Comparative Analysis of Bone Regeneration According to Particle Type and Barrier Membrane for Octacalcium Phosphate Grafted into Rabbit Calvarial Defects

Abstract

This animal study was aimed to evaluate the efficacy of new bone formation and volume maintenance according to the particle type and the collagen membrane function for grafted octacalcium phosphate (OCP) in rabbit calvarial defects. The synthetic bone substitutes were prepared in powder form with 90% OCP and granular form with 76% OCP, respectively. The calvarial defects were divided into four groups according to the particle type and the membrane application. All specimens were acquired 2 weeks (n = 5) and 8 weeks (n = 5) after surgery. According to the micro-CT results, the new bone volume increased at 2 weeks in the 76% OCP groups compared to the 90% OCP groups, and the bone volume ratio was significantly lower in the 90% OCP group after 2 weeks. The histomorphometric analysis results indicated that the new bone area and its ratio in all experimental groups were increased at 8 weeks except for the group with 90% OCP without a membrane. Furthermore, the residual bone graft area and its ratio in the 90% OCP groups were decreased at 8 weeks. In conclusion, all types of OCP could be applied as biocompatible bone graft materials regardless of its density and membrane application. Neither the OCP concentration nor the membrane application had a significant effect on new bone formation in the defect area, but the higher the OCP concentration, the less graft volume maintenance was needed.

Keywords: bone regeneration; collagen membrane; concentration; octacalcium phosphate.

Figure 1

Schematic diagram of this study.

Figure 2

Surgical procedure. (A) Four circular defects measuring 8 mm in diameter were created using a trephine bur. (B) The defects were allocated to the four study groups. Clockwise from bottom to left: 90% OCP with a membrane (90m), 90% OCP without a membrane (90n), 76% OCP without a membrane (76n), 76% OCP with a membrane (76m).

Figure 3

(A) The XRD spectra of the OCP powder (top) and granules (bottom). The OCP peaks are indicated by asterisks (*). (B) Representative high- and low-magnification FE-SEM images of the OCP power and granule.

Figure 4

Micro-CT images obtained 2 and 8 weeks after surgery. New bone formation occurred mainly around the periphery of defect, and significantly increased at 8 weeks compared to 2 weeks in all groups. The red circle represents the border of the defect, and the red arrow indicates the direction of presumed new bone formation. (A,E) 76% OCP with a membrane group; (B,F) 76% OCP without a membrane group; (C,G) 90% OCP with a membrane group; (D,H) 90% OCP without a membrane group; (right top and down) three-dimensional reconstruction images.

Figure 5

Distribution of experimental groups and statistical significance within groups according to micro-CT analysis results. Small and capital letters of the same alphabet indicate significant differences between 2-week and 8-week results compared in the same experimental group. Even though there is no significant difference, if a distinction is needed, a prime mark is used next to the letter. The asterisk * indicates statistical significance. (A) Total tissue volume, (B) new bone volume, (C) bone volume ration.

Figure 6

Representative histological images of each experimental groups after 2 or 8 weeks. (HE stain, bar = 1 mm) At 2 weeks, the new bone formation was observed around the grafted particles in the adjacent margin of the defect (blue arrows). At 8 weeks, however, new bone was observed not only growing from the marginal area but also around the centrally located remaining particles (green arrows). The border of the defect is indicated by black dotted lines, and the direction of new bone formation is indicated by black arrows.

Figure 7

Distribution of experimental groups and statistical significance within groups according to histomorphometric analysis results. Small and capital letters of the same alphabet indicate significant differences between 2-week and 8-week results compared in the same experimental group. Even though there is no significant difference, if a distinction is needed, a prime mark is used next to the letter. The asterisk indicates statistical significance. (A) Total augmented area, (B) new bone area, (C) residual bone graft area.