Quantitative expression of bone-related cytokines induced by mechanical tension-stress during distraction osteogenesis in a rabbit mandible.

AIM: The aim of the present study was to investigate the temporal and spatial gene expression of bone morphogenetic proteins (BMP)-2, -4, and -7, and transforming growth factor-β (TGF-β), during the distraction process of the rabbit mandible.

METHODS: Twenty rabbits each had an osteotomy on the left mandibular body, and distraction devices were fixed. After a delay of 3 days, distraction was started at a rate of 0.5 mm/12 h for 10 days, followed by a 3-week consolidation phase. Four rabbits were killed 5 and 10 days of distraction, and 1, 2, and 3 weeks after the completion of distraction. The clinical, histological, and radiographic appearances were evaluated and analyzed with the concomitant BMP expression pattern at each interval.

RESULTS: After the distraction was started, the fibrous interzone developed between the osteotomy fragments, where intramembranous ossification was noted. The quantitative expression of BMP-2, -4, and -7, and TGF-β, were increased immediately after active distraction before a gradual decline to normal levels after the third week of consolidation.

CONCLUSION: These results suggest that BMP and TGF-β play an important role in the induction of bone formation during distraction osteogenesis. The selective expression of each bone-related cytokine could provide useful insight into accelerated bone maturation and the treatment of poorly-healing fractures in clinical cases.