DEFINING THE NORMAL TEMPOROMANDIBULAR-JOINT - CLOSED-MOUTH, PARTIALLY OPEN-MOUTH, AND OPEN-MOUTH MR IMAGING OF ASYMPTOMATIC SUBJECTS

Fifty temporomandibular joints (TMJs) in 30 asymptomatic volunteers were imaged with a 1.5-T magnetic resonance (MR) imaging system to determine (a) the normal range of meniscus position, (b) the best definition of a normal TMJ and criteria to distinguish it from a TMJ with significant internal derangements, (c) the significance of certain findings such as joint effusion and disk distortion, and (d) the optimum mouth position(s) to be used for imaging. A method was devised to quantify meniscus displacement in terms of the number of degrees from a 12 o'clock or vertical position (relative to the condyle). The distribution of meniscus positions defined two groups in this asymptomatic study group. A strong correlation between abnormal joints and a history of orthodontics led to the exclusion of subjects with a history of orthodontics, and those with mouth trauma were also excluded, leaving a better 'normal control' group. The junction of the posterior band of the meniscus and the bilaminar zone should fall within 10° of vertical to be within the 95th percentile of normal.