## 1 Introduction  
Gingival recessions are single or multiple, partially exposed root surfaces of teeth connected with an apical shift of marginal gingiva in relation to the cemento-enamel junction [1]. The etiology of gingival recession is multifactorial. Possible morphological factors are the anatomy of bone structure as well as the size, shape and position of teeth and the surrounding soft tissues including gingiva, mucous membranes and muscles. Concerning functional factors the most significant one is mechanical damage, which most commonly is caused by improper and excessive tooth brushing. Furthermore, iatrogenic factors that occur during dental treatment, parafunctions or even chemical damage may result in the development of gingival recession. Another important etiological factor is the excessive accumulation of dental plaque, which in result will lead to the inflammation of periodontal tissue and hence to the loss of clinical attachment. Female sex and age have also been stated as possible risk factors [2]. Comprehensive treatment of gingival recession requires the elimination of most etiological factors favoring the development of gingival recession, as well as surgical root coverage and long-term maintenance of the results. Various surgical techniques are used today in the treatment of gingival recession but the most favorable and greatest documented method is the coverage of gingival recessions with the aid of an autogenous connective tissue graft taken from the hard palate together with the coronally advanced flap (CAF) technique [3; 4; 5; 6]. Despite certain differences in structure between the gingiva and the masticatory mucosa of the hard palate, the connective tissue graft collected from the hard palate is most commonly used in the treatment of gingival recession [7]. Gingival epithelial tissue shows more pronounced rete pegs, projecting locally and deeply into the underlying connective tissue layer. The lamina propria, being the first layer of connective tissue below the epithelium, shows a large number of fibroblasts and immune cells, mainly lymphocytes. On the other hand, the epithelial tissue of the mucous membrane of the hard palate is more regularly arranged, with shorter rete pegs and the lamina propria presents a smaller number of fibroblasts and a large amount of extracellular material, mainly filled with collagen fibers. There are no immune cells [8; 9]. The main component of fibrous connective tissue, constituting the lamina propria of the palatal mucosa and keratinized gingiva, are collagen fibers formed by fibroblasts [10; 11]. Fibroblasts participate not only in the formation of various fibers, mainly collagen, but also perform a role in the matrix synthesis [12]. The use of a graft increases the amount of connective tissue at the recipient site and the coronally advanced flap provides vascularization and thus nutrition for the graft. For anatomic and histological reasons, the palatal donor site is located between the canine and the second molar, bounded by the course of the greater palatine nerve and artery, resulting in a limited available graft size [13]. Generally, in case of multiple gingival recessions there is need for multistage proceeding. The minimal mucosal thickness of the donor site should be at least 2.5 mm for an optimal connective tissue graft. Given a reduced tissue thickness, the epithelial tissue is proximate to the bone and the amount of underlying connective tissue is limited. Hence, these grafts present a large number of epithelial cells [11]. The presence of a large amount of epithelial tissue in a connective tissue graft increases the risk of its rejection or even the formation of a surgical cyst and thus resulting in procedural failure [14]. Therefore, in the event of a thin palatal mucous membrane at the potential donor site, its extension and thickening (augmentation) is accomplished by biostimulation of connective tissue cells--fibroblasts. It is carried out by intramucosal implantation of collagenous biomaterial.