With similarities and differences in social economic and political

With similarities and differences in social, economic, and political contexts in Canada and the United States, it dihydrofolate reductase inhibitor antibacterial has been suggested that comparing these two countries holds important insights for understanding how structural determinants, such as social policies and economic resources, shape inequalities (Prus, 2011; Siddiqi & Hertzman, 2007). Cross-country comparative analyses have previously been performed using the Joint Canada-United States Survey of Health [JCUSH]; findings from these studies identify how societal differences have contributed to inequalities in self-rated health among individuals of different sociodemographic and socioeconomic characteristics (Siddiqi et al., 2013a, 2013b; Prus, 2011). Longitudinal analyses of health outcomes between Canada and the United States have also revealed how changes in societal factors, such as the degree of income inequality, equality in the provision of social goods, and extent of social cohesiveness have influenced health inequalities (Siddiqi et al., 2013a, 2013b).
In terms of oral health inequalities specifically, cross-country comparisons have been primarily performed across European countries (Bhandari et al., 2015; Guarnizo-Herreno et al., 2013a, 2013b; Bernabe & Sheiham, 2014; Guarnizo-Herreno, Watt, Pikhart, Sheiham, & Tsakos, 2014; Listl, 2015; Manski et al., 2015; Guarnizo-Herreno et al., 2013a, 2013b). Indeed, to date, only one study has examined inequalities in oral health between Canada and the United States. Elani and colleagues (2012) compared the prevalence of oral health and disease within and between Canada and the United States by income, place of birth, and education. They found greater narrowing of absolute differences among place of birth, education, and income in Canada in comparison to the United States (Elani, Harper, Allison, Bedos, & Kaufman, 2012). However, by relying on simple measures to quantify and compare differences in outcomes among income groups and between countries, their findings only scratched the surface towards understanding contributors to income-related oral health inequalities. Our aim was to provide breadth and depth of understanding to the nature of oral health inequalities by identifying how structural- and individual-determinants may influence oral health inequalities through a comparative analysis within and between Canada and the United States.

Structural determinants of oral health within Canada and the United States
We hypothesised that structural determinants, such as the characteristics of oral health care systems, as well as social and economic conditions shape individual-level determinants and population-level oral health inequality. Table 1 provides a comparative framework outlining changes to oral health care systems, as well as social and economic conditions in Canada and the United States from the 1970s to 2000s.



Interestingly, for measures of one or more decayed teeth, our results reveal that despite the decline in the level of untreated decay in both countries there have been increases in income-related inequalities over time (Tables 2 and 3). This is consistent with existing international literature where Mejia et al. (2014) found that as the prevalence of decayed teeth declines in a population, groups of higher socioeconomic status often experience the sharpest decline compared to other groups. They also reported greater social gradients in missing and untreated decayed outcomes with less inequality in filled teeth in an adult Australian population (Mejia et al., 2014). Our findings corroborate the claim that, although dental decay rates have declined over time, inequalities across the income gradient show the poor as having a disproportionately higher share of dental decay.
Our results indicate decreases in income-related inequalities in edentulism over time in both countries. This trend may be due to the overall decline in the prevalence of edentulism in both countries over the past 35 years. Another reason for these declines may be due to increases in tooth retention over the past four decades, which has been attributed to improved conservative dental care philosophies, such as an increased focus on prevention, as well as positive health-seeking behaviours and attitudes exhibited by the general population (U.S. Department of Health and Human Services, 2000).