In another similar experiment in sheep, the sinuses were augmented using a similar biphasic calcium phosphate (60% HA, 40% β-TCP) [24], the biomaterial used in the present study. The perforation of the sinus mucosa was performed at the test sites and a collagen membrane was placed to protect the perforation, while at control sites the elevated mucosa was left unprotected. After 12 weeks of healing, the new bone was 16.7% at the test sites and 13.7% at the control sites. These results are similar to those from the present study, which found a proportion of 12–16% of the new bone. In our study, we also found the newly formed bone interpenetrating the resorbing graft granules. This finding was possible by overexposing the slides during microscopic analysis, and this may have been the reason why it was not recognised in the previously discussed study [24]. A simple overlapping between the bone and the biomaterial could be excluded due to the thinness of the slides and the dimension of granules. This finding increased the amount of bone assessed, considering the total bone as the sum of the new bone alone and the new bone interpenetrating the biomaterial. The amount of bone interpenetrating the graft granules was 37.1% and 35.3% at the test and control sites, respectively, and the amount of the total bone was 53.5% and 47.3% at the test and control sites. This was not in agreement with the previous studies, which did not consider the bone interpenetrated to the graft granules.

The residual amount of biomaterial in the abovementioned study [24] was 36.1% and 30.2% at the test and control sites, respectively. In the present study, a higher content of graft was found, reaching a fraction of about 50% at both sites. Approximately 70–73% of the graft at the test and control sites was interpenetrated within the porosities of the biomaterial by the newly formed bone. This peculiarity had been already described for HA/β-TCP [25, 26], showing the high osteoconductivity properties of the graft used in the present study. The biphasic calcium phosphate (BCP) used in this study consisted of 60% HA and 40% β-TCP; these proportions have been previously suggested as a compromise between the solubility of β-TCP and the mechanical strength of HA [25]. The degradation of β-TCP, being more soluble, increases the porosity of the biomaterial that can be filled by the newly formed bone, while the HA remains in the defect and serves as a scaffold.