- Email: [email protected]
An Evaluation of Root ZX and iPex Apex Locators: An In Vivo Study
Clinical Research
An Evaluation of Root ZX and iPex Apex Locators: An In Vivo Study Eva K. St€ ober, DDS, MsC,* Fernando Duran-Sindreu, DDS, PhD,* Montserrat Mercade, DDS, PhD,* Jorge Vera, DDS, PhD,† Rufino Bueno, DDS, PhD,* and Miguel Roig, DDS, PhD* Abstract Introduction: iPex is a fourth-generation apex locator (EAL) that has not yet been tested in vivo. The purpose of this study was to compare the accuracy of the Root ZX (J Morita Corp, Tokyo, Japan) and iPex (NSK, Tochigi, Japan) EALs. Methods: The working length (WL) was determined electronically for 40 root canals of human teeth with a K-file and one of the two EALs. The files were fixed at the WL, and the teeth were extracted. The apical 4 mm of each canal was trimmed to expose the file tip. The samples were observed under a scanning electron microscope, and the distance from the file tip to the point 0.5 mm coronal to the major foramen (the actual WL) was measured. The data were analyzed using the Mann-Whitney U test, and significance was set at P < .05. Results: No statistically significant differences were found between the Root ZX and iPex devices. The mean distance from the actual WL to the file tip was 0.146 0.43 mm for the Root ZX and 0.128 0.49 mm for the iPex. In determining the actual WL, the Root ZX was accurate 72% of the time to 0.5 mm and 100% of the time to 1 mm, whereas the iPex was accurate 57.8% of the time to 0.5 mm and 100% of the time to 1 mm. Conclusions: Under the in vivo clinical conditions of this study, no statistically significant differences were observed between the Root ZX and iPex EALs. (J Endod 2011;37:608–610)
Key Words Electronic apex locator, major foramen, working length
From the *Department of Endodontics, Universitat Internacional de Catalunya, Barcelona, Spain; and †Department of Endodontics, Universidad de Tlaxcala, Tlaxcala, Mexico. Address requests for reprints to Dr Miguel Roig, Universitat Internacional de Catalunya, Dentistry Faculty, C/Josep Trueta s/n, 08195 Sant Cugat del Valles. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2011.02.002
D
uring root canal treatment, it is critical to determine and maintain the working length (WL) (1, 2). The WL is defined as the distance from a coronal reference point to the point at which canal preparation and obturation should terminate (3). The apical constriction is recommended as the physiological apical limit for instrumentation and filling of the root canal system (2). Underestimation of the WL can lead to insufficient debridement of the root canal, whereas overestimation can result in damage to the periapical tissues, which will delay or prevent healing (1, 2, 4). Traditionally, the root canal WL is determined by the interpretation of a radiograph of an instrument placed in the root canal. The most obvious drawback to this method is that the position of the apical constriction or major foramen cannot be determined (5–7). Furthermore, radiographs provide a two-dimensional image of a three-dimensional structure, which might affect the interpretation. Finally, the superimposition of bony structures can hinder the identification of the radiographic apex of some teeth. Cianconi et al (8) have shown that electronic apex locators (EALs) provide a more accurate estimation of the WL than radiographs. The use of electronic devices to determine the WL was proposed first by Custer (9) in 1918, and the first EAL was developed after Suzuki’s investigation of the electrical resistance properties of oral tissues (10). The first generation of EALs was resistance, based whereas the second generation was based on impedance. The main shortcoming of both types (which corresponded to poor accuracy with electrolytes) was overcome by the introduction of third-generation apex locators, such as the Root ZX (J Morita Corp, Tokyo, Japan). The Root ZX uses the ‘‘ratio’’ method to measure the root canal length. This method involves the measurement of impedance values at two frequencies (8 KHz and 0.4 KHz) simultaneously and the calculation of a quotient that expresses the position of the file tip in the canal (11). The Root ZX apex locator is considered to be the gold standard against which newer EALs are evaluated (12). The iPex (NSK, Tochigi, Japan) is claimed to be a fourth-generation apex locator, but as far as we are aware its precision has only been evaluated in vitro (12). Fourthgeneration EALs measure capacitance and resistance simultaneously to determine the location of the file tip in the canal (12). At present, the validity of measurements made with in vitro models remains unknown (13). In vitro or ex vivo models use electroconductive materials to simulate clinical conditions. Alginate, agar, saline, and gelatin have been shown to give predictable results when used with EALs (14). However, some of these materials might give greater accuracy than could be accomplished in vivo (15). Therefore, extrapolation from ex vivo–in vitro studies to the clinical setting might not be appropriate. In comparison, in vivo studies that use EALs to determine the WL emulate what will happen in the clinical situation. In such studies, the file is positioned using the EAL and then cemented in place, after which the tooth is extracted and the file tip is located in the root canal under magnification (14, 16). The purpose of this study was to compare the accuracy of the Root ZX and iPex in establishing the actual WL in vivo under clinical conditions.
