A stable band of keratinized mucosa (KM) around dental implants is believed to aid in minimizing tissue recession and provide resistance to mechanical, chemical, and biological challenges, thereby supporting the health of the surrounding hard and soft tissues. The evidence regarding the effect of KM on peri-implant health in animals is conflicting. Warrer et al. concluded that the presence of KM significantly reduced mucosal recession (MR) and attachment loss (AL), while Strub et al. observed no differences in recession or bone loss of peri-implant tissues between implants with and without adequate KM. Human studies evaluating the effect of KM on various peri-implant health-related parameters, have concluded that a lack of adequate KM around dental implants is associated with more plaque accumulation, tissue inflammation, MR, and AL. Moreover, since A stable band of keratinized mucosa (KM) around dental implants is believed to aid in minimizing tissue recession and provide resistance to mechanical, chemical, and biological challenges, thereby supporting the health of the surrounding hard and soft tissues. The evidence regarding the effect of KM on peri-implant health in animals is conflicting. Warrer et al. concluded that the presence of KM significantly reduced mucosal recession (MR) and attachment loss (AL), while Strub et al. (1991) observed no differences in recession or bone loss of peri-implant tissues between implants with and without adequate KM . Human studies evaluating the effect of KM on various peri-implant health-related parameters, have concluded that a lack of adequate KM around dental implants is associated with more plaque accumulation, tissue inflammation, MR, and AL. Moreover, since most patients do not consistently adhere to supportive peri-implant maintenance programs, it is important to evaluate the role of peri-implant soft tissue characteristics in the development of peri-implant diseases. A cross-sectional study examining the significance of KM on peri-implant and adjacent natural teeth was conducted on erratic peri-implant maintenance compliers. Implant sites with KM band width of \<2mm have been associated with significantly poorer clinical and radiographic parameters, suggesting a higher risk for peri-implant diseases. In response to this, a consensus report from the DGI/SEPA/Osteology Workshop emphasized the importance of measuring KM width as a part of the routine oral examination of peri-implant hard and soft tissues. In addition, if the prosthesis obstructs the identification of the peri-implant mucosal margin, its removal may be considered. Moreover, Implants with insufficient KM width require enhanced maintenance care, as they are more susceptible to plaque buildup and the development of peri-implant mucosal inflammation.
Soft tissue augmentation procedures are often implemented to improve the peri-implant soft tissue phenotype, namely the KM width, KM thickness, and supracrestal tissue height. Similar to natural teeth, soft tissue augmentation methods around implants have included autogenous techniques such as bilaminar- or apically positioned flap (APF) either alone or in combination with free gingival grafts (FGG), and connective tissue grafts (CTG). These approaches have demonstrated favourable medium to long term outcomes. Although autogenous grafts are still considered the gold standard for soft tissue augmentation procedures, a secondary interventional site for graft harvesting increases patients' morbidity. Additional intra and postoperative complications such as palatal bleeding, edema, infection, and sometimes necrosis has also been identified. Moreover, postoperative pain perception following palatal graft harvesting worsened and required additional treatment of the wound site to minimize discomfort and the need for analgesics. Additionally, the effectiveness of soft tissue augmentation may be limited by the availability of connective tissue at the donor site, particularly in cases requiring augmentation for deep horizontal alveolar defects or extensive edentulous gaps. To overcome these shortcomings, acellular dermal matrix (ADM) or xenogeneic collagen matrix (XCM) have been developed that may be associated with reduced pain perception, reduced surgery time, as they do not require an additional surgical site. While short term primary outcomes of achieving adequate zone of KM using these soft tissue substitutes have been comparable to those achieved with autogenous grafts, the efficacy of soft tissue augmentation procedures aimed at modifying the peri-implant soft tissue phenotype and their impact on peri-implant health have remained inconclusive . The network meta-analysis of randomized controlled trials demonstrated that bilaminar approaches involving CTG or ADM obtained the highest amount of KM gain, whereas APF in combination with FGG was the most effective technique for increasing KM width. KM augmentation via APF alone was associated with a significant reduction in peri-implant parameters like probing depths and plaque index, regardless of the soft tissue grafting material used, whereas bilaminar techniques with CTG or XCM showed beneficial effects on marginal bone level stability. The non-inferiority of XCM as compared to CTG or ADM have also been evaluated in various multi-center randomized controlled trials. Soft tissue augmentation with a cross-linked porcine-derived XCM at the time of implant placement showed substantial shrinkage of about 75% in areas between augmentation and 1-year follow-up. Overall, while 25% of the original soft tissue defect was eliminated by augmentation, XCM was deemed safe with no postoperative complications and limited marginal bone loss . Also, there is no consensus comparing the effectiveness of autogenous grafts and soft-tissue substitutes in achieving a stable, non-mobile peri-implant mucosa, which should be a key objective of these surgical procedures . Furthermore, there is no evidence regarding patient's preferences, studies assessing aesthetic outcomes have shown that soft tissue substitutes tend to deliver better results than FGG. However, no significant differences were observed when compared to CTG.
The timing of soft tissue augmentation around implants is a crucial factor, that may influence the choice of graft material, based on type of defect, quality and quantity of residual soft tissue and clinician's preference. The procedure is commonly performed before or at the time of implant placement, at the time of healing abutment connection or after final restorative phase. Soft tissue augmentation prior to implant placement or at healing abutment connection are considered the gold standard time points, due to the possibility of achieving complete coverage of the graft material through adequate tissue handling. Conversely, augmentation procedures at the time of implant placement or after crown delivery appears to be less predictable due to the different healing approaches and the unexpected shrinkage that may occur.
While the effectiveness of the XCM (Mucograft©, Geistlich Pharma® AG, Wolhusen, Switzerland) as a substitute for FGG around implants has been confirmed, its impact on peri-implant soft tissue phenotype modification when placed at the time of healing abutment connection requires further validation.
The aim of this randomized clinical trial is to evaluate clinical efficacy and patient-reported outcome measures (PROMs) of XCM compared to FGG for phenotype modification when conducted at time of healing abutment connection around dental implants over a short -term (6 months) and a long term (1- and 2- years) follow-up.
