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Clinical Accuracy of a New Apex Locator with an Automatic Compensation Circuit
JOURNAL OF ENDODONTICS Copyright © 2002 by The American Association of Endodontists
Printed in U.S.A. VOL. 28, NO. 10, OCTOBER 2002
Clinical Accuracy of a New Apex Locator with an Automatic Compensation Circuit Seung Jong Lee, DDS, MS, Ki Chang Nam, MS, Young-Joo Kim, DDS, and Deok Won Kim, PhD
the impedance ratio instead of the impedance difference. It operates on the principle that the impedance ratio is constant regardless of the kinds of conductive fluids (5). According to the manufacturer’s manual (6), the impedance ratio between the 500 Hz and 8 kHz frequencies is constant (0.72) in all canal conditions until the probe reaches the constriction point, no matter what type of irrigant remains in the canal. However, even with these improved systems, measurements may exhibit different readings according to the type of electrolytes present in the canal. Frank (7) reported that in 89.64% of moist root canals Endex showed accurate measurements within ⫾0.5 mm of the radiographic findings. Similarly, Pratten and McDonald (8) reported that in human cadavers Apit (Osada Electric Co.) located the apical foramen to the nearest 0.5 mm in 89% of cases with sodium hypochlorite. In a recent study, Dunlap et al. (9) reported that 82% of electronic values recorded with the Root ZX model were accurate to ⫾0.5 mm of the apical constriction when 2.5% NaOCl was used. In previous studies (10 –12), we found that there were tendencies toward short measurement in high electro-conductive solutions, such as NaOCl, whereas longer measurements were common in lower electro-conductive solutions. These tendencies were expressed by a voltage difference. To minimize the measurement errors, we developed a new circuit that can automatically compensate for the voltage differences of different irrigating solutions. As a result of this compensation, errors were significantly decreased on an average from ⫹0.54 mm to ⫹0.18 mm in H2O2 solution and from ⫺0.33 mm to ⫺0.01 mm in NaOCl solution in an in vitro study. The purpose of this study was to evaluate the accuracy of the newly designed electronic apex locator with an automatic compensation function in a clinical situation.
A new circuit was designed to automatically compensate for measurement errors of an electronic apex locator in various electrolytes. Thirty-one root canals were clinically tested for accuracy. A file was inserted into the canal until the apex signal was obtained, at which point the file was immobilized with glass-ionomer cement. After extraction, the apical area was exposed and the position of the file tip was examined under an operating microscope. Distances from the major foramen and cemento dentinal junction (CDJ) were recorded. The average distance from the major foramen was ⴚ0.13 mm with a range of ⴚ1.28 mm and ⴙ0.46 mm. The average distance in 26 detectable CDJ samples was ⴙ0.18 mm with a range of ⴚ0.98 mm and ⴙ0.65 mm. The measurements, which were within ⴞ0.5 mm, were 94% (29/31) from the major foramen and 92% (24/26) from the CDJ. Measurement consistencies within one SD were 81% for the major foramen and 65% for the CDJ, respectively. Measurements within two SD were 97% for the major foramen and 92% for the CDJ. There were no differences between the smaller (<#25) and larger apical foramens (>#25) or vital and nonvital pulps.
The use of an electronic apex locator has improved the accuracy of the working length measurement in clinical endodontics. Sunada (1) first reported that a constant electronic resistance existed between the periodontal ligament and oral mucosa. On the basis of this concept, a number of devices were introduced to the market. However, these first generation devices did not produce consistent readings in the presence of various root canal contents (2, 3). To solve this problem, new types of apex locators were advocated. The Endex (Osada Electric Co., Tokyo, Japan) model uses the relative value of different electric currents, 5 kHz and 1 kHz, operating on the principle that the impedance measurements of the different frequencies used differ greatly at the area of the apical constriction (4). The working mechanism of the Root ZX (Morita Corp., Japan) is similar to the Endex. However, the Root ZX uses
MATERIALS AND METHODS Compensation Circuit The electronic mechanism of the new circuit for automatic compensation has been described elsewhere (11, 12). Briefly, impedance ratios and voltage differences were obtained from three different irrigating solutions (saline, NaOCl, and H2O2) in an extracted tooth model. This was performed by using the conventional impedance ratio method (5) with two sinusoidal waves (0.5 and 10 kHz). From a total of 45 root canals examined in each 706
Vol. 28, No. 10, October 2002
FIG 1. Distributions of voltage difference versus error for the three solutions in the canal. LL and UL are decision boundaries that classify smaller voltage difference solutions (NaOCl) and larger voltage difference solutions (H2O2) for 45 extracted root canals (in vitro).
