## 4 Discussion  
From the SEM observations carried out emerged that all the implants analyzed are of a modern concept. That is, they have a very well-developed micro-structure as the result of the specific process of double treatment with acid, which is one of the cornerstones of implant surface treatment nowadays. The measured roughness values reflect the current debate and related schools of thought regarding the eternal dilemma of implantology: the increase in surface roughness is favorable with regards to the formation of peri-implant bone, but it can be disadvantageous in the case of bacterial infiltration and peri-implantitis [7; 17]. This is particularly evident in the 3i T3 system which, although treated in its entire surface, that is, without a polished collar, it has a lower roughness in the coronal area, while roughness is increased by a pre-process of vigorous sandblasting in the apical portion. For Syra and Prama implants, instead, a more delicate preliminary sandblasting process is adopted which entails a lower roughness than that obtained with the traditional SLA process. On the other hand, Shard Implant takes advantage of the double acidification process only and obtains a significant increase in surface area with a slight increase in vertical roughness in order to reduce the possible effects of bacteria accumulation. We need to remember that when this study was conducted, the Shard Implant was not yet commercially available and the samples provided by the manufacturer where completely roughened up to their coronal portion. In contrast, the final design of the Shard Implant presents a machined coronal portion. NobelPearl is a separate case since it is produced in zirconia and also because there is a well-developed micro-roughness with only a minor increase in height. By comparing roughness outcomes reported in Table 2, a very important aspect was observed: while the roughness characteristics have often been discussed in terms of vertical parameters, that is height parameters (two-dimensional roughness Ra, Rq, Rz when the measurement prevailed along a line, as opposed to Sa, Sq, and Sz in modern roughness measurements which exploit image analysis and therefore do not process data along a line but within an area), in several cases, the real difference is provided by Sdr (i.e., see values for Syra implant). This parameter indicates how developed the contact area is, that is, how much the treatment has amplified the exposed implant surface compared to the geometric one [1]. Cells behavior seems to be more affected by the surface morphology and organization than by the absolute value of roughness [18]. It should be noted that the roughness data reported in different studies or provided by the manufacturers might be slightly different from values found in the present study. In this regard, it should be remembered that in roughness measurements, the quantitative values obtained in areas of similar dimensions are directly comparable when the same technique is used. If reported values have been obtained with different methods, they are not directly comparable from the quantitative point of view, while from the qualitative point of view, they are in obvious agreement. In general, all surfaces investigated in the present study appear not only well conceived according to scientific and rational criteria from the topographic point of view, but also clean in terms of contamination. This was evident in SEM-EDX analysis and was confirmed by the analysis of the surface chemical composition using XPS. To better understand the data provided by the XPS analysis, some preliminary reflection on the peculiarities of the surface analysis is important. As a general consideration, in the surface analysis of Ti, the presence of at least three elements is expected: titanium, oxygen (because titanium oxide is present on the surface), and carbon. The latter element derives from the presence of carbonaceous molecules (CO\({}_{2}\) or hydrocarbon type compounds) inevitably present in the Earth's atmosphere [10].