Effects of parathyroid hormone on odontogenesis of the mouse embryonic molar tooth in vitro.

Mandibular first molars of 17-day-old mouse embryos were cultured in vitro to examine the histological effects of various concentrations of parathyroid hormone (PTH) on odontogenesis of the molars. PTH did not affect the cytodifferentiation of mesenchymal cells into preodontoblasts but inhibited that of preodontoblasts into odontoblasts. Consequently, the odontoblasts failed to undergo dentinogenesis. On the other hand, inner enamel epithelium achieved terminal cytodifferentiation into secretory ameloblasts and these cells partially formed enamel in spite of the absence of dentin. All treated molars showed the same histological disturbances and these effects were independent of PTH dose. The present study indicated that PTH had an influence on mesenchyme-derived cells, inhibiting both the differentiation of odontoblasts and the formation of predentin and dentin.