Tests of model-predicted TMJ eminence morphologies in subjects with/without pain

TMJ eminence morphology provides important constraint forces in static mandibular mechanics, and thus, affects activities of muscles and subsequent joint loads during biting. In healthy subjects, eminence morphologies were reported to be consistent with a neuromuscular objective of minimization of joint load (MJL). Objective: To test for significant differences between measured and MJL model-predicted eminence morphologies of subjects with (+P) and without (–P) pain. Methods: Twenty-nine subjects were ascribed to +P (n=11; 6 females, 5 males) and –P (n=19; 10 females, 8 males) groups using Research Diagnostic Criteria. MRI images confirmed normal TMJ disc position. Video images from two experimental sessions captured condylar movements during symmetrical mandibular protrusion/retrusion. Digitized coordinate data were measured from these images, describing sagittal plane projections of the right and left eminence morphologies. Each subject's data were fit to a 3rd order polynomial equation, which was used to calculate eminence shape over 11 sequentially protrusive condylar positions (0.0-5.0 mm, 0.5 mm increments). A computer model used each subject's 3D craniomandibular geometry to predict eminence morphology consistent with MJL. Measured and modeled data were used in ANOVA and Bonferroni post-hoc tests for effects of gender, diagnostic group (+P, -P), and condylar position (1-11). Results: Gender effects were not significant. Significant differences were found: between measured and model-predicted eminence morphologies for –P subjects at condylar protrusion positions of 4.5-5.0mm (P≤0.013) and for +P subjects at condylar protrusion positions of 4.0-5.0 mm (P≤0.002), and between measured eminence morphologies in –P and +P subjects at condylar protrusion positions of 4.5-5.0 mm (P≤0.004). Conclusion: Differences in eminence morphologies of –P and +P subjects were limited to condylar protrusion positions ≥4.5 mm, and subject-specific eminence morphology was predicted by the MJL model for up to 4.0 mm of condylar protrusion. This work was support by NIDCR R01DE016417-01A1 (J Nickel, PI).