Changing expression of intermediate filaments in fibroblasts and cementoblasts of the developing periodontal ligament of the rat molar tooth.

The distributing of vimentin and cytokeratin intermediate filaments within the cells of the dental follicle and developing periodontal ligament is described during eruption of the rat 1st molar tooth. Alcohol-fixed tissues from animals ranging from neonates to 12 wk old were cryosectioned, immunolabelled with monoclonal antibodies against vimentin and a range of cytokeratins and examined by indirect immunofluorescence. Vimentin was observed in follicular and periodontal ligament fibroblasts in all animals and at all stages of eruption. It was also observed in cementoblasts after disruption of the epithelial root sheath (of Hertwig) which is responsible for determining the shape of the developing root. Prior to eruption, cytokeratins were restricted to epithelial components of the developing tooth, including the root sheath. However, they were seen in cementoblasts on disruption of the root sheath at 2 wk and in periodontal ligament fibroblasts at 3 wk after birth, when the tooth was erupting but had not reached occlusion. On occlusion (at 4 wk), fibroblasts no longer labelled for cytokeratins but cementoblasts associated with acellular cementum formation continued to express them. These results demonstrate temporal and spatial changes within the cells of the developing periodontal connective tissues and suggest that the appearance of cytokeratins in periodontal fibroblasts and cementoblasts may be related to mechanical changes during tooth eruption. Further, the results suggest different origins for cementoblasts associated with cellular and acellular cementum formation.