- Email: [email protected]
Critical Diameter of Apical Foramen and of File Size Using the Root ZX Apex Locator: An In Vitro Study
Basic Research—Technology
Critical Diameter of Apical Foramen and of File Size Using the Root ZX Apex Locator: An In Vitro Study Manuela Herrera, DDS, MD, PhD,* Camilo Abalos, DDS, MD, PhD,† ‡ Cristina Lucena, DDS, MD, PhD, Amparo Jimenez-Planas, DDS, MD, PhD,† and Rafael Llamas, DDS, MD, PhD* Abstract Introduction: An evaluation was made of the accuracy of the Root ZX apex locator (J. Morita Corp, Tokyo, Japan) in widened foramina, considering the existing controversy over this issue in the literature. Methods: Ten single-root teeth were embedded in an alginate mold. The foramina were widened from 0.6 mm to 1.0 mm. The measurements were taken with all possible file sizes $#10. The statistical accuracy of the Root ZX was calculated for the different diameters and for the influence of file size. Results: The accuracy of the Root ZX apex locator with a range of error of 0.5 mm was 87% in an apical foramen size of 0.6 mm and 84% using files size 45 or larger in an apical foramen size of 0.7 mm. With a tolerance of 1 mm, the accuracy was 99% in an apical foramen size of 0.6 mm, 98% using files size 45 or larger in an apical foramen size of 0.7 mm, and 95% using files size 70 or larger in an apical foramen size of 0.8 mm. In the rest, accuracy was not certain. The measurements taken with smaller files were shorter. There were no cases of overestimation of the working length. Conclusions: The Root ZX apex locator was accurate for an apical size of 0.6 mm, independently of the file size; between 0.7 to 0.8 mm, we should adjust the files to the foramen, whereas above size 0.9 mm the locator is not accurate. The results show that the accuracy of this electronic apex locator is gradually lost as the foramen widens. Considering the stable conditions of in vitro studies, our findings advise caution in clinical application of the locator. (J Endod 2011;37:1306–1309)
Key Words Apical widening, electronic apex locator, file size, root length determination, Root ZX
T
he apical constriction is widely accepted as the landmark for ending endodontic instrumentation and obturation (1, 2). The accuracy of canal length measurement using electronic apex locators (EALs) is in the range of 80% to 100% as shown by in vitro (3–7) and clinical studies (6, 8–11). However, for decades, it has been reported that a number of factors may influence the accuracy of EALs, such as the size of the apical foramen (3, 4, 6, 12–15), the type and size of the measuring file (15–17), the irrigation solution used, and electroconductivity of the pulp (3, 4, 12, 16, 18). In 1994, the Root ZX (J. Morita Corp, Tokyo, Japan) was introduced to overcome the problem of moist canals or vital pulp tissue (19). Nevertheless, the size of the apical foramen and the file characteristics remain controversial topics. Previous reports indicate that the critical diameter of the foramen is 0.3 mm (ie, file size #30) (4) or 0.6 mm (ie, file size #60) (3, 20). In glass tubes that simulate canals (12) or when the apical constriction is destroyed (21), a terminal opening of 0.4 mm (ie, file size #40) or larger decreases the accuracy of measurement. For other investigators, the critical diameter is greater, and accurate measurements are obtained for diameters of 0.8 mm (18) and even 0.9 mm (7). Additionally, according to some authors (6, 15, 17), these measurements can change depending on the discrepancy between the caliber of the measuring file and the size of the apical foramen although others studies have failed to confirm this (3, 14, 18, 20–22). The apparent discrepancy can be explained by the different research methods used. Nevertheless, considering the methodologic aspects involved, the following coincidences can be observed in those studies that have used these instruments: 1. EALs were used with values measured at two frequencies (8 and 0.4 kHz), calculating an impedances ratio (19). 2. The conical shape of the canal was still maintained, even in the absence of the anatomic apical constriction (16, 18, 21). 3. Irrigation was performed with sodium hypochlorite solution with or without EDTA (16, 18, 20). The results of these investigations show that in diameters smaller than 0.6 mm of the apical constriction the measurements are accurate regardless of the size of the file and the apical diameter (14, 16, 18, 21). This finding coincides with a previous study by our group (20) in which the measurements proved accurate with a widening of 0.6 mm but not with a widening of 1.0 mm. It is also possible that there may be a critical diameter in the interval between sizes 0.6 and 1.0 mm. Thus, the aim of this study was to determine whether the accuracy of the Root ZX apex locator is affected by widening of the apical foramen at 0.6 mm, 0.7 mm, 0.8 mm,
From the Departments of *Dental Pathology and Therapeutics and †Dental Materials, School of Dentistry, University of Seville, Spain; and ‡Department of Dental Pathology and Therapeutics, School of Dentistry, University of Granada, Spain. Address requests for reprints to Dr Camilo Abalos, Universidad de Sevilla, Facultad de Odontologıa, C/ Avicena s/n, 41009 Sevilla, Spain. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2011.05.007
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JOE — Volume 37, Number 9, September 2011
#100
— — — — — — — — 1.35h 0.74 — — — — — — 0.92f 0.61 1.40h 0.69 — — — — 0.52d 0.23 0.90f 0.41 1.30h 0.64 — — 0.22b 0.24 0.57d 0.27 0.92f 0.28 1.17h 0.74 and c-d, Analysis of variance (P # .001); e-f and g-h, analysis of variance (P # .05). Ø, apical foramen diameter; SD, standard deviation. *All of the measurements have a minus symbol and n = 10 except files #10-80Ø, #15-80Ø, and #15-100Ø (n = 9).
