Authors' objectives:

The aim of this report is to assess the evidence on the positive and negative effects of population wide drinking water fluoridation strategies to prevent caries.

To achieve this aim five objectives were identified: 1: What are the effects of fluoridation of drinking water supplies on the incidence of caries? 2: If water fluoridation is shown to have beneficial effects, what is the effect over and above that offered by the use of alternative interventions and strategies? 3: Does water fluoridation result in a reduction of caries across social groups and between geographical locations, bringing equity? 4: Does water fluoridation have negative effects? 5: Are there differences in the effects of natural and artificial water fluoridation?

Authors' results and conclusions: Objective 1: The best available evidence (level B) from studies on the initiation and discontinuation of water fluoridation suggests that fluoridation does reduce caries prevalence, both as measured by the proportion of children who are caries-free and by the mean dmft/DMFT score. The degree to which caries is reduced, however, is not clear from the data available. Objective 2: An effect of water fluoridation was still evident in studies completed after 1974 in spite of the assumed exposure to fluoride from other sources by the populations studied. The meta-regression conducted for Objective 1 confirmed this finding. The studies included for Objective 2 were also of moderate quality (level B), but of limited quantity. Objective 3: The available evidence on social class effects of water fluoridation in reducing caries appears to suggest a benefit in reducing the differences in severity of tooth decay (as measured by dmft/DMFT) between classes among five and 12 year-old children. No effect on the overall measure of proportion of caries-free children was detected. However, the quality of the evidence is low (level C), and based on a small number of studies. The association between water fluoridation, caries and social class needs further clarification. Objective 4: The possible negative effects of water fluoridation were examined as broadly as possible. The effects on dental fluorosis are the clearest. There is a dose-response relationship between water fluoride level and the prevalence of fluorosis. Fluorosis appears to occur frequently at fluoride levels typically used in artificial fluoridation schemes. The proportion of fluorosis that is aesthetically concerning is lower. Although 88 studies of fluorosis were included, they were of low quality (level C). The best available evidence on the association of water fluoridation and bone fractures show no association. Similarly, the best available evidence on the association of water fluoridation and cancers show no association. The miscellaneous other adverse effects studied did not provide enough good quality evidence on any particular outcome to reach conclusions. The outcomes related to infant mortality, congenital defects and IQ indicate a need for further high quality research, using appropriate analytical methods to control for confounding factors. While fluorosis can occur within a few years of exposure during tooth development, other potential adverse effects may require long-term exposure to occur. It is possible that this long-term exposure has not been captured by these studies. Objective 5 The evidence on natural versus artificial fluoride sources was extremely limited, and direct comparisons were not possible for most outcomes. While no major differences were apparent in this review, the evidence is not adequate to reach a conclusion regarding this objective.

Authors' recommendations: This review presents a summary of the best available and most reliable evidence on the safety and efficacy of water fluoridation. Given the level of interest surrounding the issue of public water fluoridation, it is surprising to find that little high quality research has been undertaken. As such, this review should provide both researchers and commissioners of research with an overview of the methodological limitations of previous research conducted in this area. The evidence of a benefit of a reduction in caries should be considered together with the increased prevalence of dental fluorosis. The research evidence is of insufficient quality to allow confident statements about other potential harms or whether there is an impact on social inequalities. This evidence on benefits and harms needs to be considered along with the ethical, environmental, ecological, costs and legal issues that surround any decisions about water fluoridation. All of these issue fell outside the scope of this review. Any future research into the safety and efficacy of water fluoridation should be carried out with appropriate methodology to improve the quality of the existing evidence base.

Authors' methods: Systematic review

Project Status: Completed

URL for project: http://www.york.ac.uk/inst/crd/CRD_Reports/crdreport18.pdf

Year Published: 2000

English language abstract: An English language summary is available

Publication Type: Not Assigned

Country: England

Organisation Name: University of York

Contact Address: University of York, York, Y01 5DD, United Kingdom. Tel: +44 1904 321040, Fax: +44 1904 321041,

Contact Name: crd@york.ac.uk

Contact Email: crd@york.ac.uk

Copyright: Centre for Reviews and Dissemination