Steepness of articular eminence and movement of the condyle and disk in asymptomatic temporomandibular joints.

Objective: The purpose of this study was to investigate the rotational motion characteristics of the disk-condyle complex in relation to the steepness of the articular eminence of the normal temporomandibular joint.

Methods: We studied 14 asymptomatic volunteers with normal temporomandibular joints using magnetic resonance images with gradient recoil acquisition in the steady state. The degree of condyle and disk rotation within the glenoid fossa, the inclination of the condyle path, and the steepness of the articular eminence were measured and correlated.

Results: The condyle and disk both rotated during forward translation within the glenoid fossa during mouth opening. The movement of the disk was smaller than the movement of the condyle, resulting in a posterior rotation of the disk relative to the condyle. The inclination of the condyle path (mean, 61.1 degrees) was significantly smaller than the steepness of the articular eminence (mean, 68.7 degrees). The steepness of the articular eminence was statistically significantly correlated with the degree of disk rotation, which indicated that the disk tended to rotate farther backward in a temporomandibular joint with steeper articular eminence.

Conclusions: We found that on mouth opening the disk rotated backward relative to the condyle. The posterior disk rotation was more prominent in joints with a steep articular eminence than in joints with a less steep eminence. The results may be helpful for understanding the biomechanics of the temporomandibular joint, especially relative to the development of disk displacement.