Abstract
An analysis of the incidence of dental caries of one-and-a-half year-old children (n=656) was performed at Hakone, Japan, during the period from 1978 to 1982. Most caries was found at the maxillary 1st or 2nd deciduous incisors, and 100 (15.2%) had at least one df (decayed or filled) teeth at these sites. The df person rate (the rate of those who had at least one df tooth) varied by several factors: the rate was high among those who had heavier body weight than average, those who had been raised by grandparents, or those who had experienced eczema. The effects of these factors, except for the experience of eczema, could be partly explained by longer exposure of teeth to the oral environment because of an early eruption of the teeth, and partly by caries-prone environments related with sugar-rich and/or low pH conditions. However, the season of the subjects' birth also affected the df person rate. Those born in July-September had a higher rate and those born in October-December had a lower rate among both boys and girls. Only among girls, those born in January-March showed the highest df person rate (25.8%). The rate of those who had been raised by grandparents was high among the girls born in January-March, but the July-September peak was not correlated significantly with other confounding factors. When the subjects with the eczema experience were selected, those born in July-September showed a higher df person rate (40.0%). To explain the results, one could propose that some seasonal factors which affected the subjects at a particular stage of development during a pre-or perinatal period may have left some defects not only on the characteristics of teeth but also on other immunological characteristics.
