Effect of Zeta Potential and Surface Energy on Bacterial Adhesion to Uncoated and Saliva-coated Human Enamel and Dentin

Physicochemical surface characteristics of early plaque-forming bacteria and of human tooth surfaces were measured to establish their role in bacterial adhesion to intact dental tissue slabs. In addition, the influence of an experimental salivary pellicle was evaluated. Strains of S. mutans, S. sanguis, S. salivarius, A. viscosus, and A. odontolyticus showed relatively high surface free energies (range, 99-128 mJ.m-2) and carried a negative surface charge, at both physiological (mu = 0.057) and low (mu = 0.020) ionic strengths of the medium. Very large differences in hydrophobicity were detected when the hexadecane adsorption test was used for measurement. Powdered enamel and dentin were also negatively charged at low ionic strength but were slightly positively charged in the physiological buffer. The surface free energy of enamel and dentin increased upon saliva coating, whereas the surface charge was always negative. The adhesion experiments showed: (1) large differences in the binding of various bacteria to the same surface; (2) an up to 20-fold difference in the binding of the same bacterium to different surfaces, although the binding of some strains was relatively independent of the type of surface or presence of a salivary pellicle; (3) a significant decrease in adhesion when the ionic strength of the medium was lowered, due to increased electrostatic repulsion (however, the adhesion of some bacteria was independent of the ionic strength of the medium); (4) different time-dependent adherence kinetics, depending on both the bacteria and nature of the solid surface; and (5) a propensity for plaque streptococci to bind to uncoated dentin.