1.0 Ø
0.9 Ø
0.8 Ø
0.7 Ø
JOE — Volume 37, Number 9, September 2011
a-b
#70 #60
0.27 0.27 0.42b 0.42 0.70 0.45 1.05 0.56 1.60 0.89 0.30 0.20 0.35b 0.29 0.78 0.33 1.05 0.53 1.45 0.64
#55 #50
0.27 0.28 0.45b 0.40 0.88 0.43 1.00 0.67 1.47 0.61 0.25 0.29 0.40b 0.29 0.86 0.30 1.10 0.54 1.52 0.84
#45
Materials and Methods
0.30 0.29 0.57 0.31 1.03c 0.42 1.27 0.68 1.85 0.78
#40
0.9 mm, and 1.0 mm and by using all possible file sizes $#10 with a view to determining which files and at what point the latter are no longer accurate.
0.35 0.28 0.92 0.57 1.03c 0.38 1.27 0.47 1.80g 0.62
#35 #30
0.40 0.28 0.97a 0.54 1.14c 0.50 1.47e 0.62 1.87g 0.31 0.40 0.31 0.85a 0.37 1.27c 0.55 1.35e 0.44 1.92g 1.07
#25 #20
0.47 0.40 0.72a 0.29 1.20c 0.51 1.65e 0.71 2.15g 0.94 0.45 0.42 0.77a 0.27 1.23c 0.59 1.80e 0.81 2.27g 0.88
#15 #10 File
Mean* SD Mean* SD Mean* SD Mean* SD Mean* SD
Size
0.6 Ø
TABLE 1. Statistical Analysis of the Values from the Subtraction between the Electronic Measurements and the Actual Length (DL)
0.50 0.33 1.05a 0.53 1.41c 0.80 1.92e 0.70 2.20g 0.79
#80
#90
Basic Research—Technology
Ten single-root teeth were extracted and stored in distilled water containing 10% formalin at 37 C. Dental x-ray images were taken to evaluate the root canal anatomy. The teeth were all confirmed to have mature apexes as well as reasonably narrow, straight canals. The crowns were sectioned at the enamel-cement junction to gain standard root canal access and obtain a fixed, stable point of reference. The actual canal length up to the apical foramen (AL) was determined by introducing a #10 K-type file (Dentsply Maillefer, Ballaigues, Switzerland) into the canal until the tip of the file became visible at the apical foramen under a stereomicroscope Nikon HFX-IIA (Nikon Corp, Tochigi, Japan) at 20 magnification. A rubber stop was then carefully adjusted to the reference level, and the distance between the rubber stop and the file tip was measured with an endodontic ruler and 2.6 magnifying loupes (Orascoptic Research, Inc, Madison, WI) to an accuracy of 0.25 mm. The teeth were then embedded in an alginate mold that was kept moist in saline solution (23). The canal was progressively widened at a point AL + 1 mm. The root canal was irrigated during the progressive widening; 15% EDTA was used during instrumentation, and 5.25% sodium hypochlorite was used after the insertion of each file. Patency was constantly checked using a #10 K-type file. After widening to file #60 at point AL + 1 mm (foramen size 0.6 mm), the working length was routinely determined with the Root ZX apex locator (J. Morita USA, Irvine, CA) by using files from #10 to #60 (F10–F60). The measurements were taken following the instructions of the manufacturer. The file was inserted into the canal until the reading on the apex locator dial flashed ‘‘APEX.’’ This mark consistently represents the major foramen (24). All measurements were made in triplicate, and the mean value of the three measurements was taken as the result. Teeth with discrepancies in any of these measurements were eliminated (Table 1). Before each of the three measurements with the same file diameter, the canal was irrigated with sodium hypochlorite to preserve humidity. Because of poor standardization of the files (tolerance 0.02 mm), canal instrumentation and measurements were performed with the same files. Widening was continued up to an apical foramen diameter of 0.7 mm (measurements/F10-F70), 0.8 mm (measurements/F10–F80), 0.9 mm (measurements/F10–F90), and 1.0 mm (measurements/F10– F100). In order to establish possible differences in canal length during widening, AL was again measured after widening to an apical foramen diameter of 1.0 mm. Comparison of the measurements showed no evaluable differences ($0.25 mm). Because the teeth used had different root lengths, we used the difference between the measurements obtained (F10, F15, F20, and so on) in each tooth and the AL for each apical enlargement in order to ensure valid statistical comparison of the results. Thus, the data refer not to lengths but to increments or decrements in length (DL = F10AL). Positive values mean that the file extended through the apical 100 foramen, whereas negative values mean that the file tip was positioned before the apical foramen, and zero values mean that the file tip was flush with the apical foramen. Such values are considered to be a measurement of the accuracy of the Root ZX apex locator. The proportion of measurements within a tolerance of 0.5 mm and 1 mm was calculated. Statistical analysis was performed based on an analysis of variance test for the comparison of means; statistical significance was set at a # 0.05. The data were analyzed using the SPSS version 14.0 statistical package (SPSS Inc, Chicago, IL).
