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Open Access Research article

The association between social deprivation and the prevalence and severity of dental caries and fluorosis in populations with and without water fluoridation

Michael G McGrady*, Roger P Ellwood, Anne Maguire, Michaela Goodwin, Nicola Boothman and Iain A Pretty

BMC Public Health 2012, 12:1122  doi:10.1186/1471-2458-12-1122

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Are deprivation quintiles actually comparing like-with-like?

Karen Tocque   (2013-03-10 14:04)  Glyndwr University

This is a very interesting study which has the potential to add evidence to the debate about the extent to which water fluoridation and deprivation influence dental health. However, I query whether the measure of deprivation used in this paper, which asserts to compare social deprivation across the two cities, is actually comparing like-with -like. I have many years of experience of applying national quintiles of deprivation to ecological analyses such as these.

Manchester local authority was ranked 4th most deprived in England (IMD 2007) and Newcastle was ranked 66th �� ie. Newcastle is in the second most deprived decile of authorities. When using national quintiles of deprivation, Manchester does not have any small geographic areas (Census LSOA��s) in the most affluent fifth and 77% of the population lives in the most deprived national deprivation quintile (Figure 1 http://sdrv.ms/ZCe9pr). I therefore assume �� but it is not stated �� that this study has applied internal quintiles of deprivation within the two authorities. Thus, the most deprived fifth in Manchester will be significantly more deprived than the most deprived fifth in Newcastle �� likewise across all quintiles. The findings of this study, that dental caries experience is lower across all deprivation quintiles in an authority with fluoridated drinking water, is therefore (in part?) an artifact associated with this particular methodology.

I content that, whatever the extent of improvement in dental caries is actually due to water fluoridation, the analysis in this paper overestimates any reduction in dental health inequalities because it does not compare like-for-like measures of multiple deprivation. In order for the reader to make a judgment on comparability, the average IMD score for each quintile, in each city, would be useful �� not just for the overall population but also for the study sample. The authors�� conclusion that water fluoridation appears to reduce the social deprivation gradient in dental caries experience is therefore contentious.

Competing interests

No competing interest

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