Method: This study used adults aged 35-44 years from nation-wide oral health survey data from Australia (n=1,200 in 1999; n=2,729 in 2005) Brazil (n=13,431 in 2003; n=9,779 in 2010), and USA (n=2,542 in 1999; n=1,596 in 2005). Dental examinations and questionnaires gathered information to define ID (<21 teeth), household income, age, and sex. Weighted prevalence of ID and associated factors were estimated for each time and country. Absolute inequalities were calculated using the Slope Index of Inequality (SII) and Absolute Concentration Index (ACI) while relative inequalities were assessed by means of Relative Concentration Index (RRC) and Relative Index of Inequality (RII). Per cent change of the indices across time was also calculated.
Result: Prevalence of ID in the studied period dropped from 8.7% (5.7-11.1) to 3.1% (2.3-3.9) in Australia; from 42.1% (39.1-45.1) to 22.4% (19.1-25.7) in Brazil and remained stable in USA, from 8.6% (6.6-10.5) to 7.3% (5.8-8.9). Absolute income inequalities were highest in Brazil, followed by the USA and Australia; relative inequalities were lower in Brazil than in Australia and the USA. Inadequate dentition was higher among Brazilian females (2010) and for the poorest group in all countries and periods. A remarkable reduction in absolute inequalities were found in Australia (SII and AIC 60%) and in Brazil (SII 25%; ACI 33%) while relative inequalities increased both in Australia (RCI and RII 40%) and in Brazil (RCI 24%; RII 38%). No changes in absolute and relative income inequalities were found in the USA.
Conclusion: Income-related inequalities on ID exist and are persistent over time but improvements were found. As a reduction in absolute inequality may result in increased relative inequality both should be reported and interpreted.