Root caries and some related factors in 88-year-old carriers and non-carriers of Streptococcus sobrinus in saliva.

The prevalence of caries on exposed root surfaces in 88-year-old subjects with and without salivary levels of Streptococcus sobrinus was studied. Ninety-two individuals were examined with regard to root caries lesions and fillings. The root caries index (RCI) was calculated and related to salivary flow rate and buffer capacity, plaque score and salivary counts of Streptococcus mutans, S. sobrinus and lactobacilli. In 89 subjects with exposed root surfaces, all but 2 harbored mutans streptococci; 51 subjects carried S. mutans only, 35 both S. sobrinus and S. mutans, and 1 S. sobrinus only. The RCI was significantly higher in persons with than those without S. sobrinus (p < 0.05). Subjects with both S. sobrinus and S. mutans had higher counts of total mutans streptococci and lactobacilli than subjects with only S. mutans (p < 0.05). The RCI was significantly correlated to S. sobrinus and S. mutans (p < 0.05). The positive correlation between the RCI and S. sobrinus was still significant when the other tested variables were kept constant, whereas the correlation between the RCI and S. mutans was weaker when S. sobrinus and lactobacilli were kept constant. The D-component of the RCI (DSr%) was significantly correlated to S. sobrinus, S. mutans and lactobacilli, whereas the F-component of the RCI showed no significant correlation to any of the tested variables. A stepwise multiple correlation showed that the variance of DSr% was best explained in the S. sobrinus carriers by S. sobrinus and the salivary buffer effect, and in the non-carriers by S. mutans.