- Email: [email protected]
Effect of Working Length Measurement by Electronic Apex Locator or Radiography on the Adequacy of Final Working Length: A Randomized Clinical Trial
CONSORT Randomized Clinical Trial
Effect of Working Length Measurement by Electronic Apex Locator or Radiography on the Adequacy of Final Working Length: A Randomized Clinical Trial Shohreh Ravanshad, DDS, MSD, Alireza Adl, DDS, MSD, and Javad Anvar, DDS, MSD Abstract Introduction: Obtaining a correct working length is critical to the success of endodontic therapy. The aim of this clinical study was to compare the effect of working length determination using electronic apex locator or working length radiograph on the length adequacy of final working length as well as the final obturation. Methods: A total of 84 patients with 188 canals were randomized into two groups; in group 1, the working length was determined by working length radiograph, whereas in group 2, it was determined by the Raypex5 electronic apex locator (VDW, Munich, Germany). Length adequacy was assessed in each group for master cone and final obturation radiography and categorized into short, acceptable, and over cases. Results: There was no statistically significant difference between the rates of acceptable (master cone radiography: group 1 = 82.1% and group 2 = 90.4%; final radiography: group 1 = 85.7% and group 2 = 90.4%) and short cases (master cone radiography: group 1 = 7.1% and group 2 = 8.7%; final radiography: group 1 = 1.2% and group 2 = 1%) between the two groups. Over cases in master cone radiography were significantly more in group 1 (10.7%) than group 2 (1%) (c2, p = 0.00). However, this category did not show a significant difference for final obturation between group 1 (13.1%) and group 2 (8.7%). Conclusion: The results of endodontic treatment using the Raypex5 electronic apex locator are quite comparable, if not superior, to radiographic length measurement regarding the rates of acceptable and short cases. Furthermore, in addition to reducing the radiographic exposure, electronic apex locators are superior in reducing overestimation of the root canal length. (J Endod 2010;36:1753–1756)
Key Words Electronic apex locators, radiographic length measurement, root canal therapy
From the Department of Endodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. Address requests for reprints to Dr Javad Anvar, Department of Endodontics, Dental School of Shiraz University of Medical Sciences, Ghasrodasht Avenue, 71956-15878 Shiraz, Iran. E-mail address: [email protected]. 0099-2399/$ - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.08.017
JOE — Volume 36, Number 11, November 2010
O
ne of the major problems in endodontic treatment is identifying and maintaining the biological length of the root canal system. Optimal healing condition with minimal contact between the obturation material and the apical tissue is achieved when root canal treatment terminates at the apical constriction. In this way, persistent inflammatory responses, tissue destruction, and foreign-body reactions are kept at their lowest possible level (1). This fact is supported by prognostic studies that have shown the success of root canal treatment is influenced by the adequacy of working length during endodontic treatment (2–4). Although it has been a major subject of debate for decades, the exact termination point for root canal therapy is still considered a controversial topic (5, 6). However, in clinical practice, the minor apical foramen, as a more consistent anatomic feature, can be regarded as being the narrowest portion of the canal system and thus the ideal landmark for the apical endpoint for root canal treatment (7). Different methods have been used for locating the position of the canal terminus and measuring the working length of root canals as a result. Radiographic method, traditionally the most popular and trusted way for length measurement in the field of endodontics, has advantages like direct observation of the anatomy of the root canal system, the number and curvature of roots, the presence or absence of disease, and in addition acts as an initial guide for working length estimation. There are, however, a number of disadvantages that make this technique not quite suitable in every situation (eg, the danger of overestimation of the root canal length even when it seems to be short of the radiographic apex because of normal anatomic variations in the apical region) (8). Other shortcomings of radiography include technique sensitivity and subjectivity (9–11), the danger of ionizing radiation (12), and errors of superimposition caused by producing a two-dimensional representation from a three-dimensional object (13). The development and production of electronic devices for locating the canal terminus have been major innovations in root canal treatment. Their advantages include equal or higher accuracy compared with the radiographic method as shown by in vivo extraction studies (14–16), continuous monitoring of the working length in combination with intelligent rotary systems (17), discriminating between impenetrable and penetrable canals (18), and reducing the total needed radiographs and radiographic exposure as a result. There are also some limitations reported for electronic apex locators (EALs) like overpreparation in retreatment when combined with rotary systems (19), premature showing of the apex on rare occasions, and inconsistent measurements in association with partially or totally obliterated root canals (20). Several in vitro and in vivo studies have investigated these two methods solely or in comparison to each other, but randomized clinical trial studies that compare these two methods with each other in a truly clinical condition and can provide a high level of evidence for clinicians in their decisions are scarce. The purpose of this randomized clinical trial was to evaluate the effect of working length determination by radiograph or electronic apex locator on the adequacy of the final working length.
