Defining the normal temporomandibular joint: closed-, partially open-, 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 degrees of vertical to be within the 95th percentile of normal.