Confocal microscopy of cementocytes and their lacunae and canaliculi in rat molars

The present study was designed to analyze the morphological characteristics of cementocytes and osteocytes. The maxillae of 10-week-old Wistar rats were used for observations. Non-decalcified ground sections stained vitally with fluorescence dyes and decalcified frozen sections stained with FITC-phalloidin were examined by confocal microscopy. Calcein and alizarin red stained the calcification front of bone, cementum, and dentin intensely. In addition, lacunae and canaliculi of cementocytes and osteocytes as well as dentinal canals were stained with the fluorescent dyes. The staining of lacunae and canaliculi was less intense than that of the calcification front of bone, cementum and dentin. The canaliculi of cementocytes and osteocytes were connected with the canaliculi extending from the calcification front of cementum and bone, respectively. The canalicular density was less in the cellular cementum than in the bone. Areas devoid of canaliculi were numerous in the cellular cementum, whereas areas devoid of canaliculi were scarce in the alveolar bone. Further, the lacunae of cementocytes showed various shapes, from oval to tubular, while the lacunae of osteocytes were invariably oval. The cell body and the cytoplasmic processes of cementocytes were positive for FITC-phalloidin within the extracellular matrix of cellular cementum, which was negative. The distribution of actin filaments in the osteocytes and the cementocytes was predominantly cortical and appeared to be closely associated with the cell membrane of the cell bodies and the cytoplasmic processes. Intense staining was seen at the proximal part of the cytoplasmic processes in both osteocytes and cementocytes, showing a punctuated structure of the cells that was more frequent in osteocytes than in cementocytes. The stress fiber known to be present in most of the cultured cells was not evident in the these cells in situ. The cells incorporated in the cementodentinal junction were strongly stained with FITC-phalloidin. The distribution pattern of the cytoplasmic processes stained with FITC-phalloidin was similar to that of the canaliculli stained vitally. The cytoplasmic processes of osteocytes and cementocytes were connected with those of cells lining the surface of bone and cementum. The present result-that lacunae and canaliculi of cementocytes were stained vitally with the fluorescence dyes-suggests that cementocytes may have a role in secondary calcification of cellular cementum. Further, the lower density of cytoplasmic processes in cementocytes than in osteocytes suggests a lack of complexity in the intercellular network within the cellular cementum.