Materials and Methods The protocol was registered in the international trial registry ClinicalTrials.gov under the ID: NCT00901810. Calculation of sample size by setting the power of the study
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1753
CONSORT Randomized Clinical Trial to 90%, standard deviation of the outcome to 1 mm based on previous studies (21), and the minimum detectable difference to 0.5 mm gave a minimum number of 172 canals for this two treatment parallel-design study. We selected our cases from any patient aged 20 to 65 years old who presented for primary endodontic therapy to the Department of Endodontics of Shiraz Dental School. After obtaining informed written consent form from each patient, the teeth were randomly allocated to each group by flipping a coin. All selected teeth had mature apexes with no radiographic sign of root resorption. All of the cases were treated by one endodontist. During the procedure if the operator felt that the length measurement could not be done properly in either group and it was necessary for another method to be used, those cases were excluded from the study. For example, cases in which radiography alone because of superimposition was not enough to determine working length were excluded. Also, teeth with no apical patency because of different causes were excluded. In multicanalled teeth, if one canal was not suitable to enter the study, those teeth were excluded as well. At the end of the study, we managed a total of 84 teeth with 188 canals. A datasheet was used to record the number of each tooth, vitality of the tooth on access as determined by bleeding, the presence of apical lesion, length measurements, amount and direction of correction after master cone radiography, and the total number of radiographs needed for each tooth. The steps followed for each group are as follows: Group A (radiographic length determination): 1. Taking preoperative periapical radiography using bisecting angle technique 2. Placing the working file to the estimated length after access cavity preparation and taking the working length radiograph (bisecting angle technique). The primary working length is determined to be 1 mm short of the radiographic apex. 3. Finishing canal preparation to this working length, inserting the master cone to this length, and taking a master cone radiography using the bisecting angle technique. 4. Correcting the working length to be 1 mm short of the radiographic apex if needed and setting this as the final working length. 5. Obturation of the canal to the final working length using the lateral condensation technique. 6. Taking the final radiography using the bisecting angle technique. Group B (EAL): 1. The same as step 1 in group A. 2. Placing the working file to the estimated length after access cavity preparation according to preoperative radiograph, attaching the file clip of Raypex5 (VDW, Munich, Germany), and moving toward the apex until the red indicator shows the apex. The file was then withdrawn just to the point where this blinking indicator turned off. The length of the file was then measured at this point, and 0.5 mm was subtracted to get the initial working length. 3. The same as step 3 in group A. 4. If the tip of the gutta-percha is shorter than 0 to 2 mm of the apex, correcting it to be 1 mm short of the apex; otherwise, it does not change. 5. The same as step 5 in group A. 6. The same as step 6 in group A. The master cone and final radiographs were evaluated by two endodontists blinded to group allocation of each case and graded as follows: (1) short (shorter than 2 mm from radiographic apex), (2) acceptable (within 0-2 mm from radiographic apex), and (3) over (beyond the apex).
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The data were statistically analyzed using the Pearson chi-square test. The values of correction in step 4 of each group were statistically analyzed with the Mann-Whitney U test. Each statistical analysis was performed at the 5% significant level.
