The Effects of Pellicle Formation on Streptococcal Adhesion to Human Enamel and Artificial Substrata with Various Surface Free-energies

Abstract

The influence of a pellicle on streptococcal adhesion was studied. A "ripened" two-hour salivary pellicle and an "early" five-minute salivary pellicle were formed on human enamel and artificial solid substrata with varying surface free-energies. Three strains of oral streptococci, also with widely different surface free-energies, were used for adhesion studies. Pellicle formation and streptococcal adhesion took place at a constant shear rate of 21 s-1. Adhesion of S. mitis BMS to bare and pellicle-covered enamel was low and not significantly affected by the presence of a pellicle (0.7 × 106 and 0.6 x 10 6 cells.cm-2, resp.), whereas the numbers of S. sanguis 12 and S. mutans NS adhering to bare enamel (4.2 x 106 cells.cm -2 and 13.8 x 106 cells.cm-2, resp.) were significantly reduced by the presence of a pellicle. This reduction was almost complete after only five minutes of salivary protein adsorption (1. 9 × 106 and 1.1 x 106 cells.cm-2 for S. sanguis and S. mutans, resp.) but further reduced for S. sanguis adhering to a ripened pellicle (0.7 × 106 cells.cm-2). The numbers of streptococci adhering at equilibrium to bare enamel could be fitted to a thermodynamically based model, which was previously described for bacterial adhesion to homogeneous artificial substrata. Streptococcal adhesion to artificial substrata exposed to saliva was low, and the differences among uncoated materials were markedly reduced even after only five minutes' exposure to saliva.