solution, the distributions of the voltage differences and the measurement errors were obtained. The voltage differences measured were generally larger in H2O2 and smaller in NaOCl compared with saline. The measured lengths were generally longer in H2O2 and shorter in NaOCl compared with saline. Impedance ratio of the two different frequencies represented the position of the file, whereas the voltage difference represented the status of the fluid in the root canal. Each irrigant was classified statistically by Bayes linear classifier (Fig. 1). When the difference was smaller than LL, the canal irrigant was classified as a higher electro-conductive group. If it was smaller than UL, it was classified as a lower electroconductive group. The compensating value was determined in proportion to the difference between the measured voltage difference and either UL or LL; then it was added or subtracted to the impedance ratio for compensation. Therefore, during the actual determination of working length, the file would go deeper in higher electro-conductive conditions, such as NaOCl, whereas shorter in lower electro-conductive conditions, such as H2O2. A prototype apex locator was fabricated with this adjusted circuit. Clinical Experiment The study subjects included 31 canals of 25 teeth that had been scheduled to be extracted for either orthodontic or periodontal reasons. None had any previous dental caries, metallic restorations, or gross periapical lesions. After the isolation of the tooth with a rubber dam, an access cavity was prepared and the occlusal portion of the tooth was flattened to secure a consistent reference point. Once access was gained, the excessive tissue in the chamber only was removed and a file that fit snugly in the canal was inserted until the machine indicated it was at the apical foramen. No attempt to remove the canal contents was made. This was to see whether the machine operated accurately in various canal conditions. Once the file reached the apical foramen, the file was advanced further to ensure the file passed through the apical foramen. The file was then subtracted to the point where the machine indicated it was again at the apical foramen. Self-curing glass-ionomer cement was mixed and injected into the access cavity to surround the shaft of
Apex Locator
707
the file and allowed to set completely. Locked in place, the file handle and exposed shaft were separated using a high-speed bur. The tooth was then extracted, numbered serially, and the size of the inserted file was recorded. The crown portion of the extracted tooth was encased in clear acrylic resin for easy handling. The apical 3 to 4 mm portion of the root was trimmed by using a fine diamond bur and soflex discs to visualize the inserted file. The plane of the cut was made in the same plane as the greatest curvature of the root. Once the file could be visualized, the additional tooth structure was carefully removed until the terminus of the file and the root were revealed. The exposed files and root apices were examined under a dissecting microscope with a calibrated ocular grid and then photographed in digital image. The distance from the end of the file to the major foramen was measured using Adobe Photoshop 5.5 (Adobe Systems Inc.) and calculated in mm. Two measurements were made. First, the distance from the end of the file to the major foramen, and second, the distance from the end of the file to the point where it appeared there was the cemento dentinal junction (CDJ). Two evaluators performed the examination and the results were averaged.
RESULTS The average distance of the 31 measurements was ⫺0.13 mm from the major foramen with a range of ⫺1.28 mm and ⫹0.46 mm. From the 26 CDJ-detectable samples, the average distance from the estimated CDJ was ⫹0.18 mm with a range of ⫺0.98 mm and ⫹0.65 mm (Table 1). The measurement accuracy’s were 94% from the major foramen and 92% (24/26) from the detectable CDJ with a ⫾0.5 mm tolerance. The measurement consistencies within one SD were 81% for the major foramen and 65% for the CDJ, respectively. Measurements within two SD were 97% for major foramen and 92% for the CDJ. There were no differences observed between the smaller (⬍#25) and larger apical foramens (ⱖ#25) or vital and nonvital pulps, respectively.
DISCUSSION Most previous studies of this subject used a ⫾0.5 mm error range to assess the accuracy of the electronic apex locator. With this criteria, the accuracy of this prototype was 94% from the major foramen and 92% from CDJ. However, the CDJs were not always detectable even under a microscope. In this study, only 14 of 31 samples displayed the points that could certainly be regarded as a CDJ or constriction point, whereas 12 showed only a vague configuration. In five samples, it was impossible to make a definitive determination of a CDJ. Interestingly, in this study, most of the file tips terminated at the immediately flaring point regardless of the existence of detectable CDJ. This may prove the clinical assumption that the machine does not always read the constriction point but the point where the periodontal ligament meets. Therefore, the use of the major foramen seems to be more reproducible, compared with CDJ, for this kind of accuracy study. The average distance to the file tip was ⫺0.13 mm from the major foramen and ⫹0.18 mm from the CDJ. Most of the measurements (19/25) were beyond the CDJ. This tendency has also been reported in other studies. Both Mayeda et al. (13) and Shabahang et al. (14), in a clinical study with Endex, found that twothirds of the measurements were past the CDJ. This may be due to
708
Lee et al.