Results The results of length adequacy in each group for master cone and final obturation are summarized in Tables 1 and 2, respectively. Reclassification of the outcome data by focusing on each subdivision results in three cross-tabulations for the master cone and final obturation length adequacy, each focusing on one of the three outcome categories: acceptable, over, and short. Based on these reclassified tables in the EAL group, there was a higher percentage of acceptable cases, both for the master cone as a primary outcome (c2, p = 0.09) and the final obturation (c2, p = 0.32) as a secondary outcome than in the radiograph group, but the difference was not statistically significant (p > 0.05). There was a significantly lower percentage of overresults in the EAL group compared with the radiographic group for master cone results (c2, p = 0.00). There was also a lower but not statistically significant rate of the over cases for the obturation results (c2, p = 0.32). There was no statistically significant difference in the percentage of the short cases for both the master cone (c2, p = 0.70) and the final obturation results (c2, p = 0.87) between the two groups. The average number of radiographs taken was 3 in the EAL group and 4.07 in the radiographic group, which showed a highly significant difference (Mann-Whitney U test, p = 0.00) . Vitality (c2, p = 0. 789) and periapical lesions (c2, p = 0.504) were not associated with length adequacy of the master cone as a primary outcome in the EAL group. The Mann-Whitney U test revealed a borderline statistically significant difference in the amount of correction needed after taking master cone radiography between the radiographic group (mean = 0.08 mm and standard deviation = 0.5) and the EAL group (mean = 0.23 mm and standard deviation = 0.5, p = 0.049). Also, reclassification of cases based on doing or not doing correction after taking master cone radiography showed no statistical differences between the two groups (c2, p = 0.80).
Discussion Electronic methods for tooth length determination have progressed significantly and have been increasingly integrated into the modern practice of endodontics (22). The accuracy of apex locators has previously been investigated by several researchers. In some in vitro studies, the simulation of the clinical situation has been done by using electroconductive materials like alginate, gelatin, agar, or saline (18, 23). Also, in some in vivo studies, after electronic length measurement, the teeth were extracted, and different target points like apical foramen, apical constriction, or radiographic apex were compared with the point where a given electronic apex locator has been shown as the terminus of root canal system (24, 25). None of the previously mentioned studies can be a true representative of clinical situations in which the whole treatment is done in the mouth. This study, however, was a true simulation of what occurs during a typical endodontic treatment. The end result was evaluated by radiography, which is an intrinsic problem associated with such kinds of
TABLE 1. Master Cone Length Adequacy Radiography EAL
Short (%)
Acceptable (%)
Over (%)
6 (7.1) 9 (8.7)
69 (82.1) 94 (90.4)
9 (10.7) 1 (1.0)
JOE — Volume 36, Number 11, November 2010
CONSORT Randomized Clinical Trial TABLE 2. Final Obturation Length Adequacy Radiography EAL
Short (%)
Acceptable (%)
Over (%)
1 (1.2) 1 (1.0)
72 (85.7) 94 (90.4)
11 (13.1) 9 (8.7)
EAL, electronic apex locator.
study, because radiography is the only universally accepted, available, and meaningful method of length adequacy assessment in the clinic. We decided to compare the results with conventional bisecting technique because it is used more often (26), and our results can be extrapolated more easily to routine daily practice. The most favorable outcome for root canal treatment in prognostic and cohort studies has been observed when, among other factors, endodontic treatment terminated in 0 to 2 mm short of the radiographic apex (2, 27), so this interval was chosen for our study as a reasonable and practical criterion for evaluating the length adequacy on radiographs. In this study Raypex5, which like other impedance ratio apex locators shows a blinking red alarm when the file tip has just passed the apical foramen (28), was used. So when the file tip is withdrawn just to the point that the blinking apex indicator goes away but the screen still shows the file beyond or at the constriction, it means that the tip of the file is between the major and minor foramen. Our method, which demands the file to pass the apical foramen, ensures the operator of a patent canal and a definitive measurement as a result. On the other hand, microscopic observations have shown that the distance of the foramen to apical constriction is approximately 0.5 mm in the younger group and 0.8 mm in the older group (29). Therefore, reducing 0.5 mm from the above working length leads us to a point just before or at the apical constriction and secures the operator from any overinstrumentation, and also a measurement well within the clinically tolerable 0.5- to 1-mm range from the apical constriction is provided, as recommended by several authors (30, 31). This study showed a higher but not statistically significant rate of acceptable results (90%) regarding master cone radiography in the EAL group, which is in agreement with previous studies (14, 16). ElAyouti et al (13) have shown that electronic apex locators can prevent overinstrumentation, even when the working length seems within the acceptable range on radiography. In the present study, there was almost no overestimation of working length in the EAL group, which is more unfavorable compared with underestimation (2). In our study, the length adequacy of master cone radiography was considered as the primary outcome because in both groups working length correction was based on master cone radiography, and this could prevent an uncorrupted comparison for final radiographies. Therefore, length adequacy of the final obturation radiography was considered as the secondary outcome and was investigated only to find a possible significant relationship with group allocation and also to report the final result of each treatment modality. Pulp vitality and the presence of a periapical lesion was not an influential factor on the accuracy of Raypex5 as an impedance ratio– based electronic apex locator in our study. This is quite expected because the modern generation of apex locators has been developed in a way to be independent of canal contents and to be able to detect the narrowest part in the morphology of canals, regardless of possible apical root resorption as confirmed in previous studies (15, 23). Finally, the electronic apex locator reduced the number of taken radiographs by about one film for every treatment. Although a reduction of one film for the treatment of one tooth does not seem to be significant, with respect to the fact that many patients have JOE — Volume 36, Number 11, November 2010
more than one tooth for treatment and in endodontic departments a lot of teeth have to be treated, this reduction can be translated to less time, energy, and exposure to patients as suggested previously (32). Considering that root canal treatment without preoperative and postoperative radiographs is below the standard of care (33), this clinical study supports the use of electronic apex locators as an adjunctive but not a substitute of radiography for root canal treatment.