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Basic Research—Technology TABLE 2. Percentage of Acceptable Measurements According to the Size File Used for Each Apical Diameter (range of error 0.5 mm and 1 mm) Foramen size 0.6 Ø 0.7 Ø 0.8 Ø 0.9 Ø 1.0 Ø
Range error
File size
Acceptable measurements
File size
Acceptable measurements
0.5 mm 1 mm 0.5 mm 1 mm 0.5 mm 1 mm 0.5 mm 1 mm 0.5 mm 1 mm
(F10-F60)* (F10-F60)* (F10-F30) (F10-F30) (F10-F40) (F10-F40) (F10-F30) (F10-F30) (F10-F35) (F10-F35)
87.27% 99.10% 32.00% 76.00% 12.85% 45.71% 0.00% 26.00% 0.00% 2.40%
(F45-F70)* (F45-F70)* (F70-F80) (F70-F80)* (F70-F90) (F70-F90) (F70-F100) (F70-F100)
84.00% 98.00% 60.00% 95.00% 26.60% 73.30% 0.40% 62.50%
Ø, apical foramen diameter; F, file. *Percentage $80%.
Results The means and standard deviations for the measurements (DL) obtained with each file size and for each apical diameter are shown in Table 1. This table shows that the values obtained with the smaller size files were shorter than AL and that the values gradually approached AL as the file size increased. Although these differences were not significant for an apical foramen diameter of 0.6 mm (ie, file size #60), they proved significant for the rest of the diameters (0.7–1.0 mm). Table 2 shows the percentage of acceptable measurements for each apical diameter according to the file sizes with statistically significant differences, for two ranges of error ( 0.5 mm and 1.0 mm). Regarding percentage accuracy $ 80%, we found the percentage to be over 87% for apical foramen diameter 0.6 mm, with all the possible file sizes (#10–60). In the case of a foramen diameter of 0.7 mm, on using file sizes $45, the percentage was >84%. With a foramen diameter of 0.8 mm, we obtained percentages >95% with file sizes $70 although only for the range of error 1 mm. For the rest of the measurements, the percentage accuracy was <80%.
Discussion Previous studies have indicated that an error range of 0.5 mm in electronic apex locator measurements is clinically acceptable (3, 4, 8, 22). We found the Root ZX to be very accurate with this tolerance when the foramen was enlarged to 0.6 mm (ie, file size #60) regardless of the size file used. These results concur with those of previous studies (3, 14, 16, 18, 20). However, other authors (15, 16) recommend measuring with files adjusted to the diameter of the foramen, either for foramina that are too large (15) or because of the presence of blood in the canal (16). In our study, when the size of the foramen was 0.7 mm (ie, file size #70), it proved necessary to use $#45 files in order to maintain EAL accuracy. When the diameter of the foramen was $0.8 mm, the Root ZX was not accurate. In contrast, some studies (15) have found it to be accurate for files with a large diameter, and others (7, 16, 18) have found it to be accurate regardless of the size file used. One reason cited for accepting a 1.0-mm margin of error is the wide range seen in the shape of the apical zone (11). In our study, with a tolerance 1.0 mm, the critical diameter of the foramen was 0.8 mm for measurements taken with files $#70. For diameters $0.9 mm, the Root ZX is not accurate although one study (7) finds it to be accurate. Therefore, we observed not just a single critical diameter as in other publications but a range of diameters between 0.6 and 0.8 mm. This depended on the tolerance used and on whether or not it proved necessary to adjust the file size to the diameter of the foramen. In previous studies (4, 12), the critical diameter of the foramen was found to be 0.3 to 0.4 mm, and there are reasons for these 1308
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results. In some studies (12, 13), the apical constriction was destroyed, and in these cases the accuracy of EAL shows a significant negative correlation with the size of the apical foramen (21). In contrast, when the conical shape of the canal is maintained (14, 18, 21), the impedance ratio method of Root ZX identifies the narrowest diameter of the canal regardless of whether or not the constriction is intact (14, 19). In other studies, the EALs used were not as developed or as accurate as the Root ZX (4, 7, 15). This apex locator works even in the presence of electrolytes and requires no calibration (19). With either 5% sodium hypochlorite or 14% to 17% EDTA, no interference in detecting the apical foramen was observed (3, 18). Various authors (4, 13, 14, 25) have reported that as the diameter of the apical foramen increases, electronically measured lengths with files become shorter than the actual length. In our study, the proportion of exact measurements was low (<30%), which is in agreement with the observations of other authors (22, 26, 27). Factors such as the preflared procedure have increased the percentage of accurate electronic readings with the Root ZX from 50% to 75% (28). The rest of the measurements were always shorter. We found no cases in which the working length was overestimated. This coincides with another ex vivo study (7) although other authors have reported overestimated measurements in 1.7% of the cases (29). In in vivo studies (30), the percentage of overestimated measurements was found to be #0.3%. Considering the size of the file, the measurements obtained with smaller file sizes were generally shorter although the differences were not significant when the diameter was #0.6 mm, which is in agreement with other studies (3, 14, 16, 18, 20). When the size of the foramen was larger, significant differences were seen between the file sizes. For reasons we cannot explain, the #45 and #70 files marked the diameter limit for accurate measurements. Based on these findings and for establishing canal lengths with foramen diameters of >0.6 mm, we recommend the use of several files with sizes $#45. If different measurements are obtained, we should select the largest measurement because of the limited number (29, 30) or even the absence of overestimations. EAL use does not obviate the need for radiographic verification. In conclusion, the Root ZX apex locator is accurate under a diameter size of 0.6 mm. In the case of diameters of 0.7 to 0.8 mm, we must adjust the files to the foramen to maintain accuracy, whereas above size 0.9 mm the device is not accurate. Although there are studies (11) indicating that the accuracy of the Root ZX apex locator is high in vivo (96.2%), the conditions found in in vitro studies are comparatively more stable. For this reason, these results cannot be applied directly to clinical work although they reflect a tendency to gradually lose EAL accuracy when the size of the foramen increases. JOE — Volume 37, Number 9, September 2011
Basic Research—Technology Acknowledgments The authors deny any conflicts of interest related to this study.
