## 4 Discussion
The results obtained, in contrast to the findings of [PERSON]'s work, showed that diode laser was considered the safest for application on any type of surface, because it does not damage the titanium. Nd:YAG and Ho:YAG lasers determined the complete elimination of bacterial biofilm on titanium surfaces; however, the irradiation at standard energy emission settings could cause significant damage on the titanium surfaces of the fixture, making them unsuitable for decontamination of implant independently of the power output. CO\({}_{2}\) and Er:YAG lasers, with the appropriate settings and wavelengths, could be used without damaging the implant surface and bone [28]. Following the findings reported by the paper published by Ganz, the CO\({}_{2}\) laser did not cause a temperature change in excess of 3.9 \({}^{\circ}\)C if used with a power density of 2 and 4 W in a continuous mode [29]. Er:YAG laser irradiation at high energy levels produces over-heating and minor damage on titanium-implant surfaces, [PERSON] showed that the use of cooling sources, such as water spray, drastically reduce the temperature elevation of the implant during the laser irradiation [30]. [PERSON] et al. reported that Er:YAG irradiation at pulse energy with water spray in near-contact mode caused no damage and was effective for debriding microstructured implant surfaces [31]. Following the clinical studies included in our paper, Er:YAG is the best laser system to decontaminate the infected implant parts and infrabony defects. The radiation emitted by the Er:YAG laser is highly absorbed by water molecules contained within hard and soft tissue of the oral cavity. Their consequent evaporation involves the production of micro-explosion and macro-molecular fragmentation in the target tissue without significative thermal variation. This phenomenon is the rationale of the ablative effects of this laser especially on the hard tissues [32]. For this reason, Er:YAG lasers, unlike diode and CO\({}_{2}\) lasers, can be used in bone surgery and in the emotion of subgingival calculus in periodontal pockets. Some authors have compared the effectiveness of Er:YAG lasers' irradiation with conventional subgingival mechanical instrumentation (plastic curettes and air-polishing) in non-surgical peri-implant therapy [14; 15; 16]. Following the studies included in our review, it emerged that the Er:YAG laser was effective to complete the ablation of any residual subgingival bacteria from implant surfaces, and the difference in terms of therapeutic efficacy was not clinically significant when compared with conventional mechanical therapy. However, on the basis of the same clinical result obtained, conventional manual instrumentation requires manual skills and more time spent than laser irradiation. In surgical-regenerative therapy of peri-implant defects, Er:YAG lasers cannot replace conventional instrumentation and can be used like adjunctive therapy to remove inflammatory tissues and to complete the decontamination of the infected implants parts and surrounding hard and soft tissues [16]. Although the Er:YAG laser seems to be the most effective in the therapy of peri-implantitis, the diode laser is the most tested by the authors. Its greater diffusion is probably related to its simplicity of use, its versatility and its cost-effectiveness compared to other laser systems. Diode is a deeply penetrating laser-type and shows the best cutting, coagulation and biostimulation activity in oral surgery [32]. In the treatment of peri-implantitis, photodynamic therapy combined with traditional non-surgical therapy seems to have positive effects in the treatment of mucositis or peri-implantitis, in particular that with PPD less than 5 mm [21]. This result could be explained as the consequence of the antibacterial and bio-stimulating effects induced by the laser light on the periodontal tissues and on the exposed implant surfaces.