Influence of topography and hydrophilicity on initial oral biofilm formation on microstructured titanium surfaces in vitro

Biofilm formation on dental implants is a persistent problem that can cause implant failure. Once a biofilm is formed, bacterial cells become highly resistant to antibiotics and host defenses (Costerton et al. 1999), and clinical experience has shown that biofilms must be removed physically before the infection can be resolved (Costerton 2005). There is an apparent clinical and microbiological similarity between peri-implantitis and periodontitis (Papaioannou et al. 1996; Listgarten & Lai 1999). However, it remains unclear whether the first steps in biofilm formation on titanium (Ti) implants are similar to biofilm formation on teeth. The biofilm formation process is extremely complicated and this is particularly true when multiple species are present in the biofilm as in dental plaque. This process is affected by many factors including environment, bacterial properties, and material surface characteristics, such as chemical composition, surface energy, hydrophilicity, and topography (Merritt & Chang 1991; An & Friedman 1998; Katsikogianni & Missirlis 2004). in vitro studies of biofilm formation on Ti surfaces have focused on the effects of surface morphology and surface chemistry (Yoshinari et al. 2000; Grossner-Schreiber et al. 2001; Barbour et al. 2007), but most biofilm models in these studies have only included one or two bacterial strains. In the oral cavity, however, the microbial ecology is complex and can consist of hundreds of species, each with a preference for specific microenvironmental properties. Studies investigating peri-implant microbiota in vivo have examined the influence of oral health status on the presence of specific bacterial species. Some of these studies report similar supra- and sub-gingival microbiota on teeth and Ti implants (Groessner-Schreiber et al. 2004; Furst et al. 2007; Shibli et al. 2008). In contrast, some studies found an absence of periodontal pathogens like Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans and Porphyromonas gingivalis (Heuer et al. 2007). On natural dental surfaces like enamel, the composition of the primary acquired pellicle plays an important role in determining the type and amount of bacteria that will attach (Gibbons 1996; Steinberg et al. 1998; Sela et al. 2007). Salivary and serum constituents can also adsorb onto Ti surfaces (Kohavi et al. 1995, 1997), and this is influenced by the structural and chemical properties of the surface (Katsikogianni & Missirlis 2004; Mabboux et al. 2004; Jeyachandran et al. 2006). Recent iterations of dental implant design are based on in vitro and in vivo studies showing that micron-scale and submicron-scale structural features increase osteoblast differentiation and peri-implant bone formation, which can be further enhanced by increased hydrophilicity (Cochran 1999; Buser et al. 2004; Lossdorfer et al. 2004; Schwarz et al. 2005, 2007a, 2007b; Zhao et al. 2005; Jimbo et al. 2008). Hydrophilic surfaces have a wicking effect on tissue fluids including blood, leading to adsorption of cell attachment proteins like fibronectin. While many cells involved in tissue regeneration use these proteins to adhere to the implant, the same proteins could also possess binding sites for bacteria (Quirynen et al. 2001; Plummer & Douglas 2006). However, the effect of these surface modifications on the attachment and growth of oral microorganisms, particularly under conditions that simulate the oral environment, is not known. The purpose of this study was to evaluate how biofilm formation and composition are affected by implant surface properties like microtopography and hydrophilicity using a regular culture medium (CM) or human saliva (HS).