Title: Water fluoridation to prevent tooth decay
Authors: Iheozor-Ejiofor Z, Worthington HV, Walsh T, O’Malley L, Clarkson JE, Macey R, Alam R, Tugwell P, Welch V, Glenny A
Primary Review Group: Oral Health Group
Tooth decay is a significant problem worldwide affecting the majority of adults and children. Although levels of tooth decay have been decreasing in some communities (levels vary both between and within countries), generally children from poorer backgrounds (measured by income, education and employment) have greater levels of tooth decay.
Untreated tooth decay causes progressive destruction of teeth which is often accompanied by severe pain. This may lead to teeth having to be removed under local or general anaesthetic.
Fluoride is a mineral that prevents tooth decay. It occurs naturally in the soil, water and atmosphere at varying levels worldwide. Water can be artificially fluoridated (also known as community water fluoridation) through the controlled addition of a fluoride compound to a public water supply. Fluoridation is set at the ‘optimum level’, considered to be around 1 part per million (ppm).
Fluoride is also available in most toothpastes and can be provided as an extra preventive measure through products like mouth rinses, varnishes and gels.
An unwanted effect of fluoride use is the marking of permanent teeth (dental fluorosis) that is caused when young children, whose permanent teeth are developing, swallow excessive fluoride. This can range from mild white patches on the teeth to severe mottling with brown staining.
This review was conducted to assess the effects of water fluoridation (artificial or natural) for the prevention of tooth decay. It also evaluates the effects of fluoride in water on the white or brown marks on the tooth enamel that can be caused by too much fluoride (dental fluorosis).
Researchers from the Cochrane Oral Health Group reviewed the evidence – up to 19 February 2015 – for the effect of water fluoridation. They identified 155 studies in which children receiving fluoridated water (either natural or artificial) were compared with those receiving water with very low or no fluoride. Twenty studies examined tooth decay, most of which (71%) were conducted prior to 1975. A further 135 studies examined dental fluorosis.
Data suggest that the introduction of water fluoridation resulted in a 35% reduction in decayed, missing or filled baby teeth and a 26% reduction in decayed, missing or filled permanent teeth. It also increased the percentage of children with no decay by 15%. Although these results indicate that water fluoridation is effective at reducing levels of tooth decay in children’s baby and permanent teeth, the applicability of the results to current lifestyles is unclear because the majority of the studies were conducted before fluoride toothpastes and the other preventative measures were widely used in many communities around the world.
There was insufficient information available to find out whether the introduction of a water fluoridation programme changed existing differences in tooth decay across socioeconomic groups.
There was insufficient information available to understand the effect of stopping water fluoridation programmes on tooth decay.
No studies met the review’s inclusion criteria that investigated the effectiveness of water fluoridation for preventing tooth decay in adults, rather than children.
The researchers calculated that, in areas with a fluoride level of 0.7 ppm in the water, approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance.
Quality of the evidence
The review authors assessed each study included in the review for risk of bias (by examining the quality of the methods used and how thoroughly the results were reported) to determine the extent to which the results reported are likely to be reliable. This showed that over 97% of the 155 studies were at a high risk of bias, which reduces the overall quality of the results. There was also substantial variation between studies in terms of their results.
Our confidence in the size of effect shown for the prevention of tooth decay is limited due to the high risk of bias in the included studies and the fact that most of the studies were conducted before the use of fluoride toothpaste became widespread.
Our confidence in the evidence relating to dental fluorosis is also limited due to the high risk of bias and variation in the studies’ results.
Read the full abstract below
There is very little contemporary evidence, meeting the review’s inclusion criteria, that has evaluated the effectiveness of water fluoridation for the prevention of caries.
The available data come predominantly from studies conducted prior to 1975, and indicate that water fluoridation is effective at reducing caries levels in both deciduous and permanent dentition in children. Our confidence in the size of the effect estimates is limited by the observational nature of the study designs, the high risk of bias within the studies and, importantly, the applicability of the evidence to current lifestyles. The decision to implement a water fluoridation programme relies upon an understanding of the population’s oral health behaviour (e.g. use of fluoride toothpaste), the availability and uptake of other caries prevention strategies, their diet and consumption of tap water and the movement/migration of the population. There is insufficient evidence to determine whether water fluoridation results in a change in disparities in caries levels across SES. We did not identify any evidence, meeting the review’s inclusion criteria, to determine the effectiveness of water fluoridation for preventing caries in adults.