Materials and Methods Thirty-five teeth (premolars, canines, and incisors), which had a total of 40 root canals and completely formed apices, were selected. The teeth had been scheduled for extraction from adult patients for orthodontic or periodontal reasons. Informed consent was obtained from each patient in accordance with the approval of the study
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JOE — Volume 37, Number 5, May 2011
Clinical Research by the Ethical Board of the International University of Catalonia. All teeth were assigned randomly to one of two groups (each of which comprised 20 root canals). All clinical procedures and measurements were conducted by a single operator. The teeth were isolated with a rubber dam under local anesthesia. Endodontic access was performed, and the coronal portion of each canal was flared with an SX Protaper file (Maillefer, Ballaigues, Switzerland). Each canal was then irrigated with 4% NaOCl. Excess fluid was removed from the pulp chamber with an air syringe, but no attempt was made to dry the canals. The Root ZX and iPex apex locators were used in accordance with the manufacturers’ instructions. For both devices, the clip was attached to the patient’s lip, and the electrode was connected to a 15 K-file. With the Root ZX, the file was advanced within the root canal to a point just beyond the major foramen, as indicated by the flashing APEX bar on the liquid crystal display (LCD). The file was then withdrawn until the LCD display showed a flashing bar between ‘‘APEX’’ and ‘‘1.’’ With the iPex locator, the file was advanced until the ‘‘APEX’’ signal was seen on the LCD display and then withdrawn until the display showed the 0.5-mm mark. Measurements were considered to be correct if the instrument remained stable for at least 5 seconds. The K-files were fixed at the WL determined electronically with flowable light-cured composite (Ivoclar Vivadent, Schaan, Liechtenstein). The WL was checked again electronically after the K-file had been fixed to confirm that it was in the correct position. The teeth were extracted and placed in 4% NaOCl for 15 minutes to remove any residual organic tissue from the root and then stored in 0.9% saline solution. The apical 4-mm portion of the root was trimmed in a longitudinal direction using a fine diamond bur (Gebr Brasseler, Lemgo, Germany) under a microscope (DF Vasconcellos, Sao Paulo, Brazil) at 16 magnification to expose the file tip. The additional tooth structure was removed carefully with an OptiDisc Coarse/Medium Soflex disc (KerrHawe, Bioggio, Switzerland) until the file tip and the root canal were both visible. The apical portion of the specimens was observed under an FEI Quanta 200 FEG Environmental Scanning Electron Microscope (ESEM; FEI Co, Hillsboro, OR) in the low-vacuum mode, and the distance from the file tip to the major foramen (the most coronal border of the major foramen) was measured with SIS Scandium image software (FEI Co). Two examiners, who had been calibrated previously and who did not know which EAL had been used, each determined the position of the major foramen and the file tip for each root canal. Examiners were calibrated to read the most coronal border of the major foramen; for that, they were shown pictures not used for this study. If the two examiners disagreed, a third previously calibrated researcher was asked to make the final decision. The actual WL was established to be 0.5 mm coronal to the major foramen (17, 18). Once the distance between the major foramen and the file tip had been measured, the distance between the file tip and the actual WL was calculated and recorded as negative (ie, the determined WL was shorter than the actual WL) or positive (ie, the determined WL was longer than the actual WL) (Fig. 1). The WL measurements were compared between the EALs using the Mann-Whitney test for nonparametric data because the data for the Root ZX group did not have a normal distribution (goodness-of-fit ShapiroWilks test = 0.003). Significance was set at P < .05.
