Effect of carbonate apatite as a bone substitute on oral mucosal healing in a rat extraction socket: in vitro and in vivo analyses using carbonate apatite

BACKGROUND: Low bone quantity and quality are serious problems that affect the prognosis of implants in the cosmetic field. Therefore, artificial bone substitutes are frequently used. However, whether there is a difference in the effect of either bone substitute on soft tissue healing is unclear given their greatly different absorbability. In this study, we used hydroxyapatite (HAp) and carbonate apatite (CO(3)Ap) as bone substitutes to analyze the epithelial and connective tissue healing after tooth extraction. METHODS: In vitro, oral mucosa-derived epithelial cells (OECs) collected from 4-day-old Wistar rats were seeded on HAp or CO(3)Ap and evaluated for adhesion, proliferation, migration, apoptosis, and morphology. Fibroblasts (FBs) were also analyzed for their ability to express collagen. In vivo, the extraction of maxillary right first (M1) and second molars (M2) of 6-week-old male Wistar rats was performed, followed by insertion of HAp or CO(3)Ap granules into the M1 and M2 sites. The oral mucosal healing process was then evaluated histochemically after 7 and 14 days. RESULTS: In vitro, high collagen expression by FBs in the CO(3)Ap group was observed and the surface analysis showed spreading of the FBs on the CO(3)Ap surface. However, the activity of OECs was suppressed on CO(3)Ap. Two weeks after CO(3)Ap implantation, soft tissue healing was observed, and recovery of the connective tissue was observed on the remaining CO(3)Ap. CONCLUSIONS: Our results suggest that the formation of soft tissues, including connective tissue, was promoted by CO(3)Ap in the extraction socket within a short period.