Model-predicted TMJ Loads in Humans With and Without Disc Displacement

Mechanical failure of the cartilaginous disc of the human TMJ may be due, in part, to the magnitudes of applied surface loads. Therefore, it is possible that TMJ loading may be larger in subjects with TMJ disc displacement compared to individuals with normal TMJs. Objective: This study tested the hypothesis that TMJ loads during static biting are larger in subjects with TMJ disc displacement (9 females, 8 males) compared to healthy subjects without TMJ disc displacement (9 females, 8 males). Methods: Subjects participated in accordance with IRB guidelines and were categorized via Research Diagnostic Criteria and magnetic resonance images. The 3D geometry of the muscles of mastication, mandibular condyles, and dentition of each individual was determined from posteroanterior and lateral cephalometric radiographs and used in computer-assisted numerical models. First, sagittal effective eminence shapes were predicted and validated by comparison to measured shapes from jaw tracking for each subject. Then, validated eminence shapes, geometry files and a numerical model based on minimization of muscle effort were used to calculate ipsilateral and contralateral TMJ loads for a range of vertical and angled static bite-forces. ANOVA tested for the combined effects of sex, diagnostic group, biting position, and biting angle on TMJ loads. Results: Significant combined effects were seen for diagnostic group and biting position, and diagnostic group and biting angle (P<0.05-<0.002). Biting on canine teeth resulted in >40% difference in ipsilateral and contralateral TMJ loads for the same bite-force between diagnostic groups. Vertically and laterally directed bite-forces of the same magnitude produced >40%->60% higher joint loads in individuals with TMJ disc displacement. Conclusions: Mechanical analysis indicates that joint loads for the same bite-force are larger in individuals with TMJ disc displacement than those without TMJ disc displacement. This study was supported in part by NIH R01 DE016417-01A1.