Conclusion The results of endodontic treatment using electronic apex locator are quite comparable if not superior to radiographic length measurement regarding the rates of acceptable and short cases. Furthermore, in addition to reducing radiographic exposure, EALs can reduce the rate of overestimation of root canal length.
Acknowledgments The authors thank Dr Laaya Safi for her help with the evaluation of the radiographs, Dr Heydari for statistical assistance, and Dr Faranak Rabiee for helping with the clinical tasks of this study.
References 1. Ricucci D, Langeland K. Apical limit of root canal instrumentation and obturation, part 2. A histological study. Int Endod J 1998;31:394–409. 2. Sjogren U, Hagglund B, Sundqvist G, et al. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498–504. 3. Ng Y-L, Mann V, Rahbaran S, et al. Outcome of primary root canal treatment: systematic review of the literature—part 2. Influence of clinical factors. Int Endod J 2008; 41:6–31. 4. Kojima k, Inamoto K, Nagamatsu K, et al. Success rate of endodontic treatment of teeth with vital and nonvital pulps. A meta-analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;97:95–9. 5. Bergenholtz G, Spangberg L. Controversies in Endodontics. Crit Rev Oral Biol Med 2004;15:99–114. 6. Peters OA. Current challenges and concepts in the preparation of root canal systems: a review. J Endod 2004;30:559–67. 7. Ponce EH, Vilar Fernandez JA. The cemento-dentino-canal junction, the apical foramen, and the apical constriction: evaluation by optical microscopy. J Endod 2003;29:214–9. 8. ElAyouti A, Weiger R, Lo¨st C. Frequency of overinstrumentation with an acceptable radiographic working length. J Endod 2001;27:49–52. 9. Kazzi D, Horner K, Qualtrough AC, et al. A comparative study of three periapical radiographic techniques for endodontic working length estimation. Int Endod J 2007;40:526–31. 10. Radel RT, Goodell GG, McClanahan SB, et al. In vitro radiographic determination ofdistances from working length files to root ends comparing kodak RVG 6000, Schick CDR, and kodak insight film. J Endod 2006;32:566–8. 11. Williams CB, Joyce AP, Roberts S. A comparison between in vivo radiographic working length determination and measurement after extraction. J Endod 2006; 32:624–7. 12. Pendlebury ME, Horner K, Eaton KA. Selection Criteria for Dental Radiography. 1st ed. London, UK: Faculty of General Dental Practitioners, Royal College of Surgeons of England; 2004:6–17. 13. ElAyouti A, Weiger R, Lost C. The ability of Root ZX apex locator to reduce the frequency of overestimated radiographic working length. J Endod 2002;28:116–9. 14. Kim E, Marmo M, Lee CY, et al. An in vivo comparison of working length determination by only root-ZX apex locator versus combining root-ZX apex locator with radiographs using a new impression technique. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;105:e79–83. 15. Smadi L. Comparison between two methods of working length determination and its effect on radiographic extent of root canal filling: a clinical study [ISRCTN71486641]. BMC Oral Health 2006;6:4. 16. Hoer D, Attin T. The accuracy of electronic working length determination. Int Endod J 2004;37:125–31. 17. Altenburger MJ, Cenik Y, Schirrmeister JF, et al. Combination of apex locator and endodontic motor for continuous length control during root canal treatment. Int Endod J 2009;42:368–74. 18. Oishi A, Yoshioka T, Kobayashi C, et al. Electronic detection of root canal constrictions. J Endod 2002;28:361–4.
