Oral Sciences n3 Original Article Braz J Oral Sci. 8(4):189-192 Comparative analysis of the electronic and radiographic determination of root canal length of primary molars– an ex vivo study Lucineide de Melo Santos1; José Ivo Limeira dos Reis1 1 DDS, MSc, PhD, Adjunct Professor, Dental School, Federal University of Alagoas, Brazil Correspondence to: Lucineide de Melo Santos Faculdade de Odontologia-FOUFAL Av. Lourival Melo Mota, s/n, Tabuleiro do Martins - Maceió - AL, CEP: 57072-970 E-mail: jilreis@uol.com.br Abstract Aim: ́ To evaluate comparatively the radiographic and electronic root canal length determination in primary molars. Methods: 128 canals from 66 primary molars were selected. The root of each tooth was cut open on the occlusal face, and the real tooth length (RTL) was measured and the gold standard working length ( WL) was determined by subtracting 1 mm from this measurement. The teeth were then placed in a plastic receptacle holding alginate and saline for the electronic determination of the root length using a Root ZX apex locator. The radiographic determination of the WL was obtained by subtracting 1 mm from the measurement highest cusp to the root apex appearing in the radiography. The data were analyzed statistically by the Chi-square test at a 5% significance level. Results: There was statistically significant difference (p<0.05) between each tested method and the gold standard. The Root ZX apex locator and the radiographic method presented satisfactory results in 75.78% and 54.68% of the cases, respectively. Conclusions: The Root ZX apex locator is a reliable method to determine the WL of primary teeth, since it showed greater accuracy than the radiographic method. Keywords: Root ZX, radiography, root canal length measurement, primary molars. Introduction Although dental caries is well known disease, primary teeth with deep carious lesions reaching the root canals is still a reality in pediatric dentistry, especially in economically deprived regions, which makes root canal therapy on these teeth necessary1. In this context, pulpectomy is still an important treatment in primary molars when the root pulp, infected or not, is not vital or is irreversibly inflamed2-3. The determination of the working length (WL) is one of the earliest stages and is a crucial point of endodontic therapy4-5, especially in primary teeth6. Estimating the exact length of the root canal during endodontic therapy is fundamental to avoid injuring the permanent successor tooth6-7. While the factors related to pulpal damage in primary and permanent teeth are similar, the clinical management of these teeth can be different, based mainly on the differences between the two types of teeth8. Several techniques have been proposed to determine root canal length, but the ideal procedure has yet to be identified. Radiography has been widely used in the determination of root length1-2,7,9. However, radiography may generate inaccurate results, since x-rays provide a two-dimensional image of a three-dimensional streucture10. It is impossible to see, for example, the buccolingual aspect due to the superposition of the dentin, cementum, cortical bone and alveolus11. Moreover, radiographic images may suggest the presence of instruments inside the canal when, in fact, they are outside it. Small degrees of resorption are n ot clearly visible radiog raphically, resulting in an increased ri sk of overinstrumentation and/or overobturation2. Braz J Oral Sci. October/December 2009 - Volume 8, Number 4 Received for publication: July 27, 2009 Accepted: November 9, 2009 190 Braz J Oral Sci. 8(4):189-192 Table 1 – Working length scoring system. Score Situation 0 Working Length (WL) equal to gold standard 1 Working Length (WL) from 0.5 to 1mm shorter than gold standard 2 Working Length (WL) > 1mm shorter than gold standard 3 Working Length (WL) exceeds gold standard Table 2 – Means and standard deviations of the differences between the gold standard WL and the WL obtained with the Root ZX and radiographic methods Root ZX Radiography Mean a0.14mm b0.68 mm Standard deviation 0.45 0.88 Number of canals 128 128 Different letters indicate statistically significant differences (p<0.05). Groups No. of cases Total canals Percentage (%) Root ZX 97a 128 75.78 Radiography 70b 128 54.68 Tab l e 3 – Numb er of cases i n w hich th e e l ectronical ly and radiographically measured WL fell between scores 0 and 1. Different letters indicate statistically significant differences (p<0.05). Electronic apex locators were developed in 196212, in an attempt to obtain