| Summary: | Objectives: To clarify the relationship between tooth length and three-dimensional mandibular morphology in a healthy Japanese population. Materials and Methods: This study included 181 Japanese adults: 66 men and 115 women. Conebeam computed tomography (CBCT) images were acquired with a dentofacial cone-beam x-ray CT scanner. Tooth length was measured with open-source OsiriX medical image processing software. Crown height and root length were measured in the maxillary and mandibular central incisors, lateral incisors, canines, first premolars, second premolars, first molars, and second molars. Based on these measurements, principal component (PC) analysis was performed. The following measurements were used to assess three-dimensional mandibular morphology: CD-GO, GO-GN, RCD-LCD, RGO-LGO, RCP-LCP, and the gonial angle. Stepwise multiple regression analysis was performed to examine the associations between three-dimensional mandibular morphology and the patterns of crown and root lengths using the mandibular measurements as explanatory variables and each PC as the dependent variable. Results: CD-GO was positively associated with PC1, which represented overall tooth length. RGOLGO was positively associated with PC2, whereas GO-GN, RCP-LCP, and gonial angle were negatively associated with PC2, which was the axis denoting relatively longer root (+) vs higher crown (-). Being female was associated with PC3, which was the axis denoting relatively longer posterior tooth (+) vs anterior tooth (-). Conclusions: The present clinical study effectively used CBCT images and PC analysis to reveal significant correlations between tooth length and mandibular morphology in a modern human population, confirming in part the statement that ''large teeth necessitate large jaws.'' (Angle Orthod. 2018;88:403-409.) © 2018 by The EH Angle Education and Research Foundation, Inc.
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