Aims:  To detect quantitatively the total bacteria and Streptococcus mutans in dental plaque by real‐time PCR with prbac, Sm and GTF‐B primers, and to compare their presence with the prevalence of dental caries in Japanese preschool children. Methods and Results:  Human dental plaque samples were collected from the labial surfaces of the upper primary central incisors of 107 children. The dental status was recorded as dft by WHO caries diagnostic criteria. Positive dt and dft scores by the Sm or GTF‐B primer were significantly higher than negative scores (P < 0·01). The proportions of Strep. mutans to the total bacteria from sound, and sound and/or filled upper primary incisors were significantly lower than those from decayed or filled, and decayed incisors, respectively (P < 0·01). Conclusions:  The ratios of Strep. mutans to total bacteria in plaque detected by real‐time PCR with Sm and GTF‐B primers were closely associated with the prevalence of dental caries in Japanese preschool children. Significance and Impact of the Study:  These assays may be useful for the assessment of an individual's risk of dental caries.

Since 1972, we have been conducting an annual clinical dental examination for young children at 13 nursery schools in the north district in Sendai, Japan. In the present study, we have included the results of examinations conducted in 1997 and 2002, and analyzed the time trends in caries experience of the primary dentition over a 30-year period from 1972 to 2002. The caries experience in the primary dentition markedly decreased in 1977 and remained stable for about 15 years, but in 1997, it markedly decreased again and continued to decrease in a linear fashion until 2002. The time trends in caries experience in the primary dentition in each age group were further analyzed by ascertaining caries experience in each tooth type. The results showed that, in 2 to 4-year-old, the decrease of caries experience for the primary maxillary incisors, canines and first molars seemed to stop decreasing in 2002, but for the 5-year-old, the caries experience for the maxillary incisors and canines and the maxillary and mandibular first and second molars markedly decreased from 1997 to 2002. Materials and MethodsThe ages of 1 year and 6 year were excluded from this study, because the number was not sufficient as subjects. All children aged 2-5 have been selected as subjects (Table 1). Calibrated dentists registered

: The aim of this study was to estimate the magnitude of genetic factors involved in the pathogenesis of Class III malocclusion in Japanese patients. We investigated 311 index cases (112 male, 199 female ; mean age 23.7 years) with Class III malocclusion. A questionnaire was used to determine the occurrence of Class III malocclusion among relatives. There were no significant differences in 1) the occurrence of this disease in index cases and the occurrence rates between the affected fathers and mothers, or between the affected grandfathers and grandmothers (either maternal or paternal), 2) the occurrence of this disease in index cases and the occurrence of Class III malocclusion in 1 or both of the paternal or maternal grandparents, 3) the risk of developing Class III malocclusion in the risk of a case developing Class III malocclusion according to the occurrence of the condition among parents and grandparents. The sibling recurrence risk (K5) obtained was 55.7% (95% confidence interval, 52.0-59.3), and the sibling recurrence risk ratio (As) was 18.8. The high sibling recurrence risk ratio supports a strong genetic background for Class III malocclusion in Japanese, and provides a basis for designing future genetic linkage studies.