CI: Confidence Intervals; COPD: Chronic Obstructive Pulmonary Disease; EQ-5D-5L: EurQoL Instrument

It is impossible to conceive of oral health outside of general health. Evidence suggests that both the short- and long-term systemic diseases are associated with poor oral health [1], including diabetes [2], cardiovascular disease [3], renal disease [4], respiratory disease in particular for chronic obstructive pulmonary disease (COPD) [5], osteoporosis [6] and Alzheimer’s disease [7]. Oral diseases in and of themselves, such as dental caries, periodontal disease and oral cancers, can cause pain and tooth loss, impact masticatory function, and subsequently impact nutritional intake [8,9]. Oral and general diseases share common risk factors, including aging, tobacco smoking, lack of physical activity and obesity [5,10].

Indigenous Australians include Australians who identify as Aboriginal and/or Torres Strait Islander Australians, and comprise 3.3% of the total Australian population [11]. Evidence suggests that Indigenous Australians score worse on both general [12] and oral health [13], compared to their non-Indigenous counterparts. Indigenous Australians have a 2.3 times higher total burden of diseases, 2.7 times higher burden of fatal diseases and a higher mortality rate, resulting in an approximately 10 years lower life expectancy than non-Indigenous Australians [12,16,17]. Indigenous Australians experience poorer oral health than non-Indigenous Australians, with a higher prevalence of dental caries, periodontal disease, oral mucosal disease and oral cancer [18,19].

Self-reported oral and general health are widely used to provide insight into how individuals view their oral and general health in a holistic sense, which is unique and distinct from clinical diagnoses. Self-reported oral heath typically answers the question: ‘How would you rate your oral health? Or ‘How many natural teeth do you have remaining in the upper and lower jaws?’ Both questions have been validated against clinical estimates [20,21]. EurQoL (EQ-5D-5L) is a valid and reliable non-clinical standardized self-rated instrument that is widely used to estimate general health-related quality of life by assessing an individual’s wellbeing (including physical and psychological state) [22,23].

Few studies compare general health using EQ-5D with respect to its individual dimensions in relation to oral health among Indigenous and non-Indigenous peoples. The aim of this study was to therefore investigate and compare the relationship between self-reported oral and general health-related quality of life among Indigenous and non-Indigenous Australians. The hypothesis was that both self-rated oral and general health-related quality of life would be poorer in Indigenous compared with non-Indigenous Australians.

Data sources

Data from two studies was used.

• Study 1 was a large convenience sample (n=1,011) of Indigenous Australian adults in South Australia aged 18+ years, conducted between February 2018 and January 2019 [24]. Just over one-third (33.6%) of participants were male. Ethics approval was obtained from the University of Adelaide Human Research Ethics Committee (H-2016-246) and the Aboriginal Health Council of South Australia (04-17-729). All participants were provided with an information sheet outlining the study objectives and signed an informed consent form.
• Study 2 was the Spring Health Omnibus Survey [25], conducted by a market research company to provide a valid and reliable estimate for South Australians aged 15+ years. Data from n=2,891 was obtained between Sept and Dec 2013. Ethics approval was granted by the University of Adelaide’s Human Research Ethics Committee.

Instruments

The same global self-rated measures for oral and general health were used in the two studies.

• The global self-reported oral health item in Study 1 was: Would you rate your oral health as ‘excellent, very good, good, fair, or poor’, and dichotomized into ‘Fair/poor’ and ‘Excellent/very good/good’; Study 2 used the item ‘How many natural teeth do you have? remaining in the upper and lower jaw’. The response was dichotomized into ‘less than 21 teeth’ and ’21 or more teeth’. For comparison, self-reported oral health was re-named as ‘Poor’ (including ‘Fair/poor’ and ‘less than 21 teeth’) versus ‘Excellent/Good’ (including ‘Excellent/very good/good’ and ‘21 or more teeth’).
• Global self-reported general health was assessed using the EQ-5D-5L [22, 23] which is a validated tool widely used to estimate general health-related quality of life, with 5 dimensions (5D): mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension of the EQ-5D has five levels (5 L), with increasing level numbers corresponding to increasing levels of problems. Typically, a ‘disutility’ score is provided, which is a measure of people’s health status. Higher disutility scores indicate worsening general health.

Statistical analysis

Descriptive analyses were conducted to compare the descriptive, bivariate and multivariable analytical results from the two studies, and stratified by socio-demographic characteristics: age (>50 vs. ≤50 years), sex (Male vs. Female), income (Lower: including ‘Welfare support payment’ OR ‘<$ 50, 000’ vs. Higher: including ‘Job’ OR ‘≥$50, 000’), oral health (Poor vs. Excellent/good) and health-related behaviors (Current smoker vs. ‘Ex-/never smoked). The mean disutility scores and prevalence of having at least one problem for each dimension of EQ-5D-5L with corresponding 95% confidence intervals (95% CI) were reported. Differences were denoted to be statistically significant when 95% CI did not overlap. Weighted data analyses were used for study 2.

