Apical Flap Repositioning vs. Mucosa Excision With Free Gingival Grafts for Peri-Implant Keratinized Mucosa Augmentation

This superiority multicenter randomized clinical trial is coordinated by the Universitat de Barcelona (UB) and includes the Universidad Complutense de Madrid (UCM) as a collaborating center.

Participant selection Adults with osseointegrated implants in the posterior maxilla or mandible presenting keratinized mucosa width of 2 mm or less and/or vestibular depth less than 4 mm will be screened for eligibility. Participants must be in periodontal and peri-implant health and have a plaque index of 15% or less.

Randomization Eligible participants will be randomly assigned (1:1) to one of two treatment groups using an Interactive Web Response System (IWRS) provided by Sealed Envelope Ltd. Randomization will take place intraoperatively, once the partial-thickness mucosal flap has been prepared.

Interventions

Group 1 (Control): Free gingival graft with apical repositioning and suturing of the vestibular mucosal flap to the periosteum Group 2 (Experimental): Free gingival graft with excision of the vestibular mucous tissue

Outcome assessment Soft tissue changes will be assessed at 5 timepoints (T0, Tim, T6w, T3m, T6m) using intraoral scans (TRIOS 3®, 3Shape) analyzed with Geomagic Control X® software through three-dimensional digital superimposition. Clinical measurements will also be performed using a calibrated periodontal probe and a customized thermoplastic stent to standardize the measurement point across visits.

Participants will complete a pain diary during the first 7 postoperative days recording pain intensity (100 mm visual analogue scale), analgesic consumption, and days with limited activity.

Sample size A total of 46 participants (23 per group) are required, accounting for a minimum clinically relevant difference of 1 mm in KTW gain, a standard deviation of 1.3 mm, 80% statistical power, 5% significance level, an intraclass correlation coefficient of 0.30 for multiple implants per patient, and a 15% dropout rate.

Statistical analysis The primary outcome will be analyzed in the intention-to-treat population using a generalized linear mixed model (GLMM), with patient as a random effect, adjusted for baseline KTW and study center.

Inclusion criteria

• Men or women aged 18 years or older who voluntarily agree to sign the informed consent form before any study-related procedure is performed.
• Single or multiple edentulous spaces (≤3 units) located in the posterior maxilla or mandible, presenting osseointegrated implants in first-stage surgery with a -healing period of more than 8 weeks.
• ASA classification I or II.
• Periodontal and peri-implant health.
• O'Leary plaque index ≤15%.
• Keratinized mucosa width ≤2 mm and/or vestibular depth <4 mm at at least one site.
• Commitment to attend all follow-up visits over 6 months.

Exclusion criteria

• Systemic diseases that may interfere with performing FGG (free gingival graft), including but not limited to: poorly controlled diabetes mellitus (HbA1c > 8% or per clinical judgment), immunodeficiencies or immunosuppressive treatment, uncontrolled hematological diseases or coagulation disorders, anticoagulant or antiplatelet treatment that cannot be adjusted according to standard clinical practice, active neoplasms under treatment, severe renal or hepatic insufficiency, decompensated cardiovascular diseases, and any other medical condition that, in the investigator's judgment, could compromise participant safety or proper tissue healing.
• Any contraindication to oral surgical procedures.
• Periodontal and peri-implant health as defined by the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions.
• Patients who smoke tobacco or equivalent products, as well as former smokers with an abstinence period ≤12 months.
• History of substance abuse (drugs or alcohol) or any other factor (e.g., severe psychiatric illness) that, in the investigator's opinion, could interfere with the patient's ability to cooperate and comply with the study.
• Patients who have participated in a clinical trial within the last 30 days.
• Pregnant or breastfeeding women.