Volumetric changes of porcine collagen matrix and free gingival grafts for soft-tissue grafting to increase the width of keratinized tissue around dental implants: A retrospective clinical study

Aim The present study aimed at comparing three-dimensional changes of a porcine derived collagen matrix (CM) and free gingival grafts (FGG) for increasing keratinized tissue (KT) at dental implants over a 24-month follow-up period. Materials and Methods This retrospective study enrolled 25 patients exhibiting 41 implants with deficient KT width (i.e., < 2mm) at the vestibular aspect who underwent soft tissue augmentation using either CM (11 patients/15 implants) or FGG (14 patients/26 implants). The primary outcome was defined as tissue thickness change (mm) at treated implant sites between 1- (S0), 12- (S1), and 24-months (S2). Secondary outcome was the changes of KT width over a 24-month follow-up period. Results Dimensional analyses from S0 to S1 and from S0 to S2 revealed a mean decrease in tissue thickness of -0.05 ± 0.35 mm and − 0.31 ± 0.41 mm in the CM group, and − 0.23 ± 0.38 mm and − 0.22 ± 0.81 mm in the FGG group, with no significant differences found between the groups (patient-level analysis; S0-S1: p = 0.14, S0-S2: p = 0.58, Wilcoxon–Mann–Whitney U test). Within S1 and S2, the CM and FGG groups displayed comparable tissue thickness reduction (patient-level analysis; CM: -0.32 ± 0.53 mm, FGG: -0.02 ± 0.21 mm; p = 0.07). The FGG group exhibited a significantly greater KT gain after 12- and 24-months compared to the CM group (patient-level analysis: 12-months CM: 1.52 ± 1.23 mm, FGG: 4.22 ± 1.78 mm; p < 0.001; 24-months CM: 1.50 ± 1.14 mm, FGG: 4.04 ± 1.65 mm; p < 0.001, Wilcoxon–Mann–Whitney U test). Conclusions CM and FGG were associated with comparable three-dimensional thickness changes over a period of 24 months. A significantly wider KT band could be established in the FGG group.