Quantitative analysis of the adhesion of cariogenic streptococci to orthodontic metal brackets

The aim of this study was to analyze the adhesion of cariogenic streptococci to orthodontic metal brackets in terms of the type of bacterial strains, the incubation time, and saliva coating. Two strains of Streptococcus mutans (S. mutans LM7 and S. mutans OMZ65) and two strains of S. sobrinus (S. sobrinus B13 and S. sobrinus 6715) were used. Twenty metal brackets were incubated with either unstimulated whole saliva or phosphate-buffered saline for two hours. The bacterial adhesion assays were then performed by incubating the tritium-labeled streptococci with saliva-coated or noncoated orthodontic brackets for three, six, or nine hours. The results showed a characteristic binding pattern according to the type of bacterial strains used. S. mutans OMZ65 showed the highest amount of adhesion, whereas S. sobrinus B13 showed the lowest amount of adhesion. Generally, an extended incubation time increased the adhesion of cariogenic streptococci, and the amount of adhesion was the highest after nine hours of incubation. The saliva coating did not significantly influence the adhesion of bacteria. However, this saliva-mediated adhesion differed according to incubation time. The saliva coating tended to gradually decrease the adhesion by the extended incubation time, compared with the noncoated controls. This study indicates that each strain of cariogenic streptococci has a characteristic adhesion pattern and the type of bacterial strain, the incubation time, and saliva influenced the adhesion.