Relationship between orthodontic treatment, condylar position, and internal derangement in the temporomandibular joint.

The purpose of this study was to test the hypothesis that retraction of maxillary front teeth may lock the mandible in a posterior position, and to evaluate any relationship between condylar position and signs and symptoms of internal derangements in the temporomandibular joint. A total of 29 female patients treated for Angle Class II, Division 1 malocclusion with extraction of maxillary first premolars and 34 female patients treated for Angle Class I malocclusion without tooth extraction consented to participate in a radiographic and clinical follow-up examination. The mean ages of the patients were 16.9 (SD 3.0) and 16.6 (SD 2.6) years, and the mean times after treatment were 1.6 (SD 1.0) and 1.5 (SD 0.9) years, respectively. Condylar position was measured in percent anterior and posterior displacement from absolute concentricity on lateral, central, and medial tomographic sections of each joint. Mean condylar position was more posterior at right central (P less than 0.05) and medial (P less than 0.01) tomographic sections in patients treated with extraction. The difference was due to a higher frequency of anteriorly positioned condyles in the nonextraction cases. No intergroup differences in the sagittal occlusal slide from CR to CO and the number of patients with clicking were found. However, the condyles were located more posteriorly in all tomographic sections (P less than 0.05 for lateral, P less than 0.001 for central and medial) in patients with clicking than in those without.