Collagen Membrane Fixation Technique Affects Its Space Maintenance Capacity After Flap Closure: An Ex Vivo Analysis

AIMS: To quantify immediate graft displacement following tension-free flap closure in non-contained alveolar ridge defects regenerated using three membrane fixation strategies in an ex vivo human model. METHODS: Eighteen sites from six fresh cadaveric heads with non-contained defects underwent horizontal guided bone regeneration using deproteinized bovine bone mineral and a collagen membrane stabilized by no fixation (NF), periosteal sutures (PS), or titanium fixation pins (FP). Techniques were applied sequentially. Cone-beam CT scans were obtained at baseline, post-grafting, and after passive closure. Linear ridge width was measured at 12 standardized positions, and graft volumes were segmented from STL reconstructions. Mixed-effects multilevel linear regression assessed width changes, while Friedman and paired Wilcoxon tests evaluated volumetric outcomes, with Tukey-adjusted contrasts for intergroup comparisons. RESULTS: ; 44.4% ± 17.9%) (loss p = 0.030; stability p = 0.002). Ridge collapse was greatest with no fixation (-1.37 ± 0.85 mm) compared with PS (-0.40 ± 0.62 mm) and FP (-0.28 ± 0.61 mm). After adjustment, PS and FP reduced collapse by 0.96 mm (p = 0.012) and 1.11 mm (p = 0.004), respectively. CONCLUSION: Even after passive flap release and tension-free closure, membrane fixation, particularly with titanium pins, provides superior resistance to graft displacement in non-contained defects, while unfixed membranes allow substantial graft loss and are therefore not recommended in non-contained defects.