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Effectiveness and safety of public water fluoridation Critical Summary Prepared by: Gerard Byrne BDSc MSD 

OVERVIEW

  • Systematic Review Conclusion:

    Public water fluoridation may be used where culturally acceptable to prevent dental caries.

  • Critical Summary Assessment:

    The evidence from clinical studies of low to moderate quality suggests that water fluoridation effectively reduces dental caries in children and adults, but is inconclusive about safety.

  • Evidence Quality Rating:

    Limited

A Critical Summary of:

Water fluoridation

Parnell C, Whelton H, O'Mullane D. European Archives of Paediatric Dentistry: Official Journal of the European Academy of Paediatric Dentistry. 2009;10(3):141-8

  • Clinical Questions:

    Is fluoridation of the water supply an effective and safe public health measure for preventing caries?

  • Review Methods:

    The authors limited their search to recent English-language systematic reviews from 2000 - 2008. They used SIGN guidelines to assess the quality of reviews. The data from the included reviews were qualitatively analyzed.

  • Main Results:

    The search yielded eight systematic reviews, of which one review included data from five of the other reviews; thus, three of the eight reviews were selected for further evaluation. The methodological quality of the included reviews was high, whereas the methodological quality of the reviewed studies was low to moderate. The results of two reviews that included 244 studies from 1940 to 2005 suggest that fluoridation of public water reduces caries prevalence (median increase of 14.6 percent caries-free children, Range: -5.0 percent - 64 percent), and that removal of water fluoridation also increases caries prevalence. Evidence to determine whether water fluoridation was beneficial in the presence of other sources of fluoride was inconclusive. A third review (nine studies) of adults aged 20 to 60 years showed significantly higher caries levels (p<0.001) in nonfluoridated groups as compared with fluoridated groups. There was insufficient evidence to conclude that water fluoridation reduces dental inequalities across social classes in terms of caries prevalence. Two reviews reported on adverse effects of water fluoridation, mainly fluorosis, but the studies were of low quality. There was a dose/response relationship between water-F level and the prevalence of fluorosis; the estimated proportion of the population with any fluorosis ranged from 15 percent (95 percent confidence interval [CI], 10 to 22) at fluoride concentrations of 0.1 parts per million (ppm) to 72 percent (95 percent CI, 62 to 80) at 4 ppm. The calculated absolute increase in prevalence of fluorosis of aesthetic concern at optimal water levels was small (4 to 5 percent). One review showed no clear association between water fluoridation and bone fracture, bone cancers, thyroid cancer or all cancers. There was insufficient evidence to establish any correlation between water fluoridation and a host of other potential systematic outcomes.

  • Conclusion:

    Best available evidence suggests that public water fluoridation is an effective way for preventing caries, and may be a valid choice as a population intervention. More studies are needed to explore potential nondental adverse effects of fluoridation on various populations.

  • Source of funding:

    University Dental School, Cork, Ireland.

Commentary:

  • Importance and Context:

    Fluoride has been an important caries prevention strategy since the 1950s. Worldwide, more than 350 million people drink fluoridated water. Despite voluminous research, water fluoridation remains controversial with questions regarding the balance between its benefits and long-term risks. Two recent national surveys show that the prevalence of very mild and mild enamel fluorosis has increased since the 1980s (National Health and Nutrition Examination Survey (NHANES), 1999-2004 and Oral Health of United States Children Survey, 1986-87).

  • Strengths and Weaknesses of the Systematic Review:

    This review used accepted methods to identify and select systematic reviews for examination. The authors clearly stated their search sources and selection criteria. For their 51 rejected reviews, the authors presented exclusion criteria. It may have been more informative to discuss all eight selected systematic reviews rather than three (one of which included five of the reviews). Because the authors acknowledged that studies conducted on adverse effects were of "low quality," evidence on safety of water fluoridation as a public health measure may be considered inconclusive, rather than conclusive.

  • Strengths and Weaknesses of the Evidence:

    The clinical studies included in the reviews were of low to moderate quality with only a small number of prospective cohort studies and not one random controlled trial. The included studies, all of which focused on caries prevention, evaluated readily observable adverse effects like fluorosis. Instead, the studies should have attempted to evaluate any other potential oral and systemic adverse events that while more difficult to assess, may be important in terms of determining safety of a population intervention.

  • Implications for Dental Practice:

    This systematic review confirmed that fluoridated public water effectively reduces caries prevalence in children and adults. There is a clear dose/response relationship between fluorosis and fluoride intake, with the fluoride coming from water and other sources. The review also found limited evidence to draw definitive conclusions on safety relative to other potential adverse effects of fluoride intake. When fluoridation of community water supply was originally instituted, it was the primary source of fluoride. However, the number of fluoride sources has increased over the decades. Recognizing this, the U.S. Department of Health and Human Services has recently proposed narrowing the recommended level of fluoride for community water systems from a range of 0.7 mg/L - 1.2 mg/L to 0.7 milligrams per liter (1).

    REFERENCE:
    (1). Department of Health and Human Services. “Proposed HHS Recommendation for Fluoride Concentration in Drinking Water for Prevention of Dental Caries”; Accessed at http://www.hhs.gov/news/press/2011pres/01/pre_pub_frn_fluoride.html. Accessed on April 19, 2011

  • Critical Summary Publication Date: 4/20/2011

These summaries are not intended to, and do not, express, imply, or summarize standards of care, but rather provide a concise reference for dentists to aid in understanding and applying evidence from the referenced systematic review in making clinically sound decisions as guided by their clinical judgment and by patient needs. American Dental Association ©

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