## 4 Discussion  
In this study, the decontamination efficacy of six commercially available antiseptic agents against _P. gingivalis_ and _S. mutans_ biofilms on micro-rough titanium disks, and their effects on surface chemical composition, were assessed. To reach our goal, we developed an in vitro biofilm model resembling the in vivo physiological microenvironment as closely as possible. As described above, _P. gingivalis_ is one of the pathogens most often associated with peri-implantitis [13], and _S. mutans_ is able to form a greater quantity of biofilm, favoring the colonization of _P. gingivalis_[14]. The titanium disks were exposed to human saliva in order to reproduce the physiological protein layer known to mediate bacterial adhesion on the implant surface in vivo. Disks with moderate surface roughness (S\({}_{a}\):1.30 \(\upmu\)m) were used as 95% of the surfaces in currently commercialized implant systems are composed of titanium with a moderately rough topography [15], and the greater affinity of bacteria and peri-implantitis progression for this type of surfaces is well-known [16; 17]. In this study, marked antibacterial activity against _P. gingivalis_ and _S. mutans_ biofilms following 2 min of exposure was demonstrated for 5.25% NaOCI liquid and gel, followed by 37% OPA gel, 40% CA liquid, 1% CHX gel, and 0.2% CHX liquid formulations. However no significant difference in their antibacterial activity was observed despite 5.25% NaOCI appearing to be the most effective in removing the biofilms. Indeed, as evidenced by SEM analysis, disks treated with liquid 5.25% NaOCI showed a reduced biofilm matrix and no residual bacterial cells. Overall, our findings are in agreement with other studies that have not found significant differences in the decontaminating efficacy between the most commonly used antiseptics [18; 19; 20]. The antimicrobial properties of NaOCI have been thoroughly investigated with respect to its endodontic application as an irrigant [21; 22], while less is known about its effect on infected implants [23]. The germicidal action of NaOCI depends on its dissociation into sodium hydroxide and hypochlorous acid, which has a high oxidizing power and can easily penetrate inside bacterial cells leading to irreversible enzyme inhibition, lysis of the cytoplasmic membrane, degradation of phospholipids, and alterations of cellular metabolism [24]. However, NaOCI is highly cytotoxic for host cells, including osteoblasts and fibroblasts. In fact, following the exposure of canine bone samples to 5.25% NaOCI liquid for 30 min, [PERSON] et al. [25] observed macroscopic demineralization and degradation of the organic matrix. Another study demonstrated that the toxicity of NaOCI liquid on  
Figure 4: Normalized spectra of C1s of non-contaminated titanium samples after immersion in 1 mL of each antiseptic product for 2 min. (**CC**) Control; (**A**) NaOCI 5.25% liquid; (**B**) NaOCI 5.25% gel; (**C**) CHX 0.2% liquid; (**D**) CHX 1% gel; (**E**) AC 40% gel; (**F**) OPA 37% gel. human bone marrow mesenchymal stem cells was proportional to its concentration and the exposure time [26]. Thus, the 5.25% NaOCl liquid formulation cannot be recommended for surgical treatment of peri-implantitis. The NaOCl gel formulation, which is equally effective against _P. gingivalis_ and _S. mutans_ biofilms as evidenced in our study, may however represent a potential alternative treatment. Similar results were also observed for the 37% OPA and 1% CHX gel formulations, further supporting the possible use of antiseptic gels for the treatment of infected implant surfaces, since gel formulations may limit the accidental contact of the antiseptic agent to the surrounding tissues. CHX has however also been shown to possess cytotoxic effect against host tissues [27; 28; 29; 30], whereas OPA's cytotoxic properties have been highlighted by a single study and, hence, warrants further investigation [31].