Results Three samples were lost during specimen preparation because of damage to the root, which left 37 samples for analysis. The statistical analysis revealed no significant differences between the Root ZX and iPex devices with respect to their accuracy in determining the actual WL (P = .97). The mean distance from the actual WL to the file tip was JOE — Volume 37, Number 5, May 2011
Figure 1. The position of the file tip relative to the actual WL. Once the distance between the major foramen and the file tip had been measured (in this case 0.361 mm), the distance between the file tip and the actual WL, which was set at 0.5 mm from the major foramen, was calculated (in this case 0.139 mm).
0.146 0.43 mm for the Root ZX and 0.128 0.49 mm for the iPex. In determining the actual WL, which was set at 0.5 mm from the major foramen, the Root ZX was accurate 72% of the time to 0.5 mm and 100% of the time to 1 mm, whereas the iPex was accurate 57.8% of the time to 0.5 mm and 100% of the time to 1 mm (Table 1).
Discussion Numerous studies have reported the accuracy of EALs in determining the location of the apical constriction of the root canal or the major foramen (7, 16, 19–23). However, various authors have suggested that the precise location of the apical constriction cannot be determined (24, 25). In addition, it has been shown that the apical constriction might not always exist (24, 25). In the present study, the apical constriction was not used as a landmark because it was impossible to determine its location in most samples, whereas the major foramen could be located consistently (22). As a consequence, in this study, the actual WL was established to be 0.5 mm coronal to the major foramen, as suggested previously by various authors (17, 18). In this study, apical patency was confirmed because ElAyouti et al (26) observed that obliterated root canals resulted in the inconsistent function of EALs. Preflaring of root canals before measurement with EALs can increase the precision of WL determination (27). Thus, the canals were preflared in the current study before measurement. TABLE 1. Position of the File Tip Relative to the Actual WL as Determined by Root ZX and iPex Distance from the actual WL (mm) 1 to 0.5* 0.49 to 0.0* 0.01 to 0.5 0.51 to 1
Root ZX
iPex
(n = 18)
%
(n = 19)
%
2 2 11 3
11.1 11.1 61.1 16.7
3 4 7 5
15.8 21 36.8 26.3
*A negative value indicates a file position coronal to the actual WL.
