The primary aim of the present study is to compare the Sub-periosteal Peri-implant Augmented Layer (SPAL) technique and soft tissue augmentation (STA), performed simultaneously to implant placement, in terms of (i) implant survival rate and (ii) health/disease condition of the peri-implant tissues at 6 and 12 months following implant loading. The secondary aim of the project will be to compare the SPAL technique and STA in terms of intra- and post-operative morbidity.

The study is designed as a single-blind, parallel-arm, randomized clinical trial. Patients will be recruited and treated at the Operative Unit of Dentistry, Azienda Unità Sanitaria Locale (A.U.S.L.) of Ferrara, Italy, and one University center (Research Centre for the Study of Periodontal and Peri-implant Diseases, University of Ferrara, Italy). Each patient will contribute the study with one sextant ("experimental sextant"). Each eligible patient will be randomly assigned to receive SPAL technique or STA according to a computer-generated randomization list. Surgical procedures will be performed by experienced periodontal and implant surgeons. Two calibrated, blinded examiners will take care of the assessment of clinical and radiographic parameters, Case Report Form (CRF) filling, as well as data extraction from CRFs for the preparation of the study database.

The proportion of patients free from peri-implantitis at 12 months following loading will be the primary outcome variable of the study. The proportion of patients with complete resolution of the bone dehiscence (BD), dimensional variations and 12-months characteristics of BD, and patient-reported outcome measures will be the secondary outcomes. The design will test two hypotheses, with a non-inferiority trial in terms of primary outcome and a superiority trial in terms of secondary outcomes.

Patient-specific inclusion criteria

• age≥21years;
• good physical status (ASA1 and ASA2 according to Physical Status Classification System) (American Society of Anesthesiologists, 2010);
• systemic and local conditions compatible with implant placement and experimental procedures;
• indication to a fixed, implant-supported prosthetic rehabilitation with hard or soft tissue reconstructive procedures as part of the comprehensive oral rehabilitation plan;
• patient willing and fully capable to comply with the study protocol.

Sextant-specific inclusion criteria

To be considered as experimental, a sextant will have to fulfill all the following criteria:

• including at least one healed (i.e., ≥ 6 months elapsed from tooth loss) edentulous site;
• horizontal dimension of the edentulous ridge compatible with the primary stability of an implant of at least 3.5 mm in diameter;
• expected peri-implant buccal BD characterized by a height (measured as the apico-coronal height of the exposed implant surface) ≤ 5 mm or a thin (< 1 mm) peri-implant buccal bone plate as diagnosed on tridimensional planning for guided implant placement.

Patient will not be eligible for the study if presenting at least one of the following exclusion criteria:

Patient-specific exclusion criteria

• current heavy smoking (≥20 cigarettes/day for ≥6 months prior to and at the time of the surgical procedure);
• untreated periodontal disease prior to implant placement;
• history of radiation therapy in the head and neck area;
• history of chemotherapy;
• systemic disease or conditions with a documented effect on bone metabolism and/or osseous healing;
• past (within 6 months prior to enrolment in the study) or current treatment with any medication with a documented effect on bone metabolism and/or osseous healing;
• documented allergy to dental materials involved in the experimental protocol;
• pregnancy or lactation;
• history of drug or alcohol abuse.

Moreover, participants immediately exited the study upon:

• request to withdraw from further participation;
• development of acute dental, peri-implant or oral conditions requiring treatment;
• development of conditions conflicting with the inclusion criteria listed above;
• failure to comply with study instructions/requirements.

Site specific exclusion criteria

• presence of either a buccal BD > 5 mm in depth or a thick (≥ 1 mm) peri-implant buccal bone plate as clinically assessed with a periodontal probe immediately after implant placement;
• presence of endodontic lesions at teeth adjacent to the implant site;
• previous bone augmentation/preservation procedures at the designated implant areas;
• need for vertical bone augmentation.

The assignment of eligible patients to treatment will be recorded using sealed envelopes and will be disclosed to each clinical operator at the end of the screening appointment. The examiners will be kept blinded as to treatment allocation.