Influence of the incompletely erupted lower third molar on mandibular angle and condylar fractures

Background: Several studies have shown an increased risk of mandibular angle fractures by the presence of the lower third molar (M3), especially the incompletely erupted M3. The presence of M3s might influence condylar fractures, which is one of the most common fracture sites, as well as the angle fracture. Methods: Six hundred ninety-two mandibular sides among 346 patients with mandibular fracture were analyzed. They were classified into two groups according to the presence of incompletely erupted M3s and were analyzed according to fracture site, age, and cause of injury. Results: Among these patients with mandibular fractures, the frequency of occurrence of the mandibular angle fracture was higher in the group with incompletely erupted M3s (p < 0.0001) and that of the condylar fracture was higher in the group without it (p < 0.001). Conclusion: The result of this retrospective investigation shows that an incompletely erupted M3 decreases the risk of condylar fractures and increases the risk of mandibular angle fractures.