Objectives: One argument made in favour of drinking water fluoridation is that it is equitable in its impact on oral health. We examined the association between exposure to fluoridation and oral health inequities among Canadian children.

Participants, setting and intervention: We analyzed data from 1,017 children aged 6–11 from Cycle 1 of the Canadian Health Measures Survey, a cross-sectional, nationally representative survey that included a clinic oral health examination and a household interview. The outcome measure was a count of the number of decayed, missing (because of caries or periodontal disease) or filled teeth, either deciduous or permanent (DMFT). Data were analyzed using linear (ordinary least squares) and multinomial logistic regression; we also computed the concentration index for education-related inequity in oral health. Water fluoridation status (the intervention) was assigned on the basis of the site location of data collection.

Outcomes: Fluoridation was associated with better oral health (fewer DMFT), adjusting for socio-economic and behavioural variables, and the effect was particularly strong for more severe oral health problems (three or more DMFT). The effect of fluoridation on DMFT was observed across income and education categories but appeared especially pronounced in lower education and higher income adequacy households. DMFT were found to be disproportionately concentrated in lower-education households, though this did not vary by fluoridation status.

Conclusions: The robust main effect of fluoridation on DMFT and the beneficial effect across socio-economic groups support fluoridation as a beneficial and justifiable population health intervention. Fluoridation was equitable in the sense that its benefits were particularly apparent in those groups with the poorest oral health profiles, though the nature of the findings prompts consideration of the values underlying the judgement of health equity.