The primary objective is to evaluate the clinical and patient-centered outcomes of non-surgical mechanical debridement with adjunctive repeated diode laser application (test) in comparison with conventional surgical treatment and adjunctive systemic antibiotics (control), for treatment of peri-implantitis lesions, following an observation period of one year.

Peri-implantitis is a major complication for dental implant patients, with its prevalence estimated in the order of 10% of implants and 20% of patients after 5 to 10 years of implant placement. When left untreated, peri-implantitis may cause progressive tissue destruction, esthetic complications and, eventually, implant loss. Despite numerous clinical trials and systematic reviews, studies have failed to identify a standardized protocol for the treatment of such conditions. Still, current literature and expert opinions recommend mechanical debridement of the implant followed by early evaluation and surgical intervention, implant decontamination using a wide variety of mechanical and chemical methods, then adjunctive systematic antibiotics. However, given the aggressive nature of surgical interventions, the inherent difficulty of decontaminating the implants' rough surfaces with conventional methods, in addition to the growing concerns over antibiotic resistance, the search for alternative approaches has become imperative. Since implant decontamination is the key aspect to resolution of peri-implantitis, different mechanical and chemical methods have been tested in that respect. In recent years, lasers have been attracting significant attention in this particular field. Diode lasers, in particular, have been shown to have potent bactericidal and photobiomodulatory effects promoting wound healing and tissue regeneration. Therefore, the aim of this randomized controlled clinical trial is to evaluate the clinical and patient-centered outcomes of non-surgical debridement with adjunctive repeated diode laser application in comparison with conventional surgical treatment with adjunctive systemic antibiotics for treatment of peri-implantitis lesions following an observation period of one year.

The primary objective is to evaluate the clinical and patient-centered outcomes of non-surgical mechanical debridement with adjunctive repeated diode laser application (test) in comparison with conventional surgical treatment and adjunctive systemic antibiotics (control), for treatment of peri-implantitis lesions, following an observation period of one year.

40 subjects will be randomly distributed into two parallel groups:

1. Test group (n= 20); receiving non-surgical mechanical debridement and adjunctive diode laser application at days 0, 7 and 14.
2. Control group (n= 20); receiving initial mechanical debridement at day 0, followed by open flap debridement and prescription of post-operative systemic antimicrobials at day 14.

Inclusion Criteria:

• Informed Consent as documented by signature (Appendix Informed Consent Form)
• At least one solid screw-type titanium implant diagnosed with peri-implantitis; which is defined as at least one site with probing depth ≥5mm, bleeding on probing and/or suppuration, and radiographic evidence of crater-form bone loss ≥2 threads after insertion of the final prosthetic supra-structure.
• Sound prosthetic supra-structure.

Exclusion Criteria:

• Contraindications to the class of drugs under study, e.g. known hypersensitivity or allergy to Amoxicillin and/or Metronidazole,
• Systemic diseases that could compromise wound healing (i.e. uncontrolled diabetes mellitus, cancer, HIV or bone metabolic disorders), radiation or immunosuppressive therapy,
• Women who are pregnant or breast feeding,
• Known or suspected non-compliance, drug or alcohol abuse,
• Heavy smokers consuming >10 cigarettes/day,
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant,
• Participants not willing to attend regular dental maintenance visits and follow-up evaluations,
• Participation in another study with investigational drug within the 30 days preceding and during the present study,
• Previous enrolment into the current study,
• Active periodontal disease.

The treatment group will be concealed at all time points from both clinical examiners (N.C., A.Z.) and the biostatistician (D.C.). Only the operator (D.H.) will be aware of the type of treatment to be performed based on the computer-generated allocation table. The un-blinded operator will perform the first follow-up visit one week post-operatively to ensure blinding of the examiners.