Due to their generally good clinical outcomes, dental implants are now a common treatment for replacing lost or missing teeth. The key elements for the long-term success of such implants are the formation of a stable connection between the host bone tissue and the fixture surface (osseointegration) and integration of the transmucosal component, or abutment, with the soft tissues. Previously, much research has concentrated on the optimization of osseointegration but more recently the focus has shifted to include the development of biomaterials that enhance the formation of a peri-implant soft-tissue barrier. In the oral cavity, implant abutments protruding through the mucosa are exposed to a complex environment containing saliva and gingival exudate, as well as microorganisms. The microbial load in the oral cavity is very high, and up to 700 different species have been identified [
1]. After placement, the abutment surface rapidly becomes colonized by oral bacteria which can compete with epithelial and connective tissue cells for binding to the surface (for a review see [
2]). Typical examples of early colonizers on both hard and soft tissues in the oral cavity are streptococci, including
Streptococcus gordonii,
Streptococcus oralis,
Streptococcus mitis and
Streptococcus sanguinis, as well as species such as
Actinomyces naeslundii[
3,
4]. Adherence of these micro-organisms to the abutment surface can provide binding sites for a new set of colonizers eventually leading to the formation of mature plaque [
5,
6].
In natural teeth bacterial invasion into the periodontal soft-tissues is limited physically by the gingival mucosa, which forms a seal around the neck of the tooth. The epithelium also acts as a physiological barrier through the release of molecules involved in innate immunity including antimicrobial peptides and cytokines, as well as the initiation of inflammatory responses [
7]. In the case of dental implants the natural barrier consisting of junctional epithelium and the periodontal ligament is lacking, thus increasing the importance of a soft-tissue cuff of epithelial cells and fibroblasts tightly attached to the abutment. Studies in dogs have suggested the peri-implant mucosa can form a seal through a cuff of well-keratinized mucosa, analogous to that surrounding natural teeth [
8] and layers of epithelial cells have been identified in close association to titanium surfaces implanted into the oral mucosa [
9]. In addition, histological studies indicate that epithelial cells can attach to titanium surfaces by means of hemi-desmosomes similar to those found in the internal basal lamina [
10]. The arrangement of soft-tissues at the mucosal interface has been shown to be influenced by modification of titanium implant surface topography with oxidisation or acid etching, as well as chemical modification with laminin 5 [
11,
12]. Recently, the role of nanostructures on titanium implant surfaces in tissue healing has become a major focus of interest. Nanostructures, including nanopores and nanotubues, can be created by anodic oxidation, an electrochemical method in which variables such as voltage, electrolyte concentrations and time can be varied to create different nanotopographies. However, while effects of modifications on the nanometre level on osteoblast activity have been studied extensively [
13,
14], knowledge of how nanostructures influence peri-implant soft-tissue healing is currently limited. The few
in vivo studies that have been undertaken in rats [
15], dogs [
16] or humans [
17] (Wennerberg
et al.) suggest that the use of nanostructured titanium abutment surfaces might improve soft-tissue healing. One
in vitro study by Zile
et al. [
18] revealed that the density of keratinocytes on nanotubular and nanorough surfaces was increased compared to that on conventional titanium surfaces whereas for fibroblasts, such studies have shown increased cell adherence on nano-structured surfaces prepared by anodic oxidation [
19] but decreased adherence to nano-structured titanium coatings on silicone [
20]. While these
in vitro studies have shed light upon possible positive effects of such surfaces,
in vivo, the situation during the initial stages of healing is much more complex, where cell attachment occurs in the presence of early colonizing oral bacteria such as oral streptococci. Therefore in this study, we have investigated the adherence of human keratinocytes and gingival fibroblasts to nano-structured titanium surfaces and also evaluated the effect of a bacterial consortium containing
Streptococcus gordonii,
Streptococcus oralis,
Streptococcus mitis and
Streptococcus sanguinis on adhesion of keratinocytes to the surfaces.