Prevalence and Imaging Features of C‐Shaped Root With Buccal Groove in the Mandibular Second Molar in a Japanese Population

ABSTRACT Objectives This study aimed to clarify the prevalence and imaging features of C‐shaped roots with deep buccal groove (C‐shaped root [BG]) in mandibular second molars using cone‐beam computed tomography (CBCT) and panoramic radiography. Methods Among 1335 patients, a total of 2156 mandibular second molars—completely erupted and with no history of root canal treatment—were analyzed using CBCT and panoramic images. CBCT appearances were classified into seven groups based on axial slice pattern changes along the root axis. Panoramic appearances were also classified into five types based on root and canal morphology. Results C‐shaped roots were observed in 800 (37.1%) out of 2156 second molars. Nine C‐shaped roots (BG) were identified in seven patients. The prevalence of C‐shaped roots (BG) was 0.42% among all second molars and 1.13% among the 800 molars with C‐shaped roots. On CBCT images, C‐shaped roots (BG) were clearly identifiable; all nine were classified as Group IV or VI, which are also commonly seen in C‐shaped roots with lingual groove (C‐shaped roots (LG)). On panoramic images, these molars exhibited Type 3 or 4 appearances—similar to those of C‐shaped (LG)—making differentiation difficult. Conclusion C‐shaped roots (BG) in mandibular second molars are rare in the Japanese population and cannot be distinguished from C‐shaped roots (LG) using panoramic images alone. CBCT examination is recommended when C‐shaped roots are suspected on panoramic radiographs to ensure correct diagnosis and treatment planning.