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CONSORT Randomized Clinical Trial 19. Uzun O, Topuz O, Tinaz C, et al. Accuracy of two root canal length measurement devices integrated into rotary endodontic motors when removing gutta-percha from root-filled teeth. Int Endod J 2008;41:725–32. 20. ElAyouti A, Dima E, Ohmer J, et al. Consistency of apex locator function: a clinical study. J Endod 2009;35:179–81. 21. Venturi M, Breschi L. A comparison between two electronic apex locators: an ex vivo investigation. Int Endod J 2007;40:362–73. 22. Lee M, Winkler J, Hartwell G, et al. Current trends in endodontic practice: emergency treatments and technological armamentarium. J Endod 2009;35:35–9. 23. Jenkins JA, Walker WA, Schindler WG, et al. An in vitro evaluation of the accuracy of the root ZX in the presence of various irrigants. J Endod 2001;27:209–11. 24. Welk AR, Baumgartner JC, Marshall JG. An in vivo comparison of two frequencybased electronic apex locators. J Endod 2003;29:497–500. 25. Dunlap CA, Remeikis NA, BeGole EA, et al. 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.
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26. Chandler NP, Koshy S. Radiographic practices of dentists undertaking endodontics in New Zealand. Dentomaxillofac Radiol 2002;31:317–21. 27. Farzaneh M, Abitbol S, Lawrence HP, et al., Toronto Study. Treatment outcome in endodontics—the Toronto Study. Phase II: initial treatment. J Endod 2004;30: 302–9. 28. Availabe at: http://www.vdw-dental.com/pdf/raypex_e.pdf. Accessed June 25, 2009. 29. 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. 30. Seltzer S, Soltanoff W, Sinai I, et al. Biologic aspects of endodontics. Part III. Periapical tissue reactions to root canal instrumentation. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1968;26:534–46. 31. Weiger R, John C, Geigle H, et al. An in vitro comparison of two modern apex locators. J Endod 1999;25:765–8. 32. Fouad AF, Reid LC. Effect of using electronic apex locators on selected endodontic treatment parameters. J Endod 2000;26:364–7. 33. Gordon MP, Chandler NP. Electronic apex locators. Int Endod J 2004;37:425–37.
JOE — Volume 36, Number 11, November 2010
Effect of Working Length Measurement by Electronic Apex Locator or Radiography on the Adequacy of Final Working Length: A Randomized Clinical Trial Shohreh Ravanshad, DDS, MSD, Alireza Adl, DDS, MSD, and Javad Anvar, DDS, MSD Abstract Introduction: Obtaining a correct working length is critical to the success of endodontic therapy. The aim of this clinical study was to compare the effect of working length determination using electronic apex locator or working length radiograph on the length adequacy of final working length as well as the final obturation. Methods: A total of 84 patients with 188 canals were randomized into two groups; in group 1, the working length was determined by working length radiograph, whereas in group 2, it was determined by the Raypex5 electronic apex locator (VDW, Munich, Germany). Length adequacy was assessed in each group for master cone and final obturation radiography and categorized into short, acceptable, and over cases. Results: There was no statistically significant difference between the rates of acceptable (master cone radiography: group 1 = 82.1% and group 2 = 90.4%; final radiography: group 1 = 85.7% and group 2 = 90.4%) and short cases (master cone radiography: group 1 = 7.1% and group 2 = 8.7%; final radiography: group 1 = 1.2% and group 2 = 1%) between the two groups. Over cases in master cone radiography were significantly more in group 1 (10.7%) than group 2 (1%) (c2, p = 0.00). However, this category did not show a significant difference for final obturation between group 1 (13.1%) and group 2 (8.7%). Conclusion: The results of endodontic treatment using the Raypex5 electronic apex locator are quite comparable, if not superior, to radiographic length measurement regarding the rates of acceptable and short cases. Furthermore, in addition to reducing the radiographic exposure, electronic apex locators are superior in reducing overestimation of the root canal length. (J Endod 2010;36:1753–1756)
