Our findings indicate that poor oral health-related outcomes - as assessed by dental behaviours, dental disease experience and oral health-related quality of life - were associated with poor social and emotional well-being - as assessed by anxiety, resilience, depression, suicide risk and mental health - in a birth cohort of Indigenous Australian young adults, after adjustment for socio-demographics, substance use, discrimination and cultural knowledge. The results highlight the importance of including oral health-related factors when determining the broad range of factors associated with poor Indigenous social and emotional well-being, and support inclusion of oral health-related initiatives when developing interventions aimed at fostering social and emotional development among Indigenous Australian groups.
It is important to bear in mind that, being a longstanding birth cohort, the study was not designed at the outset to examine the relationship between social and emotional wellbeing and oral health. The sample size was determined at birth and not able to be increased in later stages. This study represents the largest cohort of an Australian Indigenous population that has ever been assembled, with this, in turn, being the largest study to examine social and emotional wellbeing and oral health in an Indigenous young adult population.
Before discussing implications of the findings, it is important to consider the study's limitations. We have suggested that oral health-related factors are associated with poor social and emotional well-being, but it is not possible to determine the exact causal pathway. The true relationship may be bi-directional. Although the study is longitudinal in design, oral health and social and emotional well-being items were only collected in the most recent phase. The self-report nature of many of the items may have led to an under-estimation of these factors. Although high concordance between self-report and biological measures of factors such as smoking have been reported , this has not been explored among a marginalised group such as Indigenous Australians, where incorrect responses may be given for any number of reasons (social desirability bias, difficulty understanding English, recall and yea-saying bias).
It is worth expanding upon each of the oral health-related components that were associated with social and emotional well-being in this study.
The only dental behaviour significantly associated with social and emotional well-being in multivariate analysis was toothbrush ownership, with ownership of a toothbrush being positively associated with resilience. In Kuwait, Honkala and colleagues  reported associations between recommended brushing and life- or school-satisfaction and self-esteem indicators. Factors additionally associated with resilience in our study included being male, having a job, having a filling and having more cultural knowledge. Employment and cultural identification are recognised as being among the broader determinants of health associated with social and emotional well-being [30, 31].
Dental disease experience
Untreated dental disease in our study was associated with anxiety. The most intuitive reason for this is because untreated dental disease can cause pain, limit function and look unsightly . Anxiety was also associated with being female and discrimination. In the literature it is reported that females are more likely to feel concerned about the appearance of their teeth . Facial attractiveness has also been found to affect social attitudes and actions, and is important in employment situations [33, 34].
Experience of one or more decayed, missing or filled teeth was associated with poor mental health. Most evidence in the literature suggests the opposite; that poor mental health is a risk indicator for dental disease. Severity of untreated dental disease was associated with suicide risk in this study. There is limited evidence of this relationship in the literature, although at a qualitative level, suicide has been linked to toothache in the Indigenous Australian context . The most common cause of toothache is severe, untreated dental disease .
Oral health-related quality of life
In our study, experience of dental pain in the last year was associated with depression. Depression is a complex psychological condition with many elements of pain acting as an underlying stimulus . It has been reported that pain and depression share underlying neurochemical mechanisms , with stressful life events preceeding the onset of symptoms of both chronic facial pain  and depression . It is quite possible that they may have a common underlying pathophysiology, with evidence suggesting that a larger proportion of chronic pain patients may develop depression than patients with various other chronic medical conditions .
Dissatisfaction with dental appearance was associated with poor overall mental health. A study of young adults in Japan found that dental malocclusion had a negative impact on self-reported mental health status  and, among an adult population in Karachi, perceived severity of malocclusion was significantly associated with poor psychosocial well-being . People suffering from problems in their tempero-mandibular joints (the joint linking the lower jaw with the rest of the skull) are more likely to suffer from mental disorders  and to be more severely depressed than healthy individuals . Indeed, depression has a high co-morbidity with chronic facial pain . In a qualitative study of rural-dwelling Indigenous Australian adults, it was reported that '...It affects your whole body, having toothache, your way of thinking...' and '..You see a lot of young people today with missing teeth and stuff....some feel shame about it too you know, like how it looks and everything.' .
Additional associations with poor social and emotional well-being among Indigenous young adults in this study warrant mention. Others have recognised that Indigenous Australian females (as with Australian females in general) have poorer social and emotional well-being than their male counterparts . Although reasons for this disparity are unclear, they may include Indigenous females having greater social responsibilities, less career or education options, early motherhood and general chronic disease comorbidity . Having a job was associated with resilience, which is intuitive given that maintaining any form of employment requires some degree of commitment and responsibility . Substance misuse, in the form of alcohol and marijuana, were associated with depression, supported in the literature for both Indigenous  and non-Indigenous  populations. Discrimination was associated with four of the five social and emotional well-being domains; anxiety, depression, suicide risk and overall mental ill health. This is an important finding that mirrors emerging Australian [47–51] and international evidence that racism is an important cause of ill-health [52, 53]; suggesting that further investigation of this topic in Australia is warranted . Cultural knowledge was associated with resilience, which is again supported by the literature.
It is important to consider the relevance of the findings for dental health policy and practice, specifically in delivering services to people in locations in which this study was undertaken. Indigenous young adults in the Northern Territory who own a means-tested health care card are eligible for free dental services through the public sector. Although these services are available on a reasonably regular basis, our findings indicate that many social and emotional-related factors may contribute to an individual not presenting for recommended care. Most Indigenous Australians visit a dentist because of a problem . Increased understanding of the associations between social and emotional well-being and oral health may help encourage policies that reflect an appreciation of this, which may, in time, result in more preventive-based dental visiting patterns.