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 j oint. Study design. 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 dis k rotation within the glenoid fossa, the inclination of the condyle pa th, and the steepness of the articular eminence were measured and corr elated. Results. The condyle and disk both rotated during forward tran slation 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 inclinati on 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 c orrelated with the degree of disk rotation, which indicated that the d isk tended to rotate farther backward in a temporomandibular joint wit h steeper articular eminence. Conclusion. We found that on mouth openi ng the disk rotated backward relative to the condyle. The posterior di sk rotation was more prominent in joints with a steep articular eminen ce than in joints with a less steep eminence. The results may be helpf ul for understanding the biomechanics of the temporomandibular joint, especially relative to the development of disk displacement.