Patterns of third-molar agenesis in an orthodontic patient population with different skeletal malocclusions

Objective: To examine the relationship between third-molar agenesis and different skeletal malocclusion patterns. Materials and Methods: Pretreatment records of 1046 orthodontic patients (aged 13–17 years; mean age, 14.07 ± 1.27) were used. Third-molar agenesis was calculated with respect to genders, number of missing teeth, jaws, and skeletal malocclusion patterns. The Pearson chi-square test was performed to determine potential differences. Results: Among the 1046 subjects, 237 subjects were diagnosed with third-molar agenesis (22.7%) with no statistical gender difference (P > .05). It was more common in the maxilla than in the mandible or in both jaws (P < .01). The prevalence of patients with a third-molar agenesis was the most commonly found type (P < .001). The prevalence of third-molar agenesis in those with a Class III malocclusion was significantly higher than in those with Class I or Class II (P < .05). However, there was similar prevalence among the hyper-divergent (24.5%), normal (23.8%), and hypo-divergent (19.2%) groups (P > .05). Conclusion: These results suggest that agenesis of the third molar does not depend on vertical patterns of the skeletal malocclusions, but does depend on sagittal skeletal malocclusions in this orthodontic patient population.