Accuracy of Apex Locators
609
Clinical Research In the present study, only teeth that were being extracted from adult patients for periodontal or orthodontic reasons were used. Different results might have been obtained for teeth with periradicular periodontitis, which in most cases presents with some degree of root resorption (28). Goldberg et al (29) evaluated the accuracy of the Root ZX device in teeth with simulated apical root resorption and showed an accuracy of 62.7% with a tolerance of 0.5 mm. In determining the actual WL, the Root ZX was accurate 72% of the time to 0.5 mm and 100% of the time to 1 mm. In vitro studies have shown that the Root ZX locator is very accurate in determining the position of the actual WL when this landmark is set at 0.5 mm coronal to the major foramen (17, 18). Plotino et al (17) and D’Assunc¸~ao et al (18), who used ex vivo research models, found that the Root ZX was 97.37% and 97.44% accurate in determining the actual WL within 0.5 mm, respectively. The mean distance from the actual WL to the file tip was 0.146 mm for the Root ZX (0.35 short of the major foramen because in this study the actual WL was set at 0.5 mm from the major foramen). This result is similar to those obtained by Jung et al (30) and Ding et al (31) who reported that the file tip was identified 0.26 mm and 0.261 mm short of the major foramen when using the Root ZX, respectively. Some other in vivo studies that used the Root ZX have produced results that, in general, are in agreement with our results despite the fact that some of them measured the distance to the apical constriction (7, 20), which could not be located predictably in our study. As far as we could determine from a search of the literature, no studies have been performed in vivo to evaluate the accuracy of the iPex EAL. In the study described herein, the mean distance from the actual WL to the file tip was 0.146 mm for the Root ZX and 0.128 mm for the iPex. Statistical analysis showed no significant differences between the two EALs. In this study, the file tip extended beyond the major foramen in 16.7% of the samples in the Root ZX group and in 26.3% in the iPex group. Wrbas et al (19), Shabahang et al (16), and Dunlap et al (20) have reported that, with the Root ZX, the file tip extended beyond the major foramen in 40%, 30.8%, and 26% of the samples, respectively. Because of these results, some authors have proposed that, when determining the WL, the instrument should be withdrawn by approximately 0.5 mm from the position given by some EALs (7, 13, 19). This is the reason why a point 0.5 mm from the major foramen was established as the actual WL in this study and some others (17, 18). However, this practice is not accepted universally, and differences remain among clinicians with respect to their preferences for the ideal WL for cleaning, shaping, and filling of the root canal system. Under the conditions of this in vivo study, the Root ZX and iPex EALs performed equally well when determining a position 0.5 mm short of the major foramen.
Acknowledgments The authors deny any conflicts of interest related to this study.
References 1. Ricucci D. Apical limit of root canal instrumentation and obturation, part 1. Literature review. Int Endod J 1998;31:384–93. 2. Ricucci D, Langeland K. Apical limit of root canal instrumentation and obturation, part 2. Histological study. Int Endod J 1998;31:394–409. 3. Glossary of endodontic terms. 7th ed. Chicago: American Association of Endodontists; 2003.
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4. Sj€ogren U, Hagglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498–504. 5. ElAyouti A, Weiger R, L€ost C. Frequency of overinstrumentation with an acceptable radiographic working length. J Endod 2001;27:49–52. 6. ElAyouti A, Weiger R, L€ost C. The ability of Root ZX apex locator to reduce the frequency of overestimated radiographic working length. J Endod 2002;28: 116–9. 7. Tselnik M, Baumgartner JC, Marshall JG. An evaluation of Root ZX and Elements Diagnostic Apex Locators. J Endod 2005;31:507–9. 8. Cianconi L, Angotti V, Felici R, Conte G, Mancini M. Accuracy of three electronic apex locators compared with digital radiography: an ex vivo study. J Endod 2010;36:2003–7. 9. Custer LE. Exact methods of locating the apical foramen. J Natl Dent Assoc 1918;5: 815–9. 10. Suzuki K. Experimental study on iontophoresis. J Jap Stomatol 1942;16:411. 