References 1. Kuttler Y. Microscopic investigation of root apexes. J Am Dent Assoc 1955;50: 544–52. 2. Dummer PM, McGinn JH, Rees DG. The position and topography of the apical canal constriction and apical foramen. Int Endod J 1984;17:192–8. 3. Saito T, Yamashita Y. Electronic determination of root canal length by newly developed measuring device. Influences of the diameter of apical foramen, the size of Kfile and the root canal irrigants. Dent Jpn (Tokyo) 1990;27:65–72. 4. Fouad AF, Rivera EM, Krell KV. Accuracy of the Endex with variations in canal irrigants and foramen size. J Endod 1993;19:63–7. 5. Katz A, Tamse A, Kaufman AY. Tooth length determination: a review. Oral Surg Oral Med Oral Pathol 1991;72:238–42. 6. Stein TJ, Corcoran JF, Zillich RM. Influence of the major and minor foramen diameters on apical electronic probe measurements. J Endod 1990;16: 520–2. 7. ElAyouti A, Kimionis I, Chu AL, Lost C. Determining the apical terminus of root-end resected teeth using three modern apex locators: a comparative ex vivo study. Int Endod J 2005;38:827–33. 8. Fouad AF, Krell KV, McKendry DJ, Koorbusch GF, Olson RA. Clinical evaluation of five electronic root canal length measuring instruments. J Endod 1990;16:446–9. 9. McDonald NJ, Hovland EJ. An evaluation of the Apex Locator Endocater. J Endod 1990;16:5–8. 10. Pallares A, Faus V. An in vivo comparative study of two apex locators. J Endod 1994; 20:576–9. 11. Shabahang S, Goon WW, Gluskin AH. An in vivo evaluation of Root ZX electronic apex locator. J Endod 1996;22:616–8. 12. Huang L. An experimental study of the principle of electronic root canal measurement. J Endod 1987;13:60–4. 13. Hulsmann M, Pieper K. Use of an electronic apex locator in the treatment of teeth with incomplete root formation. Endod Dent Traumatol 1989;5:238–41. 14. Nguyen HQ, Kaufman AY, Komorowski RC, Friedman S. Electronic length measurement using small and large files in enlarged canals. Int Endod J 1996;29:359–64.
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15. Ebrahim AK, Wadachi R, Suda H. Ex vivo evaluation of the ability of four different electronic apex locators to determine the working length in teeth with various foramen diameters. Aust Dent J 2006;51:258–62. 16. Ebrahim AK, Yoshioka T, Kobayashi C, Suda H. The effects of file size, sodium hypochlorite and blood on the accuracy of Root ZX apex locator in enlarged root canals: an in vitro study. Aust Dent J 2006;51:153–7. 17. McDonald NJ. The electronic determination of working length. Dent Clin North Am 1992;36:293–307. 18. Ebrahim AK, Wadachi R, Suda H. An in vitro evaluation of the accuracy of Dentaport ZX apex locator in enlarged root canals. Aust Dent J 2007;52: 193–7. 19. Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20:111–4. 20. Herrera M, Abalos C, Planas AJ, Llamas R. Influence of apical constriction diameter on Root ZX apex locator precision. J Endod 2007;33:995–8. 21. Cheng L, Su Q, Huang YX. In vitro evaluation of correlation between the size of apical foramen and the accuracy of root ZX. Hua Xi Kou Qiang Yi Xue Za Zhi 2008;26:56–9. 22. Briseno-Marroquin B, Frajlich S, Goldberg F, Willershausen B. Influence of instrument size on the accuracy of different apex locators: an in vitro study. J Endod 2008; 34:698–702. 23. Czerw RJ, Fulkerson MS, Donnelly JC. An in vitro test of a simplified model to demonstrate the operation of electronic root canal measuring devices. J Endod 1994;20:605–6. 24. Jung IY, Yoon BH, Lee SJ, Lee SJ. Comparison of the reliability of ‘‘0.5’’ and ‘‘APEX’’ mark measurements in two frequency-based electronic apex locators. J Endod 2011;37:49–52. 25. Kaufman AY. Reliability of Root ZX apex locator tested by an in vitro model. J Endod 1993;19:201–7. 26. Hoer D, Attin T. The accuracy of electronic working length determination. Int Endod J 2004;37:125–31. 27. Plotino G, Grande NM, Brigante L, Lesti B, Somma F. Ex vivo accuracy of three electronic apex locators: root ZX, Elements Diagnostic Unit and Apex Locator and ProPex. Int Endod J 2006;39:408–14. 28. de Camargo EJ, Zapata RO, Medeiros PL, et al. Influence of preflaring on the accuracy of length determination with four electronic apex locators. J Endod 2009;35:1300–2. 29. Ding J, Gutmann JL, Fan B, Lu Y, Chen H. Investigation of apex locators and related morphological factors. J Endod 2010;36:1399–403. 30. ElAyouti A, Dima E, Ohmer J, Sperl K, von Ohle C, Lost C. Consistency of apex locator function: a clinical study. J Endod 2009;35:179–81.
