Fracture Patterns Associated With the Presence of Mandibular Third Molars

Purpose: The mandible is the most commonly fractured bone in the facial skeleton.  Studies have shown that 50% of fractures of the mandible occur in dentate regions. As mandibular third molars are located near the angle of the mandible, they have been suggested to contribute to an increased risk of mandibular fracture at this site due to the presence of a tooth (rather than bone) at a relatively thin area in the jaw.  Additionally, it has been suggested that the absence of a mandibular third molar may predispose to fracture at other sites, particularly the subcondylar region.  The aim of this study was to assess any correlation between mandibular fracture patterns, specifically in the region of the angle or condyle/subcondyle, and the presence or absence of mandibular third molars.

Methods: This study was an IRB-approved retrospective analysis of all patients who were evaluated for mandible fractures by the Oral and Maxillofacial Surgery Service at the Erie County Medical Center (ECMC) for the years 2010 through 2012.  The presence and location of third molar teeth, including degree of any impaction, were recorded.  The location of all mandibular fractures and their degree of complexity were then documented upon review of available radiographs.  The relationship between fracture patterns and the presence or absence of third molar teeth was then evaluated.  Odds ratios were calculated to determine relative risk of angle and condylar/subcondylar fractures in the presence or absence of third molar teeth on the same side of the mandible.

Results: Two hundred thirty-four patient records were reviewed from the three-year time period, with 468 mandibular halves available for analysis.  Ninety-three mandibular angle fractures had third molars present, 30 had no third molar, 206 had a third molar without fracture, and 139 had neither a third molar nor a fracture. If a third molar was present, the risk of mandibular angle fracture was two times greater than if no third molar was present (odds ratio 2.09; 95% confidence interval, 1.31 to 3.35).  There were 39 condylar/subcondylar fractures in the presence of a third molar, 42 fractures without a third molar present, 255 areas with a third molar but no fracture, and 132 sites with neither a third molar nor a fracture.  A condylar/subcondylar fracture was twice as likely to be avoided if a third molar was present on the same side (odds ratio 2.08; 95% confidence interval, 1.30 to 3.32).

Conclusions:  We conclude that there is a twofold increase in the likelihood of mandibular angle fracture in the presence of a retained third molar tooth.  Conversely, there is a twofold decrease in the risk of condylar/subcondylar fracture if a third molar is present on the same side, suggesting that retained third molars may serve a “protective” function against condylar and condylar neck fractures.  We do not believe these findings should promote retention of third molar teeth in the presence of other indications for removal since condylar and subcondylar fracture management is often less complex than mandibular angle fracture management.