Materials and Methods
This research was carried out on 845 schoolchild-ren aged 9 years in Kerman, Iran, in 2012. In Iran, trained school nurses regularly examine health information of pupils in primary schools. Dental examination was carried out by school nurses to detect dental caries in accordance with WHO criteria (17). These health records and registered family structure information were used for selected pupils. Schoolchildren were selected through cluster random sampling technique. Nineteen schools were considered as clusters selected by random selection and all the schoolchildren in these schools were included in this study as samples.