## 4 Discussion
According to the Albrektsson and Wennerberg classification, the HA/TCP group would show a surface with moderate roughness (Sa: 1-2 \(\upmu\)m) and the other two groups would show minimum roughness (Sa: 0.5-1 \(\upmu\)m). This moderate roughness is considered optimal to promote osseointegration [32], Rp and Sp parameters are related to Ra and Sa and are important components in outstanding peaks and valleys, which increase the average roughness value. The fact that the HA/TCP surface has the highest roughness is due to the fact that it is only sandblasted, which is the procedure that achieves the highest roughness. The other two groups (SLA and HA + AW) have less roughness, which would be due to the etching or acid washing treatment. Viability was evaluated on MG-63 osteoblastic cells, which are used commonly to carry out this type of study [33]. A JC-1 test was performed to determine the mitochondrial activity ratio. Although it is true that the rougher surfaces show greater adhesion, proliferation, and osteoblastic differentiation [6; 33], no statistically significant differences were observed at the level of cell viability despite the differences in topography and surface roughness. All three surfaces are considered to be biocompatible. Implant stability depends on the bone density surrounding the implant as well as the bone-implant contact [5]. This last factor is linked to the transition from primary to secondary implant stability, obtained by the progression from a mechanical bond to the biological bond of new bone positioned on the implant surface at the end of the osseointegration period, which was a 6-week period in our study. The bone deposited on the surface irregularities of the implant and in the chambers that form between the spirals of the implants matures and increases in volume and density through the formation of a greater number of blood vessels after 4 weeks [34]. Our study is not a \"chambers\" type as we used commercial implants, so new bone cannot be evaluated. Von Kossa stain is not able to detect new bone but only mineralized bone which is one of the aims of the study. New bone could be seen weeks before osseointegration, but this was not the goal of our study as it was evaluated after 6 weeks of implantation, considering this point in time as the end of the osseointegration process. According to the literature reviewed, the maximum percentage of bone-implant contact is approximately 60%. Environmental contamination particles were detected on the EDS of the SLA surface (calcium and phosphorus) [35]. This contamination is inevitable and may also be due to the deposition of carbon impurities on the surface of the implant, which affects the complete adaptation of the bone-implant surface [35; 36]. However, in this study, the HA/TCP group presented a higher percentage of carbon (18.46%) and was also the one with the highest BIC. Conversely, the HA + AW group obtained a significantly lower BIC value but with a carbon percentage of only 2.14%; it also had the lowest percentage of titanium of the three groups (91.69%). It is therefore reasonable to think that carbon accumulation did not have a determining influence, as has been observed in other studies [23]. In the same way, it can be stated that it did not influence either the cell viability or the bone variables analyzed. Although, EDS may not prove to be the most suitable method for measuring hydrocarbon impurities, X-ray photoelectron spectroscopy (XPS) should have been conducted. The HA + AW group had significantly lower roughness than the other two groups, and its BIC value was also the lowest of the three. These BIC values are in accordance with roughness results, with HA/TCP and HA + AW being the groups with better profile and surface parameters (Ra, Rp, Rq, Rv, Sa, Sp, Sq, and Sv). These parameters define the surface microtopography and the latter has a key role in osseointegration [13], although some authors consider Sds and Sdr better options [37].