Journal of Endodontics TABLE 1. Raw data of 31 samples, including measurements from the major diameter and CDJ
Sample
Age
Tooth
IAF Size
Major D* (mm)
CDJ (mm)
Pulp Status
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
45 47 48 49 49 45 48 48 19 20 52 47 19 48 19 21 54 21 25 25 49 49 49 47 49 47 48 45 19 19 49
14DB 10 24 14P 31D 14P 15MB 25 21 21 9 7 5P 15P 12 16 20 13 13B 21 29 25 26 9 14DB 8 15DB 24 28 5B 14MB
10 35 15 30 10 40 15 15 25 30 25 20 20 40 25 40 15 20 25 20 30 10 10 20 15 25 15 25 25 20 15
⫺1.28 ⫺0.57 ⫺0.46 ⫺0.41 ⫺0.34 ⫺0.28 ⫺0.28 ⫺0.26 ⫺0.25 ⫺0.21 ⫺0.2 ⫺0.16 ⫺0.16 ⫺0.14 ⫺0.08 0 0 0 0 0 0 0 0 0 0 0.08 0.09 0.14 0.19 0.24 0.46
⫺0.98 ⫺0.17 ⫺0.23 0.47 0 ⫺0.08 0.1 0 0.13 — 0.25 0.06 — — — 0.26 0.18 0.26 0.31 0.39 0.29 0.25 0.16 0.36 0.1 0.39 0.45 — 0.5 0.49 0.65
NV NV V NV NV NV V V V V NV NV V V V V NV V V V NV NV NV NV NV NV V NV V V NV
⫺0.13 0.30
0.18 0.32
Average SD * Samples were arranged in the order of the measurement from major diameter. CDJ ⫽ cemento dentinal junction; V ⫽ vital pulp; NV ⫽ nonvital pulp.
the fact that the machine reads the largest gradient of impedance ratio at the point where the periodontal ligaments meet. However, more important than where to read is the question of how the measurements can be consistently reproduced. No matter where the machine indicates, if the machine indication is consistent, if we know where we are, and if we know the average distance between the file tip and the true CDJ, then we can obtain an accurate length by subtracting the average distance from the machine reading. In this study, we used standard deviations to evaluate the measurement consistency. Measurements within one SD were 81% for the major foramen and 65% for CDJ, respectively. Measurements within two SD were 97% for the major foramen and 92% for CDJ. Again, these results showed that measurements from the major foramen were more consistent than from the CDJ. The most important question to bear in mind when using the electronic apex locator is how to eliminate possible operation errors. During the process of clinical experiment, we found that the same type of errors occurred as in the other types of apex locators, such as errors related to metallic restoration, leaky gingival margin, or excessive hydration and dehydration. In sample 1 of Table 1, the SD was shown to be four times (major diameter) and three times (CDJ) larger than the other samples. We do not know why this occurred but presume it to be an error in file stabilization.
In conclusion, we feel that our new protocol of an automatic compensation circuit may be helpful in reducing the measurement error of the electronic apex locator. We recommend using SD for the accuracy test, rather than a simple average with a ⫾0.5 mm error range. This study was supported by a grant of the Generic Industrial Technology Program (No. 981-75-03) of the Ministry of Industry and Energy, Korea, in 1998. Drs. Lee and Y.J. Kim are affiliated with the Department of Conservative Dentistry and the Oral Science Research Center, College of Dentistry, Seoul, Korea. Drs. Nam and D.W. Kim are affiliated with the Department of Medical Engineering, College of Medicine, Yonsei University, Seoul, Korea. Address requests for reprints to either Seung-Jong Lee, DDS, MS, Professor, Department of Conservative Dentistry, College of Dentistry, or Deok-Won Kim, PhD, Professor, Department of Medical Engineering, College of Medicine, Yonsei University, 134 Shinchon-Dong, Sudaemun-Ku, Seoul, Korea, 120-752.
