Objective To observe the relapse ratio of interparietal s agittal suture after removing the expansion device in rats. Methods
32 10-week old SD rats were divided into 4 groups, 8 rats each. They were one normal control group, one
expansion control group, and two other group s that were covered with atelo-typeⅠcollagen and recombinant human bone morpho genetic protein (rhBMP)-2 collagen composite on the suture before subjected to the expansion force. The distance between the two holes of the interparietal sut ure bone was calculated on days 0, 21 and 28, then the relapse ratio was evaluat ed. At the same time the bone mineral density of the sagittal suture was also me asured with the dual X-ray absorptiometry (DEXA). Results There were no significant difference among the distance between the two holes in the expanded groups (P>0.05), but the distance of the expanded groups we re bigger than that of the normal control group on the 21st day. The distance of
rhBMP-2 collagen composite group was the biggest among the expanded group on da y 28 ( P<0.05) , the distance of all three expanded groups were still big ger than that of normal control group (P<0.01). The relapse ratio was (53.2 5±8.80) %, (51.98±5.55) %, and (2.50±0.71) % in the expansion group, pure c ollagen membrane group and rhBMP-2 collagen composite groups, respectively. Th ere was a significant difference among the rhBMP-2/collagen composite group and the other two groups (P<0.01). We failed to find any difference of the bo ne mineral density (BMD) in the normal control group among the three time points (P>0.05). The BMD decreased on the 21st day although there was slightly in crease on day 28, but the BMD was still less than that of day 0 both in the expa nsion control group and the pure collagen membrane group. The BMD in the rhBMP- 2 collagen composite group increased on the 21st day and was higher than that of day 0 (P< 0.01 ), on the 28th day, the BMD got an sustained increase .Conclusion The DEXA can be used to measure the regenerative bo ne quantitatively during suture expansion and to monitor the process of bone reg eneration. RhBMP-2 collagen composite may be of therapeutic benefit in decreas ing relapse ratio after suture expansion.