Water fluoridation and ethnic inequities in dental caries profiles of New Zealand children aged 5 and 12–13 years: analysis of national cross-sectional registry databases for the decade 2004–2013

BACKGROUND: Gross and important inequities have historically existed in the oral health profiles of New Zealand children. Following the New Zealand Government’s strategic oral health vision, launched in 2006, nationally collected information from 2004 to 2013 was used to analyze patterns in the prevalence of no obvious decay experience (caries-free) and mean decayed-missing-filled teeth indices over time and by community water fluoridation (CWF) and ethnic classifications in New Zealand children aged 5 years and in school year 8 (generally aged 12–13 years). METHODS: National aggregated data collected from children’s routine child oral health service dental examinations were retrieved, and combined with demographic information from Statistics New Zealand. Children’s CWF status was defined by the public water supply status of their school. Crude and standardized population estimates of caries-free prevalence and mean decayed-missing-filled teeth indices over time were derived. Unweighted linear regression models of main effects and two-factor interactions were investigated by age group. RESULTS: Dental examination data were available from 417,318 children aged 5 years and 471,333 year 8 children; of whom 93,715 (22.5 %) and 94,001 (19.9 %), respectively, were Māori. Dental examination coverage of Māori children was significantly less than their non-Māori counterparts (approximately 11 % and 14 % for aged 5 and year 8 children, respectively). Regression analysis revealed that caries-free prevalence and mean decayed-missing-filled teeth indices significantly improved over the study period for both age groups. Significant and sustained differences were observed between Māori and non-Māori children, and between CWF and non-CWF exposed groups. However, a convergence of dental profiles between non-Māori children in CWF and non-CWF regions was observed. DISCUSSION: Significant and important gains in New Zealand children’s oral health profiles appear to have been made over the last decade. Māori children continued to carry a disproportionate oral health burden, even for those in CWF regions. The apparent profile convergence between non-Māori children in CWF and non-CWF regions is noteworthy; although a likely consequence of demographic shifts and unmeasured confounders. CONCLUSIONS: CWF itself did not remove disparities in caries levels between Māori and non-Māori children. Multiple, multi-pronged strategies are needed that overcome the array of factors which disadvantage Māori.