Odontoblast differentiation of human dental pulp cells in explant cultures

In order to elucidate the mechanisms involved in human dentin formation, we developed a cell culture system to promote differentiation of dental pulp cells into odontoblasts. Explants from human teeth were cultured in Eagle's basal medium supplemented with 10% or 15% fetal calf serum, with or withou t beta-glycerophosphate (beta GP). Addition of beta GP to the culture mediu m induced odontoblast features in the cultured pulp cells. Cells polarized and some of them exhibited a typical cellular extension. In some cases, cel ls aligned with their processes oriented in the same direction and develope d junctional complexes similar to the terminal web linking odontoblasts in vivo. Fine structural analyses showed the presence of typical intracellular organelles of the odontoblast body, whereas the process contained only cyt oskeleton elements and secretory vesicles. Polarized cells deposited onto t he plastic dishes an abundant and organized type I collagen-rich matrix wit h areas of mineralization appearing thereafter. X-ray microanalysis showed the presence of calcium and phosphorus and the electron diffraction pattern confirmed the apatitic crystal structure of the mineral. High expression o f alpha 1(1) collagen mRNAs was detected in all polarized cells whereas den tin sialoprotein gene was mainly expressed in mineralizing areas. This cell culture system allowed for the differentiation of pulp cells into odontobl asts, at both the morphological and functional level. Moreover, these cells presented a spatial organization similar to the odontoblastic layer.