Relationships between skeletal morphology and patterns of bilateral agenesis of third molars in Japanese orthodontic patients.

The aim of this study was to reveal the correlations between bilateral agenesis of third molars (M3s) and skeletal morphology in Japanese male and female orthodontic patients. Sixty patients (30 males, 30 females), with bilateral agenesis of maxillary M3s and without agenesis of mandibular M3s (group U), and 60 patients (30 males, 30 females), with bilateral agenesis of mandibular M3s and without agenesis of maxillary M3s (group L), were selected as agenesis groups. Additionally, 60 patients (30 males, 30 females) with all four M3s were selected as the control group (group C). Patients in these three groups had no agenesis of teeth other than M3s. Lateral cephalograms of each patient were used to evaluate skeletal morphology of the maxilla and mandible. Two-way analysis of variance was used for statistical comparisons. Groups U and L had significantly smaller maxillary length and area than group C. Group U exhibited a significantly smaller lower facial height than group C. Males showed significantly larger maxillary length; total mandibular and mandibular body length; mandibular ramus height; SNB angle; maxillary area; and mandibular symphysis, corpus and ramus areas than females. Females had significantly larger lower facial height, gonial angle and ANB angle than males. Smaller maxillary length and area and lower facial height should be considered in planning orthodontic treatment for patients with bilateral agenesis of maxillary and mandibular M3s.