The tissue reaction, however, did not only differ in bone substitute materials of different origin but also in bone substitute materials of the same origin. In an in vivo trial, two xenogeneic bone substitute materials processed with different techniques were implanted subcutaneously in CD-1 mice for up to 60 days. Both bone substitute materials showed good integration within the peri-implant tissue with no signs of adverse inflammatory effects. However, within the implantation bed of the bone substitute of low sintering temperature, few MNGCs were obvious on the surface of small bone substitute granules in the early integration period, while the tissue reaction to the larger granules at later stages consisted mainly of mononuclear cells. In contrast, the tissue reaction to the bone substitute material of high sintering temperature consisted mainly of biomaterial surface-associated MNGCs. Previous in vivo and clinical investigations indicated that MNGCs, which are widely known to be an expression of an ongoing foreign body reaction, are expressed especially on the surface of synthetic biomaterial granules, trying to degrade the biomaterial, but without really reducing the ratio of the biomaterial. In fact, multinucleated giant cells, which do not have the ability of degrading synthetic bone substitute materials, can be characterized more as foreign body giant cells than as osteoclastic cells [17,18,19].

Previously, our group performed another retrospective study with the same bone level implant system placed immediately after the extraction of teeth not worth preserving [14]. In a collective of 21 patients (11 female, 10 male), 50 dental implants were placed immediately in fresh extraction sockets in the upper (31 implants) and lower jaws (19 implants). The same clinical and radiological parameters were applied to investigate implants 2 years after loading. During the mean observation period of 2 years, none of the implants failed or presented an acute infection or peri-implantitis. All of the implants presented a sufficient amount of peri-implant keratinized soft tissue, low rates of probing depth (mean 2.25 mm), and presence of BOP (34%). The peri-implant bone level was stable, with a mean bone loss 2 years after loading of 0.83 mm [14].