Adhesion of oral streptococci to enamel and dental materials : studies using a flow chamber and microcalorimetry

Dental plaque formation on human teeth is the crucial etiologic factor in the pathogenesis of oral diseases: caries, periodontal diseases, and peri-implantitis. Dental plaque has been defined as a diverse community of microorganisms found on teeth as a biofilm, embedded in an extracellular polymer matrix of bacterial origin and including host components. Bacterial colonization starts with the adhesion of early colonizers, called pioneer bacteria, to the salivary pellicle on teeth as well as on dental materials within minutes after tooth cleaning. The early colonizers, mostly streptococcoci, contribute to plaque development and ultimately to oral diseases. Investigations of dental plaque, including bacterial adhesion, employ various in vivo and in vitro models and use microscopic methods to assess surface phenomena. The complexity of the oral environment makes it difficult to generate an in vitro system including all relevant aspects. The studies presented (paper I-III) were aimed to adapt two in vitro models, a flow chamber system and a microcalorimetric technique, for investigating adhesion of oral streptococci to human enamel, glass and different dental materials. The dental materials used for the flow chamber experiments (paper I + II) were titanium (Rematitan®M), gold (Neocast 3), ceramic (Vita Omega 900), composite (Tetric Ceram), and four different all-ceramics. The early colonizing Streptococcus sanguinis, S. oralis, and the caries-inducing S. mutans, and S. sobrinus were used as the model organisms. The saliva-coated materials were incubated with the bacteria in the flow chamber during one hour. Number and vitality of adhering bacteria were determined microscopically after staining. The results suggested that variations in the number and vitality of the adherent oral streptococci depend on the surface characteristics of the substrata and the acquired salivary pellicle. It also depended on the bacterial species, as S. mutans and S. sobrinus adhered about 10 x less than S. sanguinis and S. oralis.
Isothermal Microcalorimetry (paper III) indeed allowed evaluation of initial bacterial
adhesion of S. sanguinis to glass. Maximum heat flow measurements during adhesion were
about 10 fold lower than during bacterial growth. Experiments showed that increased surface
areas, provided by increased amounts of glass beads, were associated with higher energy
release. Heat flow was higher when cells were suspended in human saliva than in PBS.
Based on these results both methods appear to be applicable to study bacterial adhesion to
new dental restorative or implant materials. Advantages and disadvantages of the methods are
discussed.