C-shaped canal system in mandibular second molars evaluated by cone-beam computed tomography.

Aim: To evaluate the presence of mandibular second molars with C-shaped roots and to classify and analyse them by evaluation of cone-beam computed tomography (CBCT) imaging obtained at the Department of Diagnostic Imaging, Dentistry School, University of Buenos Aires. Methods: 3035 CBCT images were examined. 225 of them corresponded to patients who met the inclusion criteria. In accordance with this inclusion criteria: both mandibular second molars were present, with completion of root development, no destruction of the pulp chamber floor, nor previous treatment. Once confirmed the presence of C-shape canal, the canals were classified according to the anatomical and radiographic features of the classification of Fan et al. (2004). Data were expressed as frequencies and percentages with confidence intervals of 95% (CI95), according to score test. Comparisons were analysed by Chi-square test with a 5% significance level. Results: 44 out of 225 selected patients had C-shape canal (20%; CI95: 15% to 25%). 70% (CI95: 56% to 82%) of the patients presented C-shaped canals bilaterally. Regarding to the anatomical classification -cross section-, there was a significant association between configuration and radicular third (Chi-square=76,89; p<0,05): at the coronal third C1 configuration predominated (47%; CI95: 36% to 58%); at the middle third C3d configuration predominated (39%; CI95: 28% to 50%); and at the apical third C4 configuration predominated (35%; CI95: 25% to 46%). There was no significant association between the tooth and radiographic classification -sagittal plane- (Chi-square=0,99; p=0,61): type 1 predominated in both teeth, 4.7 (58%; CI95: 42% to 71%) and 3.7 (66%; CI95: 49% to 79%). In 72% (CI95: 61% to 81%) of the cases, there have been configuration changes in the three thirds, whereas in 28% (CI95: 19% to 39%) of the cases, the same configuration was observed in the three thirds, being this difference significant (Chi-square=14,52; p<0,05). Conclusion: This study contributes to epidemiological knowledge of an anatomical variant of the tooth internal configuration and to its extrapolation in clinical practice. The endodontist should consider the descripted variants in order to achieve a successful treatment.