Oral Health-Related Quality of Life among a large national cohort of 87,134 Thai adults

Oral health is an important component of both overall health and quality of life. Oral disease creates a major public health burden worldwide and receives inadequate attention in many low and middle income countries [1]. Recently, particular attention is given to increasing the global awareness of the significance and inequity of oral health and the importance of its social determinants [2]. Oral diseases including oral cancers, periodontal disease, dental caries, and tooth loss are linked to emerging chronic non-communicable diseases primarily because of common risk factors such as poor dietary habits, poor oral hygiene, and use of tobacco and alcohol [3]. The joint effects of poor oral health and chronic diseases are major impediments to overall population health and quality of life, especially among the socioeconomically disadvantaged.

Oral Health-Related Quality of Life (OHRQoL) is defined by individual assessment of several oral health dimensions including physical dental function, tooth pain, psychological discomfort, and social impacts--all of which affect overall well-being [4‐6]. Self-reported subjective indicators of OHRQoL correlate well with objective clinical measures of oral health status [4‐8]. So OHRQoL at the individual level points to the need for clinical treatment and at the population level can be used to evaluate oral health interventions.

In the past decade, there have been several Asian studies on OHRQoL focused on adult populations in Hong Kong, Sri Lanka and Vietnam [9‐11]. In Thailand, most population-based OHRQoL studies have focused on children because poor oral health at the early life can lead to a high lifelong impact [12]. Among Thai children, poor socioeconomic status has a powerful adverse effect on OHRQoL [13, 14]. There are very few studies on adult OHRQoL in Thailand especially at the population-based level [15, 16].

To fill the knowledge gap regarding OHRQoL among young and middle aged adults in Thailand, we included a broad oral health-related quality of life assessment in a large national Thai cohort study that began in 2005. Here we report the baseline distribution of OHRQoL among the cohort of 87,134 Thai adults; we investigate relationships with sociodemographic characteristics, health behaviours, and tooth loss. By linking OHRQoL status to its key determinants among such a large group of Thai adults, we generate evidence that can provide information on oral health goals for Thai adults and may incorporate the OHRQoL into oral health policy of the country in the future.

Our analysis of Oral Health-Related Quality of Life (OHRQoL) among a large cohort of Thai adults contributes to the growing population-based literature. We found that discomfort chewing, discomfort with social interaction, and pain were the most common oral impacts, affecting 10-16% of the respondents. Being of old age, having a very low income, (ever or current) smoking, and regular alcohol drinking were all associated with adverse oral impacts. Compared to the adverse effects on speaking and swallowing attributable to certain sociodemographic or behavioral characteristics, having < 20 remaining teeth was even more detrimental.

We used standard methods to de-confound our effect measures and produced adjusted odds ratios; however, some effects were quite small (e.g., less than 1.10) but still statistically significant due to the large sample size. Such small effects are reported but are not considered to be important from a public health point of view. Also, we noted that small bivariate effects with odds ratio close to 1 were sometimes reversed to the other side of 1 when adjusted in the multivariate analysis. Furthermore, certain explanatory variables were dropped by the stepwise process of multivariate logistic regression as a consequence of collinearity with another explanatory variable already in the model. For example, sex and household assets are dropped from the final multivariate model for speaking (Table 4). We also noted that there is probably some interaction occurring among various explanatory variables such as smoking, drinking and age but we did not attempt to model these effects separately.

Our findings were generally consistent with a previous study in Thailand [16]. Of particular note is the adverse consequences of oral diseases on daily life including in the psychosocial dimension: feeling embarrassed in social settings, especially for females. Another report for Thai adults revealed that those of low socioeconomic status, with poor oral health-related behaviors such as smoking, and older age were more likely to self-report worse oral health and associated poor quality of life [15]. Another Asian report is notably consistent with the data from Thailand; Indian adults responding to a general health questionnaire reported that poor oral health had an important adverse effect on psychological distress [26].

Individual perceptions of oral health vary substantially at different points in the life cycle and cumulative risks could subsequently impact on later years [27, 28]. We found an increasing gradient between age and difficulty speaking, swallowing and chewing with progressive deterioration for middle- and older-aged groups. One of the main domains of OHQRL noted in literature was the difficulty chewing, especially among the elderly [29, 30] which could result in limited choices of food, poor nutrition, and subsequently underweight [31]. In addition, poor oral health and under nutrition in older people could increase the incidence of life-threatening conditions, such as atherosclerosis and cancer [32]. In Thailand, a community dental study of Thai elderly has shown a strong association between number of natural teeth and being underweight after controlling for sex, socioeconomic status and current smoking (OR = 2.27, 95% CI 1.25-4.13) [33]. Using the Oral Impact on Daily Performance indicators, another Thai study among elderly showed significant associations between oral impacts and a variety of clinical measures [34]. More specifically, edentulous people experience higher levels of impacts in comparison to the dentate, especially notable for pain, chewing, and nutrition.

The strength of our study is its large national scale with nearly 90,000 adults representing the Thai population well in terms of socioeconomic and geographic background in Thailand. Our study is based on educated Thais and the true magnitude of the poor oral health will be even greater in the general population as reported in other studies that show an education gradient in OHRQoL, with worse outcome at lower levels of education [35]. Outcomes and findings derived from self-reported research may vary in cross-cultural context which could impact on the measured health-related quality of life [36, 37].

It should also be noted that our analyses depended on cross-sectional data so it was difficult to definitively establish causal associations. Furthermore, we could not link reported outcomes to dental care and prevention, nor could we assess the utility of early diagnosis and completion of treatment. Our Thai cohort could potentially shed light on the causal pathway between OHRQoL and other health outcomes when it becomes possible to make longitudinal analyses across adequate time spans. In addition, OHRQoL deserves particular attention in national health surveys.

Oral health quality deserves to be promoted in the national oral health plan to meet the needs of the population and achieve the optimal benefits from available resources. OHRQoL can measure the effectiveness of dental public health programmes, assessing the oral health needs of populations. At the population level, tailored strategies for different groups such as the elderly, low income persons, smokers, and people with less than 20 teeth will yield maximum benefit within limited resources. As revealed in our study, OHRQoL is a significant component of overall health among the whole population. The goal of oral health goes beyond the prevention of oral diseases. Oral health-related quality of life converges well with the holistic 1948 World Health Organization definition of health as 'complete physical, mental and social well-being and not merely the absence of disease'.