Participant characteristics from the two studies are presented in Table 1. Compared with non-Indigenous Australians, a higher proportion of Indigenous Australians were in the younger age group (≤50 years), female, in the lower income group and were current tobacco smokers. The proportion of poor self-rated oral health was three times higher in Indigenous than in non-Indigenous Australians.

The average disutility scores are presented in Table 2. Overall, the mean disutility score was 2 times higher in Indigenous than in non-Indigenous Australian adults. A higher mean disutility score was observed among Indigenous adults with poor self-rated oral health (0.25, 95% CI: 0.22-0.27) than among non-Indigenous adults with poor self-rated oral health (0.16, 95% CI: 0.14-0.18). When stratified by socio-demographic characteristics and health-related behaviors, the mean disutility scores were 1.5-2 times higher from every individual group/classification among Indigenous Australians compared with non-Indigenous Australians.

Overall, the prevalence of having at least one problem was higher for all dimensions among Indigenous than non-Indigenous peoples (Table 3), with the exception of the ‘Mobility’ dimension. The prevalence of having at least one problem was higher among those with ‘excellent/good’ self-rated oral health among Indigenous compared with non-indigenous Australian adults, with the exception of the ‘Mobility’ and ‘Pain/discomfort’ dimensions. There were no statistically significant differences of the prevalence of having at least one problem for most EQ-5D dimensions, with the exception of ‘Anxiety/depression’.

Associations between self-rated oral health and EQ-5D after adjusting for covariates are shown in Table 4. The same findings were observed among both Indigenous and non-Indigenous Australians: poor self-rated oral health was positively associated with total disutility score and each EQ-5D dimension. However, the prevalence ratio was more than 2 times higher among Indigenous than non-Indigenous Australians across each individual EQ-5D dimension.

The findings support the hypothesis that both self-rated oral and general health-related quality of life would be poorer among Indigenous compared with non-Indigenous Australians. The findings demonstrate that poor self-rated oral health was associated not only with higher overall disutility scores, but across each individual dimension of EQ-5D. The findings held even after adjusting for socio-demographic factors and health-related behaviors. For both Indigenous and non-Indigenous Australians, higher disutility scores were observed among lower income and current tobacco smoker groups compared with those with higher incomes/who did not smoke.

Lower socioeconomic status, including low education attainment and income, was an important risk factor associated with both poor oral and general health. Our findings are similar to those reported by Hakeberg et al. [26] and Sabbah et al. [27], who observed that the lower income position, the poorer oral and general health among adult’s population in Sweden (OR=2.1 and 6.8, respectively) and in U.S (OR=2.3 and 3.7, respectively). A higher proportion of Indigenous Australians have low household income and education levels compared with non-Indigenous Australians [28], which affects not only health literacy, but also health service utilization, resulting in lower rates of public health insurance [16], dental/general health check-ups and visiting [29]. Our tobacco association findings were consistent across the globe [30,31]. Tobacco smoking is associated with oral disease, such as dental caries [32], periodontal disease [33], and oral cancer [34], as well as general illness, including type 2 diabetes and cardiovascular disease [35], lung cancer [36], and premature death [37].

The long-lasting impacts of colonization as part of the core fabric of the social determinants of health are unique to most global Indigenous populations. Indigenous Australians suffer from the substantive burden of post-colonial consequences on almost every indicator of economic, social and health well-being [38]. Indigenous Australians residing in remote or very remote locations are especially impacted, with additional barriers including lack of access to higher education, lack of fresh food, inequitable access to primary dental and health care services, increased psychological distress, trauma, socioeconomic disadvantage, and a higher burden of chronic diseases [17,39]. These factors interact with one another to create a vicious circle, resulting in systemic and inter-generational poor oral and general health.

There are several limitations to our study. Study 1 data was derived from a large convenience sample which was not representative, and Study 2 data was not the newest data which might not represent recent oral and general health conditions among Australian adults. The same instrument was not used across both studies to assess self-rated oral health. Similarly, the covariates used in multivariable analysis were not exactly the same across both studies.

Our findings indicate that self-rated oral and general health-related quality of life remain poorer among Indigenous relative to non-Indigenous Australians. The social determinants of health are likely to be root causes. Interventions that address social, economic and political constructs are required to reduce oral and general health inequalities between Indigenous and non-Indigenous Australians.

The authors confirm that they have no competing interests.

Indigenous Australians study was governed by an Indigenous Reference Group, who oversaw the orchestration, delivery and feedback of the study findings as it relates to the health and well-being of Indigenous Australians. We sincerely acknowledge and appreciate all that this Reference Group did. The authors grateful to Harrison Research, who conducted the Spring Health Omnibus Survey. The authors also thank and acknowledge all study participants, and the staff who collected data.

XJ and LMJ conceived and designed the study. LMJ and KK are guarantors for this article. All authors contributed to data acquisition and interpretation, and critically reviewed and approved the manuscript.