Abstract
There is currently no unified understanding of the mechanism underlying the commonly observed malposition （buccal inclination of the maxillary second molar） in the maxillary molar region. The aim of this study was to clarify the factors associated with the buccal inclination of the maxillary second molar. Thirty-two participants with skeletal Class Ⅰ or Ⅱ malocclusion were classified into four groups according to the presence or absence of buccal inclination of the maxillary second molars. Cone-beam computed tomography in centric occlusion was used to evaluate the horizontal relationship between the upper and lower alveolar bones in the molar region. Statistical analysis was performed using an analysis of covariance and a mixed-effects model analysis, with tooth inclination and skeletal classification serving as explanatory variables. The buccal inclination of the maxillary second molars was defined according to the buccolingual positional relationship between the first and second molars. Compared to the Class Ⅰ group with buccal inclination, the Class Ⅱ group with buccal inclination had a pronounced lingual inclination of the first molars, and the lingual cancellous bone width at the level of the first molar showed a significant difference in the main effect of tooth inclination （p＝0.002） and the interaction effect between tooth inclination and skeletal classification （p＝0.041）. A significant main effect of tooth inclination was observed for the overlap width between the upper and lower alveolar bones （p＝0.035）. No significant difference was observed between the groups regarding the alveolar distance posterior to the maxillary first molar. This study suggests that the positional relationship between the upper and lower alveolar bones and the associated change in the degree of inclination of the first molar are involved in the buccal inclination of the maxillary second molar.
