The human temporomandibular joint region in different positions of the mandible

The anatomy of the human temporomandibular joint region has been investigated mainly under the conditions of dental occlusion. The aim of the present study was to elucidate the topographical situations in other functional positions such as wide-open mouth, protrusion and lateral displacement. The respective mouth positions were adjusted before fixation and controlled by magnetic resonance tomography. The temporomandibular joint regions were embedded in epoxy resin, and cut serially in the sagittal or the frontal plane. Wide-open mouth: The articular disc lies with its intermediate zone between the articular tubercle and the dorsal convexity of the condylar process, and thus adapts the articulating surfaces of the bones perfectly to each other. Massive enlargement of the retroarticular cushion is seen, whereas the loose connective tissue on the anterior side of the joint appears completely compressed. Protrusion: The disc lies with its intermediate zone between the convexities of the condylar process and the articular eminence. On the lateral side it appears to be compressed between mandible and temporal bone. The retroarticular cushion is moderately enlarged. The anterior compartment of loose connective tissue is smaller than in occlusion. Lateral displacement: On the working side the articular disc is in a stabilized position between the bony joint elements. The balancing condyle is in a protruded position with the retroarticular cushion reaching into the dorso-lateral half of the mandibular fossa. Conclusion: Protrusion appears as the position with the highest mechanical stress upon the articular disc.