Three-rooted mandibular first molars in Taiwanese population

Objectives: To investigate the occurrence of 3-rooted mandibular first molars and the morphology of the extra distolingual roots by 3D dental computed tomography (CT) images analyses. Methods: A total of 568 I-Cat CT images were screened to obtain 71 samples with existing 142 mandibular first molars. Comparison of the occurrence of such 3-rooted molars according to gender, the relative incidence of such dental anomalies and the correlation between left- and right-side occurrence were analyzed the means by Chi-square tests. The angulations from the four canals to the long axis of the tooth in the center, and the distances from the distolingual orifice to the other two orifices in 3-rooted molars were analyzed by an ImplantMax software system and compared by t-test. Results: The prevalence of 3-rooted molars was 38.03%, and the bilateral incidence was 59.26%. There was no significant difference in the incidence between gender, the right- and the left-side, unilateral or bilateral. The lingual angulations of the distolingual canal was more eccentric from the long axis buccolingually than other three canals (mesiobuccal, mesiolingual and distobuccal) (in male: 30° vs. 16.4°, 13°, 22.7°; in female: 32° vs. 16.3°, 13°, 20°). Orifice distance from distolingual canal to distobuccal canal and to mesiobuccal canal was 2.7 mm and 4.4 mm respectively. Conclusions: Dentists should be aware of the high racial prevalence of the distolingual roots in mandibular first molars in Taiwanese population before initiating endodontic treatment. The distance estimation among canal orifices as described in the present study might be valuable for dentists to achieve a successful endodontic treatment.