Transmission and scanning electron microscopic analysis of mineralized loci formed by human periodontal ligament cells in vitro.

Fibroblasts isolated from human periodontal ligament (PDL) were cultured under a medium supplemented with ascorbic acid, beta-glycerophosphate and dexamethasone. The cultures were assessed for their ability to elaborate a mineralized matrix. Cell cultures stained positive when analyzed for alkaline phosphatase activity throughout the culture period. After about 3 weeks in culture, the cells produced a calcified matrix. Light microscopy showed formation of clusters of different shapes and sizes. Von Kossa staining revealed mineral deposits as amorphous brown-black precipitates. Transmission electron microscopy showed cells in multilayers and mineralized formations in close association with a dense network of collagen fibers. Scanning electron microscopy revealed smooth formations rising over the cultures with an abundant fiber matrix. We conclude that human PDL fibroblasts can be induced to form a mineralized matrix which shares features with bone mineralized matrix but most likely represents a more immature type of in vitro mineralization. Moreover, the present study further supports the osteoblastic potential of these cells.