Stress distribution in the mandible with unilateral condylar fracture.

OBJECTIVE: The purpose of this study was to investigate the influence of unilateral condylar neck fracture upon the stress distribution in the mandible and the temporomandibular joint (TMJ) to realize primarily the biomechanical mechanism of the temporomandibular joint disorders (TMD) caused by TMJ injury. METHODS: The character of stress distribution in the mandible of a normal human and a patient with TMD induced by unilateral condylar neck fracture followed by malpositioned healing was analyzed quantitatively and compared during centric occlusion by combining spiral computed tomography scanning technology with the three-dimensional finite element method. RESULTS: The patient with unilateral condylar neck fracture followed by malpositioned healing had unbalanced stress distribution in the mandible, such as differing nature and value of stress. The stress in the fractured side was higher than in the nonfractured side, in which the condyle was more evident. The maximum principal stress and minimum principal stress of each region in the fractured mandible were much higher than those in a normal mandible. Stress quality also differed. CONCLUSIONS: The abnormal stress changes after unilateral condylar neck fracture with malpositioned healing may be related to the effect of condylar shape change on masticatory muscle function and occlusion. TMJ injury not only damaged the condylar structure, but also compromised its biomechanic environment. It is preliminarily thought that unbalanced stress distribution, evidently increased stress, and varied stress character are biomechanic mechanisms of TMD. Condylar dislocated fracture should be treated promptly and properly to maintain the proper prognostic stress distribution.