References 1. Sunada I. New method for measuring the length of the root canal. J Dent Res 1962;41:375– 87. 2. O’Neill LJ. A clinical evaluation of electronic root canal measurement. Oral Surg Oral Med Oral Pathol 1974;38:469 –73. 3. Lee SJ. The effect of the canal irrigants on the electronic working length device. J Korean Acad Conserv Dent 1990;15:127–33. 4. Saito T, Yamashita Y. Electronic determination of root canal length by
Vol. 28, No. 10, October 2002 a newly developed measuring device: influences of the diameter of apical foramen, the size of K-file and root canal irrigants. Dent Japan 1990;27:65–72. 5. Kobayashi C, Suda H. New electronic canal length measuring device based on the ratio method. J Endodon 1994;20:111– 4. 6. J Morita Corp. Root ZX sales manual, 1995. 7. Frank AL, Torabinejad M. An in vivo evaluation of Endex electronic apex locator. J Endodon 1993;19:177–9. 8. Pratten DH, McDonald NJ. Comparison of radiographic and electronic working lengths. J Endodon 1996;22:173– 6. 9. Dunlap CA, Remeikis NA, BeGole EA, Rauschenberger CR. An in vivo evaluation of an electronic apex locator that uses the ratio method in vital and necrotic canals. J Endodon 1998;24:48 –50. 10. Lee SJ, Kim DW, Nam KC. Development of new frequency-dependent
Apex Locator
709
type apex locator: voltage difference compensating type. J Korean Acad Conserv Dent 1997;22:809 –19. 11. Kim DW, Nam KC, Lee SJ. Development of a frequency dependent type apex locator with automatic compensation. Crit Rev Biomed Eng 1998; 26:369 –70. 12. Kim DW, Nam KC, Lee SJ. Development of a frequency-dependent type apex locator with automatic compensation. Crit Rev Biomed Eng 2000; 28:473–9. 13. Mayeda DL, Simon JH, Aimar DF, Finley K. In vivo measurement accuracy in vital and necrotic canals with the Endex apex locator. J Endodon 1993;19:545– 8. 14. Shabahang S, Goon WW, Gluskin AH. An in vivo evaluation of Root ZX electronic apex locator. J Endodon 1996;22:616 – 8.
Printed in U.S.A. VOL. 28, NO. 10, OCTOBER 2002
Clinical Accuracy of a New Apex Locator with an Automatic Compensation Circuit Seung Jong Lee, DDS, MS, Ki Chang Nam, MS, Young-Joo Kim, DDS, and Deok Won Kim, PhD
the impedance ratio instead of the impedance difference. It operates on the principle that the impedance ratio is constant regardless of the kinds of conductive fluids (5). According to the manufacturer’s manual (6), the impedance ratio between the 500 Hz and 8 kHz frequencies is constant (0.72) in all canal conditions until the probe reaches the constriction point, no matter what type of irrigant remains in the canal. However, even with these improved systems, measurements may exhibit different readings according to the type of electrolytes present in the canal. Frank (7) reported that in 89.64% of moist root canals Endex showed accurate measurements within ⫾0.5 mm of the radiographic findings. Similarly, Pratten and McDonald (8) reported that in human cadavers Apit (Osada Electric Co.) located the apical foramen to the nearest 0.5 mm in 89% of cases with sodium hypochlorite. In a recent study, Dunlap et al. (9) reported that 82% of electronic values recorded with the Root ZX model were accurate to ⫾0.5 mm of the apical constriction when 2.5% NaOCl was used. In previous studies (10 –12), we found that there were tendencies toward short measurement in high electro-conductive solutions, such as NaOCl, whereas longer measurements were common in lower electro-conductive solutions. These tendencies were expressed by a voltage difference. To minimize the measurement errors, we developed a new circuit that can automatically compensate for the voltage differences of different irrigating solutions. As a result of this compensation, errors were significantly decreased on an average from ⫹0.54 mm to ⫹0.18 mm in H2O2 solution and from ⫺0.33 mm to ⫺0.01 mm in NaOCl solution in an in vitro study. The purpose of this study was to evaluate the accuracy of the newly designed electronic apex locator with an automatic compensation function in a clinical situation.
