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

## TL;DR

This study finds that including explicit mention of fluoride mouth-rinse in dental health policies in Japan led to greater adoption of school-based fluoride programs.

## Contribution

The study demonstrates that explicit policy language about fluoride mouth-rinse increases program adoption more than vague or absent language.

## Key findings

- Prefectures with explicit 'fluoride mouth-rinse' language saw a 12% increase in program participation.
- The FMR group had a larger effect (8%) compared to the FA group (5%) in longitudinal analysis.
- Event-study estimates showed growing effects over time, especially in the FMR group.

## Abstract

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.

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.

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.

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.