Study designs of evaluations included in the review
Any study design that compared populations exposed to different water fluoride concentrations was considered. In addition, the authors applied inclusion criteria relating to the level of evidence, based on the risk of bias. Studies rated below level B (moderate quality, moderate risk of bias) was not considered in the evaluation of efficacy. All levels of evidence were included in the assessment of safety.
Specific interventions included in the review
Any study that examined changes to water fluoridation levels was included. The inclusion criteria specified that the work had to be a primary study involving humans, relate directly to fluoride in drinking supplies, and involve two groups with different fluoride concentrations. Studies of caries had to evaluate two points in time, one of which was less than three years since the change in water fluoridation status in one of the two groups. The results obtained from areas using artificially and naturally fluoridated water supplies were compared to investigate any differences in effect.
Participants included in the review
Populations receiving fluoridated water (natural or artificial) and those with unfluoridated water were considered. The efficacy studies usually included children aged 5 to 15 years.
Outcomes assessed in the review
The efficacy outcomes were any measure of dental decay in primary or permanent teeth and the proportion of children with dental caries. Safety was measured by dental or skeletal fluorosis, hip fractures, cancer congenital malformation, mortality and any other negative effect reported in the literature.
How were decisions on the relevance of primary studies made?
Three reviewers independently assessed each title and abstract located through the searches, then independently assessed each paper for the predetermined inclusion criteria. Any disagreements were resolved through consensus.