# Longitudinal study of dental caries incidence associated with Streptococcus mutans and Streptococcus sobrinus in patients with intellectual disabilities

## TL;DR

This study shows that people with intellectual disabilities who have both S. mutans and S. sobrinus bacteria have more dental caries than those with only S. mutans.

## Contribution

The study is the first to longitudinally compare the caries incidence of S. mutans and S. sobrinus in patients with intellectual disabilities.

## Key findings

- Most subjects (83.5%) had S. sobrinus, and 78.7% had S. mutans.
- Subjects with both bacteria had significantly higher caries scores after one year.
- Caries increment was significantly greater in those with both bacteria.

## Abstract

Mutans streptococci (Streptococcus mutans and S. sobrinus) are considered to be major etiologic agents of dental caries. Using a polymerase chain reaction method, we detected those bacteria from 145 outpatients (6–30 years old) with intellectual disabilities (ID) and their presence was compared with the incidence of dental caries.

Plaque samples were collected from all erupted tooth sites in subjects with a sterile toothbrush. A dental examination was performed to determine the number of decayed and filled teeth (DFT score) in permanent dentition using the WHO caries diagnostic criteria. A Mann–Whitney U-test was employed to compare the caries scores between combinations of the bacteria, and with a Wilcoxon rank test used to compare caries scores between the baseline and after 1 year.

Among all subjects, S. mutans and S. sobrinus were possessed by 78.7 and 83.5 %, respectively, while 13.1 % were positive for S. mutans alone, 17.9 % for S. sobrinus alone, and 65.6 % for both organisms, with 3.4 % were negative for both. The mean DFT score of subjects positive for both S. mutans and S. sobrinus at after 1 year was significantly higher than that of those positive for S. mutans alone (P < 0.01). The increase in caries increment was also significantly greater in subjects with both bacteria detected (P < 0.001).

Our results indicate that patients with ID harboring both S. mutans and S. sobrinus have a significantly higher incidence of dental caries than those with S. mutans alone.