All experimental sites healed uneventfully, and were maintained without complications such as infection and wound dehiscence during the entire study period. At sacrifice, it could be seen that all of the BCP blocks remained within the grafted site.
Micro-CT volumetric analysis (Fig. 5, Fig. 6, Fig. 7, Table 1)
At 2 weeks, the BCP block groups exhibited a significantly greater NBV (mean [± SD] of 16.76 [± 3.36], 15.06 [± 2.77] and 16.02 [± 3.61] mm3 for 0.8, 1.0 and 1.2 groups, respectively) compared to the control group (6.56 [± 3.53] mm3) (p < 0.05) (Table 1). However, there were no significant differences between the BCP block groups. Regarding the TAV, all BCP block groups (161.86 [± 8.06], 177.21 [± 26.96], and 177.35 [± 18.40] mm3 for 0.8, 1.0 and 1.2 groups, respectively) were significantly larger than the control group (p < 0.05). However, there was no significant difference between the BCP groups (p > 0.05). The 0.8 group showed a significantly greater RMV (67.89 [± 5.75] mm3) compared to the 1.0 group (28.24 [± 3.65] mm3) and 1.2 group (31.19 [± 1.24] mm3) (p < 0.05).
At 8 weeks, the mean [± SD] NBV was the greatest in the 1.0 group (35.81 [± 5.73mm3], followed by 1.2 group (34.10 [± 5.91] mm3), 0.8 group (32.02 [± 3.41] mm3), and the control group (24.11 [± 1.79] mm3). All BCP block groups showed significantly greater NBV compared to the control group, however, there was no statistically significant difference between the BCP groups. There were no significant differences in TAV between the BCP groups. Only the 1.2 group and the 0.8 group (190.33 [± 16.60] mm3 and 189.91 [± 24.60] mm3, respectively) exhibited significantly greater TAV compared to the control group (151.68 [± 16.94] mm3). The 0.8 group (70.53 [± 5.52] mm3) exhibited significantly greater RMV compared to the 1.0 group (33.78 [± 2.68] mm3) and 1.2 group (34.69 [± 3.09] mm3).
When the 2- and 8-week groups were compared, all groups in the 8-week group had significantly greater NBV than their corresponding 2-week group. TAV showed no significant difference between 2 and 8 weeks.
Histomorphometric analysis (Fig. 8, Fig. 9, Table 2)
At 2 weeks, all BCP block groups exhibited significantly greater NBA (mean[± SD] of 0.30 [± 0.17], 0.38[± 0.38], 0.39[± 0.19] mm2 for 0.8, 1.0 and 1.2 groups, respectively) compared to the control group (0.09[± 0.06]mm2) (p < 0.05) (Table 2). However, there was no significant difference between the BCP groups. TAA was also significantly greater in all BCP block groups (15.74[± 1.95], 15.88[± 1.00], 16.83[± 1.24] mm2 for 0.8, 1.0, 1.2 groups, respectively) compared to the control group (6.13[± 1.13] mm2) (p = 0.008 < 0.05). RMA was greatest in the 0.8 group (9.61[± 2.14]mm2), but there was no statistically significant difference.
At 8 weeks, only the 1.0 group (3.42[± 0.48]mm2) showed a significantly greater NBA than the control group (2.26[± 0.59]) (p = 0.03 < 0.05). Between the BCP block groups, 1.0 and 1.2 groups exhibited significantly greater NBA compared to the 0.8 group. TAA was significantly larger in all BCP block groups (16.52[± 0.84], 15.85[± 1.04], 15.88[± 1.29] mm2 for 0.8, 1.0, 1.2 groups, respectively) compared to the control group (5.78[± 1.10] mm2) (p < 0.05). However, there was no significant difference between the BCP groups. In terms of the RMA, the 0.8 group (11.57[± 0.81]mm2) was statistically significantly larger than the 1.0 group (5.24[± 0.14], p = .0.016 < 0.05) and 1.2 group (4.70[± 0.59], p = 0.008 < 0.05).
When the 2- and 8-week groups were compared, all groups in the 8-week group had significantly greater NBV than their corresponding 2-week group Compared with the 2-week groups, all BCP blocks at the 8-weeks showed a statistically significantly larger RMA (p < 0.05).
An example of histologic analysis results for each group at each time period was shown in Fig. 7.
At 2 weeks, the defect was partially filled with connective tissue and the center of the defect was sunk down with reduced total volume. New bone formation started from the adjacent native bone at the periphery of the defect.
At 8 weeks, none of the defects were fully filled with new bone, and some bony islands and bone bridge was observed.
0.8mm pore size group
At 2-weeks, the volume and shape of the defect were maintained by the BCP block and completely encapsulated with fibro-vascular tissue. The formation of new blood vessels for bone regeneration was observed and the initial bone regeneration started from periphery of the calvarial defect.
At 8-weeks, BCP block remained in place without notable degradation, new bone formation from the periphery to the center along the surface of the BCP block was observed. But the new bone did not merge with each other. In addition, new bone formation was observed in the pore area and mature bone was observed from the periphery of the defect. Overall, remarkable pattern of bone regeneration and growth was observed in the BCP block close to the dura meter.
1.0mm pore size group
At 2-weeks, the BCP block maintained the morphology of the formed defect, and an initial healing pattern was observed. Most of the interspaces between the BCP block lattice structure were filled with fibro-vascular tissue, but loosely structured tissue was observed in the center of the BCP block. A concave lower boundary due to the pressure of the brain tissue was observed on the dura meter contacted with the BCP block.
At 8 weeks, 1.0mm pore size group showed greatest new bone formation among the groups using the BCP block, and bone regeneration occurred on all surface of BCP block. A ring-shaped bone regeneration pattern surrounding the surface of BCP block was observed. In addition, the new bone was fused and matured with a pattern of connecting lattice structure of BCP block.
1.2mm pore size group
At 8-weeks, various types of bone growth were observed. Ring-shaped new bone regeneration surrounding the BCP block near to dura meter was observed. At the upper part of BCP block, osteogenesis with semi-lunar shape rather than ring shape was observed. However, fusion of regenerated bone was not observed, showing an independent bone regeneration pattern including independent island-shape bone formation