more precise measurements for the determination of root length and to establish the apical limit of instrumentation, and have been widely used on permanent teeth since then5,13-16. The Root ZX apex locator (Morita®, São Paulo, Brazil) is a third-generation electronic device which can detect the smallest diameter of the root canal in both moist and dry conditions, and performs well on permanent teeth17, even when these teeth present root resorption18. The literature does not indicate differences when using the locator in permanent and primary teeth. However, there are some limitations in evaluating the accuracy of apex locators in primary teeth, including millimeter measurements and visualizing the exact location of the file tip, particularly in resorbed primary teeth19. Moreover, the shape, dimension, and position of the root apex are often continuously altered2. Several studies have focused on evaluating the use of these devices in primary dentition2,6-7,20-22, achieving accuracy rates of 64-96.7%. In view of the above considerations, this ex vivo study evaluated the electronic and radiographic determination of root canal length in primary molars comparatively with the measurement obtained by direct viewing of the endodontic file. Materials and methods This work was approved by the Research Ethics Committee of the Federal University of Alagoas (UFAL), under the protocol number 011436/2005-98. Sixty-six primary molars with up to one third of root resorption were obtained from the Tooth Bank of the Dental School of Federal University of Alagoas, totalizing 128 canals. Molar roots with more than 1/3 apical resorption were excluded from this study. All the teeth showed some degree of root resorption. The root of each tooth was cut open on the occlusal face with carbide ( Jet Brand; Wheeling, IL, USA) and Endo-Z burs (Dentsply-Maillefer, Ballaigues, Switzerland) mounted in a high-speed handpiece. The real tooth length (RTL) was then measured using a magnifying glass (x2). A 21-mm-long size 10 K-file (Dentsply-Maillefer) was introduced into the canal until its tip appeared at the apical foramen, or at the point of root resorption, and this measurement was marked with a rubber stop at the height of the reference cusp. The file was then placed in a digital caliper (Mitutoyo, Tokyo, Japan) and the RTL was measured. This measure minus 1mm was recorded as the WL gold standard. The measurements were taken by a calibrated examiner and recorded on specific charts. Each tooth was measured three times, and the mean value was calculated. The root canal length was determined electronically using a Root ZX (Morita, São Paulo, SP, Brazil) apex locator. For such purpose, the teeth were numbered 1 to 66 and embedded in alginate ( Jeltrate; Dentsply Ind. e Com. Ltda., Rio de Janeiro, RJ, Brazil) with saline, which acts as a conductor simulating the periodontium23. The canals were then flushed with 2.5% sodium hypochlorite and dried with a paper point. T he WL was m easured w ith a size 10 K-f il e. Al l measurements were taken within a 2-h interval, when the gel was still sufficiently damp. The device was used according to the manufacturer’s instructions. The lip electrode was attached to the alginate. The file was inserted slowly into the canal until the signal on the LCD screen display bar reached the apex signal. At this point, the instrument was removed gradually until it displayed a measurement of 1 2 1. Measurements were considered valid if the instrument remained stable for at least 5s20. Each tooth was measured three times with the device and the mean value was calculated. All measurements were made by the same operator, who was blinded to the resorption stage of the teeth. The WL was determined radiographically according to the paralleling technique) using an x-ray equipment operating at 8Ma and 70Kvp (Dabi Atlante®, Ribeirão Preto, SP, Brazil). A conventional dental x-ray film (Ektaspeed E-speed group; Kodak, Rochester, NY, USA) was placed perpendicular to the teeth, maintaining a 20 cm focus-film object and 0.4 exposure time. The WL was determined as follows: the length of the tooth was measured on the diagnostic radiographic image, from the highest cusp to the root apex, and 1 mm was subtracted from this length. The same procedure was employed in the case of curved roots. All measurements were taken by the same operator. The electronically and radiographically measured WLs were compared with the gold standard WL and scores were attributed to the resulting values24 (Table 1). Data were analyzed statistically by the Chi-square