The structure and function of periodontal ligament cells in acellular cementum in rat molars.

To elucidate the structure and function of periodontal ligament cells at the periodontal ligament-cementum interface in advanced acellular cementogenesis, the cervical regions of molars in rats aged 6 weeks were observed by light and electron microscopy. The light and transmission electron microscopy showed the periodontal ligament cells to be elongated between dense, well-developed principal fibers. The transmission and scanning electron microscopy showed that these cells extended wing-like projections from the lateral surface, forming cylindrical compartments surrounding the principal fibers. In addition, finger-like projections extended toward the cementum from the cementum-facing ends. The main results suggest the following: at the periodontal ligament-cementum interface, the periodontal ligament cells maintain the architecture of the principal fibers by means of extracellular compartments. The arrangement of finger-like projections results in the formation of acellular cementum containing only Sharpey's fibers as a fibrous component.