Sequential histomorphometric analysis of regenerate osteogenesis following mandibular distraction in the rat

Few studies of distraction osteogenesis in the craniofacial region have examined the dynamic nature of the bone healing process. This study investigated bone formation in distraction sites at various times following slow, moderate, and rapid rates of mandibular distraction in adult rats. After a 3-day latency period, 16 groups of 8-9 rats underwent unilateral mandibular distraction for 5 days at four different rates (0, 0.2, 0.4, and 0.6 mm/day) and were sacrificed at four different time points (6, 10, 24, and 38 days). Vital bone labels were injected prior to sacrifice and histological sections were examined under epifluorescence to measure mineral apposition rate (MAR) and the number of red and green pixels that corresponded to the wavelengths of the two bone labels. These pixel counts were designed to quantify the amount of fluorescent bone formation. For MAR and the pixel counts, no significant differences were found between the distraction rate groups. Over time, MAR was significantly higher (p < 0.001) at 24 days (4.50 microm/day) compared to 38 days (3.78 microm/day). Thus, MAR appears to be elevated at mid-consolidation compared to late consolidation. The pixel counts showed that the 6-day (mid-distraction) and 10-day (early consolidation) time points had significantly lower total fluorescent activity compared to the 24-day (mid-consolidation) and 38-day (late consolidation) time points (p < 0.001). The red, green, and red + green pixel counts were found to correlate significantly but weakly with microdensity (r = 0.318, 0.307, and 0.334, respectively). The pixel counts and microdensity both showed similar patterns over time.