No developmental failure of cultured tooth germs from osteopetrotic (op/op) mice

Background: Incisor tooth germs of osteopetrotic (op/op ) mice are known to fail to erupt, but form odontomas in their root apices instead, due to invasion of alveolar bone trabeculae into the tooth germs. The purpose of this study is to determine if the tooth developmental failures in op/op mice are intrinsic or secondarily arise as a result of the defective bone metabolism due to lack of macrophage colony-stimulating factor (M-CSF). Methods: We isolated mandibular first molar tooth germs from normal and op/op mice and cultured them under conditions with or without bone tissues which had been formed around tooth germs. Results: Tooth germs from normal mice, cultured for a week, showed almost the same developmental features as those of mice with the corresponding age. They were surrounded with dental follicular tissues and were never invaded by bone trabeculae. On the other hand, op/op tooth germs cultured in the presence of bone components were invaded by alveolar bone trabeculae around tooth germs in the same manner as shown in vivo . When cultured without bone, they developed without any interruptions. Conclusions: These findings indicated that op/op tooth germs had potential for normal development and that their abnormal development was a secondary phenomenon caused by lack of bone remodeling in the early phase of odontogenesis.