Dental implants are used to support removable and fixed reconstructions both at implant level as well as at the reconstruction level and exhibit long-term predictable outcomes in fully and partially edentulous patients (Gallucci et al. 2009, Jung et al. 2012, Pjetursson et al. 2012). The high survival and success rates of dental implants are based on the understanding of the principle of osseointegration, and on the soft tissue attachment in the transition zone (Abrahamsson et al. 1999, Abrahamsson et al. 1996, Berglundh et al. 1991, Branemark et al. 1977, Schroeder et al. 1976).

Following the initial healing phase, a soft tissue attachment is established surrounding the dental implant. The structure of the peri-implant mucosa has been investigated in a number of studies and has been shown to be similar to the soft-tissue barrier at teeth, with only minimal differences (Berglundh & Lindhe 1996, Berglundh et al. 1991, Berglundh et al. 1994, Berglundh et al. 1992, Ericsson et al. 1992).

The mucosal attachment appears to be independent of the surface texture of the implants as well as of the healing process, i.e. one-stage or two-stage procedures (Abrahamsson et al. 1999, Buser et al. 1992, Ericsson et al. 1996). In contrast, it was shown that the material selected for the transmucosal part of the implant influenced the healing pattern (Abrahamsson et al. 1998). The mucosal attachment for titanium and aluminium-based sintered ceramic abutments was similar, whereas impaired healing was observed around abutments made of a gold alloy or dental porcelain (Abrahamsson et al. 1998). Consequently, resorption of the marginal peri-implant bone took place and the mucosal attachment formed against the surface of the endosseous part of the implant body.

The quantity and quality of soft tissue attachment may affect the esthetic and functional outcome of implant reconstructions. A prerequisite for the development of optimal soft tissue conditions is the correct three-dimensional position of the dental implant. It was demonstrated that the presence of papillae at implant restorations depended on the vertical position of the periodontal attachment of the neighboring tooth (Choquet et al. 2001). The horizontal distance between the implant and the adjacent tooth also needs to be considered. It was suggested that a minimal distance of 1.5 mm would be necessary to compensate for remodeling processes (Esposito et al. 1998a, Esposito et al. 1998b). This indicates that the anatomy of implants and teeth is substantially different and has to be carefully considered during implant placement.

The soft tissue volume dimension on the buccal side of dental implants can influence the esthetic outcome (Jung et al. 2008). The critical soft tissue dimension at the buccal aspect of dental implants appears to be 2 mm. Where less than 2 mm of soft tissue are available, the reconstruction material can significantly influence the esthetic outcome (Jung et al. 2007, van Brakel et al. 2011).

According to systematic reviews, the scientific evidence for clinical studies on soft tissue volume augmentation is limited (Thoma et al. 2009, Thoma et al. 2014). The free gingival graft (FGG) and the subepithelial connective tissue graft (SCTG) were those most often used to increase soft tissue volume in the oral cavity (Thoma et al. 2009) (Figs 1 - 8). Long-term data on soft tissue volume augmentation are limited to pontic sites and are not available for implant sites (Sanz-Martin, et al. 2016).

The use of autogenous tissue is a disadvantage mainly attributed to the second surgical site (Griffin et al. 2006, Sanz et al. 2009). The harvesting procedure most often performed at the palate requires an additional surgical site, thus increasing patient morbidity with pain and numbness on the days following surgery (Del Pizzo et al. 2002, Farnoush 1978, Griffin et al. 2006, Soileau & Brannon 2006). The quantity and quality of tissue varies depending on the anatomical and individual shape of the palatal vault, the patient's gender and age. Further, the location of the palatal vessels and nerves limits the amount that is available when obtaining autogenous soft tissue grafts (Reiser et al. 1996, Soileau & Brannon 2006).

Alternative materials would be desirable to avoid a second surgical site. From a technical, biological and clinical aspect, any potential substitute intended to be used as a replacement for autogenous connective tissue grafts needs to fulfill the following criteria: i) successful integration of the graft into the surrounding tissue, ii) ability to degrade and be replaced by connective tissue, and iii) three-dimensional volume stability over time.

Even though recent research focused on the development of collagen-based matrices as a replacement for autogenous tissue (Thoma et al. 2011), these soft tissue substitutes are not available on the market yet. Today, the autogenous soft tissue graft harvested from the patient’s palate still remains the gold standard to achieve soft tissue volume augmentation at implant sites. It was shown that soft tissue volume augmentation contributed to more than 40% of the final volume at esthetic implant sites (Schneider et al. 2011).

There is controversy in the dental literature with respect to the question whether or not there is a need to augment keratinized tissue around dental implants in cases with a lack of or reduced width (Figs 9 - 15). A number of clinical studies suggested associations between an adequate width of keratinized tissue, higher survival rates of dental implants, health of the peri-implant mucosa, and an improved esthetic outcome (Adell et al. 1986, Artzi et al. 1993, Langer 1996). Based on three systematic reviews, this association could not be validated (Cairo et al. 2008, Esposito et al. 2007, Wennstrom & Derks 2012). Still, an increase in the width of keratinized tissue may be considered in order to simplify a patient’s oral hygiene and to maintain the mucosal tissue level.

Therapeutic intervention to increase the width of keratinized tissue is indicated and most predictably performed prior to the insertion of the dental implant or major bone augmentation surgeries. The procedure of increasing the width of the keratinized tissue makes subsequent surgical intervention simpler and minimizes the risk of wound dehiscences.

Based on the outcomes of two systematic reviews, the use of an apically positioned flap (APF) is a predictable therapeutic option to increase the width of keratinized tissue around teeth and dental implants (Thoma et al. 2009, Thoma et al. 2014). It was also demonstrated that, by the addition of autogenous tissue, treatment outcomes could be improved. Therefore, an APF in combination with autogenous tissue is considered to be the gold standard (Thoma et al. 2009).

Apart from autogenous tissue, a number of soft tissue substitutes were evaluated in the past. The main products used were of allogenic origin and in use in dental medicine for more than 15 years (Gapski et al. 2005) or of xenogenic origin (Lorenzo et al. 2012). Results from two randomized controlled clinical trials demonstrated that collagen matrices are as effective and predictable as the gold standard, the connective tissue graft, to attain a band of keratinized tissue around teeth and dental implants (Sanz et al. 2009) and around implants only (Lorenzo et al. 2012). In addition, patient-reported outcome measures were more favorable for the collagen matrix in both clinical studies. These data support the use of soft tissue substitutes in the future to reduce patient morbidity, while still rendering the desired clinical outcome (Esposito et al. 2012).