As a consequence, recent research focused on soft tissue augmentation of thin gingiva types prior to or simultaneous to implant insertion. Wiesner et al. published a significant gain of soft tissue by thickening the gingiva with a connective soft tissue graft harvested from the palate [12]. Soft tissues at augmented sites were 1.3 mm thicker than on control sites and had a better pink esthetic score. However, this technically sensitive procedure did not lead to less peri-implant bone loss (0.8 mm in the grafted group, 0.6 mm in the non-grafted group after 1-year loading).

Lai et al. and Linkevicius et al. reported a successful vertical augmentation of soft tissue by using an acellular dermal matrix membrane [13, 14]. Furthermore, Linkevicius showed that thickening with an allogenic membrane resulted in significantly reduced initial bone loss (0.21-mm bone loss in the augmented group, 1.17-mm bone loss in the control group after 1-year follow-up) [14].

Another attempt to influence the peri-implant bone structures is the use of platelet-rich fibrin (PRF). This second-generation platelet concentrate described by Choukroun et al. is a fibrin matrix enriched with cytokines, circulating progenitor cells, and growth factors which can be used as a resorbable membrane in surgery. Studies show a constant release of growth factors such as PDGF (platelet-derived growth factor) or TGF-b (transforming growth factor) for at least 1 week [15, 16] up to 28 days [17] and proved its accelerating effect on the healing process. The application of PRF has been tested in various disciplines of dentistry so far. However, no data of vertical soft tissue augmentation with PRF has yet been published.

The aim of this randomized, controlled clinical trial was to evaluate whether the use of PRF is suitable for soft tissue thickening of the peri-implant mucosa and to assess the marginal bone level changes.