The Morphologic Characteristics of the Distolingual Roots of Mandibular First Molars in a Taiwanese Population

IntroductionThe prevalence of extra distolingual (DL) roots in mandibular first molars in Chinese population is about 20%. The purpose of this study was to evaluate the difference of root length and root curvatures between distobuccal (DB) and DL roots of three-rooted mandibular first molars in a Taiwanese (Chinese) population.MethodsOf the 293 extracted mandibular first molars, DL roots were present in 29 (9.9%) teeth. Excluding teeth with fractured DB or DL roots, 21 mandibular first molars were further investigated. DB and DL root lengths were measured from the lower level of furcation at the distal surface to the root apex. The curvature of the DL root was measured on mesial-distal and buccal-lingual radiographs by Schneider's technique.ResultsThe DL roots were significantly (p < 0.001) shorter than the DB roots with an average of 1.48 ± 0.81 mm. Most DL roots had a greater curvature in a buccal-lingual orientation (36.35° ± 9.38°) than a mesial-distal orientation (9.24° ± 6.10°) and 28.57% of the curved DL roots had the curvature at the apical one third (p < 0.001).ConclusionThe results of this study verified the characteristics of shorter root length and severe buccal-lingual inclination of DL roots in three-rooted mandibular first molars.