11. Kobayashi C, Suda H. New electronic canal measuring device based on the ratio method. J Endod 1994;20:111–4. 12. de Vasconcelos BC, do Vale TM, de Menezes AS, et al. An ex vivo comparison of root canal length determination by three electronic apex locators at positions short of the apical foramen. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;110: e57–61. 13. Pascon EA, Marrelli M, Congi O, Ciancio R, Miceli F, Versiani MA. An ex vivo comparison of working length determination by 3 electronic apex locators. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:e147–51. 14. Gordon MP, Chandler NP. Electronic apex locators. Int Endod J 2004;37:425–37. 15. Czerw RJ, Fulkerson MS, Donnelly JC, Walmann JO. In vitro evaluation of the accuracy of several electronic apex locators. J Endod 1995;21:572–5. 16. Shabahang S, Goon WW, Gluskin AH. An in vivo evaluation of Root ZX electronic apex locator. J Endod 1996;22:616–8. 17. 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. 18. D’Assunc¸~ao FL, de Alburquerque DS, Salazar-Silva JR, et al. The accuracy of root canal measurements using the Mini Apex Locator and Root ZX-II: an evaluation in vitro. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:e50–3. 19. Wrbas KT, Ziegler AA, Altenburger MJ, Schirrmeister JF. In vivo comparison of working length determination with two electronic apex locators. Int Endod J 2007;40:133–8. 20. 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 Endod 1998;24:48–50. 21. Welk AR, Baumgartner JC, Marshall JG. An in vivo comparison of two frequencybased electronic apex locators. J Endod 2003;29:497–500. 22. Jakobson SJ, Westpalhen VPD, da Silva Neto UX, Fariniuk LF, Picoli F, Carneiro E. The accuracy in the control of the apical extent of rotary canal instrumentation using Root ZX and ProTaper instruments: an in vivo study. J Endod 2008;34: 1342–5. 23. Pagavino G, Pace R, Bacceti T. A SEM study of in vivo accuracy of the Root ZX electronic apex locator. J Endod 1998;24:438–41. 24. Lee SJ, Nam KC, Kim YJ, Kim DW. Clinical accuracy of a new apex locator with an automatic compensation circuit. J Endod 2002;28:706–9. 25. Martınez-Lozano MA, Forner-Navarro L, Sanchez-Cortes JL, Llena-Puy C. Methodological considerations in the determination of working length. Int Endod J 2001;34: 371–6. 26. ElAyouti A, Dima E, Ohmer J, Sperl K, von Ohle C, L€ost C. Consistency of apex locator function: a clinical study. J Endod 2009;35:179–81. 27. 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. 28. Malueg LA, Wilcox LR, Johnson W. Examination of external apical resorption with scanning electron microscopy. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;82:89–93. 29. Goldberg F, De Silvio AC, Manfre S, Nastri N. In vitro measurement accuracy of an electronic apex locator in teeth with simulated apical root resorption. J Endod 2002; 28:461–3. 30. 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. 31. Ding J, Gutmann JL, Fan B, Lu Y, Chen H. Investigation of apex locators and related morphological factors. J Endod 2010;36:1399–403.
JOE — Volume 37, Number 5, May 2011
An Evaluation of Root ZX and iPex Apex Locators: An In Vivo Study Eva K. St€ ober, DDS, MsC,* Fernando Duran-Sindreu, DDS, PhD,* Montserrat Mercade, DDS, PhD,* Jorge Vera, DDS, PhD,† Rufino Bueno, DDS, PhD,* and Miguel Roig, DDS, PhD* Abstract Introduction: iPex is a fourth-generation apex locator (EAL) that has not yet been tested in vivo. The purpose of this study was to compare the accuracy of the Root ZX (J Morita Corp, Tokyo, Japan) and iPex (NSK, Tochigi, Japan) EALs. Methods: The working length (WL) was determined electronically for 40 root canals of human teeth with a K-file and one of the two EALs. The files were fixed at the WL, and the teeth were extracted. The apical 4 mm of each canal was trimmed to expose the file tip. The samples were observed under a scanning electron microscope, and the distance from the file tip to the point 0.5 mm coronal to the major foramen (the actual WL) was measured. The data were analyzed using the Mann-Whitney U test, and significance was set at P < .05. Results: No statistically significant differences were found between the Root ZX and iPex devices. The mean distance from the actual WL to the file tip was 0.146 0.43 mm for the Root ZX and 0.128 0.49 mm for the iPex. In determining the actual WL, the Root ZX was accurate 72% of the time to 0.5 mm and 100% of the time to 1 mm, whereas the iPex was accurate 57.8% of the time to 0.5 mm and 100% of the time to 1 mm. Conclusions: Under the in vivo clinical conditions of this study, no statistically significant differences were observed between the Root ZX and iPex EALs. (J Endod 2011;37:608–610)
