A 40-year decline in permanent-tooth caries among 12-year-olds in Japan in the absence of systemic fluoride-based prevention: public health implications

OBJECTIVES: To re-examine Japan's long-term decline in permanent-tooth caries among 12-year-olds and assess its implications for population-level caries prevention beyond historically dominant systemic fluoride-centered prevention frameworks. STUDY DESIGN: Ecological analysis of national surveillance data. METHODS: We assembled long-term nationwide data from Japan on caries experience in 12-year-olds. Data were derived from standardized school dental examinations with high coverage and low temporal variability. Trends were examined descriptively and interpreted in relation to historically established systemic fluoride-caries prevention frameworks, including population fluoride exposure and long-term changes in sugar availability. RESULTS: Japan experienced a near-continuous decline in caries among 12-year-olds over approximately 40 years, reaching a national mean DMFT of 0.53 in 2023-well below levels historically reported in populations exposed to systemic fluoride through community water fluoridation. This decline occurred without community water fluoridation and largely before the approval of high-fluoride toothpaste in 2017 and its recommendation for school-aged children in 2023. Although sugar availability declined early, caries levels continued to fall long after sugar intake stabilized. CONCLUSIONS: Japan represents a rare natural social experiment demonstrating that sustained population-level caries reduction can occur through cumulative non-systemic fluoride pathways. These findings suggest fluoride-centered frameworks alone may not fully explain long-term population trends and support a broader multicausal approach to caries prevention. They may inform population-level oral health strategies in settings where reliance on systemic fluoride alone may be insufficient.