A new circuit was designed to automatically compensate for measurement errors of an electronic apex locator in various electrolytes. Thirty-one root canals were clinically tested for accuracy. A file was inserted into the canal until the apex signal was obtained, at which point the file was immobilized with glass-ionomer cement. After extraction, the apical area was exposed and the position of the file tip was examined under an operating microscope. Distances from the major foramen and cemento dentinal junction (CDJ) were recorded. The average distance from the major foramen was ⴚ0.13 mm with a range of ⴚ1.28 mm and ⴙ0.46 mm. The average distance in 26 detectable CDJ samples was ⴙ0.18 mm with a range of ⴚ0.98 mm and ⴙ0.65 mm. The measurements, which were within ⴞ0.5 mm, were 94% (29/31) from the major foramen and 92% (24/26) from the CDJ. Measurement consistencies within one SD were 81% for the major foramen and 65% for the CDJ, respectively. Measurements within two SD were 97% for the major foramen and 92% for the CDJ. There were no differences between the smaller (<#25) and larger apical foramens (>#25) or vital and nonvital pulps.
The use of an electronic apex locator has improved the accuracy of the working length measurement in clinical endodontics. Sunada (1) first reported that a constant electronic resistance existed between the periodontal ligament and oral mucosa. On the basis of this concept, a number of devices were introduced to the market. However, these first generation devices did not produce consistent readings in the presence of various root canal contents (2, 3). To solve this problem, new types of apex locators were advocated. The Endex (Osada Electric Co., Tokyo, Japan) model uses the relative value of different electric currents, 5 kHz and 1 kHz, operating on the principle that the impedance measurements of the different frequencies used differ greatly at the area of the apical constriction (4). The working mechanism of the Root ZX (Morita Corp., Japan) is similar to the Endex. However, the Root ZX uses
MATERIALS AND METHODS Compensation Circuit The electronic mechanism of the new circuit for automatic compensation has been described elsewhere (11, 12). Briefly, impedance ratios and voltage differences were obtained from three different irrigating solutions (saline, NaOCl, and H2O2) in an extracted tooth model. This was performed by using the conventional impedance ratio method (5) with two sinusoidal waves (0.5 and 10 kHz). From a total of 45 root canals examined in each 706
Vol. 28, No. 10, October 2002
FIG 1. Distributions of voltage difference versus error for the three solutions in the canal. LL and UL are decision boundaries that classify smaller voltage difference solutions (NaOCl) and larger voltage difference solutions (H2O2) for 45 extracted root canals (in vitro).
solution, the distributions of the voltage differences and the measurement errors were obtained. The voltage differences measured were generally larger in H2O2 and smaller in NaOCl compared with saline. The measured lengths were generally longer in H2O2 and shorter in NaOCl compared with saline. Impedance ratio of the two different frequencies represented the position of the file, whereas the voltage difference represented the status of the fluid in the root canal. Each irrigant was classified statistically by Bayes linear classifier (Fig. 1). When the difference was smaller than LL, the canal irrigant was classified as a higher electro-conductive group. If it was smaller than UL, it was classified as a lower electroconductive group. The compensating value was determined in proportion to the difference between the measured voltage difference and either UL or LL; then it was added or subtracted to the impedance ratio for compensation. Therefore, during the actual determination of working length, the file would go deeper in higher electro-conductive conditions, such as NaOCl, whereas shorter in lower electro-conductive conditions, such as H2O2. A prototype apex locator was fabricated with this adjusted circuit. Clinical Experiment The study subjects included 31 canals of 25 teeth that had been scheduled to be extracted for either orthodontic or periodontal reasons. None had any previous dental caries, metallic restorations, or gross periapical lesions. After the isolation of the tooth with a rubber dam, an access cavity was prepared and the occlusal portion of the tooth was flattened to secure a consistent reference point. Once access was gained, the excessive tissue in the chamber only was removed and a file that fit snugly in the canal was inserted until the machine indicated it was at the apical foramen. No attempt to remove the canal contents was made. This was to see whether the machine operated accurately in various canal conditions. Once the file reached the apical foramen, the file was advanced further to ensure the file passed through the apical foramen. The file was then subtracted to the point where the machine indicated it was again at the apical foramen. Self-curing glass-ionomer cement was mixed and injected into the access cavity to surround the shaft of
Apex Locator
707
the file and allowed to set completely. Locked in place, the file handle and exposed shaft were separated using a high-speed bur. The tooth was then extracted, numbered serially, and the size of the inserted file was recorded. The crown portion of the extracted tooth was encased in clear acrylic resin for easy handling. The apical 3 to 4 mm portion of the root was trimmed by using a fine diamond bur and soflex discs to visualize the inserted file. The plane of the cut was made in the same plane as the greatest curvature of the root. Once the file could be visualized, the additional tooth structure was carefully removed until the terminus of the file and the root were revealed. The exposed files and root apices were examined under a dissecting microscope with a calibrated ocular grid and then photographed in digital image. The distance from the end of the file to the major foramen was measured using Adobe Photoshop 5.5 (Adobe Systems Inc.) and calculated in mm. Two measurements were made. First, the distance from the end of the file to the major foramen, and second, the distance from the end of the file to the point where it appeared there was the cemento dentinal junction (CDJ). Two evaluators performed the examination and the results were averaged.