Key Words Electronic apex locator, major foramen, working length
From the *Department of Endodontics, Universitat Internacional de Catalunya, Barcelona, Spain; and †Department of Endodontics, Universidad de Tlaxcala, Tlaxcala, Mexico. Address requests for reprints to Dr Miguel Roig, Universitat Internacional de Catalunya, Dentistry Faculty, C/Josep Trueta s/n, 08195 Sant Cugat del Valles. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2011 American Association of Endodontists. doi:10.1016/j.joen.2011.02.002
D
uring root canal treatment, it is critical to determine and maintain the working length (WL) (1, 2). The WL is defined as the distance from a coronal reference point to the point at which canal preparation and obturation should terminate (3). The apical constriction is recommended as the physiological apical limit for instrumentation and filling of the root canal system (2). Underestimation of the WL can lead to insufficient debridement of the root canal, whereas overestimation can result in damage to the periapical tissues, which will delay or prevent healing (1, 2, 4). Traditionally, the root canal WL is determined by the interpretation of a radiograph of an instrument placed in the root canal. The most obvious drawback to this method is that the position of the apical constriction or major foramen cannot be determined (5–7). Furthermore, radiographs provide a two-dimensional image of a three-dimensional structure, which might affect the interpretation. Finally, the superimposition of bony structures can hinder the identification of the radiographic apex of some teeth. Cianconi et al (8) have shown that electronic apex locators (EALs) provide a more accurate estimation of the WL than radiographs. The use of electronic devices to determine the WL was proposed first by Custer (9) in 1918, and the first EAL was developed after Suzuki’s investigation of the electrical resistance properties of oral tissues (10). The first generation of EALs was resistance, based whereas the second generation was based on impedance. The main shortcoming of both types (which corresponded to poor accuracy with electrolytes) was overcome by the introduction of third-generation apex locators, such as the Root ZX (J Morita Corp, Tokyo, Japan). The Root ZX uses the ‘‘ratio’’ method to measure the root canal length. This method involves the measurement of impedance values at two frequencies (8 KHz and 0.4 KHz) simultaneously and the calculation of a quotient that expresses the position of the file tip in the canal (11). The Root ZX apex locator is considered to be the gold standard against which newer EALs are evaluated (12). The iPex (NSK, Tochigi, Japan) is claimed to be a fourth-generation apex locator, but as far as we are aware its precision has only been evaluated in vitro (12). Fourthgeneration EALs measure capacitance and resistance simultaneously to determine the location of the file tip in the canal (12). At present, the validity of measurements made with in vitro models remains unknown (13). In vitro or ex vivo models use electroconductive materials to simulate clinical conditions. Alginate, agar, saline, and gelatin have been shown to give predictable results when used with EALs (14). However, some of these materials might give greater accuracy than could be accomplished in vivo (15). Therefore, extrapolation from ex vivo–in vitro studies to the clinical setting might not be appropriate. In comparison, in vivo studies that use EALs to determine the WL emulate what will happen in the clinical situation. In such studies, the file is positioned using the EAL and then cemented in place, after which the tooth is extracted and the file tip is located in the root canal under magnification (14, 16). The purpose of this study was to compare the accuracy of the Root ZX and iPex in establishing the actual WL in vivo under clinical conditions.
Materials and Methods Thirty-five teeth (premolars, canines, and incisors), which had a total of 40 root canals and completely formed apices, were selected. The teeth had been scheduled for extraction from adult patients for orthodontic or periodontal reasons. Informed consent was obtained from each patient in accordance with the approval of the study
608
St€ober et al.
