OBJECTIVE: To isolate and identify Streptococcus mutans (Sm) and Streptococcus sobrinus (Ss) in dental plaque of children with high dmft and no caries by selective medium, biochemical methods and arbitrarily primed-polymerase chain reaction (AP-PCR). METHODS: A total of 401 3-4-year-old children from seven kindergartens were recruited using cluster sampling and their dental caries status were examined. From 30% of children with the highest dmft score (dmft >/= 5), 20 children were chosen randomly as test group and 20 age and gender-matched caries-free children were selected as control. Plaque samples were collected from buccal surfaces of the molars and plated onto TYCSB plate. Sm and Ss were primarily identified by colony morphology and biochemical characteristics. Then chromosomal DNA of the strains was isolated and Sm or Ss were confirmed by AP-PCR. RESULTS: The proportion positive for Sm and Ss in children with high dmft was 100% and 40% respectively while that in caries-free children was 75% and 5% by AP-PCR analysis. The differences were statistically significant between the two groups. CONCLUSIONS: The proportions positive for Sm and Ss detected by AP-PCR method were significantly higher in children with high dmft than in caries-free children and it is a risk factor for high dmft in deciduous teeth harboring Sm and Ss.
OBJECTIVE: To isolate and identify Streptococcus mutans (Sm) and Streptococcus sobrinus (Ss) in dental plaque of children with high dmft and no caries by selective medium, biochemical methods and arbitrarily primed-polymerase chain reaction (AP-PCR). METHODS: A total of 401 3-4-year-old children from seven kindergartens were recruited using cluster sampling and their dental caries status were examined. From 30% of children with the highest dmft score (dmft >/= 5), 20 children were chosen randomly as test group and 20 age and gender-matched caries-free children were selected as control. Plaque samples were collected from buccal surfaces of the molars and plated onto TYCSB plate. Sm and Ss were primarily identified by colony morphology and biochemical characteristics. Then chromosomal DNA of the strains was isolated and Sm or Ss were confirmed by AP-PCR. RESULTS: The proportion positive for Sm and Ss in children with high dmft was 100% and 40% respectively while that in caries-free children was 75% and 5% by AP-PCR analysis. The differences were statistically significant between the two groups. CONCLUSIONS: The proportions positive for Sm and Ss detected by AP-PCR method were significantly higher in children with high dmft than in caries-free children and it is a risk factor for high dmft in deciduous teeth harboring Sm and Ss.