Key Words Electronic apex locators, radiographic length measurement, root canal therapy
From the Department of Endodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. Address requests for reprints to Dr Javad Anvar, Department of Endodontics, Dental School of Shiraz University of Medical Sciences, Ghasrodasht Avenue, 71956-15878 Shiraz, Iran. E-mail address: [email protected]. 0099-2399/$ - see front matter Copyright ª 2010 American Association of Endodontists. doi:10.1016/j.joen.2010.08.017
JOE — Volume 36, Number 11, November 2010
O
ne of the major problems in endodontic treatment is identifying and maintaining the biological length of the root canal system. Optimal healing condition with minimal contact between the obturation material and the apical tissue is achieved when root canal treatment terminates at the apical constriction. In this way, persistent inflammatory responses, tissue destruction, and foreign-body reactions are kept at their lowest possible level (1). This fact is supported by prognostic studies that have shown the success of root canal treatment is influenced by the adequacy of working length during endodontic treatment (2–4). Although it has been a major subject of debate for decades, the exact termination point for root canal therapy is still considered a controversial topic (5, 6). However, in clinical practice, the minor apical foramen, as a more consistent anatomic feature, can be regarded as being the narrowest portion of the canal system and thus the ideal landmark for the apical endpoint for root canal treatment (7). Different methods have been used for locating the position of the canal terminus and measuring the working length of root canals as a result. Radiographic method, traditionally the most popular and trusted way for length measurement in the field of endodontics, has advantages like direct observation of the anatomy of the root canal system, the number and curvature of roots, the presence or absence of disease, and in addition acts as an initial guide for working length estimation. There are, however, a number of disadvantages that make this technique not quite suitable in every situation (eg, the danger of overestimation of the root canal length even when it seems to be short of the radiographic apex because of normal anatomic variations in the apical region) (8). Other shortcomings of radiography include technique sensitivity and subjectivity (9–11), the danger of ionizing radiation (12), and errors of superimposition caused by producing a two-dimensional representation from a three-dimensional object (13). The development and production of electronic devices for locating the canal terminus have been major innovations in root canal treatment. Their advantages include equal or higher accuracy compared with the radiographic method as shown by in vivo extraction studies (14–16), continuous monitoring of the working length in combination with intelligent rotary systems (17), discriminating between impenetrable and penetrable canals (18), and reducing the total needed radiographs and radiographic exposure as a result. There are also some limitations reported for electronic apex locators (EALs) like overpreparation in retreatment when combined with rotary systems (19), premature showing of the apex on rare occasions, and inconsistent measurements in association with partially or totally obliterated root canals (20). Several in vitro and in vivo studies have investigated these two methods solely or in comparison to each other, but randomized clinical trial studies that compare these two methods with each other in a truly clinical condition and can provide a high level of evidence for clinicians in their decisions are scarce. The purpose of this randomized clinical trial was to evaluate the effect of working length determination by radiograph or electronic apex locator on the adequacy of the final working length.