JOE — Volume 37, Number 5, May 2011
Clinical Research by the Ethical Board of the International University of Catalonia. All teeth were assigned randomly to one of two groups (each of which comprised 20 root canals). All clinical procedures and measurements were conducted by a single operator. The teeth were isolated with a rubber dam under local anesthesia. Endodontic access was performed, and the coronal portion of each canal was flared with an SX Protaper file (Maillefer, Ballaigues, Switzerland). Each canal was then irrigated with 4% NaOCl. Excess fluid was removed from the pulp chamber with an air syringe, but no attempt was made to dry the canals. The Root ZX and iPex apex locators were used in accordance with the manufacturers’ instructions. For both devices, the clip was attached to the patient’s lip, and the electrode was connected to a 15 K-file. With the Root ZX, the file was advanced within the root canal to a point just beyond the major foramen, as indicated by the flashing APEX bar on the liquid crystal display (LCD). The file was then withdrawn until the LCD display showed a flashing bar between ‘‘APEX’’ and ‘‘1.’’ With the iPex locator, the file was advanced until the ‘‘APEX’’ signal was seen on the LCD display and then withdrawn until the display showed the 0.5-mm mark. Measurements were considered to be correct if the instrument remained stable for at least 5 seconds. The K-files were fixed at the WL determined electronically with flowable light-cured composite (Ivoclar Vivadent, Schaan, Liechtenstein). The WL was checked again electronically after the K-file had been fixed to confirm that it was in the correct position. The teeth were extracted and placed in 4% NaOCl for 15 minutes to remove any residual organic tissue from the root and then stored in 0.9% saline solution. The apical 4-mm portion of the root was trimmed in a longitudinal direction using a fine diamond bur (Gebr Brasseler, Lemgo, Germany) under a microscope (DF Vasconcellos, Sao Paulo, Brazil) at 16 magnification to expose the file tip. The additional tooth structure was removed carefully with an OptiDisc Coarse/Medium Soflex disc (KerrHawe, Bioggio, Switzerland) until the file tip and the root canal were both visible. The apical portion of the specimens was observed under an FEI Quanta 200 FEG Environmental Scanning Electron Microscope (ESEM; FEI Co, Hillsboro, OR) in the low-vacuum mode, and the distance from the file tip to the major foramen (the most coronal border of the major foramen) was measured with SIS Scandium image software (FEI Co). Two examiners, who had been calibrated previously and who did not know which EAL had been used, each determined the position of the major foramen and the file tip for each root canal. Examiners were calibrated to read the most coronal border of the major foramen; for that, they were shown pictures not used for this study. If the two examiners disagreed, a third previously calibrated researcher was asked to make the final decision. The actual WL was established to be 0.5 mm coronal to the major foramen (17, 18). Once the distance between the major foramen and the file tip had been measured, the distance between the file tip and the actual WL was calculated and recorded as negative (ie, the determined WL was shorter than the actual WL) or positive (ie, the determined WL was longer than the actual WL) (Fig. 1). The WL measurements were compared between the EALs using the Mann-Whitney test for nonparametric data because the data for the Root ZX group did not have a normal distribution (goodness-of-fit ShapiroWilks test = 0.003). Significance was set at P < .05.
Results Three samples were lost during specimen preparation because of damage to the root, which left 37 samples for analysis. The statistical analysis revealed no significant differences between the Root ZX and iPex devices with respect to their accuracy in determining the actual WL (P = .97). The mean distance from the actual WL to the file tip was JOE — Volume 37, Number 5, May 2011
Figure 1. The position of the file tip relative to the actual WL. Once the distance between the major foramen and the file tip had been measured (in this case 0.361 mm), the distance between the file tip and the actual WL, which was set at 0.5 mm from the major foramen, was calculated (in this case 0.139 mm).
0.146 0.43 mm for the Root ZX and 0.128 0.49 mm for the iPex. In determining the actual WL, which was set at 0.5 mm from the major foramen, the Root ZX was accurate 72% of the time to 0.5 mm and 100% of the time to 1 mm, whereas the iPex was accurate 57.8% of the time to 0.5 mm and 100% of the time to 1 mm (Table 1).
