Development of periodontal ligament and alveolar bone in homografted recombinations of enamel organs and papillary, pulpal and follicular mesenchyme in the mouse.

Mandibular first-molar tooth germs were dissected from 16-day-embryo and new-born CD1 mice. By incubation in collagenase they were separated into enamel organ, papilla and follicle. Dental pulp was obtained from mandibular first molars of 3-, 7- and 10-day-old mice. Various combinations of epithelial and mesenchymal tissues were grown for periods up to four weeks in the anterior chamber of the eye of homologous adult male mice. Recombinations of enamel organ and papilla formed teeth with regeneration of the investing layer of follicle and a root-related periodontal ligament, but no formation of alveolar bone. Bone only formed in those grafts which also included follicle. Recombinations of enamel organ and pulp produced dysplastic dentine with no enamel formation or proper tooth development. It was impossible, therefore, to assess whether the potential to regenerate an investing layer extends to the pulp later in development. At an earlier stage, however, the papillary mesenchyme has the ability to regenerate investing-layer cells which lack the capacity to form bone.