According to the Glossary of Periodontal Terms (2001), gingival recessions are defined as "location of marginal periodontal tissues apical to the cemento-enamel junction " . It is well known that the major causative factors in the development of marginal tissue recessions are a bucal/lingual malposition of the tooth, a thin gingival biotype, dehiscence and fenestration of the bucal alveolar bone and iatrogenic factors such as orthodontic treatment. A possible influence of occlusal trauma is still discussed. Localized gingival recessions and root exposure may cause an aesthetic problem for the patient and are often associated with dentine hypersensitivity . Further, root caries and persisting gingival inflammation are frequently observed. All of these situations represent an indication for regenerative periodontal therapy. In these cases the coverage of the recession is highly beneficial as it will facilitate plaque control, improve aesthetics and reduce root sensitivity. While complete root coverage can be achieved in class I and II defects, only partial coverage may be expected in class III. Class IV defects are not amenable for coverage. Consequently, in recessions that are suitable for coverage, the critical decisive clinical variable to estimate the possible outcome of root coverage procedures is the level of periodontal tissue support at the proximal surfaces of the tooth.
Various root coverage procedures have been used to cover localized gingival recessions, such as laterally repositioned flaps [3–5] coronally advanced flaps  free gingival grafts [7, 8] connective tissue pedicle flaps with a free gingival graft subepithelial connective tissue grafts [9–14] acellular human dermal matrix allografts  and guided tissue regeneration .
Collagen membranes, mostly bovine and porcine derived collagen types 1 and 3  are the membranes most frequently used in clinical routine. The ability of collagen to promote progenitor cell adhesion, chemotaxis, homeostasis and physiological degradation, together with easy manipulation and low immunogenicity makes it an ideal material for barrier preparation. Collagen is degraded by matrix metalloproteases (MMPs) . During wound healing, neutrophils, monocytes, and fibroblasts release MMPs to the wounded area, thus contributing to collagen membrane degradation. Some advantageous properties of collagen over other materials include hemostatic function, allowing early wound stabilization. Its chemotactic properties attract fibroblasts and their semi permeability allows nutritient transfer . Native collagen, however, has been reported to undergo a fast biodegradation. Common approach to slow down degradation is by increasing the amount of collagen cross liking by means of ultraviolet and γ radiation, hexamethylenediisocyanate, glutaraldehyde, diphenylphosphorilazide, and ribose have been successful in achieving collagen cross-linking [20, 21]. Chemical cross-linking, however, has been reported to inhibit the attachment and proliferation of osteoblasts and fibroblasts .
In an in vivo study Ghanaati et al. proved that a non-cross linked porcine derived collagen types 1 and 3 matrix i.e. Mucograft® remains stable as matrix after its well integration within the subcutaneous tissue of mice and human . However, only a mild vascularization of both, the matrix and its implantation bed was observed in both species.
It seems that non-cross linked porcine derived collagen types 1 and 3 are well integrated in the implantation bed and are able to contribute to soft tissue augmentation by undergoing integration and only a slow physiological biodegradation without the induction of a foreign body response . Accordingly, all non-cross linked collagen type I and III-based matrices, independent of the origin of the species, i.e. bovine or porcine with compositions similar to Mucograft® might bear the above-mentioned capacity to augment and enhance the soft tissue. To assess that, a new non-cross linked bovine pericardium derived collagen type I was clinically used, in order to evaluate its contribution to the periodontal plastic surgery. In this study a new method of increasing gingival thickness by implantation of acellular deproteinised soluble degraded bovine pericardium (Copios®) was used. Coverage, thickness, clinical attachment level and width of keratinized gingiva were examined.