Experimental study of bone defect repair process with different sizes of β-TCP granules

In this study, bone defects were repaired by filling different sizes of β-tricalcium phosphate (β-TCP) granules, and observed by scanning electron microscope (SEM), light microscope (LM), and micro-CT. We extracted bilateral mandibular molars of 8 crabeating monkeys, and used β-TCP granules in two granular sizes, large (type L) and small (type S). Three months after extraction, bone defects had formed in the sites of the extracted molars, and type L or type S granules were then filled into those sites. The animals were euthanized at 2, 4, 8, and 12 weeks after operation. Bone specimens and histological slides of 4 monkeys were prepared, which were observed by SEM and LM, respectively. Those of the remaining 4 monkeys were fixed with 10% formalin for micro-CT examinations with three-dimensional image processing software. Based on the results of image analysis, the volume ratio of opaque images was obtained. SEM, LM and micro-CT findings revealed that the bone defects were filled with trabecular bone from 4 to 8 weeks after operation in the type L group. Granules were seen in some superficial areas at those time points, however, none were observed at 12 weeks. In the type S group, the repair process was not as extensive at 4 weeks and the presence of granules was confirmed. However, after 8 weeks, the findings in the type S group were the same as those in the type L group. The opaque images in micro-CT contained trabecular bone and β-TCP granules. Image analysis results showed that the volume ratio of the opaque images reached the maximum at 4 weeks and then declined from 8 to 12 weeks in the type L group, while in the type S group, the ratio gradually declined from 2 to 12 weeks. In conclusion, bone repair progressed at a faster rate in the type L group than in the type S group at 4 weeks. However, both experimental groups had nearly the same level of osteogenesis after 12 weeks. Further, granule size did not influence the bone defect repair. In addition, it was suggested that micro-CT can be used in clinical treatment. (author)