CDA Essentials 2018 • Volume 5 • Issue 1

36 | 2018 | Issue 1 S upporting Y our P ractice 4.3–17.8, p < 0.05). The magnitude of the effect is larger in the exposed group, although the 95% CIs overlap. Based on home postal code, survey respondents represented 216 communities. Information about fluoridation status was obtained for 62 (29%) of these. Of these, only 5 communities (all rural) would be classified differently based on the more precise geographic information. Because of the very small number of communities for which reclassification would make any difference, the initial intention to re-run urinary fluoride comparisons based on reclassifications was deemed unecessary. Discussion Findings suggest that fluoridation status based on data collection site, which seems quite crude, is reasonably accurate when compared with fluoride from urine, in the context of a large national Canadian population-based survey of both urban and rural residents. This statement is based on the statistically significant differences in mean urinary fluoride level between survey respondents classified as fluoridated versus non-fluoridated based on data collection site, which was robust to adjustment for covariates and was somewhat stronger among exposed (based on tap water consumption and residential history) versus non- exposed subpopulations. In addition to supporting the findings of our earlier paper, 5 where we used a site-based measure of exposure, these results are important in terms of options for monitoring fluoridation status at the population level. Specifically, population-based research on fluoridation exposure can be undertaken even in the absence of biomarker data, which is expensive and logistically complex to collect, as long as one has a general idea of each individual’s area of residence. A secondary objective of this study was to assess the added value of using more precise geographic information (home postal code) to classify fluoridation status. A noteworthy finding (although somewhat unexpected) was that it was not at all easy to obtain information on fluoridation status for communities in Canada. Of the 7 provinces represented in the survey, only 4 were able to provide some information, either specific information about the communities or a link to a resource (e.g., http://gis4.natr.gov.ns.ca/website/ nsgroundwater/viewer.htm). Conversations with provincial representatives revealed that, in some cases, this reflects limitations on data-sharing across ministries or agencies, such that databases that could link public water systems to postal codes may be incomplete, inaccessible or simply not exist. Based on the subset of communities for which fluoridation status was available, it appears to make little difference whether data collection site (crude) or geographic community of residence (more precise) is used to assign fluoridation status: only 5 communities (of 62), all rural, would have been classified differently. Based on the difficulty of securing fluoridation information at the community level, this is good news. However, because of these difficulties, information was only obtained for fewer than a third of communities (62 of 216), and the discrepancy may have been larger if it were based on all communities. Even if more precise geographic information has little added value for population-based fluoridation research, there may still be a reason to work toward a system where fluoridation information is readily available at a small area level in Canada. Such a resource would allow dental professionals to know and inform patients about local fluoride levels and to assist with treatment planning. Furthermore, it could permit members of the public to easily find reliable information about the fluoride content of their tap water, including how it fits into Health Canada safety guidelines. 7 There are excellent existing systems from which we could learn, such as the Water Fluoridation Reporting System in the United States 11 and the database of fluoridated local council areas in New South Wales, Australia. 12 An important study limitation is the use of spot urine samples, which are vulnerable to fluctuations. 6 The creatinine-adjusted estimates help offset this limitation to some extent. Another limitation is the absence of information on the use of supplemental fluoride or fluoride toothpaste and, thus, the role of these important potential confounders is unknown. Finally, findings are of limited utility for individual-level risk- factor analysis, such as fluoride intake and fluorosis risk. Strengths of the study include the use of a large, nationally representative sample, high-quality data and rigorous analysis. In conclusion, these findings may be useful to dental public health researchers and those engaged in public health surveillance, because they inform efficient and reasonably accurate options for monitoring fluoridation status in populations. a References Complete listofreferencesavailableat: jcda.ca/g17