Three sinuses were grafted with a bioactive glass bone substitute (Biogran) mixed with autogenous bone retrieved from intraoral donor sites. In two of the three sinuses a platelet-rich plasma (PRP) gel was added to the graft. Bone biopsies retrieved after 5, 6, and 15 months were analyzed. Micro-computerized tomography (micro-CT) values of total bone volume/total volume (TBV/TV) were very reliable compared to histomorphometry. Biogran mixed with autogenous bone and PRP seems to have a positive effect in sinus grafting, with TBV/TV values ranging between 40% and 68%. Micro-CT results have never been compared with histomorphometry for the evaluation of grafted biomaterials. Micro-CT evaluation of some morphometric parameters was difficult, because the radiodensities of Biogran and a certain grade of bone mineralization were similar.