Effectiveness of Community Water Fluoridation in Queensland: A Population-Based Causal Analysis Following the 2008 Policy Change

Water fluoridation (WF) is an important preventive program against dental caries. Recent Cochrane reviews reported only limited new scientific evidence of WF. This research aimed to provide contemporary evidence on the causal relationship between WF and oral health. A causal framework was used to ensure methodological rigour in repeated cross-sectional, population-based studies of randomly selected 5 to 14 y old children in Queensland, thereby enabling controlled difference-in-differences (DiD) analyses. The primary exposure was access to WF, defined as newly fluoridated (New-WF; areas that became fluoridated since 2010), never fluoridated (No-WF), or long-term fluoridated areas (Long-WF). The outcomes were dental caries experience (decayed, missing, or filled tooth surfaces) and prevalence in the primary and permanent dentition, collected by dental examiners who were uniformly trained and calibrated during both phases. The DiD estimands were the differences in changes in outcomes between New-WF and the control (No-WF), estimated from multivariable regression models. Data of 5,407 children during 2010-2012 and 7,718 children during 2022-2024 were collected. Variations in key confounders (area and individual socioeconomic factors) were controlled for using inverse probability of treatment weights. Dental caries among children in New-WF had consistently declined relative to the control groups. In the primary dentition, the New-WF children had a 1.40-fold (95% confidence interval [CI]: 1.08 to 1.80) reduction in caries experience and a 1.28-fold (1.00 to 1.67) reduction in caries prevalence, equivalent to 1.1 fewer affected tooth surfaces and a 10.8% lower prevalence. In the permanent dentition, reductions were smaller: a 1.32-fold (0.95 to 1.84) reduction in caries experience and a 1.04-fold (0.81 to 1.33) reduction in prevalence. These findings show that WF is effective in preventing dental caries in children when disease levels are low and other preventive programs are available. This controlled DiD study provides robust contemporary scientific evidence of the effects of WF on dental caries, strengthening WF as a public health policy.