RESULTS The average distance of the 31 measurements was ⫺0.13 mm from the major foramen with a range of ⫺1.28 mm and ⫹0.46 mm. From the 26 CDJ-detectable samples, the average distance from the estimated CDJ was ⫹0.18 mm with a range of ⫺0.98 mm and ⫹0.65 mm (Table 1). The measurement accuracy’s were 94% from the major foramen and 92% (24/26) from the detectable CDJ with a ⫾0.5 mm tolerance. The measurement consistencies within one SD were 81% for the major foramen and 65% for the CDJ, respectively. Measurements within two SD were 97% for major foramen and 92% for the CDJ. There were no differences observed between the smaller (⬍#25) and larger apical foramens (ⱖ#25) or vital and nonvital pulps, respectively.
DISCUSSION Most previous studies of this subject used a ⫾0.5 mm error range to assess the accuracy of the electronic apex locator. With this criteria, the accuracy of this prototype was 94% from the major foramen and 92% from CDJ. However, the CDJs were not always detectable even under a microscope. In this study, only 14 of 31 samples displayed the points that could certainly be regarded as a CDJ or constriction point, whereas 12 showed only a vague configuration. In five samples, it was impossible to make a definitive determination of a CDJ. Interestingly, in this study, most of the file tips terminated at the immediately flaring point regardless of the existence of detectable CDJ. This may prove the clinical assumption that the machine does not always read the constriction point but the point where the periodontal ligament meets. Therefore, the use of the major foramen seems to be more reproducible, compared with CDJ, for this kind of accuracy study. The average distance to the file tip was ⫺0.13 mm from the major foramen and ⫹0.18 mm from the CDJ. Most of the measurements (19/25) were beyond the CDJ. This tendency has also been reported in other studies. Both Mayeda et al. (13) and Shabahang et al. (14), in a clinical study with Endex, found that twothirds of the measurements were past the CDJ. This may be due to
708
Lee et al.
Journal of Endodontics TABLE 1. Raw data of 31 samples, including measurements from the major diameter and CDJ
Sample
Age
Tooth
IAF Size
Major D* (mm)
CDJ (mm)
Pulp Status
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
45 47 48 49 49 45 48 48 19 20 52 47 19 48 19 21 54 21 25 25 49 49 49 47 49 47 48 45 19 19 49
14DB 10 24 14P 31D 14P 15MB 25 21 21 9 7 5P 15P 12 16 20 13 13B 21 29 25 26 9 14DB 8 15DB 24 28 5B 14MB
10 35 15 30 10 40 15 15 25 30 25 20 20 40 25 40 15 20 25 20 30 10 10 20 15 25 15 25 25 20 15
⫺1.28 ⫺0.57 ⫺0.46 ⫺0.41 ⫺0.34 ⫺0.28 ⫺0.28 ⫺0.26 ⫺0.25 ⫺0.21 ⫺0.2 ⫺0.16 ⫺0.16 ⫺0.14 ⫺0.08 0 0 0 0 0 0 0 0 0 0 0.08 0.09 0.14 0.19 0.24 0.46
⫺0.98 ⫺0.17 ⫺0.23 0.47 0 ⫺0.08 0.1 0 0.13 — 0.25 0.06 — — — 0.26 0.18 0.26 0.31 0.39 0.29 0.25 0.16 0.36 0.1 0.39 0.45 — 0.5 0.49 0.65
NV NV V NV NV NV V V V V NV NV V V V V NV V V V NV NV NV NV NV NV V NV V V NV
⫺0.13 0.30
0.18 0.32
Average SD * Samples were arranged in the order of the measurement from major diameter. CDJ ⫽ cemento dentinal junction; V ⫽ vital pulp; NV ⫽ nonvital pulp.
