The effect of community water fluoridation on social inequalities in dental caries

INTRODUCTION: Dental caries disproportionately affects those of low socio-economic status (SES). Such disparities are lower in areas with community water fluoridation (CWF). The Dunedin Study has followed 1037 babies born in 1972/73. Previous findings have identified lower social inequalities in deciduous-dentition caries experience among residents of areas with CWF. 

METHODS:   Participants were assessed at birth and ages 3, 5, 7, 9, 11, 13, 15, 18, 21, 26, 32, and 38 (when 95% of those surviving participated). The average family SES between birth and 15 was used here. Dental caries data reported here are for the permanent dentition only, and are presented as the Decayed, Missing, and Filled Surfaces index (DMFS). Exposure to CWF was categorised as pre-eruptive (prior to the eruption of the first permanent teeth at age 5-6) and post-eruptive. Data were analysed using group-based trajectory modelling. 

RESULTS: Low, medium, and high trajectories of dental caries experience were identified (resulting in DMFS scores averaging approximately 5, 20, and 50 tooth surfaces by age 38). Those with pre-eruptive exposure to CWF were less likely to follow the high and medium trajectories and more likely to follow the low trajectory. Low-SES individuals not exposed to pre-eruptive CWF were more likely to follow the high caries trajectory than those not of low SES who did have pre-eruptive exposure to CWF (RR 9.2, P<0.001);  low-SES individuals exposed to CWF did not have greater risk (RR 1.3, P=0.154). In all trajectory groups, the slope of each trajectory curve was significantly lower with post-eruptive CWF exposure and was greatest among those of low SES who were not exposed to post-eruptive CWF.

CONCLUSIONS:  Residence in an area with CWF before permanent-dentition eruption led to reduced SES inequalities and lower risk of high caries rates. Post-eruptive CWF exposure was also associated with lower caries rates.