Evaluation of buccal strip gingival graft with xenogeneic collagen matrix versus free gingival graft for keratinized mucosa augmentation at implant sites: a randomized controlled clinical trial

Abstract

Free gingival grafts (FGG) are the gold standard for peri-implant phenotype augmentation in sites with inadequate keratinized mucosa (KM 2mm) and adhered mucosal width (AMW 1mm). However, FGGs are historically associated with postoperative morbidity due to palatal harvesting and esthetic shortcomings. Previous studies demonstrate Buccal Strip Gingival Graft (BSGG) combined with a xenogeneic collagen matrix (XCM) as a minimally invasive, patient-centered alternative to achieve phenotype modification and improved esthetic results. To compare the clinical, ultrasonographic, and patient-reported outcome measures (PROMs) of both methods, a randomized control trial with 12 months of follow up is presented under a non-inferiority framework. Thirty-two participants (38 implants) were randomized (1:1) to receive either BSGG + XCM (n = 16) or FGG (n = 16). The primary success criteria were successful phenotype modification defined as KM ≥ 2 mm with adherent, non-movable tissue (AMW ≥ 1mm) at 12 months. Secondary endpoints included KM gain, AWM gain, vestibular depth, mucosal thickness, volumetric changes, and peri-implant soft-tissue stability. Ultrasonographic biomarkers and measurements such as soft tissue thickness gain, perfusion index (PI), elasticity, and echo intensity (EI) were evaluated as a surrogate marker of graft vascularization and collagen maturation. Peri-implant crevicular fluid (PICF) biomarkers were analyzed via ELISA to explore early wound-healing dynamics and their predictive value for final outcomes. PROMs, including postoperative pain, recovery time, esthetic satisfaction, oral health-related quality of life, and willingness to retreat, were recorded through standardized questionnaires and analyzed under a superiority framework. Mixed-effects regression models and Fisher’s exact tests were used for continuous and categorical analyses, respectively. Correlations between ultrasonographic perfusion parameters, clinical healing indices, and PROMs were also examined. Non-inferiority of BSGG + XCM relative to FGG was demonstrated when comparing the primary outcome of achieving KM ≥ 2mm and AMW ≥ 1mm (BSGG + XCM = 88.2%; FGG = 89.5%). KM gain, PD, and recession changes between both groups were statistically equivalent (p > 0.05). While FGG produced greater increased vestibular depth (p = 0.04), BSGG + XCM demonstrated significantly lower postoperative pain (p 0.01), faster functional recovery, higher esthetic satisfaction, quicker recovery time, and greater willingness to retreat (all p 0.05). Comparable soft tissue maturity between groups at 12 months were confirmed by ultrasonographic analysis. Early PICF biomarker expression patterns differed between groups, suggesting distinct biologic healing pathways; exploratory analyses indicated potential associations between early angiogenic and inflammatory mediator levels and final tissue outcomes. The BSGG + XCM approach achieves non-inferior clinical, ultrasonographic, and biomarker outcomes compared with FGG. The BSGG + XCM PROMs reported greater patient comfort, recovery, and esthetic satisfaction. FGG may yield greater dimensional soft tissue gains and vestibular depth, but it is associated with increased postoperative morbidity. BSGG + XCM provides a minimally invasive soft tissue alternative for peri-implant phenotype modification.