Association between third molar agenesis and sagittal skeletal discrepancies in an orthodontic patient population.

BACKGROUND: Previous studies have reported differences in the prevalence of tooth agenesis according to sagittal skeletal discrepancies, while third molars have often not been considered. The aim of the present study was to investigate the association between third molar agenesis and sagittal skeletal discrepancies. METHODS: This cross-sectional study comprised 484 orthodontic patients. Pre-orthodontic lateral cephalometric radiographs were digitally analyzed using OnyxCeph³. SNA, SNB, and ANB angles were determined, and the skeletal classification based on ANB was performed as Class I, Class II, and Class III. In addition, sagittal jaw positions were classified as retrognathic, orthognathic, or prognathic. Third molar agenesis was evaluated on panoramic radiographs. The control group consisted exclusively of individuals with a complete permanent dentition of 32 teeth. Statistical analysis was performed at α = 0.05. RESULTS: A total 244 females and 240 males were included: 216 patients had skeletal Class I malocclusion, 201 had skeletal Class II malocclusion, and 67 had skeletal Class III malocclusion. A total of 117 patients had third molar agenesis. Patients with skeletal Class III malocclusion showed a higher prevalence of third molar agenesis (total) (p = 0.0086) and a higher prevalence of maxillary third molar agenesis (p = 0.0003). The number of missing third molars ranged from 1 to 4, and a statistically significant difference was observed, with patients with skeletal Class III malocclusion showing a higher number of missing third molars compared with patients with skeletal Class II malocclusion (p = 0.0309) and skeletal Class I malocclusion (p = 0.0432). Logistic regression analysis was performed, in which gender and age were included in the model as covariates showed that Skeletal class III malocclusion remained associated with third molar agenesis (p < 0.05). CONCLUSION: Third molar agenesis was significantly more prevalent in patients with skeletal Class III malocclusion.