## 4 Discussion  
In this radiological and histological study, we observed the bone formed after the placing of different bone regenerative materials to which silicon was added in order to evaluate its role as a stimulator of bone formation. In the radiological study (Table 2) it was observed that groups PSB and SB showed higher values in terms of the amount and percentage of healthy bone observed. However, these differences were not statistically significant with regard to the CONTROL group. On the other hand, the PS group did present significantly lower values compared to the rest of the groups. The histological study (Table 3) revealed that the PSB group was the one that presented the greatest area, percentage and perimeter of mineralised bone compared to the other groups. Conversely, on evaluating calcein deposition on the bone matrix, no difference was observed across groups with regard to bone area and area percentage. The SB group presented a significantly larger bone perimeter. The bone height variable showed no differences across the groups. Silicon is a bioinorganic ion which has been employed as a regenerative material in several studies, usually with other inorganic biomaterials such as calcium phosphate or hydroxyapatite [34]. The advantages they offer are a low cost and a longer useful life [35]. The bioactivity of silicon will depend on the accumulation of silicon ions when it is exposed  
Figure 5: Images of histological sections made using [PERSON] (**A,B**) and fluorescence staining (**C,D**) after 3 weeks. Blue and white asterisks indicate new bone formation in the defect. Red pointers indicate areas of calcein deposition around the bone defect. The images present a calibration of 2 mm. to body fluids, such as blood as in the case of this study. This phenomenon was to give rise to the formation of a layer similar to biologically active apatite [36]. As far as we know, there is no evidence in the literature of the use of silicon versenate as a regenerative material, thus the comparison with other studies must be undertaken with caution. The method usually employed is carried out by substituting hydroxyapatite or calcium phosphate with silicon by precipitation methods, enabling regenerative biomaterials with better properties to be obtained [37; 38]. Several in vitro studies have shown that silicon is a biocompatible and bioinert element [36]. Furthermore, it promotes angiogenesis, osteoblastic differentiation and increases bone mineral density, by accelerating its formation [16; 17; 22; 23; 27; 39; 40]. In a recent study defects were regenerated on the cranial vaults of rats and, after 4 weeks, it was observed that significantly larger bone formation occurred when compared with a similar mixture to which silicon had not been added [30]. Likewise, mixed in vitro and in vivo studies have been undertaken in which it has been possible to compare the behaviour of silicon in both situations. [PERSON] et al. carried out a study in which silicon was added to a mixture of calcium phosphate and glass ceramic to regenerate cranial vault defects in rabbits. Cellular viability was observed similar to the one which presented in spongy bovine bone, but with a greater rate of cellular proliferation. All this was attributed to the inclusion of silicon ions, which was to also boost other cellular functions such as cellular adhesion [41]. In the histological study undertaken, increased new bone formation was observed in the experimental group. In accordance with the reviewed literature, a greater amount of mineralised bone would be expected to be found in the groups containing silicon. In our study, the PS and SB groups showed no difference compared to the control group, the combination of silicon, platelet-rich fibrin and autologous bone [the PSB group] being the one which enabled a significantly higher level of mineralised bone than the rest.