Foramen and File Size Using Apex Locator
1309
Critical Diameter of Apical Foramen and of File Size Using the Root ZX Apex Locator: An In Vitro Study Manuela Herrera, DDS, MD, PhD,* Camilo Abalos, DDS, MD, PhD,† ‡ Cristina Lucena, DDS, MD, PhD, Amparo Jimenez-Planas, DDS, MD, PhD,† and Rafael Llamas, DDS, MD, PhD* Abstract Introduction: An evaluation was made of the accuracy of the Root ZX apex locator (J. Morita Corp, Tokyo, Japan) in widened foramina, considering the existing controversy over this issue in the literature. Methods: Ten single-root teeth were embedded in an alginate mold. The foramina were widened from 0.6 mm to 1.0 mm. The measurements were taken with all possible file sizes $#10. The statistical accuracy of the Root ZX was calculated for the different diameters and for the influence of file size. Results: The accuracy of the Root ZX apex locator with a range of error of 0.5 mm was 87% in an apical foramen size of 0.6 mm and 84% using files size 45 or larger in an apical foramen size of 0.7 mm. With a tolerance of 1 mm, the accuracy was 99% in an apical foramen size of 0.6 mm, 98% using files size 45 or larger in an apical foramen size of 0.7 mm, and 95% using files size 70 or larger in an apical foramen size of 0.8 mm. In the rest, accuracy was not certain. The measurements taken with smaller files were shorter. There were no cases of overestimation of the working length. Conclusions: The Root ZX apex locator was accurate for an apical size of 0.6 mm, independently of the file size; between 0.7 to 0.8 mm, we should adjust the files to the foramen, whereas above size 0.9 mm the locator is not accurate. The results show that the accuracy of this electronic apex locator is gradually lost as the foramen widens. Considering the stable conditions of in vitro studies, our findings advise caution in clinical application of the locator. (J Endod 2011;37:1306–1309)
Key Words Apical widening, electronic apex locator, file size, root length determination, Root ZX
T
he apical constriction is widely accepted as the landmark for ending endodontic instrumentation and obturation (1, 2). The accuracy of canal length measurement using electronic apex locators (EALs) is in the range of 80% to 100% as shown by in vitro (3–7) and clinical studies (6, 8–11). However, for decades, it has been reported that a number of factors may influence the accuracy of EALs, such as the size of the apical foramen (3, 4, 6, 12–15), the type and size of the measuring file (15–17), the irrigation solution used, and electroconductivity of the pulp (3, 4, 12, 16, 18). In 1994, the Root ZX (J. Morita Corp, Tokyo, Japan) was introduced to overcome the problem of moist canals or vital pulp tissue (19). Nevertheless, the size of the apical foramen and the file characteristics remain controversial topics. Previous reports indicate that the critical diameter of the foramen is 0.3 mm (ie, file size #30) (4) or 0.6 mm (ie, file size #60) (3, 20). In glass tubes that simulate canals (12) or when the apical constriction is destroyed (21), a terminal opening of 0.4 mm (ie, file size #40) or larger decreases the accuracy of measurement. For other investigators, the critical diameter is greater, and accurate measurements are obtained for diameters of 0.8 mm (18) and even 0.9 mm (7). Additionally, according to some authors (6, 15, 17), these measurements can change depending on the discrepancy between the caliber of the measuring file and the size of the apical foramen although others studies have failed to confirm this (3, 14, 18, 20–22). The apparent discrepancy can be explained by the different research methods used. Nevertheless, considering the methodologic aspects involved, the following coincidences can be observed in those studies that have used these instruments: 1. EALs were used with values measured at two frequencies (8 and 0.4 kHz), calculating an impedances ratio (19). 2. The conical shape of the canal was still maintained, even in the absence of the anatomic apical constriction (16, 18, 21). 3. Irrigation was performed with sodium hypochlorite solution with or without EDTA (16, 18, 20). The results of these investigations show that in diameters smaller than 0.6 mm of the apical constriction the measurements are accurate regardless of the size of the file and the apical diameter (14, 16, 18, 21). This finding coincides with a previous study by our group (20) in which the measurements proved accurate with a widening of 0.6 mm but not with a widening of 1.0 mm. It is also possible that there may be a critical diameter in the interval between sizes 0.6 and 1.0 mm. Thus, the aim of this study was to determine whether the accuracy of the Root ZX apex locator is affected by widening of the apical foramen at 0.6 mm, 0.7 mm, 0.8 mm,
From the Departments of *Dental Pathology and Therapeutics and †Dental Materials, School of Dentistry, University of Seville, Spain; and ‡Department of Dental Pathology and Therapeutics, School of Dentistry, University of Granada, Spain. Address requests for reprints to Dr Camilo Abalos, Universidad de Sevilla, Facultad de Odontologıa, C/ Avicena s/n, 41009 Sevilla, Spain. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2011.05.007
1306
Herrera et al.
