Eruption of third molars: relationship to inclination of adjacent molars.

The purpose of this study was to determine the relationship between the sagittal inclination of the first and second maxillary molars and the eruption of the third molars. The sample consisted of 2 groups. The subjects in the first group (n = 28) had complete normal dentitions including third molars; those in the second group (n = 32) had impacted right and left third molars. The sagittal inclinations to the palatal plane of the first and second maxillary molars were measured on computed tomography sagittal images obtained with multiplanar reconstructions. The Mann-Whitney U test was used to compare mean angular values between the 2 groups. Spearman correlation coefficients were calculated to assess the relationship with age. A multivariate analysis was used to evaluate the relationship between the eruption of the third molars and the sagittal inclination of the first molar, the second molar, sex, and age. Maxillary first and second molars were more mesially inclined in the first group, particularly in the younger subjects (16-25 years). This inclination increased with age. The logistic regression showed that the sagittal inclination of the first molar is a predictor of the eruption of the third molar. This finding suggests that a more mesially inclined maxillary dentition is likely to be associated with third molar eruption. The absence of data on space requirements in the maxillary arch and interarch relationships warrants further exploration in an orthodontic population.