Elimination of ‘the Glasgow effect’ in levels of dental caries in Scotland’s five-year-old children: 10 cross-sectional surveys (1994–2012)

BACKGROUND Socioeconomic inequalities in health within Glasgow, Scotland, are among the widest in the world. This is largely attributed to socio-economic conditions. The 'Glasgow Effect' labels the finding that the high prevalence of some diseases cannot be fully explained by a conventional area-based socio-economic metric. This study aimed to investigate whether differences in dental caries between Glasgow's resident children and those in the Rest of Scotland could be explained by this metric and whether differences were of fixed magnitude, over time. METHODS Scotland's National Dental Inspection Programme (NDIP) cross-sectional data for five-year-old children in years: 1994, 1996, 1998, 2000, 2003, 2004, 2006, 2008, 2010, and 2012 (n = 92,564) were utilised. Endpoints were calculated from the mean decayed, missing and filled teeth score (d3mft) and percentage with obvious decay experience. Socioeconomic status was measured by DepCat, a Scottish area-based index. The Glasgow Effect was estimated by the odds-ratio (OR) of decay for Glasgow versus the Rest of Scotland adjusted by age, gender and DepCat. Inequalities were also assessed by the Significant Caries Index (SIC), SIC 10, and Scottish Caries Inequality Metric (SCIM 10). RESULTS Decay levels for deprived Glasgow children have reduced to be similar to those in the Rest of Scotland. In 1993, OR for d3mft > 0 for those living in the Glasgow area was 1.34(1.10, 1.64), p = 0.005. This reduced below unity in 2012, OR = 0.85(0.77, 0.93), p < 0.001. There were downward trends (p < 0.001) in absolute inequality measured by SIC and SIC 10 in each of the geographic areas. The SCIM 10 demonstrated further reductions in inequality across the population. The downward trends for all the inequality measures were larger for Glasgow than the Rest of Scotland. CONCLUSIONS Over the interval, Glasgow has eliminated the earlier extra health inequalities. When comparing 'like for like' by socioeconomic status there is now no higher level of dental caries in the Greater Glasgow area.