Dental caries remains a significant public health problem. The 2010 Global Burden of Disease study finding that untreated caries in permanent teeth was the most prevalent condition, affecting 35% of global population. Links between fluoride and caries prevention were first identified in the 1930s, with community water fluoridation being introduce in American in 1945 and is now practiced in about 25 countries.

Although a large number of reviews of water fluoridation have been conducted the first comprehensive systematic review of water fluoridation was only published in 2000 (McDonagh 2000). One of the aims of this review was to update the McDonagh review however this review has narrower objectives focusing only on evaluation of the effects of water fluoridation (artificial or natural) on the prevention of dental caries and dental fluorosis.

Methods

Searches were conducted in the Cochrane Oral Health Group’s Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase, Proquest, Web of Science Conference Proceedings , ZETOC Conference Proceedings, US National Institutes of Health Trials Register and the WHO Clinical Trials Registry Platform.

For caries data, 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 least two points in time were considered. Any type of study design, with concurrent control, that compared populations exposed to different water fluoride concentrations was considered for the assessment of fluorosis.

Two reviewers independently selected studies, extracted data and assessed risk of bias. All studies including those from the previous McDonagh review were assessed using the Cochrane risk of bias tool modified for non-randomised studies.   Primary analysis was based on all studies regardless of risk of bias. A post hoc decision not to use GRADE terminology to describe the data was taken.

Results

• 155 studies met the inclusion criteria,
• 107 ((15 caries studies; 92 fluorosis studies)studies contributed to the quantitative synthesis.
• Most studies (71%) were conducted prior to the introduction of fluoridated toothpaste.
• Results from the caries severity data indicate that the initiation of water fluoridation results in a 35% reduction in dmft and a 26% reduction in DMFT compared to the median control group mean values.

	No. of studies	No. of patients	Mean	95% Confidence limit
Primary dentition
dmft reduction	9	44,268	1.81	1.31 to 2.31
% caries free	10	39,966	15%	11% to 19%
Permanent dentition
DMFT reduction	10	78,764	1.16	0.72 to 1.61
% caries free	8	53,538	14%	5% to 23%

•  There is insufficient information to determine if water fluoridation 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 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.

Fluorosis	No. of studies	No. of patients	Mean	95% Confidence limit
Of aesthetic concern	40	59,630	12%	8% to 17%
Any fluorosis	90	180,530	40%	35% to 44%

• Over 97% of the fluorosis studies were at high risk of bias and there was substantial between-study variation.

Conclusions

The authors concluded: –

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.

Comments

It is now 15 years since the publication of the York Review (McDonagh 2000) on water fluoridation so this thorough updating of two key aspects, caries reduction and fluorosis is welcome. More rigorous approaches have resulted in changes from that review in relation to evaluation of the cessation of water fluoridation programmes and the evaluation of socio-economic disparities in caries levels. Essential this means that there was insufficient data on these two elements.

The findings for caries reduction and fluorosis are similar to those in the York Review but it is worth noting that the included evidence only relates to children. The authors also highlight that the bulk of the evidence comes from before 1975, ie. prior to the widespread availability of fluoridated toothpaste and other topical fluoride preparation.

One area not addressed by this review is that of harms other than fluorosis, a wide range of potential harms (e.g. cancer, lowered intelligence, endocrine dysfunction) have been claimed and a number of these were considered by the York Review and more recently by the National Health and Medical Research Council (NHMRC 2007).

Links

Iheozor-Ejiofor Z, Worthington HV, Walsh T, O’Malley L, Clarkson JE, Macey R, Alam R, Tugwell P, Welch V, Glenny AM. Water fluoridation for the prevention of dental caries. Cochrane Database of Systematic Reviews 2015, Issue 6. Art. No.: CD010856. DOI: 10.1002/14651858.CD010856.pub2.

McDonagh M, Whiting P, Bradley M, Cooper J, Sutton A, Chestnutt I, et al. A Systematic Review of Community Water Fluoridation. NHS Centre for Reviews and Dissemination, University of York 2000.

CRD York Fluoridation Statement 2003

National Health and Medical Research Council (NHMRC), Australian Government. A Systematic Review of the Efficacy and Safety of Water Fluoridation. Canberra: National and Medical Research Council 2007.