## 4 Discussion

Table 1: Evaluation of RA (roughness average) and RMS (root mean square) before and after treatment with different powders, expressed as means and standard deviations (S.D.) for machined surface and moderately rough surface discs. Today, in clinical practice, implant surface decontamination is mandatory for a lasting successful implant treatment. Air-powder devices have been successfully employed to this purpose; however, no consensus exists on which powder should be used to maximize plaque removal while conserving the implant surface microstructure [19; 31]. _S. sanguinia_ was incubated for 3 days [35; 36]. _S. sanguinia_ displays an important role in the formation of bacterial plaque and is generally accepted as a suitable model for adherence studies [22; 24; 25; 37]. In previous studies, sodium bicarbonate resulted effective in _S. sanguinia_ biofilm removal [22; 24; 25]. However, despite the encouraging evidence coming from these previous studies, the efficacy of sodium bicarbonate was not further investigated in comparison with other powders or by assessing the structural changes of the titanium surface. Concerning the ultrastructural changes, we ought to look at the changes in surface roughness values before and after treatment, rather than the absolute Ra and RMS values. It was noted that none of the tested treatments was able to cause changes in surface roughness values after 20s of treatment neither in M nor in MRS discs. These findings agree with other studies in the literature, which showed that different air-powders caused no titanium surface changes [31; 38; 39; 40]. However, other studies showed surface roughness changes after different air-powder treatments [41; 42; 43; 44]. The disparity between our findings and these studies findings could be attributed to either different tested titanium surfaces or different experiment parameters such as machine pressure, length of treatment time, angulation and distance of the handpiece from the tested surface or different settings of the machine used to measure surface roughness [19]. Moreover, most of previously published studies only performed a qualitative evaluation of such changes without a quantitative synthesis [19; 38; 45; 46; 47; 48; 49; 50; 51]. Considering the insignificant differences regarding biofilm removal among the different powders utilized, we would suggest the use of small-sized particle powders in everyday clinical practice. In fact, it has been shown that they are safe, effective and less aggressive on soft tissues [52; 53]. Although in our controlled experiment no surface topography changes were induced using the larger particle air-powders, it has been shown in other studies that repeated use of large particle air-polishing powders caused changes to the titanium surface [26; 27; 47; 54; 55]. It is reasonable to consider small-particle size powders--such as erythroid--less aggressive on implant and tooth surfaces compared to large-particle size powders such as carbonates, as supported also by the results of a similar study [17]. As highlighted earlier, although there was significant improvement with all the tested modalities, none of the tested treatments rendered the tested surfaces biofilm-free. To date, this is one of the major shortcomings of peri-implant mechanical therapy, as none of the available mechanical treatments are able to completely remove the biofilm. This is of paramount importance during peri-implantitis treatment, as biofilm removal creates a biologically acceptable implant surface, an environment conducive to healing and regeneration. To compensate for this discrepancy, combined mechanical and chemical decontamination methods are recommended to achieve maximum biofilm removal during peri-implantitis treatment, matched with a collaborative self-care oral hygiene performed by patients. One of the limitations of this study was the use of titanium discs instead of dental implants.