Internal structure of the temporomandibular joint and the circumferential bone: comparison between dentulous and edentulous specimens.

To clarify changes in the trabecular structure due to loss of the teeth, the author compared soft X-ray images and morphological measurement values of the mandibular condyle and articular eminence between dentulous and edentulous specimens. The center of the skull base containing the temporomandibular joint was removed along the Frankfort horizontal and median sagittal planes. A block in the center of the cranial base was rejected using the Frankfort horizontal plane and median sagittal plane as references. The specimens were embedded in polyester resin by the routine method. The hardened specimens were horizontally cut into 500 microns sections and photographed using soft X-ray films. Soft X-ray of each section was taken for observation by naked eye and morphometry by computer. Observation of the compact bone in the articular eminence showed thinner compact bone on the posterior slope of the articular eminence, which is a functional plane, than on the anterior slope of the articular eminence. There was a trabecular bone group on the lateral area running from the compact bone on the posterior surface of the articular eminence into the zygomatic arch and a thick trabecular bone group in a network pattern on the medial area. In the central area of the mandibular condyle, spongy bone was surrounded by oval compact bone, and the internal trabecular bone ran anteromedially in nearly the same pattern as the arrangement of the lateral pterygoid muscle. At all sites, the density, width, extent, and index indicating the complexity of the trabecular bone had higher values in dentulous specimens than in edentulous specimens.