Fracture Injury Risk of the Restrained Mandible to Anterior-Posterior Blunt Impacts

This study describes the results of anterior-posterior impacts conducted on the mandibles of 22 male postmortem human subjects (PMHSs). The objective of this study was to develop an injury criterion for the mandible based on blunt impact while the jaw was restrained. Previous studies have attempted to characterize the injury risk of blunt impact to the mandible; however, due to the translation of the mandible during impact and a limited number of fractured specimens, previous studies were not able to produce an injury criterion. Blunt impact to a restrained mandible is relevant to a wide array of helmeted individuals, including the military population and sports that require helmets with chinstraps. Therefore, in this study, specimens were positioned with restrained jaws and impacted using a monorail drop tower with a gravity-driven cylindrical impactor. Nineteen of 22 specimens sustained at least one fracture during testing. Injury cases had an average impact energy of 15.0 ± 5.7 J (11.1 ± 4.2 ft-lb) and a fracture force of 2684 ± 726 N (603 ± 163 lbf). Results were used to generate an impactor force based injury criterion through survival analysis. Risk of injury was modeled using a Weibull distribution and a 50% risk of injury was found to occur at approximately 2834 N (637 lbf). The developed injury risk curve can be used to characterize injury to the restrained mandible for future testing and research studies, especially in the development of maxillofacial protective equipment.