Influence of exposure to fluoridated water on socioeconomic inequalities in children's caries experience.

This study aimed to evaluate inequalities in children's dental caries experience among socioeconomic status (SES) groups and to investigate effects of exposure to fluoride in water on those inequalities. Cross-sectional data were obtained from 6704 Queensland children aged 5-12 years and 6814 South Australian children aged 5-15 years. School dental therapists and dentists recorded dmfs and DMFS data. A questionnaire to parents sought information about household SES and each child's lifetime exposure to fluoridated drinking water. SES fluoride exposure and multiplicative interactions between the two were used as explanatory variables in least squares models in which dmfs and DMFs were dependent variables. Additive interactions were evaluated by calculating the excess rate of disease. In both states, children from low SES groups (categorized by household income or parental education) had higher mean dmfs and DMFS values than children from high SES groups (P < 0.01). Independent effects of income and education remained significant (P < 0.01) after controlling for exposure to fluoride in drinking water. In Queensland, there was a significant multiplicative interaction whereby SES inequalities were lower among children exposed to fluoride: dmfs ratios between low- and high-income groups ranged among ages from 1.54 to 3.56 for children with no exposure to fluoride and from 0.84 to 2.07 for children with lifetime exposure to fluoride. Multiplicative interactions were not statistically significant in South Australia or when DMFS was the dependent variable. However, additive interactions were consistent and most pronounced for deciduous teeth in both States. Absolute differences in caries experience between low and high SES children were greater among non-exposed groups due to the higher underlying levels of caries experience of children with no exposure to fluoride in water.