Discussion Numerous studies have reported the accuracy of EALs in determining the location of the apical constriction of the root canal or the major foramen (7, 16, 19–23). However, various authors have suggested that the precise location of the apical constriction cannot be determined (24, 25). In addition, it has been shown that the apical constriction might not always exist (24, 25). In the present study, the apical constriction was not used as a landmark because it was impossible to determine its location in most samples, whereas the major foramen could be located consistently (22). As a consequence, in this study, the actual WL was established to be 0.5 mm coronal to the major foramen, as suggested previously by various authors (17, 18). In this study, apical patency was confirmed because ElAyouti et al (26) observed that obliterated root canals resulted in the inconsistent function of EALs. Preflaring of root canals before measurement with EALs can increase the precision of WL determination (27). Thus, the canals were preflared in the current study before measurement. TABLE 1. Position of the File Tip Relative to the Actual WL as Determined by Root ZX and iPex Distance from the actual WL (mm) 1 to 0.5* 0.49 to 0.0* 0.01 to 0.5 0.51 to 1
Root ZX
iPex
(n = 18)
%
(n = 19)
%
2 2 11 3
11.1 11.1 61.1 16.7
3 4 7 5
15.8 21 36.8 26.3
*A negative value indicates a file position coronal to the actual WL.
Accuracy of Apex Locators
609
Clinical Research In the present study, only teeth that were being extracted from adult patients for periodontal or orthodontic reasons were used. Different results might have been obtained for teeth with periradicular periodontitis, which in most cases presents with some degree of root resorption (28). Goldberg et al (29) evaluated the accuracy of the Root ZX device in teeth with simulated apical root resorption and showed an accuracy of 62.7% with a tolerance of 0.5 mm. In determining the actual WL, the Root ZX was accurate 72% of the time to 0.5 mm and 100% of the time to 1 mm. In vitro studies have shown that the Root ZX locator is very accurate in determining the position of the actual WL when this landmark is set at 0.5 mm coronal to the major foramen (17, 18). Plotino et al (17) and D’Assunc¸~ao et al (18), who used ex vivo research models, found that the Root ZX was 97.37% and 97.44% accurate in determining the actual WL within 0.5 mm, respectively. The mean distance from the actual WL to the file tip was 0.146 mm for the Root ZX (0.35 short of the major foramen because in this study the actual WL was set at 0.5 mm from the major foramen). This result is similar to those obtained by Jung et al (30) and Ding et al (31) who reported that the file tip was identified 0.26 mm and 0.261 mm short of the major foramen when using the Root ZX, respectively. Some other in vivo studies that used the Root ZX have produced results that, in general, are in agreement with our results despite the fact that some of them measured the distance to the apical constriction (7, 20), which could not be located predictably in our study. As far as we could determine from a search of the literature, no studies have been performed in vivo to evaluate the accuracy of the iPex EAL. In the study described herein, the mean distance from the actual WL to the file tip was 0.146 mm for the Root ZX and 0.128 mm for the iPex. Statistical analysis showed no significant differences between the two EALs. In this study, the file tip extended beyond the major foramen in 16.7% of the samples in the Root ZX group and in 26.3% in the iPex group. Wrbas et al (19), Shabahang et al (16), and Dunlap et al (20) have reported that, with the Root ZX, the file tip extended beyond the major foramen in 40%, 30.8%, and 26% of the samples, respectively. Because of these results, some authors have proposed that, when determining the WL, the instrument should be withdrawn by approximately 0.5 mm from the position given by some EALs (7, 13, 19). This is the reason why a point 0.5 mm from the major foramen was established as the actual WL in this study and some others (17, 18). However, this practice is not accepted universally, and differences remain among clinicians with respect to their preferences for the ideal WL for cleaning, shaping, and filling of the root canal system. Under the conditions of this in vivo study, the Root ZX and iPex EALs performed equally well when determining a position 0.5 mm short of the major foramen.
Acknowledgments The authors deny any conflicts of interest related to this study.
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JOE — Volume 37, Number 5, May 2011