Materials and Methods The protocol was registered in the international trial registry ClinicalTrials.gov under the ID: NCT00901810. Calculation of sample size by setting the power of the study
WL Measurement by Electronic Apex Locator or Radiography
1753
CONSORT Randomized Clinical Trial to 90%, standard deviation of the outcome to 1 mm based on previous studies (21), and the minimum detectable difference to 0.5 mm gave a minimum number of 172 canals for this two treatment parallel-design study. We selected our cases from any patient aged 20 to 65 years old who presented for primary endodontic therapy to the Department of Endodontics of Shiraz Dental School. After obtaining informed written consent form from each patient, the teeth were randomly allocated to each group by flipping a coin. All selected teeth had mature apexes with no radiographic sign of root resorption. All of the cases were treated by one endodontist. During the procedure if the operator felt that the length measurement could not be done properly in either group and it was necessary for another method to be used, those cases were excluded from the study. For example, cases in which radiography alone because of superimposition was not enough to determine working length were excluded. Also, teeth with no apical patency because of different causes were excluded. In multicanalled teeth, if one canal was not suitable to enter the study, those teeth were excluded as well. At the end of the study, we managed a total of 84 teeth with 188 canals. A datasheet was used to record the number of each tooth, vitality of the tooth on access as determined by bleeding, the presence of apical lesion, length measurements, amount and direction of correction after master cone radiography, and the total number of radiographs needed for each tooth. The steps followed for each group are as follows: Group A (radiographic length determination): 1. Taking preoperative periapical radiography using bisecting angle technique 2. Placing the working file to the estimated length after access cavity preparation and taking the working length radiograph (bisecting angle technique). The primary working length is determined to be 1 mm short of the radiographic apex. 3. Finishing canal preparation to this working length, inserting the master cone to this length, and taking a master cone radiography using the bisecting angle technique. 4. Correcting the working length to be 1 mm short of the radiographic apex if needed and setting this as the final working length. 5. Obturation of the canal to the final working length using the lateral condensation technique. 6. Taking the final radiography using the bisecting angle technique. Group B (EAL): 1. The same as step 1 in group A. 2. Placing the working file to the estimated length after access cavity preparation according to preoperative radiograph, attaching the file clip of Raypex5 (VDW, Munich, Germany), and moving toward the apex until the red indicator shows the apex. The file was then withdrawn just to the point where this blinking indicator turned off. The length of the file was then measured at this point, and 0.5 mm was subtracted to get the initial working length. 3. The same as step 3 in group A. 4. If the tip of the gutta-percha is shorter than 0 to 2 mm of the apex, correcting it to be 1 mm short of the apex; otherwise, it does not change. 5. The same as step 5 in group A. 6. The same as step 6 in group A. The master cone and final radiographs were evaluated by two endodontists blinded to group allocation of each case and graded as follows: (1) short (shorter than 2 mm from radiographic apex), (2) acceptable (within 0-2 mm from radiographic apex), and (3) over (beyond the apex).
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The data were statistically analyzed using the Pearson chi-square test. The values of correction in step 4 of each group were statistically analyzed with the Mann-Whitney U test. Each statistical analysis was performed at the 5% significant level.
Results The results of length adequacy in each group for master cone and final obturation are summarized in Tables 1 and 2, respectively. Reclassification of the outcome data by focusing on each subdivision results in three cross-tabulations for the master cone and final obturation length adequacy, each focusing on one of the three outcome categories: acceptable, over, and short. Based on these reclassified tables in the EAL group, there was a higher percentage of acceptable cases, both for the master cone as a primary outcome (c2, p = 0.09) and the final obturation (c2, p = 0.32) as a secondary outcome than in the radiograph group, but the difference was not statistically significant (p > 0.05). There was a significantly lower percentage of overresults in the EAL group compared with the radiographic group for master cone results (c2, p = 0.00). There was also a lower but not statistically significant rate of the over cases for the obturation results (c2, p = 0.32). There was no statistically significant difference in the percentage of the short cases for both the master cone (c2, p = 0.70) and the final obturation results (c2, p = 0.87) between the two groups. The average number of radiographs taken was 3 in the EAL group and 4.07 in the radiographic group, which showed a highly significant difference (Mann-Whitney U test, p = 0.00) . Vitality (c2, p = 0. 789) and periapical lesions (c2, p = 0.504) were not associated with length adequacy of the master cone as a primary outcome in the EAL group. The Mann-Whitney U test revealed a borderline statistically significant difference in the amount of correction needed after taking master cone radiography between the radiographic group (mean = 0.08 mm and standard deviation = 0.5) and the EAL group (mean = 0.23 mm and standard deviation = 0.5, p = 0.049). Also, reclassification of cases based on doing or not doing correction after taking master cone radiography showed no statistical differences between the two groups (c2, p = 0.80).
