Immunolocalization of osteopontin, osteocalcin, and dentin sialoprotein during dental root formation and early cementogenesis in the rat.

Using immunohistochemical methods we studied the tissue localization of the extracellular matrix proteins osteopontin (OPN), osteocalcin (OC), and dentin sialoprotein (DSP) during the formation of acellular and cellular cementum in newly born rats. In the layer of acellular cementum of developing incisor and molar teeth we found a very strong staining for OPN but not for DSP or OC. Many cells immediately adjacent to acellular cementum and PDL cells were also positive for OPN but not for DSP or for OC. In contrast, cellular cementum in molar teeth stained strongly for OPN and OC but not for DSP. Consistent with these observations, the cells engaged in the formation of cellular cementum (cementoblasts and cementocytes) reacted strongly for OPN and OC but not for DSP. In advanced stages of dentinogenesis, both crown and root odontoblasts and dentin stained for OPN, OC, and DSP. Cells and matrices of surrounding alveolar bone stained for OPN and OC but not for DSP. We conclude that cementoblasts and cementocytes of cellular cementum produce OPN and OC but not DSP and thus express an osteoblast-like, not an odontoblast-like, phenotype. The cells responsible for the production of acellular cementum are likely cells of the PDL in close contact with the dental root surface. These fibroblast-like cells express OPN but not OC or DSP and accordingly express only a partial osteoblastic phenotype.