JOE — Volume 37, Number 9, September 2011
#100
— — — — — — — — 1.35h 0.74 — — — — — — 0.92f 0.61 1.40h 0.69 — — — — 0.52d 0.23 0.90f 0.41 1.30h 0.64 — — 0.22b 0.24 0.57d 0.27 0.92f 0.28 1.17h 0.74 and c-d, Analysis of variance (P # .001); e-f and g-h, analysis of variance (P # .05). Ø, apical foramen diameter; SD, standard deviation. *All of the measurements have a minus symbol and n = 10 except files #10-80Ø, #15-80Ø, and #15-100Ø (n = 9).
1.0 Ø
0.9 Ø
0.8 Ø
0.7 Ø
JOE — Volume 37, Number 9, September 2011
a-b
#70 #60
0.27 0.27 0.42b 0.42 0.70 0.45 1.05 0.56 1.60 0.89 0.30 0.20 0.35b 0.29 0.78 0.33 1.05 0.53 1.45 0.64
#55 #50
0.27 0.28 0.45b 0.40 0.88 0.43 1.00 0.67 1.47 0.61 0.25 0.29 0.40b 0.29 0.86 0.30 1.10 0.54 1.52 0.84
#45
Materials and Methods
0.30 0.29 0.57 0.31 1.03c 0.42 1.27 0.68 1.85 0.78
#40
0.9 mm, and 1.0 mm and by using all possible file sizes $#10 with a view to determining which files and at what point the latter are no longer accurate.
0.35 0.28 0.92 0.57 1.03c 0.38 1.27 0.47 1.80g 0.62
#35 #30
0.40 0.28 0.97a 0.54 1.14c 0.50 1.47e 0.62 1.87g 0.31 0.40 0.31 0.85a 0.37 1.27c 0.55 1.35e 0.44 1.92g 1.07
#25 #20
0.47 0.40 0.72a 0.29 1.20c 0.51 1.65e 0.71 2.15g 0.94 0.45 0.42 0.77a 0.27 1.23c 0.59 1.80e 0.81 2.27g 0.88
#15 #10 File
Mean* SD Mean* SD Mean* SD Mean* SD Mean* SD
Size
0.6 Ø
TABLE 1. Statistical Analysis of the Values from the Subtraction between the Electronic Measurements and the Actual Length (DL)
0.50 0.33 1.05a 0.53 1.41c 0.80 1.92e 0.70 2.20g 0.79
#80
#90
Basic Research—Technology
Ten single-root teeth were extracted and stored in distilled water containing 10% formalin at 37 C. Dental x-ray images were taken to evaluate the root canal anatomy. The teeth were all confirmed to have mature apexes as well as reasonably narrow, straight canals. The crowns were sectioned at the enamel-cement junction to gain standard root canal access and obtain a fixed, stable point of reference. The actual canal length up to the apical foramen (AL) was determined by introducing a #10 K-type file (Dentsply Maillefer, Ballaigues, Switzerland) into the canal until the tip of the file became visible at the apical foramen under a stereomicroscope Nikon HFX-IIA (Nikon Corp, Tochigi, Japan) at 20 magnification. A rubber stop was then carefully adjusted to the reference level, and the distance between the rubber stop and the file tip was measured with an endodontic ruler and 2.6 magnifying loupes (Orascoptic Research, Inc, Madison, WI) to an accuracy of 0.25 mm. The teeth were then embedded in an alginate mold that was kept moist in saline solution (23). The canal was progressively widened at a point AL + 1 mm. The root canal was irrigated during the progressive widening; 15% EDTA was used during instrumentation, and 5.25% sodium hypochlorite was used after the insertion of each file. Patency was constantly checked using a #10 K-type file. After widening to file #60 at point AL + 1 mm (foramen size 0.6 mm), the working length was routinely determined with the Root ZX apex locator (J. Morita USA, Irvine, CA) by using files from #10 to #60 (F10–F60). The measurements were taken following the instructions of the manufacturer. The file was inserted into the canal until the reading on the apex locator dial flashed ‘‘APEX.’’ This mark consistently represents the major foramen (24). All measurements were made in triplicate, and the mean value of the three measurements was taken as the result. Teeth with discrepancies in any of these measurements were eliminated (Table 1). Before each of the three measurements with the same file diameter, the canal was irrigated with sodium hypochlorite to preserve humidity. Because of poor standardization of the files (tolerance 0.02 mm), canal instrumentation and measurements were performed with the same files. Widening was continued up to an apical foramen diameter of 0.7 mm (measurements/F10-F70), 0.8 mm (measurements/F10–F80), 0.9 mm (measurements/F10–F90), and 1.0 mm (measurements/F10– F100). In order to establish possible differences in canal length during widening, AL was again measured after widening to an apical foramen diameter of 1.0 mm. Comparison of the measurements showed no evaluable differences ($0.25 mm). Because the teeth used had different root lengths, we used the difference between the measurements obtained (F10, F15, F20, and so on) in each tooth and the AL for each apical enlargement in order to ensure valid statistical comparison of the results. Thus, the data refer not to lengths but to increments or decrements in length (DL = F10AL). Positive values mean that the file extended through the apical 100 foramen, whereas negative values mean that the file tip was positioned before the apical foramen, and zero values mean that the file tip was flush with the apical foramen. Such values are considered to be a measurement of the accuracy of the Root ZX apex locator. The proportion of measurements within a tolerance of 0.5 mm and 1 mm was calculated. Statistical analysis was performed based on an analysis of variance test for the comparison of means; statistical significance was set at a # 0.05. The data were analyzed using the SPSS version 14.0 statistical package (SPSS Inc, Chicago, IL).
