Early cellular events of osteomucosal healing in the tooth extraction socket.

Healing after dentoalveolar trauma, such as tooth extraction, is unique to the oral cavity that involves osteomucosal healing - healing of soft and hard tissues at the same time - through a series of healing stages. The healing process of soft or hard tissues is well-documented previously; however, inter-dependency and cross-talks during the progression of their simultaneous healing processes remain unclear. In this study, we investigated spatial and temporal changes of epithelial, connective, and bone tissues, as well as the presence of osteoclasts, during the early stages of osteomucosal healing. We extracted the maxillary first molars in mice and examined the osteomucosal healing process daily for 7 days using histology, immunohistochemistry, and micro-computed tomography (microCT). Epithelial tissues closed progressively throughout 7 days. Collagen deposition began in the extraction sockets as early as day 2, forming a scaffold essential for both epithelial tissue closure and bone formation. Osteoclasts appeared on day 2, steadily increasing until day 5 and remained around the socket walls but not within the sockets. Woven bone formed rapidly around day 5, with significant mineralization observed by day 7. Notably, we identified elevated expression of RANKL throughout the process and a sharp increase in OPG near new bone on day 6. These findings demonstrated the sequential and coordinated mechanisms underlying early osteomucosal healing and provide novel insights into the critical early steps required for proper healing in the oral cavity.