Water fluoridation was introduced in the UK against a background of high dental decay within the population. Levels of decay have dramatically reduced over the last 40 years following widespread use of fluoride toothpaste.
The aim of the CATFISH (Cumbrian Assessment of Teeth a Fluoride Intervention Study for Health) study was to address the question of whether or not the addition of fluoride to community drinking water, in a contemporary population, lead to a reduction in the number of children with caries and, if so, is this reduction cost-effective?
A longitudinal prospective cohort design was used in two distinct recruited populations: (1) a birth cohort to assess systemic and topical effects of water fluoridation and (2) an older school cohort to assess the topical effects of drinking fluoridated water.
The study was conducted in Cumbria, UK. Broadly, the intervention group (i.e. individuals receiving fluoridated drinking water) were from the west of Cumbria and the control group were from the east of Cumbria.
Children who were lifetime residents of Cumbria were recruited. For the birth cohort, children were recruited at birth (2014–15), and followed until age 5 years. For the older school cohort, children were recruited at age 5 years (2013–14) and followed until the age of 11 years.
The provision of a ‘reintroduced fluoridated water scheme’.
Main outcome measures
The primary outcome measure was the presence or absence of decay into dentine in the primary teeth (birth cohort) and permanent teeth (older school cohort). The cost per quality-adjusted life-year was also assessed.
In the birth cohort (n = 1444), 17.4% of children in the intervention group had decay into dentine, compared with 21.4% of children in the control group. The evidence, after adjusting for deprivation, age and sex, with an adjusted odds ratio of 0.74 (95% confidence interval 0.56 to 0.98), suggested that water fluoridation was likely to have a modest beneficial effect. There was insufficient evidence of difference in the presence of decay in children in the older school cohort (n = 1192), with 19.1% of children in the intervention group having decay into dentine, compared with 21.9% of children in the control group (adjusted odds ratio 0.80, 95% confidence interval 0.58 to 1.09). The intervention was found to be likely to be cost-effective for both the birth cohort and the older school cohort at a willingness-to-pay threshold of £20,000 per quality-adjusted life-year. There was no significant difference in the performance of water fluoridation on caries experience across deprivation quintiles.
The prevalence of caries and the impact of water fluoridation was much smaller than previous studies have reported. The intervention was effective in the birth cohort group; however, the importance of the modest absolute reduction in caries (into dentine) needs to be considered against the use of other dental caries preventative measures. Longer-term follow-up will be required to fully understand the balance of benefits and potential risks (e.g. fluorosis) of water fluoridation in contemporary low-caries populations.
The low response rates to the questionnaires reduced their value for generalisations. The observed numbers of children with decay and the postulated differences between the groups were far smaller than anticipated and, consequently, the power of the study was affected (i.e. increasing the uncertainty indicated in the confidence intervals).
This study is registered as Integrated Research Application System 131824 and 149278.
This project was funded by the National Institute for Health and Care Research (NIHR) Public Health Research programme and will be published in full in Public Health Research; Vol. 10, No. 11. See the NIHR Journals Library website for further project information.
Plain English summary
Tooth decay is the most common disease of childhood, and tooth extraction due to decay is the main reason why children have a general anaesthetic in hospital. It is known that fluoride can prevent tooth decay and can be provided via the water. Research in the USA and UK in the 1940s/50s showed that water fluoridation produced dramatic falls in tooth decay. However, the introduction of fluoride toothpaste in the 1970s also caused large reductions in dental decay. We undertook a study in Cumbria to see if water fluoridation, reintroduced in 2013, was still useful in reducing tooth decay and if it represented good value for money.We recruited a group of children at birth from September 2014 to September 2015 (referred to as the birth cohort). In addition, a second group of children who were turning 5 years old in 2013–14 were recruited from primary schools (referred to as an older school cohort). We followed the birth cohort until age 5 years and followed the older school cohort until age 11 years, and measured whether or not the younger children had any obvious dental decay in their baby (milk) teeth and the older children had decay in their permanent (adult) teeth. We compared levels of decay in children living in areas with fluoridated water and in children living in areas without fluoridated water. We found that, in the case of the children followed since they were born, fluoridation did make a modest difference, with 4% fewer children who drank fluoridated water having obvious decay in their baby teeth. Although a difference of a similar size (3%) was seen in children in the older school cohort, where we looked at the permanent teeth, there was not enough evidence to determine if this difference was achieved by chance. For both groups of children, fluoridated water was likely to represent value for money. The 4% difference we found may not be large enough to convince communities to support water fluoridation schemes. Other ways of preventing tooth decay may be better now that use of fluoride toothpaste is so common and levels of tooth decay are much lower than they were 40 years ago.