Objective: This study was designed to investigate root development of a rat tooth germ implanted in a tooth socket or in a subcutaneous region. Materials and methods: Tooth germs of the upper left first molars in 2-week-old rats were extracted and implanted in the original tooth socket or in the subcutaneous region of the back. The upper right first molar was used as a control. The rats were fixed in weeks 1, 2, 4, 8 and 12. The root development was examined quantitatively with X-ray radiographic morphometry. The cellular activity of producing matrix proteins was assessed using in situ hybridization for type I collagen. Results: Root development was observed in the implanted teeth in the tooth socket as also in the control teeth. In contrast, roots hardly developed in subcutaneously implanted teeth. Histology showed that periodontal ligaments were arranged around roots of implanted teeth in the tooth socket as around control teeth, but few periodontal ligaments were identified in the subcutaneous implantation. Dentin and cementum formed in both the implanted teeth as also in the control teeth and odontoblasts, cementoblasts and cementocytes expressed type I collagen. Conclusion: Tooth sockets may possess specific environments that allow root development of a tooth germ.
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