Brazilian Journal of Oral Sciences Piracicaba Dental School - UNICAMP EISSN: 1677-3225 Vol. 8, Num. 4, 2009, pp. 189-192

Braz J Oral Sci, Vol. 8, No. 4, October-December, 2009, pp. 189-192

Original Article

Comparative analysis of the electronic and radiographic determination of root canal length of primary molars- An ex vivo study

Lucineide de Melo Santos ¹ ; José Ivo Limeira dos Reis ¹

¹ DDS, MSc, PhD, Adjunct Professor, Dental School, Federal University of Alagoas, Brazil

Correspondence Address: Lucineide de Melo Santos, Faculdade de Odontologia-FOUFAL Av. Lourival Melo Mota, s/n, Tabuleiro do Martins - Maceió - AL, CEP: 57072-970

jilreis@uol.com.br

Date of Submission: 27-Jul-2009

Date of Acceptance: 09-Nov-2009

Code Number: os09040

Abstract

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 necessary ^[1] . 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 inflamed ^[2],[3] .

The determination of the working length (WL) is one of the earliest stages and is a crucial point of endodontic therapy ^[4],[5] , especially in primary teeth ^[6] . Estimating the exact length of the root canal during endodontic therapy is fundamental to avoid injuring the permanent successor tooth ^[6],[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 teeth ^[8] . 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 length ^{[1],[2],[7],[9]} . However, radiography may generate inaccurate results, since x-rays provide a two-dimensional image of a three-dimensional streucture ^[10] . It is impossible to see, for example, the buccolingual aspect due to the superposition of the dentin, cementum, cortical bone and alveolus ^[11] . Moreover, radiographic images may suggest the presence of instruments inside the canal when, in fact, they are outside it. Small degrees of resorption are not clearly visible radiographically, resulting in an increased risk of overinstrumentation and/or overobturation ^[2] .

Electronic apex locators were developed in 1962 ^[12] , 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 then ^{[5],[13],[14],[15],[16]} . The Root ZX apex locator (Morita^® , Sao 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 teeth ^[17] , even when these teeth present root resorption ^[18] . 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 teeth ^[19] . Moreover, the shape, dimension, and position of the root apex are often continuously altered ^[2] . Several studies have focused on evaluating the use of these devices in primary dentition ^{[2],[6],[7],[20],[21],[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, Sao 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 periodontium ^[23] . The canals were then flushed with 2.5% sodium hypochlorite and dried with a paper point. The WL was measured with a size 10 K-file. All 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 ^[21] Measurements were considered valid if the instrument remained stable for at least 5s ^[20] . 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 ^®, Ribeirao 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 values ^[24] [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 [Table - 2].

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 being statistically superior to radiography [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].

Discussion

The correct determination of the length of root canals is essential to avoid injuring the permanent successor tooth during root canal therapy ^[6],[7] . Most root canal length determination methods are based on radiographic examination ^[1],[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 image ^[9] . Moreover, the exposure of children to x-rays should be reduced ^[25] . Hence, the electronic method has been proposed as an alternative ^[2],[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 radiographically ^[6],[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 cases ^[18] . It should be emphasized, at this point, that physiological ^[26] 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 defect ^[23] . 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 studies ^{[2],[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 studies ^[6],[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 to82.3% ^[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. This means that the use of the electronic apex locator enabled us to obtain WL measurements that are closer to the gold standard WL and shorter than the apical foramen or the earliest stages of resorption. Considering that the objective of the endodontic therapy in primary teeth is to eliminate infection and keep the tooth functional until its physiological exfoliation, without compromising the permanent successor ^[28] , it can be inferred that the radiographic technique is less accurate than the Root ZX technique, since it presented a higher proportion of cases in which the WL was more than 1 mm shorter than the gold standard WL.

It may be concluded that the Root ZX locator is a reliable method to determine the WL of primary teeth, since the Root ZX method showed s smaller difference from the gold standard in determining the acceptable WL than the radiographic method.

References

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