The aim of this investigation was to study the effects of prolonged breast-or bottlefeeding on dental caries in Japanese infants. This longitudinal study was conducted by means of a questionnaire and clinical examination of 592 children at 18 months, 2 years and 3 years of age. The children were divided into three groups: 1) children still being breast-fed at 18 months of age (n‫;)24ס‬ 2) children still being bottle-fed at 18 months of age (n‫;)54ס‬ and 3) children weaned off of breast-or bottle-feeding and with no nonnutritive-sucking habits at 18 months of age (n‫.)502ס‬ Results showed that breast-feeding at 18 months of age produced many significant differences to the control children, including a higher prevalence of caries and higher number of dft. However, no significant differences were observed between bottle-fed and control children. In conclusion, our results suggest that prolonged breast-feeding at an early age before primary dentition has fully erupted is a risk factor for dental caries. Therefore, breast-fed children need to be monitored more closely, and aggressive methods of preventive care need to be instituted. It is also important to identify factors related to dental caries among breastfed children as soon as possible, and develop effective preventive programs.

The purpose of this study was to determine the time-window of infection for Streptococcus mutans between mother and child in Japan and which factors affected colonization by this microorganism. After obtaining informed consent, saliva was collected from the mothers and their children. These samples were serially diluted and inoculated onto Mitis-Salivarius agar and Mitis-Salivarius bacitracin plates, and then cultured under anaerobic conditions at 37°C for 5 days. Isolated mutans streptococci were identified by conventional biochemical characteristics and species-specific polymerase chain reaction based on the dextranase gene. No mutans streptococci groups were isolated from 0-5-month-old children with no erupted teeth. No statistically significant difference was found in detection rates in S. mutans among mother's milk, bottled milk or mixture. Cross-sectional study revealed that detection rates of S. mutans in the saliva samples increased with number of erupted teeth. Pulse-field gel-electrophoresis patterns obtained from isolated S. mutans using SmaI from the mothers and their children indicated that colonization by S. mutans in some Japanese children resulted from vertical transmission. In strains in which vertical transmission was observed, the mutacin IV and Smb A and B genes were detected from 8 out of 12 isolates. These results suggest that the window of infection for S. mutans is at around 6-23 months, and that colonization by this microorganism is mainly affected by number of erupted teeth. S. mutans between mothers and children or other family member has been reported 6,7). These reports suggest that S. mutans is acquired by horizontal transmission. It has been also demonstrated that children harbor plural genotypes of S. mutans, and that type changes with age 8). Genotypes of S. mutans have a fairly high consistency in children aged 3 to 8 years, indicating persistence in some strains 9). The conservation of S. mutans strains in a mother-child pair over a 3-year period has also been shown 10). However, the stability of the S. mutans genotype detected at initial acquisition time remains to be determined. The purpose of the present study was to determine