This is a multi-centre, randomized clinical trial which evaluates the efficiency of the collagen xenograft (Muco-Graft®) in comparison to the autologous connective tissue graft for the augmentation of keratinized mucosa and gaining hygienic access to the implants diagnosed with peri-implantitis.

Nowadays, there is not enough evidence that evaluates the patient's perception of utilizing the soft tissue substitutes in comparison to the autologous connective tissue graft for the augmentation of the keratinized mucosa and gain of hygienic access to the implants with infectious pathology and with minimum or absent keratinized mucosa.

Therefore, the aim of the study is to evaluate the change of clinical parameters of peri-implant health and the patient perception of the procedure for augmentation of the keratinized tissues around dental implants with peri-implantitis.

The hypothesis is that collagen matrix of porcine origin is associated with lower patient morbidity, in comparison with autologous connective-tissue graft, when used for the augmentation of the keratinized tissues around endosseous dental implants with infectious pathology and with minimum or absent KT mucosa.

A sample 48 patients will be recruited basing upon the diagnosis of peri-implantitis and absent or insufficient peri- implant mucosa. 1 month after the non-surgical treatment, surgical procedure will be performed.

Peri-implant clinical and radiographic parameters, as well as patient perception of the therapy provided, will be evaluated before and at various stages (up to 52 weeks) after the surgical intervention. Also, change of vestibulum depth will be analyzed, as well as the time spent for the procedure measured.

Inclusion Criteria:

• Informed consent after the detailed information on the study.
• Adults aged at least 18 years old.
• Candidates for receiving augmentation of the peri-implant keratinized mucosa.
• Presence of the implant diagnosed with peri-implantitis (radiographic bone loss > 2 mm, with a probing depth > 5 mm, bleeding and/or suppuration (Lang et al., 2011)).
• Absent or insufficient keratinized peri-implant mucosa (<2 mm).

Exclusion Criteria:

• General contraindications for the dental/surgical treatment;
• Inflammatory or autoimmune disease of the oral cavity;
• Implant with radiographic intraosseous defects more than 3 mm;
• Smokers > 10 cig/day;
• Allergy to collagen or analgesics/anti-inflammatory non-steroid drugs;
• History of cancer in various parts of the body which required radiotherapy or chemotherapy during the last 5 years;
• Radiotherapy of the head or neck in the last 5 years;
• Actual medication with immunosuppressors, bisphosphonates or high doses of corticosteroids;
• Pregnant or lactating women;
• Women in fertile age, who do not use effective methods of contraception;
• Participants of other studies of biomedical investigation during the last 24 weeks before initiation of the study.

The examiners will be blinded. Envelopes will be prepared by a research assistant not involved as clinician or examiner. The clinicians involved will have no access to the data collection sheets or the group allocation, whilst the examiners will have no access to the patients' treatment notes or group allocation. The examiners will be blinded with regards to the participant treatment assignments. The measures will include no access to the dental records as to which treatment has been assigned. The patients are not to reveal their treatment assignment to the examiners. Unblinding is expected when patients present with adverse outcomes during the course of the study, e.g., emphysema.