Abstract: Objective To examine the buccolingual inclination of first molars in patients with different skeletal malocclusions to provide theoretical and clinical reference for how to select preadjusted appliances, make treatment plan and prevent complications in different cases. Methods CBCT data of 236 patients (88 males, 148 females) treated at Department of Orthodontics in the Affiliated Stomatological Hospital of Nanjing Medical University from 2016 to 2017, were analyzed to evaluate the discrepancy of buccolingual inclination of first molars with respect to different sagittal and vertical classifications. Results The study showed that the maxillary first molars were more buccally inclined in skeletal Class Ⅲ subjects than Class Ⅰ or Ⅱ subjects, while the mandibular ones were more buccally inclined in skeletal Class Ⅱ subjects than Class Ⅰ or Ⅲ subjects. Differences were statistically significant. Large differences in angle were found among different growth patterns, which showed the most buccal inclination in the maxilla and the most lingual inclination in the mandible for subjects in the high angle group. ANB angle was negatively correlated with buccolingual inclination of maxillary molars but positively correlated with buccolingual inclination of mandibular molars. Conclusion With the increase of sagittal skeletal deformity, the tendency of lingual inclination of maxillary molars and buccal inclination of mandibular molars in skeletal Class Ⅱ patients increases while the tendency in skeletal Class Ⅲ patients is the opposite. The inclinations compensate for the transverse skeletal discrepancy. These should be taken into consideration to avoid clinical complications when treating different skeletal malocclusions.

Key words: molar, buccolingual inclination, transverse discrepancy, cone-beam computed tomography