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Basic Research—Technology TABLE 2. Percentage of Acceptable Measurements According to the Size File Used for Each Apical Diameter (range of error 0.5 mm and 1 mm) Foramen size 0.6 Ø 0.7 Ø 0.8 Ø 0.9 Ø 1.0 Ø
Range error
File size
Acceptable measurements
File size
Acceptable measurements
0.5 mm 1 mm 0.5 mm 1 mm 0.5 mm 1 mm 0.5 mm 1 mm 0.5 mm 1 mm
(F10-F60)* (F10-F60)* (F10-F30) (F10-F30) (F10-F40) (F10-F40) (F10-F30) (F10-F30) (F10-F35) (F10-F35)
87.27% 99.10% 32.00% 76.00% 12.85% 45.71% 0.00% 26.00% 0.00% 2.40%
(F45-F70)* (F45-F70)* (F70-F80) (F70-F80)* (F70-F90) (F70-F90) (F70-F100) (F70-F100)
84.00% 98.00% 60.00% 95.00% 26.60% 73.30% 0.40% 62.50%
Ø, apical foramen diameter; F, file. *Percentage $80%.
Results The means and standard deviations for the measurements (DL) obtained with each file size and for each apical diameter are shown in Table 1. This table shows that the values obtained with the smaller size files were shorter than AL and that the values gradually approached AL as the file size increased. Although these differences were not significant for an apical foramen diameter of 0.6 mm (ie, file size #60), they proved significant for the rest of the diameters (0.7–1.0 mm). Table 2 shows the percentage of acceptable measurements for each apical diameter according to the file sizes with statistically significant differences, for two ranges of error ( 0.5 mm and 1.0 mm). Regarding percentage accuracy $ 80%, we found the percentage to be over 87% for apical foramen diameter 0.6 mm, with all the possible file sizes (#10–60). In the case of a foramen diameter of 0.7 mm, on using file sizes $45, the percentage was >84%. With a foramen diameter of 0.8 mm, we obtained percentages >95% with file sizes $70 although only for the range of error 1 mm. For the rest of the measurements, the percentage accuracy was <80%.
Discussion Previous studies have indicated that an error range of 0.5 mm in electronic apex locator measurements is clinically acceptable (3, 4, 8, 22). We found the Root ZX to be very accurate with this tolerance when the foramen was enlarged to 0.6 mm (ie, file size #60) regardless of the size file used. These results concur with those of previous studies (3, 14, 16, 18, 20). However, other authors (15, 16) recommend measuring with files adjusted to the diameter of the foramen, either for foramina that are too large (15) or because of the presence of blood in the canal (16). In our study, when the size of the foramen was 0.7 mm (ie, file size #70), it proved necessary to use $#45 files in order to maintain EAL accuracy. When the diameter of the foramen was $0.8 mm, the Root ZX was not accurate. In contrast, some studies (15) have found it to be accurate for files with a large diameter, and others (7, 16, 18) have found it to be accurate regardless of the size file used. One reason cited for accepting a 1.0-mm margin of error is the wide range seen in the shape of the apical zone (11). In our study, with a tolerance 1.0 mm, the critical diameter of the foramen was 0.8 mm for measurements taken with files $#70. For diameters $0.9 mm, the Root ZX is not accurate although one study (7) finds it to be accurate. Therefore, we observed not just a single critical diameter as in other publications but a range of diameters between 0.6 and 0.8 mm. This depended on the tolerance used and on whether or not it proved necessary to adjust the file size to the diameter of the foramen. In previous studies (4, 12), the critical diameter of the foramen was found to be 0.3 to 0.4 mm, and there are reasons for these 1308
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results. In some studies (12, 13), the apical constriction was destroyed, and in these cases the accuracy of EAL shows a significant negative correlation with the size of the apical foramen (21). In contrast, when the conical shape of the canal is maintained (14, 18, 21), the impedance ratio method of Root ZX identifies the narrowest diameter of the canal regardless of whether or not the constriction is intact (14, 19). In other studies, the EALs used were not as developed or as accurate as the Root ZX (4, 7, 15). This apex locator works even in the presence of electrolytes and requires no calibration (19). With either 5% sodium hypochlorite or 14% to 17% EDTA, no interference in detecting the apical foramen was observed (3, 18). Various authors (4, 13, 14, 25) have reported that as the diameter of the apical foramen increases, electronically measured lengths with files become shorter than the actual length. In our study, the proportion of exact measurements was low (<30%), which is in agreement with