Prevalence and morphological characteristics of disto-lingual roots in mandibular first molars: a cone beam CT study with diagnostic and therapeutic implications

Objectives High prevalence of disto-lingual roots (DLR) at the mandibular molar in Chinese can complicate the management of periodontitis. This study assessed the prevalence and morphological features of mandibular first molar DLR and furcation entrances in a Hong Kong population by analysis of cone beam computed tomography (CBCT). Materials and methods CBCT including the mandibular 1st molar region were identified from the Prince Philip Dental Hospital archive and analyzed by a single investigator. Morphologic features and location of DLR were studied and presented as 95% confidence intervals. Results A total of 398 CBCTs with 716 mandibular first molars were analyzed. The prevalence of DLRs in mandibular first molars on subject based was 20.1% (95% C.I. 16.2–24%). DLR was located 44.5° ± 8.9° (95% C.I. 42.8–46.1°) to the mid-lingual of the mandibular first molar, with a bucco-lingual width 3.3 mm ± 0.5 mm (95% C.I. 3.2–3.4 mm). The mesial furcation entrance was located 4.0 mm ± 0.9 mm (95% C.I. 3.8–4.2 mm) apical to the cemento-enamel junction (CEJ) while the distal was 5.2 mm ± 1.3 mm (95% C.I. 5.0–5.4 mm) from the CEJ. The surface area of the DLR was 106.9 mm 2 ± 41.2 mm 2 (95% C.I. 98.9–114.8 mm 2 ). Conclusions Chinese population has a high prevalence of DLRs. The present information is critical for understanding the morphological features of DLR and guide diagnosis and treatment of stage III periodontitis as well as for secondary prevention and supportive care of stage II periodontitis. Clinical relevance Little is known about the location and morphology of disto-lingual roots of mandibular 1st molars, yet they are frequently present in patients with Chinese ethnic background, thus complicating diagnosis and treatment. The present study utilized CBCT to analyze the prevalence and morphological features of the mandibular first molar DLR and furcation entrance. It is the first study reporting on the position of the DLR, degree of separation of the furcation, and the surface area of the DLR.