How effective and cost-effective is water fluoridation for adults and adolescents? The LOTUS 10-year retrospective cohort study

Objective: To pragmatically assess the clinical and cost-effectiveness of water fluoridation for preventing dental treatment and improving oral health in a contemporary population of adults and adolescents, using a natural experiment design.Methods: A 10-year retrospective cohort study (2010-2020) using routinely collected NHS dental treatment claims data. Participants were patients aged 12 years and over, attending NHS primary dental care services in England (17.8 million patients). Using recorded residential locations, individuals exposed to drinking water with an optimal fluoride concentration (>= 0.7 mg F/L) were matched to non-exposed individuals using propensity scores. Number of NHS invasive dental treatments, DMFT and missing teeth were compared between groups using negative binomial regression. Total NHS dental treatment costs and cost per invasive dental treatment avoided were calculated.Results: Matching resulted in an analytical sample of 6.4 million patients. Predicted mean number of invasive NHS dental treatments (restorations 'fillings'/extractions) was 3% lower in the optimally fluoridated group (5.4) than the non-optimally fluoridated group (5.6) (IRR 0.969, 95% CI 0.967, 0.971). Predicted mean DMFT was 2% lower in the optimally fluoridated group (IRR 0.984, 95% CI 0.983, 0.985). There was no difference in the predicted mean number of missing teeth per person (IRR 1.001, 95% CI 0.999, 1.003) and no compelling evidence that water fluoridation reduced social inequalities in dental health. Optimal water fluoridation in England 2010-2020 was estimated to cost 10.30 pound per person (excludes initial set-up costs). NHS dental treatment costs for optimally fluoridated patients 2010-2020 were 5.5% lower, by 22.26 pound per person (95% CI -21.43 pound, -23.09) pound.Conclusions: Receipt of optimal water fluoridation 2010-2020 resulted in very small positive health effects which may not be meaningful for individuals. Existing fluoridation programmes in England produced a positive return on investment between 2010 and 2020 due to slightly lower NHS dental care utilization. This return should be evaluated against the projected costs and lifespan of any proposed capital investment in water fluoridation, including new programmes.