| Purpose:The purpose of this study was to investigate the effects of exogenous rhBMP-2 on the new bone regeneration of the interparietal sagittal suture in the rats after rapid expansion, and to observe the relapse ratio of the interparietal sagittal suture after removing the expansion device.Methods:36 10-week old SD rats were divided into 4 groups consisting of 9 rats each. They were comprised of one normal control group and three expansion groups. All expansion groups were subjected to an initial force of 100g exerted by open coil spring. In two of the three groups expansion groups, a piece of absorbable atelo-type I collagen membrane or a piece of rhBMP-2/collagen membrane composite was simultaneously covered under the sagittal suture of the rat, the pure expansion control group only an initial force of lOOg was given. Each rat in the normal control group wasn't given any intervention. The expansion device was removed on the 21st day, and the animal was sacrificed on the 28th day. The distance between the two holes of the interparietal bone was calculated on days 0, 21 and 28. At the same time, the bone mineral density of the sagittal suture was also measured with the dual energy X-ray absorptiometry (DEXA) after the animal was anesthetized on the corresponding day. The amount of relapse was evaluated in terms of relapse ratio. The interparietal bone was resected completely and X-ray examination was taken with a dental X-ray unit after the animals were sacrificed. The bone regeneration in the sagittal suture was estimated by histological method, the osteocalcin content was measured by radioimmunoassay and the calcium content was measured by atomic absorption spectrophotometer.Results:(1) The distance between the two holes of the rat interparietal bones: There was no significant difference among the expanded groups (P>0.05), but the distance of the rats in the expanded groups' were bigger than that of the normal control group's on the 21st day. The distance of the rats in the rhBMP-2/collagen membrane composite group were the biggest among the expanded groups on day 28 (P<0.05), the distance of the rats in all the three expanded groups were still bigger than that of the normal control group's (P<0.01). (2) X-ray examination: The roentgenography showed a "thread-like" transparent zone in the sagittal suture area of the rats in the normal control group; the translucent zone in the sagittal suture area of the rats were widened in both the expansion control group and the pure collagen membrane group; there was radiopacit vaguely in the sagittal suture area of the rat in the rhBMP-2/collagen membrane composite group instead of a transparent zone. (3) The bone regeneration was more active in the suture after an expanding force was given. Even bone bridge could be formed in the rats of the rhBMP-2/collagen membrane composite group. (4) The calcium content was 92.01 ± 14.76μg/mg, the osteocalcin content was 87.56 ± 8.65ng/mg in the rhBMP-2/collagen membrane composite group on the 28th day, both of them were much higher than that of other three groups (P<0.01). (5) Bone mineral density: There failed to find any difference of the BMD in the normal control group among the three different time points (P>0.05). The BMD decreased on the 21st day and was less than the BMD of 0 day (P<0.01), although there was slightly increase on day 28,but the BMD was still less than that of 0 day both in the expansion control group and the pure collagen membrane group. The BMD in the rhBMP-2/collagen membrane composite group increased on the 21st day, and was higher than that of 0 day (P<0.01), on the 28th day, the BMD got a sustained increase, but there hadn't any difference as compared with the BMD on day 21 (P>0.05). (6) The relapse ratio: The relapse ratio was 53.25 % ± 8.80% in the expansion control group and 51.98 % ±5.55 % in the pure collagen membrane group, the ratio was 2.50%±0.71% in the rhBMP-2/collagen membrane composite group. There was a significant differenceamong the rhBMP-2/collagen... |
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