Abstract
Sir, we are writing with regards to a recently published Comment in Evidence-Based Dentistry.1 This commentary on the Lotus study looking at the effectiveness of water fluoridation for adults and adolescents concluded that water fluoridation remains a cost-saving public health measure and pointed out some of the limitations of the study:
- The data extracted were not validated against an epidemiological standard
- The study looked at patients accessing NHS dental care, so it is representative only of those engaging with services (estimated at 63% of the population by the 2021 adult oral health survey).
However, the commentary did not discuss other limitations, which may have had significant impact on the results and interpretation:
- The fluoridated cohort had a greater proportion of people from the most deprived quintile
- Dentists have differing views on clinical intervention and this will impact on treatment provided; much restorative dental care is replacing failed restorations rather than addressing new carious lesions
- Tracing NHS numbers is less reliable for patients living in deprived areas so more of this population will have been excluded from the study
- Differential uptake of dental care and increasing privatisation of dental care for adults make reliance on NHS treatment data problematic as it is not representative of dental disease experience across the population
- The study compares people on average receiving more than 0.7 mg F/l with those receiving less than 0.7 mg F/l. As there is a recognised gradient of benefit for fluoridation, this approach may obscure benefits. The PHE Fluoridation Monitoring Report 2018 compared populations in receipt of public water supplies with a fluoridation scheme where the fluoride concentration averaged ?0.7 mg/l, versus populations where fluoride concentration averaged <0.2 mg/l. This comparison would have been more appropriate
- The fluoridation experience of the participants before 2010 is not considered. It is probable that some of the subjects in the fluoridated areas moved there from non-fluoridated areas before their first course of NHS dental care during the window 2010-2020, and vice versa for those in the non-fluoridated areas, who would have benefited from exposure to fluoridated water at a younger age.
Overall, this retrospective cohort study, which was pragmatic and achievable in the timescales available, adds to the research on community water fluoridation. In summary, the findings were:
- 3% fewer invasive treatments in the fluoridated group
- Mean DMFT in the optimally fluoridated group was 2% lower than in the non-optimally fluoridated group
- A saving in NHS treatment costs for optimally fluoridated patients over the study period of £22.26 per person
- A relative reduction in costs to the NHS of 5.5% per person
- The predicted Return on Investment (ROI) was estimated to be £16,884,595 (a 36% ROI made between 2010 and 2020).
However, the limitations of the study may greatly underestimate the impact of water fluoridation. Therefore, it is important that the limitations of this study are described clearly, so that policymakers can understand their significance.
J. Lewney, Paris, France, and D. Ramasubbu and B. Duane, Dublin, Ireland respond: Thank you for the opportunity to respond to this letter.
We were invited to produce a commentary on an already summarised version of the full LOTUS study.2As with many studies examining water fluoridation, the quality of evidence was graded as ‘Low’. This is due to the large number of limitations inherent in all studies aiming to examine the effects of water fluoridation.
We therefore chose to focus on the main limitations, alongside the key ways in which this summary paper outlined novel ways of measuring the effects of water fluoridation in this population. The authors of the original study outline some of these in more detail in the summary paper, and in particular, devote several pages to both the strengths and limitations of this study in the full report.3
We are pleased that our commentary is providing an opportunity to discuss this important topic in more detail.
References
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Ramasubbu D, Lewney J, Duane B. Investigating the effectiveness of water fluoridation. Evid Based Dent 2024; doi: 10.1038/s41432-024-01032-4.
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Moore D, Nyakutsikwa B, Allen T et al. How effective and cost-effective is water fluoridation for adults and adolescents? The LOTUS 10-year retrospective cohort study. Community Dent Oral Epidemiol 2024; 52: 413-423.
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Moore D, Nyakutsikwa B, Allen T et al. Effect of fluoridated water on invasive NHS dental treatments for adults: the LOTUS retrospective cohort study and economic evaluation. Public Health Res (Southampt) 2024; 12: 1-147.