Critical regions in the human mandible during mastication and trauma: a finite element study

Faulty mandible implant designs with stress concentration regions result in failure in cyclic loading during daily activities. Difficulties in biomechanical evaluation of the mandible arise from multi-bellied muscle groups. This study aimed to identify and characterise critical stress concentration regions in an intact mandible, and to study the effects of combining masticatory muscle sub-groups on these critical regions. A finite element analysis was conducted on an intact mandible subjected to various mastication and punching tasks. Jaw-closing muscles were simulated in four configurations, either isolating or combining the masseter and temporalis sub-groups. Critical mandible regions were sought based on stress values exceeding the fatigue shear strength and yield strength of cortical bone. Maximum shear stress was less than the critical stress value for all mastication tasks. For tasks constituting the alternating bilateral mastication pattern, maximum shear stress regions were predominantly observed on the mandible body; whereas, condylar necks were critical during fist punching. This implies avoiding stress concentration features in the mandibular body and condylar neck when designing mandibular implants. Different muscle configurations resulted in similar magnitudes (variations < 10%) and regions of critical stress, which supports combining muscle sub-groups for quasi-static computational and experimental testing of the mandible.