test at 5% significance level. Results There was statistically significant difference (p<0.05) between the gold standard WL and the WLs obtained with the Root ZX and radiographic methods (Table2). A comparison of the number and proportion of cases in which the WL measurements were scored 0 and 1 indicated a significant difference (p<0.05) between the two techniques, with the Root ZX method b eing statistical ly superior to radiog raphy (Table 3). Comparison of the data referring to the number and proportion of cases in which the WL measurements fell between scores 2 and 3 also showed statistically significant difference (p<0.05) between the two techniques (Table 4). Comparative analysis of the electronic and radiographic determination of root canal length of primary molars– an ex vivo study 191 Braz J Oral Sci. 8(4):189-192 Groups No. of cases Total canals Percentage (%) Root ZX 31a 128 24.21 Radiography 58b 128 45.31 Different letters indicate statistically significant differences (p<0.05). Tabl e 4 – Numbe r of cas es in w hich th e e l ectronical ly and radiographically measured WL fell between scores 0 and 1. Discussion The correct determination of the length of root canals is essential to avoid injuring the permanent successor tooth during root canal therapy6-7. Most root canal length determination methods are based on radiographic examination1-2,7. However, radiographic images may lead to misinterpretations, since slight degrees of resorption may not be visible and the superposition of adjacent anatomical structures may impair the clarity of the image9. Moreover, the exposure of children to x-rays should be reduced25. Hence, the electronic method has been proposed as an alternative2,7. In the present study, the Root ZX device provided WL measures that were closer to the gold standard than those obtained with the radiographic technique. These data were confirmed in the comparison with the mean scores attributed to the differences of the measurements, since it was found that most measurements obtained radiographically were 1 mm shorter than the gold standard WL, while those obtained with the Root ZX device were closer with the gold standard. These findings are similar to several studies reported in the literature that evaluate the accuracy of the Root ZX method in primary teeth, which have demonstrated that electronic measurements are closer to the WL than those obtained radiographically6-7, 9. When the apical constriction is destroyed by apical root resorption, it is very difficult to determine the WL based only on an x- ray image, and the Root ZX method can be used in these cases18. It should be emphasized, at this point, that physiological26 or pathological root resorption frequently occurring in primary teeth should not be seen as an obstacle preventing the use of electronic apex locators. Root resorption does not involve more than two thirds of the root; therefore, endodontic therapy is counter-indicated in these cases. The electronic apex locator can work accurately in primary teeth with root resorption because the root canal typically has a decreasing taper towards the defect23. In the present study, all teeth presented root resorption, though without affecting the performance of the Root ZX device, which confirms the findings of previous studies2,6-7,19-20. With regard to the number and proportion of cases when the WL measurements were the same or 0.5 to 1 mm shorter than the gold standard WL, it was observed that the Root ZX technique presented a higher percentage (75.78%) than the radiographic technique (54.68%), a statistically significant difference. These results are partially consistent with those obtained in previous studies6-7. By comparing radiographic and electronic measurements to determine the root canal length, Katz et al.7 and Subramaniam et al.9 found no significant difference between the methods, although the x-ray based measurements were higher than those obtained with the Root ZX device. A probable explanation for this difference in results lies in the methodology used in the present research, which established scores to evaluate the data obtained, unlike the cited studies. Some studies investigating the accuracy of electronic apex locators in permanent teeth have shown that the accuracy of the Root -ZX device varied from 75 to 82.3%5, 27. The proportion of cases in which the WL measurements were more than 1 mm shorter or longer than the gold standard WL was different, although the Root ZX method presented superior results. 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