CONFOCAL MICROSCOPY OF CEMENTOCYTES AND THEIR LACUNAE AND CANALICULI IN RAT MOLARS

The present study was designed to analyze the morphological characteri stics of cementocytes and osteocytes. The maxillae of 10-week-old Wist ar rats were used for observations. Non-decalcified ground sections st ained vitally with fluorescence dyes and decalcified frozen sections s tained with FITC-phalloidin were examined by confocal microscopy. Calc ein and alizarin red stained the calcification front of bone, cementum , and dentin intensely. In addition, lacunae and canaliculi of cemento cytes and osteocytes as well as dentinal canals were stained with the fluorescent dyes. The staining of lacunae and canaliculi was less inte nse 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 bon e, respectively. The canalicular density was less in the cellular ceme ntum 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 in variably oval. The cell body and the cytoplasmic processes of cementoc ytes were positive for FITC-phalloidin within the extracellular matrix of cellular cementum, which was negative. The distribution of actin f ilaments in the osteocytes and the cementocytes was predominantly cort ical and appeared to be closely associated with the cell membrane of t he cell bodies and the cytoplasmic processes. Intense staining was see n at the proximal part of the cytoplasmic processes in both osteocytes and cementocytes, showing a punctuated structure of the cells that wa s more frequent in osteocytes than in cementocytes. The stress fiber k nown to be present in most of the cultured cells was not evident in th e these cells in situ. The cells incorporated in the cementodentinal j unction were strongly stained with FITC-phalloidin. The distribution p attern of the cytoplasmic processes stained with FITC-phalloidin was s imilar to that of the canaliculli stained vitally. The cytoplasmic pro cesses of osteocytes and cementocytes were connected with those of cel ls lining the surface of bone and cementum. The present result - that lacunae and canaliculi of cementocytes were stained vitally with the f luorescence dyes - suggests that cementocytes may have a role in secon dary calcification of cellular cementum. Further, the lower density of cytoplasmic processes in cementocytes than in osteocytes suggests a l ack of complexity in the intercellular network within the cellular cem entum.