Biodegradation process of alpha-TCP particles and new bone formation in a rabbit cranial defect model

The purpose of the present study was to observe the biodegradation process of pure alpha-tricalcium phosphate (alpha-TCP) particles and to determine the efficacy of alpha-TCP as a space maintainer in a bone defect. We used 14 rabbits and prepared two cranial bone defects in each rabbit. One defect was left empty as a control, whereas the other was filled with alpha-TCP particles about 300 mum in diameter. Animals were sacrificed at 1 week, 4 weeks, and 8 weeks. The cranial bone was then embedded either in paraffin wax for the preparation of decalcified specimens, or in polyester resin for the preparation of nondecalcified specimens. All specimens were evaluated histologically and histomorphometrically. As a consequence of the degradation of alpha-TCP, a "reticulate structure" appeared in the particles at 1 week and new bone was observed in this structure at 8 weeks. The amount of new bone between the control and experimental groups was not significantly different at any of the time points. However, in the experimental group, new bone at the surface of alpha-TCP was evident even in the center of the defect whereas fibrous connective tissue was dominant in the control group. These results indicate that alpha-TCP is a degradable osteoconductive material that is able to act as a space maintainer for bone regeneration when applied to a bone defect. While there was no significant difference in total bone formation between the experimental and negative control groups, the space-maintaining and osteoconductive properties of the particles may result in more complete bone formation in longer-term studies.