Discussion Electronic methods for tooth length determination have progressed significantly and have been increasingly integrated into the modern practice of endodontics (22). The accuracy of apex locators has previously been investigated by several researchers. In some in vitro studies, the simulation of the clinical situation has been done by using electroconductive materials like alginate, gelatin, agar, or saline (18, 23). Also, in some in vivo studies, after electronic length measurement, the teeth were extracted, and different target points like apical foramen, apical constriction, or radiographic apex were compared with the point where a given electronic apex locator has been shown as the terminus of root canal system (24, 25). None of the previously mentioned studies can be a true representative of clinical situations in which the whole treatment is done in the mouth. This study, however, was a true simulation of what occurs during a typical endodontic treatment. The end result was evaluated by radiography, which is an intrinsic problem associated with such kinds of
TABLE 1. Master Cone Length Adequacy Radiography EAL
Short (%)
Acceptable (%)
Over (%)
6 (7.1) 9 (8.7)
69 (82.1) 94 (90.4)
9 (10.7) 1 (1.0)
JOE — Volume 36, Number 11, November 2010
CONSORT Randomized Clinical Trial TABLE 2. Final Obturation Length Adequacy Radiography EAL
Short (%)
Acceptable (%)
Over (%)
1 (1.2) 1 (1.0)
72 (85.7) 94 (90.4)
11 (13.1) 9 (8.7)
EAL, electronic apex locator.
study, because radiography is the only universally accepted, available, and meaningful method of length adequacy assessment in the clinic. We decided to compare the results with conventional bisecting technique because it is used more often (26), and our results can be extrapolated more easily to routine daily practice. The most favorable outcome for root canal treatment in prognostic and cohort studies has been observed when, among other factors, endodontic treatment terminated in 0 to 2 mm short of the radiographic apex (2, 27), so this interval was chosen for our study as a reasonable and practical criterion for evaluating the length adequacy on radiographs. In this study Raypex5, which like other impedance ratio apex locators shows a blinking red alarm when the file tip has just passed the apical foramen (28), was used. So when the file tip is withdrawn just to the point that the blinking apex indicator goes away but the screen still shows the file beyond or at the constriction, it means that the tip of the file is between the major and minor foramen. Our method, which demands the file to pass the apical foramen, ensures the operator of a patent canal and a definitive measurement as a result. On the other hand, microscopic observations have shown that the distance of the foramen to apical constriction is approximately 0.5 mm in the younger group and 0.8 mm in the older group (29). Therefore, reducing 0.5 mm from the above working length leads us to a point just before or at the apical constriction and secures the operator from any overinstrumentation, and also a measurement well within the clinically tolerable 0.5- to 1-mm range from the apical constriction is provided, as recommended by several authors (30, 31). This study showed a higher but not statistically significant rate of acceptable results (90%) regarding master cone radiography in the EAL group, which is in agreement with previous studies (14, 16). ElAyouti et al (13) have shown that electronic apex locators can prevent overinstrumentation, even when the working length seems within the acceptable range on radiography. In the present study, there was almost no overestimation of working length in the EAL group, which is more unfavorable compared with underestimation (2). In our study, the length adequacy of master cone radiography was considered as the primary outcome because in both groups working length correction was based on master cone radiography, and this could prevent an uncorrupted comparison for final radiographies. Therefore, length adequacy of the final obturation radiography was considered as the secondary outcome and was investigated only to find a possible significant relationship with group allocation and also to report the final result of each treatment modality. Pulp vitality and the presence of a periapical lesion was not an influential factor on the accuracy of Raypex5 as an impedance ratio– based electronic apex locator in our study. This is quite expected because the modern generation of apex locators has been developed in a way to be independent of canal contents and to be able to detect the narrowest part in the morphology of canals, regardless of possible apical root resorption as confirmed in previous studies (15, 23). Finally, the electronic apex locator reduced the number of taken radiographs by about one film for every treatment. Although a reduction of one film for the treatment of one tooth does not seem to be significant, with respect to the fact that many patients have JOE — Volume 36, Number 11, November 2010
more than one tooth for treatment and in endodontic departments a lot of teeth have to be treated, this reduction can be translated to less time, energy, and exposure to patients as suggested previously (32). Considering that root canal treatment without preoperative and postoperative radiographs is below the standard of care (33), this clinical study supports the use of electronic apex locators as an adjunctive but not a substitute of radiography for root canal treatment.
Conclusion The results of endodontic treatment using electronic apex locator are quite comparable if not superior to radiographic length measurement regarding the rates of acceptable and short cases. Furthermore, in addition to reducing radiographic exposure, EALs can reduce the rate of overestimation of root canal length.
Acknowledgments The authors thank Dr Laaya Safi for her help with the evaluation of the radiographs, Dr Heydari for statistical assistance, and Dr Faranak Rabiee for helping with the clinical tasks of this study.
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