Bone regeneration with BMP-2 and hydroxyapatite in critical-size calvarial defects in rats

This study describes the effect of bone formation by BMP-2 (bone morphogenetic protein-2), a bone formation inducer, with or without hydroxyapatite (HAP) application to critical-size defects in rat calvarial bone.

Twenty male Wistar rats were divided into four groups of 5 animals each: control, HAP, BMP, and mixed BMP/HAP. A Critical-size defect of 4mm was made using a trephine in the calvarial bone and, after that, BMP and/or HAP was applied to the defect according to the grouping. Defects were evaluated radiographically and histologically using ImageJ color analyzer software at 4 weeks postoperatively.

The histological data were more precise than the radiologic data due to the white color of the porous-type HAP material. The highest radiopacity was noted in the mixed BMP/HAP group (162.07±9.06), followed by the HAP group (133.15±21.8), then the BMP group (100.79±8.27), and, lastly, the control group (54.45±8.39). After subtracting the white background and using ImageJ for histological analysis, the highest rate of osteochondrogenesis was in the mixed BMP/HAP group (85.29%±8.21), and then the BMP group (77.34%±7.39), followed by the HAP group (59.82%±11.23), and, lastly, the control group (40.27%±7.44). Differences in the values between groups were then analyzed using confidence intervals (CI) of 95 and 99%.

Within 4 weeks, the mixed BMP/HAP group showed the highest level of bone induction, especially compared to the BMP group, but this was non-significant; even with a 95% CI, the result was negative. This reveals that BMP alone can be applied, with a final result the same as that seen in the mixed BMP/HAP group. BMP and HAP, both being osteoinducting agents, even though they differ from a material classification point of view, have a positive effect on osteogenesis.