## 4 Discussion
Autologous bone is still deemed the gold standard material for regeneration since it is the only one with osteogenic, osteoinductive and osteoconductive properties and this gives it an advantage in comparison with the rest of available materials. Notwithstanding, its limited availability, morbidity and its higher resorption rate have prompted the search for new biomaterials [35]. In our study, autologous bone combined with silicon [SB] showed no significant difference compared to the PS and control groups with regard to calcified bone. However, it was, after the PSB group, the one which presented a greater amount of bone and the one which presented greater bone perimeter of osteoid bone. There are no publications in which any of the study groups have employed autologous bone with silicon; and our preliminary results suggest that we would need to see how the autologous bone behaves over longer periods. Fibrin-rich plasma has been used before in bone regeneration as the only filler material [42; 43; 44], or in combination with autologous bone [45], xenografts [46] or alloplastic grafts [47] providing better results regarding bone regeneration and faster healing compared to negative control groups. However, there is limited evidence on the combination of silicon and platelet-rich concentrates. Only two studies have been found in the literature which combine both materials. Their results differ and with ours as well. In the first study a combination of PRP/silicon was subsequently gelled with calcium chloride. It was applied on a cell culture of osteoblasts, and greater proliferation, greater cell viability and greater cell deposition of calcium was observed in the experimental group than in the group without silicon [48]. Conversely, in the second study a cell-generating factor (CGF) was combined with sodium orthosilicate on human osteoblasts. No statistically significant differences were observed in respect of cellular proliferation or growth compared to the groups in which only orthosilicate or only platelet concentrate was administered. Conversely, a greater production of type I collagen was observed [49]. In both studies it was concluded that the osteoconductive properties of the silicon would be boosted by the growth factors in the CGF. Both results differed in our study, in which the PS group was the one that obtained significantly lower radiological values, although histologically it showed no difference compared to the control group. The comparison with both publications must be made with caution because they were in vitro studies with a different material. Notwithstanding, our results would be in accordance with two trials undertaken on rabbit bone in which it was observed that the PRF did not significantly improve bone regeneration when compared with the negative control group [47; 50]. In our study, greater formation of mineralised bone occurred in the PSB group and this could be due to two factors: the first of these is that the silicon and the PRF would boost its osteoconductive capacity on combining with each other and at the same time it would accelerate bone mineralisation. This could explain the better performance of the PSB group in our study. The second factor is the addition of autologous bone to the biomaterial which, as mentioned earlier, is deemed the reference material in bone regeneration. As limitations of the study, it is worth noting the low number of specimens in the sample, as well as the time period evaluated. The PSB and SB study groups offered good regeneration results, however, radiologically they did not present a significant difference compared to the control group. A way of improving the study would be to evaluate longer time periods, which would perhaps offer more revealing results on the behaviour of these regenerative materials. Furthermore, the use of a positive control group (filling the defect with autologous bone without silicon or a mixture of just autologous and heterologous bone) could have been contemplated.