Collagen Substitutes in Oral Soft Tissue Augmentation: An In Vitro–Ex Vivo Study on Expansion and Elasticity

ABSTRACT Objective This study aimed to evaluate the hydration‐induced volumetric expansion and elasticity of collagen‐based soft tissue substitutes following exposure to blood using three‐dimensional (3D) analysis and high‐frequency ultrasonography (HFUS). Materials and Methods Seven commercially available collagen matrices were analyzed: Fibro‐Gide (6 mm and 3 mm), Mucogain (5 mm and 3 mm), Volumax, Collagen Graft II, and Mucograft. The investigation consisted of two experimental phases. In the in vitro phase, samples were immersed in stabilized porcine blood to assess absorption index (AI), 3D volumetric changes, and ultrasonographic (HFUS) parameters, including density and elasticity. In the ex vivo phase, matrices were placed beneath envelope flaps in porcine maxillae, with optical 3D scanning performed before and after blood saturation. Statistical analysis included generalized estimating equations for repeated measures and nonparametric testing, with significance set at α  = 0.05. Results Volume stable matrices exhibited significantly greater absorption and volumetric expansion compared to non‐stable matrices. Fibro‐Gide 6 mm demonstrated the highest absorption index (17.0 ± 0.6 mg) and volumetric increase (268.4 ± 54.8 mm 3 ), while Mucogain 5 mm showed the greatest vertical expansion (0.83 ± 0.08 mm). Non‐stable matrices displayed reduced expansion or partial collapse. A positive, though non‐significant, correlation was observed between density (HFUS) and volumetric expansion ( r  = 0.29, p  = 0.535). Conclusions Volume‐stable collagen matrices show pronounced fluid uptake and expansion. Clinically, this effect should be considered, as excessive swelling may increase flap tension and compromise wound stability, necessitating careful trimming and adequate flap release.