Objective: The objective of the investigation was to observe the degree of apoptosis in the osteoblast, pre-osteoblast and osteoprogenitor populations in the rat tooth socket at various intervals after extraction.

Methods: With ethical committee approval, the upper right maxillary first molar of 7 mature rats was removed under general anesthesia. The rats were given a soft diet and killed at days 3, 5, 7, 10, 14, 21, and 28 after extraction. The cranio-maxillary tissues were processed for wax embedding. 5µm thick sections were prepared and stained using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end-labeling method (TUNEL).

Results: Maximum staining in the socket and periosteal region of the facial alveolar bone occurred at 5, 7 and 10 days after extraction, which corresponds to the onset of woven bone formation. During this time interval, TUNEL-positive staining was seen in the osteoprogenitor and pre-osteoblast populations and especially strongly in the osteocytes of the woven bone. Staining was generally absent from osteoblasts, contradicting previous in-vitro studies. At the later time points, days 21 and 28 after extraction, TUNEL-staining was present only in some marrow cells and outer layers of the periosteum.

Conclusions: Cell death was most evident in the osteoprogenitor cells during active bone formation in the extraction socket and in osteocytes in the woven bone prior to secondary remodeling

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