## 2 Materials and Methods  
A supportive therapy to prevent peri-implantitis should be calibrated on each single patient [17]. In clinical practice, these interventions consist of monitoring of peri-implant conditions, patient education and motivation for home oral hygiene, professional oral hygiene, and control of risk factors (e.g., history of periodontal disease). According to the authors' clinical experience, two levels of implant maintenance can be considered: ordinary, performed by dental hygienist, and extraordinary, carried out by the dentist together with the hygienist. The ordinary hygiene session includes soft tissue evaluation, plaque index, probing depth, bleeding on probing, presence of pus, mobility, plaque and calculus removal, and individual instructions for oral hygiene (emphasizing the use of interdental cleaning devices). Full-mouth plaque score (FMPS), full-mouth bleeding score (FMBS), periodontal probing depth (PPD), and bleeding on probing (BOP) are assessed at 6 sites using a periodontal probe [18]. Excellent motivation and compliance from patient are associated to values of FMPS < 20% and of FMBS < 20% [19]. Clinically, peri-implant health is characterized by the absence of signs of inflammation (such as edema and redness) and bleeding on probing, stability of probing depth in measurements taken at different times and absence of further bone loss compared to post-bone remodeling surgical [13; 14]. The scaling and root planing procedures include the use of specific instruments, such as modified curettes and piezoelectric or ultrasonic tips (in plastic material) for the removal of submucosal microbial deposits on implants and polishing with rubber cup or air polishing [20; 21]. The patient should also receive personalized instructions for home oral hygiene. It is necessary to properly instruct the patient in order to respect the delicate peri-implant attachment apparatus. Given the cross-sectional differences between teeth and dental implants, using interdental brushes and other tools, such as subgingival irrigators, for interdental cleaning around dental implants allow for better plaque removal than flossing alone [22]. Extraordinary maintenance involves the removal of the prosthetic structure, operated by the dentist, to better evaluate the probing depth and the bleeding on probing, the mobility of the implants, and the state of the soft tissues, as well as to more accurately clean the implants by removing, in presence of plaque and signs of inflammation, implant abutment [23]. The same specific instruments described for the ordinary hygiene are used. Furthermore, every time the prosthesis is removed, it is decontaminated eliminating plaque and dental calculus while respecting the prosthetic surfaces. This particular machine the authors use works by gentle cleaning of the prosthesis with soft stainless-steel brushes. It helps clean and preserve dental prostheses without affecting the precision of the original design of the components. Its principle is based on soft brushes turned by powerful magnets fitted round a container which has the effect of cleaning and polishing objects (Figure 1). To decide on an adequate maintenance choice, one must calibrate cadence and type (ordinary and extra-ordinary) in relation to the different prostheses and clinical situations. The types of prosthetic rehabilitations have been divided into (1) single crown, (2) fixed partial prosthesis, (3) fixed full-arch, and (4) overdentures (OVD). However, these implant prosthetic scenarios can be associated with different clinical situations, which also have to be taken into consideration: patient compliance; history of periodontitis; implants placed in augmented bone; short [24; 25; 26; 27], zygomatic [28; 29], pterygoid, and tilted implants; and complex prosthesis with false gingiva.