What question did this study set out to answer?

To estimate how explicit fluoride-related language in dental health ordinances affects participation in school-based fluoride mouth-rinse programs.

March 5, 2026Open Access

Impact of explicit fluoride-related language in prefectural dental health ordinance on fluoride mouth-rinse programs dissemination in Japan: a quasi-experimental study

Key Points

To estimate how explicit fluoride-related language in dental health ordinances affects participation in school-based fluoride mouth-rinse programs.
Longitudinal ecological design to analyze prefectural-level data from 2007 to 2018.
Categorization of ordinances based on explicit fluoride language: FMR, FA, and NF groups.
Use of Callaway and Sant'Anna Difference-in-Differences method to estimate treatment effects.
39 prefectures were analyzed for S-FMR participation.
FMR group saw a 12% increase in participation compared to FA and NF groups, which both had 5% increases.
Significant increases in S-FMR participation for FMR and FA groups compared to NF, with larger effects in the FMR group (8% increase).

Abstract

Objectives To estimate the impact of explicit fluoride-related language in prefectural dental health ordinance on the dissemination of school-based fluoride mouth-rinse (S-FMR) programs. Methods A longitudinal ecological design was employed to analyze prefectural-level panel data from Japan spanning 2007 to 2018. Ordinances enacted between 2010 and 2014 were categorized by the presence of explicit fluoride-related terms: 1) explicit mention of “fluoride mouth-rinse” (FMR group); 2) explicit mention of “fluoride application” (FA group); and 3) no fluoride-related policy language (NF group). The outcome was the proportion of children aged 4–15 years participating in S-FMR programs. Total prefectural income per year, prefectural mean age, and prefectural mean number of decayed, missing, or filled primary teeth (dmft) among 3-year-old children were included as covariates. The Callaway and Sant'Anna Difference-in-Differences (CSDID) method was applied to estimate the average treatment effects on the treated (ATT) for the FMR and FA groups under a conditional parallel trends assumption. Results A total of 39 prefectures were analyzed. The pre–post increase in S-FMR participation was greater in the FMR group than in the FA or NF groups, with comparable differences (FMR: 12%; FA and NF: 5% each). In the CSDID analysis, both the FMR and FA groups showed a significant increase in S-FMR participation compared with the NF group, with a larger effect in the FMR group FMR: 8% (95% CI: 2%–15%); FA: 5% (95% CI: 0%–9%). The event-study estimates indicated that the effects strengthened over time, particularly in the FMR group. Conclusions Prefectural dental health ordinances explicitly refer to fluoride, particularly FMR, are associated with a greater dissemination of the proportion of children participating in S-FMR programs. These findings suggest that more specific and explicit policy language in dental health ordinances may enhance the dissemination of S-FMR programs.

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