Determination of the existence of hinge movements of the temporomandibular joint during normal opening by Cine-MRI and computer digital addition.

PURPOSE The purpose of the first phase of this two-part investigation was to determine if the opening motion of the mandible could be illustrated and described using a dynamic imaging method. The purpose of the second phase of the investigation was to determine if a center of rotation would be discovered. MATERIALS AND METHODS Five volunteer subjects, 2 female and 3 male, whose temporomandibular joints had previously been determined to be asymptomatic, were examined by magnetic resonance imaging (MRI) during opening from a standardized position. The serial static images were reconstructed by the MRI's computer in "cine mode" to simulate dynamic motion, similar to a motion picture. For the second phase, each patient's series of static images were digitally added and manipulated by a computer graphics program to locate the center of hinge motion. RESULTS After reviewing the animated images recorded on videotape, three independent dentist observers confirmed that the opening movement of the mandible was initially rotational, followed by translation within the glenoid fossa. A center of rotation was calculated to be in the anatomic center of the condylar head of all of the subjects in this study. CONCLUSIONS This study showed that opening dynamics of the mandibular condyle could be studied by cine-MRI and that an opening hinge axis appears to be located in the anatomic center of the condylar head.