There is insufficient information to determine the effect on caries levels of stopping water fluoridation programmes.
There is a significant association between dental fluorosis (of aesthetic concern or all levels of dental fluorosis) and fluoride level. The evidence is limited due to high risk of bias within the studies and substantial between-study variation.
Dental caries is a major public health problem in most industrialised countries, affecting 60% to 90% of school children. Community water fluoridation was initiated in the USA in 1945 and is currently practised in about 25 countries around the world; health authorities consider it to be a key strategy for preventing dental caries. Given the continued interest in this topic from health professionals, policy makers and the public, it is important to update and maintain a systematic review that reflects contemporary evidence.
To evaluate the effects of water fluoridation (artificial or natural) on the prevention of dental caries.
To evaluate the effects of water fluoridation (artificial or natural) on dental fluorosis.
We searched the following electronic databases: The Cochrane Oral Health Group’s Trials Register (to 19 February 2015); The Cochrane Central Register of Controlled Trials (CENTRAL; Issue 1, 2015); MEDLINE via OVID (1946 to 19 February 2015); EMBASE via OVID (1980 to 19 February 2015); Proquest (to 19 February 2015); Web of Science Conference Proceedings (1990 to 19 February 2015); ZETOC Conference Proceedings (1993 to 19 February 2015). We searched the US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization’s WHO International Clinical Trials Registry Platform for ongoing trials. There were no restrictions on language of publication or publication status in the searches of the electronic databases.
For caries data, we included only prospective studies with a concurrent control that compared at least two populations – one receiving fluoridated water and the other non-fluoridated water – with outcome(s) evaluated at at least two points in time. For the assessment of fluorosis, we included any type of study design, with concurrent control, that compared populations exposed to different water fluoride concentrations. We included populations of all ages that received fluoridated water (naturally or artificially fluoridated) or non-fluoridated water.
Data collection and analysis:
We used an adaptation of the Cochrane ‘Risk of bias’ tool to assess risk of bias in the included studies.
We included the following caries indices in the analyses: decayed, missing and filled teeth (dmft (deciduous dentition) and DMFT (permanent dentition)), and proportion caries free in both dentitions. For dmft and DMFT analyses we calculated the difference in mean change scores between the fluoridated and control groups. For the proportion caries free we calculated the difference in the proportion caries free between the fluoridated and control groups.
For fluorosis data we calculated the log odds and presented them as probabilities for interpretation.
A total of 155 studies met the inclusion criteria; 107 studies provided sufficient data for quantitative synthesis.
The results from the caries severity data indicate that the initiation of water fluoridation results in reductions in dmft of 1.81 (95% CI 1.31 to 2.31; 9 studies at high risk of bias, 44,268 participants) and in DMFT of 1.16 (95% CI 0.72 to 1.61; 10 studies at high risk of bias, 78,764 participants). This translates to a 35% reduction in dmft and a 26% reduction in DMFT compared to the median control group mean values. There were also increases in the percentage of caries free children of 15% (95% CI 11% to 19%; 10 studies, 39,966 participants) in deciduous dentition and 14% (95% CI 5% to 23%; 8 studies, 53,538 participants) in permanent dentition. The majority of studies (71%) were conducted prior to 1975 and the widespread introduction of the use of fluoride toothpaste.
There is insufficient information to determine whether initiation of a water fluoridation programme results in a change in disparities in caries across socioeconomic status (SES) levels.
There is insufficient information to determine the effect of stopping water fluoridation programmes on caries levels.
No studies that aimed to determine the effectiveness of water fluoridation for preventing caries in adults met the review’s inclusion criteria.
With regard to dental fluorosis, we estimated that for a fluoride level of 0.7 ppm the percentage of participants with fluorosis of aesthetic concern was approximately 12% (95% CI 8% to 17%; 40 studies, 59,630 participants). This increases to 40% (95% CI 35% to 44%) when considering fluorosis of any level (detected under highly controlled, clinical conditions; 90 studies, 180,530 participants). Over 97% of the studies were at high risk of bias and there was substantial between-study variation.