The review team searched four major databases—PubMed, Web of Science, MEDLINE, and Scopus—for both observational and interventional studies that assessed whether fluoride interventions reduced social inequalities in tooth decay. They deliberately kept the focus tight. Studies conducted in institutional populations were excluded, as were studies that combined fluoride with other preventive measures, since bundling interventions makes it impossible to isolate what fluoride itself contributes to equity. The methodological rigor of the exercise was considerable: the team assessed the risk of bias in each included study using the ROBINS-E tool, designed specifically for non-randomized studies of exposures, and graded the certainty of the evidence with an adapted GRADE approach. Because the studies were too heterogeneous in design, populations, and outcome measures to pool statistically, no meta-analysis was possible—a limitation that itself says something about the state of this field.

What emerged from the search was a body of evidence dominated by a single intervention. Of the twenty-eight studies that met the inclusion criteria, twenty-six examined community water fluoridation, the practice of adjusting the fluoride concentration of public drinking water to a level known to protect teeth against decay. Only one study looked at fluoride toothpaste and one at fluoride mouth rinse. That imbalance matters, because water fluoridation is the flagship population-level fluoride policy in many countries, and it is precisely the kind of universal intervention that equity theorists argue should disproportionately benefit the most disadvantaged—reaching everyone regardless of income, dental insurance status, or access to a dentist.

The theoretical case for fluoridation as an equalizer is straightforward. Dental caries is driven by frequent sugar exposure, inadequate oral hygiene, and limited access to preventive care, all of which cluster along socioeconomic lines. A fluoride intervention delivered through the water supply requires no behavior change, no appointment, and no out-of-pocket payment, so it should, in principle, lift the oral health of those with the fewest resources the most. The review’s findings offered partial support for that logic. Some studies reported narrower social inequalities in dental caries in the presence of community water fluoridation, particularly when inequality was measured in absolute terms—for example, the raw difference in decayed, missing, and filled teeth or surfaces between socioeconomic groups.

But the picture darkened when the reviewers examined relative measures of inequality, such as ratios or indices that express the gap as a proportion of overall disease levels, and when they looked at formal effect-modification analyses, which test whether the fluoride effect differs by socioeconomic position. Across those analyses, the findings were inconsistent. This distinction between absolute and relative inequality is not a statistical nicety. Because tooth decay is generally more common in disadvantaged groups, an intervention that reduces decay everywhere can narrow the absolute gap while leaving the relative gap unchanged, or even widening it, simply because the baseline difference is so large. Which measure matters most is a value judgment as much as a scientific one, and the review’s inability to find consistent results across both types of measurement underscores how sensitive equity conclusions are to methodological choices.

There was also a striking demographic blind spot. Every one of the included studies focused on children and adolescents; not a single study examined adults or older populations. That is a significant gap given that dental caries is a lifelong, cumulative disease, and given that older adults—particularly those in aged care or on fixed incomes—face some of the highest rates of decay and the worst access to dental services. If fluoridation and other fluoride interventions are to be justified as equity-promoting policies, the evidence base will eventually need to extend beyond childhood. For now, claims about fluoride and inequality in adults rest on inference rather than direct evidence.

The quality assessment was, frankly, sobering. Twenty-seven of the twenty-eight included studies were rated as being at high or very high risk of bias, and only one achieved a moderate rating. None were judged low risk. This is not necessarily an indictment of the individual research teams; studying the population-level effects of water fluoridation is inherently difficult. Randomized trials are practically and ethically fraught when the exposure is a public water supply, so researchers rely on natural experiments, cross-sectional surveys, and before-and-after comparisons, all of which are vulnerable to confounding. Communities that fluoridate their water may differ systematically from those that do not, in wealth, in health infrastructure, in other preventive programs, and disentangling the fluoride signal from that background noise is genuinely hard.

Reflecting those limitations, the certainty of the evidence was graded as very low across the board: for community water fluoridation among children and adolescents, for topical fluoride interventions such as toothpaste and mouth rinse, and for evidence emerging from low- and middle-income country settings. In GRADE terminology, very low certainty means that the true effect could plausibly be substantially different from what the available studies suggest. The reviewers were careful in their conclusion: the findings suggested that community water fluoridation may contribute to narrower inequalities in dental caries among children and adolescents, but the certainty underpinning that suggestion was very low, and high-quality research is needed to establish both the causal relationship and the magnitude of the effect across different populations and settings.

Why does this matter beyond academic circles? Community water fluoridation remains politically contested in many countries, with periodic referendums and campaigns questioning its safety, its ethics, and its effectiveness. Proponents have long cited its equity benefits as a core justification, and the World Health Organization has endorsed it as a cornerstone population strategy against dental decay. This review does not overturn that case, but it does reveal how thin the evidentiary foundation for the equity argument actually is. Policymakers weighing fluoridation decisions are being asked to act on evidence that is suggestive rather than definitive, and on studies whose risk-of-bias ratings would make any clinical guideline committee wince.

The review also carries a message for researchers. The dominance of water fluoridation in the literature leaves topical fluoride—varnishes, toothpastes, rinses—almost unstudied from an equity perspective, despite the fact that these interventions require adherence and access, the very resources that disadvantaged populations lack. And the near-total absence of evidence from low- and middle-income countries means that global oral health policy is being guided by findings generated almost entirely in high-income settings, where water infrastructure, sugar consumption patterns, and dental care systems differ profoundly. The reviewers’ call for high-quality research is therefore not a routine academic plea; it is a roadmap. If fluoride is to serve as a genuine instrument of health equity, the next generation of studies will need to measure inequality explicitly, in both absolute and relative terms, across the full life course, and in the populations where the dental divide is widest.

Subject of Research: The effectiveness of fluoride interventions in reducing social inequalities in dental caries

Article Title: The effectiveness of fluoride interventions in reducing social inequalities in dental caries: a systematic review

Article References: Ge, Z., Guarnizo-Herreño, C. C., Ye, L., Kaur, G., Chen, Z., Hopcraft, M., & Singh, A. (2026). The effectiveness of fluoride interventions in reducing social inequalities in dental caries: a systematic review. International Journal for Equity in Health. https://doi.org/10.1186/s12939-026-03045-0

Image Credits: AI Generated

DOI: 10.1186/s12939-026-03045-0

Keywords: fluoride, community water fluoridation, dental caries, health inequalities, systematic review, socioeconomic position, oral health, public health, epidemiology, health equity, topical fluoride, children and adolescents