necrotic or vital (Table 1). The electronic foramen was located 0.1 to 1 m m short of the anatomical foramen in 27% of the necrotic cases and in 42% of the vital cases. It coincided with the anatomical foramen in 55% of the necrotic cases and in 41.5% of the vital cases, and was located 0.1 to 0.7 mm beyond it in 18% of the necrotic cases and in 16.5% of the vital cases. The error margin was ~< -+0.5 m m in 82% of the cases with a necrotic pulp and in 87.5% with a vital pulp. The difference between vital and necrotic cases was not statistically significant at the p 0.05 level, using the chi-square test.
Vol. 17, No. 11, November 1991
DISCUSSION In this study, several guidelines were followed: (a) the measurement made in vivo was verified after the endodontic instrument was sealed in place, (b) the teeth were extracted enabling the actual localization of the apical foramen, and (c) an accurate method of measurement was used. Moreover, the range of values shown in Fig. 2 was slightly overestimated because of our method of measurement since in our direct measurement on extracted teeth the greatest distance between the tip of the file and the foramen edge (Fig. 1) was measured, thus putting the RCM Mark II at a disadvantage. In light of these considerations, the reliability of the RCM device could be considered acceptable since an accurate location within +0.5 m m of the anatomical apical foramen defined as being the base of the cemental cone ( F in Fig. 1) was obtained in more than 86% of all cases. These results were similar to those obtained with the Sono-Explorer (Mark II and Mark III) by Inoue and Skinner (11), Trope et al. (12), Kaufman et al. (13), O'Neill (14), Blank et al. (15), Plant and Newman (16), or with the Neosono D by Berman and Fleischman (18), the reported accuracy of which ranged from 83 to 94%. These results were obtained using two basic methods. In one method, the evaluation was based, as in our experiment, on the measurement of the real distance between the tip of the file and the apical foramen, after extraction of the tooth. However, most of these studies did not mention which anatomical reference points on the apical foramen were used for the direct measurements. In the other method, a visual examination of a radiograph was used. We believe that this method is misleading since the radiograph which serves as reference displays considerable dimensional distorsions itself. Chunn el al. (17) reported that 43% of the files, which were taken as being short of the apex on the radiographs, actually extended past the foramen opening. These findings indicate that radiographic methods for determining the root canal length or for evaluating the reliability of electronic apex locators are inaccurate (6). In this study, in 14% of the cases, the tip of the file was located 0.5 mm to 1.0 m m short of or beyond the foramen. This relative inaccuracy is probably related to what the apex locator recognizes as the foramen. Indeed, it would be surprising if there were a sudden change in the electrical properties at any specific level of the apex, e.g. at level F as shown in Fig. 1. Many factors can modify the electrical properties of the apical tissues. For example, Huang (20) has demonstrated that the moisture content in the root canal or the diameter of the apical foramen, especially in the case of a necrotic pulp with periapical pathosis which may widen the foramen opening, could influence the accuracy of the electronic root canal
RCM Apex Locator Evaluation
569
measurement. However, and in agreement with the findings of other authors (9, 10) using different electronic devices, this study showed no statistically significant difference between the results obtained in vital pulps and necrotic pulps. Finally, it should be noted that only the apical foramen can be detected by apex locators (17). The authors wish to thank S. Millien and A. M. Moins-Gaydier for assistance with the manuscript preparation, M. Leroux for the photography, and J. Cane for the English translation. Drs. Ricard, Roux, Bourdeau, and Woda are affiliated with the Laboratoire de Physiologie Orofaciale, Facult6 de Chirurgie Dentaire, Clermont-Ferrand, France. Address requests for reprints to Dr. Alain Woda, Laboratoire de Physiologie Orofaciale, Facult~ Chirurgie Dentaire, 11, Bd Charles de Gaulle, 63000 Clermont-Ferrand, France.
References 1. Kuttler Y. Microscopic investigation of root apices. J Am Dent Assoc 1955;50:544-52. 2. Vertucci J. Root canal anatomy of the human permanent teeth. Oral Surg 1984;58:589-99. 3. Burch JG, Hulen S. The relationship of the apical foramen to the anatomic apex of the tooth root. Oral Surg 1972;34:262-8. 4. Dummer Paul MH, Mc Ginn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. Int Ended J 1984; 17:192-8. 5. Tidmarsh BG, Sherson W, Stalker NL. Establishing endodontic working length: a comparison of radiographic and electronic methods. NZ Dent J 1985;81:93-6. 6. Levy AB, Glatt L. Deviation of the apical foramen from the radiographic apex. JNJ State Dent Soc 1970;41:12-3. 7. Suzuki K. Experimental study on ionophoresis. J Jpn Stomatol 1942;16:411-7. 8. Sunada I. New method for measuring the length of the root canal. J Dent Res 1962;41:375-87. 9. Busch LR, Chiat LR, Goldstein LG, Held SA, Rosenberg PA. Determination of the accuracy of the Sono-Explorer for establishing endodontic measurement control. J Endodon 1976;2:295-7. 10. Cohen HP. A clinical evaluation of the Neosono M electronic apex locater. J Conn State Dent Assoc 1984;58:151-5. 11. Inoue N, Skinner DH. A simple and accurate way of measuring root canal length. J Endodon 1985;11:421-7. 12. Trope M, Rabie G, Tronstad L. Accuracy of an electronic apex locater under controlled clinical conditions. Ended Dent Traumato11985;1:142-5. 13. Kaufman AY, Szajkis S, Niv N. The efficiency and reliability of the dentometer for detecting root canal length. Oral Surg 1989;67:573-7. 14. O'Neill LJ. A clinical evaluation of electronic root canal measurement. Oral Surg 1974;38:469-73. 15. Blank LW, Tenca JI, Pelleu GB_ Reliability of electronic measuring devices in endodontic therapy. J Endodon 1975;1:141-4. 16. Plant JJ, Newman RF. Clinical evaluation of the Sono-Explorer. J Endodon 1976;2:215-6. 17. Chunn CB, Zardiackas LD, Menke RA. In vivo root canal length determination using the forameter. J Endodon 1981 ;7:515-20. 18. Berman LH, Fleischman SB. Evaluation of the accuracy of the Neosono D electronic apex locater. J Endodon 1984;10:164-7. 19. Ricci C, Dupont AM, Laurichesse JM. Etude clinique de I'efficacit~ des appareils de mesure ~lectronique de la Iongueur de travail. Rev Fr Ended 1986;5:13-26. 20. Huang L. An experimental study of the principle of electronic root canal measurement. J Endodon 1987;13:60-4.