the fact that the machine reads the largest gradient of impedance ratio at the point where the periodontal ligaments meet. However, more important than where to read is the question of how the measurements can be consistently reproduced. No matter where the machine indicates, if the machine indication is consistent, if we know where we are, and if we know the average distance between the file tip and the true CDJ, then we can obtain an accurate length by subtracting the average distance from the machine reading. In this study, we used standard deviations to evaluate the measurement consistency. Measurements within one SD were 81% for the major foramen and 65% for CDJ, respectively. Measurements within two SD were 97% for the major foramen and 92% for CDJ. Again, these results showed that measurements from the major foramen were more consistent than from the CDJ. The most important question to bear in mind when using the electronic apex locator is how to eliminate possible operation errors. During the process of clinical experiment, we found that the same type of errors occurred as in the other types of apex locators, such as errors related to metallic restoration, leaky gingival margin, or excessive hydration and dehydration. In sample 1 of Table 1, the SD was shown to be four times (major diameter) and three times (CDJ) larger than the other samples. We do not know why this occurred but presume it to be an error in file stabilization.
In conclusion, we feel that our new protocol of an automatic compensation circuit may be helpful in reducing the measurement error of the electronic apex locator. We recommend using SD for the accuracy test, rather than a simple average with a ⫾0.5 mm error range. This study was supported by a grant of the Generic Industrial Technology Program (No. 981-75-03) of the Ministry of Industry and Energy, Korea, in 1998. Drs. Lee and Y.J. Kim are affiliated with the Department of Conservative Dentistry and the Oral Science Research Center, College of Dentistry, Seoul, Korea. Drs. Nam and D.W. Kim are affiliated with the Department of Medical Engineering, College of Medicine, Yonsei University, Seoul, Korea. Address requests for reprints to either Seung-Jong Lee, DDS, MS, Professor, Department of Conservative Dentistry, College of Dentistry, or Deok-Won Kim, PhD, Professor, Department of Medical Engineering, College of Medicine, Yonsei University, 134 Shinchon-Dong, Sudaemun-Ku, Seoul, Korea, 120-752.
References 1. Sunada I. New method for measuring the length of the root canal. J Dent Res 1962;41:375– 87. 2. O’Neill LJ. A clinical evaluation of electronic root canal measurement. Oral Surg Oral Med Oral Pathol 1974;38:469 –73. 3. Lee SJ. The effect of the canal irrigants on the electronic working length device. J Korean Acad Conserv Dent 1990;15:127–33. 4. Saito T, Yamashita Y. Electronic determination of root canal length by
Vol. 28, No. 10, October 2002 a newly developed measuring device: influences of the diameter of apical foramen, the size of K-file and root canal irrigants. Dent Japan 1990;27:65–72. 5. Kobayashi C, Suda H. New electronic canal length measuring device based on the ratio method. J Endodon 1994;20:111– 4. 6. J Morita Corp. Root ZX sales manual, 1995. 7. Frank AL, Torabinejad M. An in vivo evaluation of Endex electronic apex locator. J Endodon 1993;19:177–9. 8. Pratten DH, McDonald NJ. Comparison of radiographic and electronic working lengths. J Endodon 1996;22:173– 6. 9. Dunlap CA, Remeikis NA, BeGole EA, Rauschenberger CR. An in vivo evaluation of an electronic apex locator that uses the ratio method in vital and necrotic canals. J Endodon 1998;24:48 –50. 10. Lee SJ, Kim DW, Nam KC. Development of new frequency-dependent
Apex Locator
709
type apex locator: voltage difference compensating type. J Korean Acad Conserv Dent 1997;22:809 –19. 11. Kim DW, Nam KC, Lee SJ. Development of a frequency dependent type apex locator with automatic compensation. Crit Rev Biomed Eng 1998; 26:369 –70. 12. Kim DW, Nam KC, Lee SJ. Development of a frequency-dependent type apex locator with automatic compensation. Crit Rev Biomed Eng 2000; 28:473–9. 13. Mayeda DL, Simon JH, Aimar DF, Finley K. In vivo measurement accuracy in vital and necrotic canals with the Endex apex locator. J Endodon 1993;19:545– 8. 14. Shabahang S, Goon WW, Gluskin AH. An in vivo evaluation of Root ZX electronic apex locator. J Endodon 1996;22:616 – 8.