the observations of other authors (22, 26, 27). Factors such as the preflared procedure have increased the percentage of accurate electronic readings with the Root ZX from 50% to 75% (28). The rest of the measurements were always shorter. We found no cases in which the working length was overestimated. This coincides with another ex vivo study (7) although other authors have reported overestimated measurements in 1.7% of the cases (29). In in vivo studies (30), the percentage of overestimated measurements was found to be #0.3%. Considering the size of the file, the measurements obtained with smaller file sizes were generally shorter although the differences were not significant when the diameter was #0.6 mm, which is in agreement with other studies (3, 14, 16, 18, 20). When the size of the foramen was larger, significant differences were seen between the file sizes. For reasons we cannot explain, the #45 and #70 files marked the diameter limit for accurate measurements. Based on these findings and for establishing canal lengths with foramen diameters of >0.6 mm, we recommend the use of several files with sizes $#45. If different measurements are obtained, we should select the largest measurement because of the limited number (29, 30) or even the absence of overestimations. EAL use does not obviate the need for radiographic verification. In conclusion, the Root ZX apex locator is accurate under a diameter size of 0.6 mm. In the case of diameters of 0.7 to 0.8 mm, we must adjust the files to the foramen to maintain accuracy, whereas above size 0.9 mm the device is not accurate. Although there are studies (11) indicating that the accuracy of the Root ZX apex locator is high in vivo (96.2%), the conditions found in in vitro studies are comparatively more stable. For this reason, these results cannot be applied directly to clinical work although they reflect a tendency to gradually lose EAL accuracy when the size of the foramen increases. JOE — Volume 37, Number 9, September 2011
Basic Research—Technology Acknowledgments The authors deny any conflicts of interest related to this study.
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15. Ebrahim AK, Wadachi R, Suda H. Ex vivo evaluation of the ability of four different electronic apex locators to determine the working length in teeth with various foramen diameters. Aust Dent J 2006;51:258–62. 16. Ebrahim AK, Yoshioka T, Kobayashi C, Suda H. The effects of file size, sodium hypochlorite and blood on the accuracy of Root ZX apex locator in enlarged root canals: an in vitro study. Aust Dent J 2006;51:153–7. 17. McDonald NJ. The electronic determination of working length. Dent Clin North Am 1992;36:293–307. 18. Ebrahim AK, Wadachi R, Suda H. An in vitro evaluation of the accuracy of Dentaport ZX apex locator in enlarged root canals. Aust Dent J 2007;52: 193–7. 19. Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20:111–4. 20. Herrera M, Abalos C, Planas AJ, Llamas R. Influence of apical constriction diameter on Root ZX apex locator precision. J Endod 2007;33:995–8. 21. Cheng L, Su Q, Huang YX. In vitro evaluation of correlation between the size of apical foramen and the accuracy of root ZX. Hua Xi Kou Qiang Yi Xue Za Zhi 2008;26:56–9. 22. Briseno-Marroquin B, Frajlich S, Goldberg F, Willershausen B. Influence of instrument size on the accuracy of different apex locators: an in vitro study. J Endod 2008; 34:698–702. 23. Czerw RJ, Fulkerson MS, Donnelly JC. An in vitro test of a simplified model to demonstrate the operation of electronic root canal measuring devices. J Endod 1994;20:605–6. 24. Jung IY, Yoon BH, Lee SJ, Lee SJ. Comparison of the reliability of ‘‘0.5’’ and ‘‘APEX’’ mark measurements in two frequency-based electronic apex locators. J Endod 2011;37:49–52. 25. Kaufman AY. Reliability of Root ZX apex locator tested by an in vitro model. J Endod 1993;19:201–7. 26. Hoer D, Attin T. The accuracy of electronic working length determination. Int Endod J 2004;37:125–31. 27. Plotino G, Grande NM, Brigante L, Lesti B, Somma F. Ex vivo accuracy of three electronic apex locators: root ZX, Elements Diagnostic Unit and Apex Locator and ProPex. Int Endod J 2006;39:408–14. 28. de Camargo EJ, Zapata RO, Medeiros PL, et al. Influence of preflaring on the accuracy of length determination with four electronic apex locators. J Endod 2009;35:1300–2. 29. Ding J, Gutmann JL, Fan B, Lu Y, Chen H. Investigation of apex locators and related morphological factors. J Endod 2010;36:1399–403. 30. ElAyouti A, Dima E, Ohmer J, Sperl K, von Ohle C, Lost C. Consistency of apex locator function: a clinical study. J Endod 2009;35:179–81.
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