Nevertheless, the vitamin D deficiency prevalence in the European population indicates that a vitamin D deficiency is probably not a sole causative factor for early implant failure; otherwise, the early implant failure rate would be significantly higher. However, a synergistic effect with other factors is conceivable. Some authors stated that implant osseointegration is not simply a wound healing phenomenon but rather complex foreign body reaction with activation of the immune system [56]. Titanium and metal particle release is discussed as cause for implant failure as well as implant dentistry [5, 6, 9, 56, 57]. It is assumed that metal particles influence the macrophage or lymphocyte pathways and provoke a release of pro-inflammatory cytokines, leading to an increased osteoclastogenesis and decreased osteoblastogenesis and consequently to peri-implant bone loss [58]. This osteolytic effect could be enhanced by vitamin D deficiency, since Maier et al. demonstrated in an epidemiological study that vitamin D deficiency is associated with a higher risk to develop aseptic loosening around joint replacements caused by wear particles [59]. Vitamin D could also be essential for the antibacterial response, as monocyte-macrophage reaction is influenced by vitamin D [60]. Xu et al. demonstrated that vitamin D can inhibit Porphyromonas gingivalis-induced proinflammatory cytokine expression and improve the expression of anti-inflammatory cytokines in macrophages [53].

Interestingly, in the present investigation, the osseointegration of dental implants seems to be more influenced by the vitamin D level than the autologous graft incorporation as the graft incorporation was not compromised. The eventually minor effect of vitamin D on the incorporation of bone grafts appears to be addressed by the results of a current randomized, double-blind, and placebo-controlled clinical investigation with a high-dose vitamin D3 supplementation combined with calcium. The results could not demonstrate a statistically significant difference in the amount of bone formation or graft resorption after maxillary sinus augmentation compared to a placebo medication [40].