Histological observations did not show inflammatory cells in the tissue adjacent to the bone substitute particles. Bone marrow-like tissue, which included blood vessels, was observed in between the bone trabeculae (Fig. 4). Reinforcement by lamellar bone was shown in some areas after 9 and 12 months (Figs. 5 and 6). No Howship’s lacunae could be detected on the characteristic outlines of the substitute particles. Fragments of the substitute particles were present in the sections of the 9-month group and the 12-month group, as confirmed by Von Kossa staining. Regardless of the histological process, the contours of the bone substitute remnants were clearly detectable which enabled analyses.

In the 9-month group, the average vital bone volume was 35.2% of the total biopsy volume (SD ±9.5) of which 8.8% (SD ±3.8) was osteoid. The osteoid surface covered 42.4% (SD ±12.1) of the bone surface. The BS covered 4.2 mm²/mm³ (SD ±1.9). In the total area for the 12-month group, the average vital bone volume was 28.2% of the total biopsy volume (SD ±3.2) of which 3.4% (SD ±2.5) was osteoid. The osteoid surface covered 8.2% (SD ±5.3) of the bone surface. The BS covered 8.3 mm²/mm³ (SD ±1.3). In conclusion, vital bone volume and bone turnover decreased in the 12-month group compared to the 9-month group. An overview of the individual histomorphometric findings is listed in Tables 3 and 4.