Bone wound healing after maxillary molar extraction in ovariectomized aged rats

We studied bone wound healing processes after maxillary molar extraction in ovariectomized (OVX) aged rats, as an experimental model of postmenopausal osteoporosis, by means of scanning electron microscopy. Six-month-old female rats were either sham-operated or bilaterally OVX; and at 60 days postoperatively, the maxillary first molars were extracted. On postextraction days 4, 7, 30 and 60, the dissected maxillae were fixed and the alveolar bone surfaces around the extracted alveolar sockets were examined. In sham-operated controls, new bone formation was recognized on the buccal-side bone surfaces on day 4 and then increased in extent daily through day 60 mainly on the buccal and mesial sides. On day 60, the extracted sockets were filled with new bone mass and the surrounding alveolar bone surfaces had become smooth, indicating decreased bone metabolism. Bone resorption was prominent throughout the bone surfaces around and within the extracted sockets, increased in extent through day 7, but had decreased by day 60. In comparison to sham-operated controls, new bone formation in OVX rats was slightly increased in the early phase but subsequently showed a marked decrease. Bone resorption in OVX rats was greatly stimulated and was comparatively long-lasting. These results suggest that, under the present experimental conditions, in bone wound healing after maxillary molar extraction, (i) ovariectomy stimulates sustained bone resorption and (ii) bone formation and resorption both take place at specific sites on alveolar bone surfaces.