Association Between Community Water Fluoridation and Severe Dental Caries Experience in 4-Year-Old New Zealand Children.

Importance: Robust contemporary epidemiologic evidence for the population-wide efficacy of reticulated community water fluoridation is required. Objective: To evaluate whether community water fluoridation is associated with the national rates of severe caries among 4-year-old children in New Zealand after accounting for key sociodemographic characteristics. Design, Setting, and Participants: This was a near whole population-level, natural, geospatial cross-sectional study of 4-year-old children who had a health and development assessment as part of the nationwide B4 School Check screening program conducted in New Zealand between July 1, 2010, and June 30, 2016. The extracted database included 391 677 children. However, geospatial information was missing for 18 558 children, another 32 939 children were unable to be geospatially matched, 5551 children resided in areas with changing fluoridation status, and 58 786 children had no oral health screen recorded, leaving 275 843 (70.4%) eligible children. Data were released in August 2019; statistical analysis was performed from September 2019 to December 2019. Exposures: Community water fluoridation status from 2011 through 2016. Main Outcomes and Measures: Severe caries experience derived from the "lift the lip" oral health screening. Analyses were adjusted for age, sex, ethnicity, area-level deprivation, and residential location differences. Multilevel mixed-effects logistic regression models were used. Sensitivity analyses based on multiple imputed data were undertaken to measure any differential influence of missing data. Results: In the eligible sample of 275 843 children, the median age was 4.3 years (interquartile range, 4.1-4.6 years), 141 451 children (51.3%) were boys, and 153 670 children (55.7%) resided within fluoridated areas. Severe caries were identified for 24 226 children (15.8%) in fluoridated and 17 135 children (14.0%) in unfluoridated areas, yielding an unadjusted odds ratio of 0.93 (95% CI, 0.90-0.95). However, in the adjusted analyses, children residing in areas without fluoridation had higher odds of severe caries compared with those within fluoridated areas (odds ratio, 1.21; 95% CI, 1.17-1.24). The population attributional fraction associated with unfluoridated community water was 5.6% (95% CI, 4.7%-6.6%) in a complete case analysis. Conclusions and Relevance: This study finds that community water fluoridation continues to be associated with reduced prevalence of severe caries in the primary dentition of New Zealand's 4-year-old children.

Area-level deprivation, childhood dental ambulatory sensitive hospitalizations and community water fluoridation: evidence from New Zealand.

BACKGROUND: We examined the association between area-level deprivation and dental ambulatory sensitive hospitalizations (ASH) and considered the moderating effect of community water fluoridation (CWF). The hypothesis was that higher levels of deprivation are associated with higher dental ASH rates and that CWF will moderate this association such that children living in the most deprived areas have greater health gain from CWF. METHODS: Dental ASH conditions (dental caries and diseases of pulp/periapical tissues), age, gender and home address identifier (meshblock) were extracted from pooled cross-sectional data (Q3, 2011 to Q2, 2017) on children aged 0-4 and 5-12 years from the National Minimum Dataset, New Zealand (NZ) Ministry of Health. CWF was obtained for 2011 and 2016 from the NZ Institute of Environmental Science and Research. Dental ASH rates for children aged 0-4 and 5-12 years (/1000) were calculated for census area units (CAUs). Multilevel negative binomial models investigated associations between area-level deprivation, dental ASH rate and moderation by CWF status. RESULTS: Relative to CWF (2011 and 2016), no CWF (2011 and 2016) was associated with increased dental ASH rates in children aged 0-4 [incidence rate ratio (IRR) = 1.171 (95% confidence interval 1.064, 1.288)] and aged 5-12 years [IRR = 1.181 (1.084, 1.286)]. An interaction between area-level deprivation and CWF showed that the association between CWF and dental ASH rates was greatest within the most deprived quintile of children aged 0-4 years [IRR = 1.316 (1.052, 1.645)]. CONCLUSIONS: CWF was associated with a reduced dental ASH rate for children aged 0-4 and 5-12 years. Children living in the most deprived areas showed the greatest effect of CWF on dental ASH rates, indicating that the greater health gain from CWF occurred for those with the highest socio-economic disadvantage. Variation in CWF contributes to structural inequities in oral-health outcomes for children.