Development of mouse embryonic molars in vitro: an attempt to design defined culture conditions allowing mineralization.

Mandibular first molars from 17 day old mouse embryos were cultivated in vitro for 14 days in BGJb-medium supplemented with 20% horse serum and 10% chick embryo extract or in BGJb containing various compounds suggested to have a role in biological mineralization. The incubation atmosphere consisted either of 5% CO2 in air or 50% O2, 45% N2 and 5% CO2. Histologically, explants grown in serum-supplemented medium frequently showed dentin mineralization, the frequency being highest, 90%, in high oxygen partial pressure. In medium without serum, only two out of 43 explants which were cultured in BGJb containing 5 mM Na-beta-glycerophosphate, formed mineralized dentin. The amounts of DNA and calcium, and the activity of alkaline phosphatase in explants after culture showed no direct correlation to mineralization potential. Calcified dentin was always confined to one or two clearly demarcated areas, which were intensely stained by the von Kossa method. It appears that mineralization continues readily when it has started and that it is the initiation of mineralization that is the critical threshold and depends on serum factors.