Stress is a psychological reaction, like anxiety or threat that a person feels when faced with a physically or mentally difficult situation [1]. It can also cause symptoms such as headaches and fatigue, and negatively affect the physical, mental and social condition of an individual, as well as their quality of life [2]. Stress can occur at any time throughout human life and has a slow rate of recovery, especially in the elderly [3]. The main causes of stress in the elderly include illness and financial loss [4]. Since elderly people lacks the ability to cope with stress, they are greatly impacted by it. In addition, it had been reported that the worse the health status, higher is the stress level [5]. Unexpected changes such as difficult economic conditions, loss of physical and mental function, and loss of their roles, are the common causes of stress in the elderly [6]. Physical aging and vulnerability to disease work as a stress for older people [7].

Functional disorders that affect oral functions including food intake, pronunciation, and aesthetics can adversely affect overall life [8]. In terms of oral health, stress is associated with dental caries, periodontal disease, and dry mouth [9,10]. The subjective oral health was reported to be poor in cases with high levels of stress [3]. Goyal et al. [11] reported that stress induced Cortisol release has a significant effect on periodontal disease and Akhter et al. [12] also reported that stress can be a potential risk factor for periodontal disease. Periodontal disease is a chief factor of tooth loss, which affects the chewing ability. In addition, an active masticatory ability can help reduce pain and stress [13]. Stress is also a potentially important factor in temporomandibular joint disorder (TMD) [14]. Hwang et al. [15] reported an association between stress and chewing discomfort, while Jung et al. [16] reported no relationship between the total number of tooth loss and perceived stress. Choi and Cho [3] also confirmed the relationship between stress and oral health.

However, few studies have previously examined an association between stress and chewing function in older adults [17,18]. Therefore, this study aimed to investigate whether stress in older adults affects number of residual teeth and chewing function using the Korea National Health and Nutrition Examination Survey (KNHANES) VI data that can represent the elderly people.

Lee and Yoon [8] examined the stress level according to various general characteristics and reported that the higher the education level and the higher the household income, the higher was the stress level. However, Cho et al. [21] reported that the lower the educational background and the lower the household income, the more severe was the stress level.

The increased average lifespan has resulted in serious social problems like early retirement of the aging population, which and lead to depression or a sense of alienation due to the increased time spent in isolation physical and mental damage. And the natural death of those around them can be a major stressor for the elderly [22]. Since stress can accumulate negative emotional states such as anxiety and depression, a countermeasure is needed [23]. Although the correlation between stress and various diseases has been previously studied, no clear solution has been found [24]. In order to relieve the stress of the elderly, there are various programs related to the community as well as the individual. In this regard, it is thought that everyone should be interested so that the elderly can share information with each other.

In addition, negligence of oral health due to stress can increase the incidence of oral diseases like dental caries and periodontitis, which can make the chewing and swallowing of food uncomfortable, and also interfere with daily life due to abnormal taste and difficulty in pronunciation [25]. Conditions like excessive mental strain or stress can increase the prevalence of oral conditions, including dry mouth, oral mucosal disease and halitosis [26]. Decreased salivary flow in the elderly causes bad breath, which in turn can cause mental damage in the form of psychological atrophy and anxiety and thus, result in stress and lead to social avoidance and disrupt interpersonal relationships [27]. Cho et al. [19] investigated an association between stress and the number of residual teeth in adults over 40 years old, there was no significant difference between stress and the number of residual teeth, as in this study (p>0.05). Rai et al. [28] reported that salivary stress markers and stress were significantly related with periodontal disease, and ignoring to brush teeth during stress was related with missing teeth.

Roohafza et al. [18] reported that masticatory ability was significantly correlated with depression, anxiety , and stress. Furthermore males reported significantly higher level for masticatory ability than females. And they reported that participants with higher score of anxiety, depression, and stress suffer lower masticatory ability. Petrowski et al. [29] reported that psychosocial stress was related with an rise in chewing frequency measured with sound-based devices.

The discomfort in chewing was found to affect not only the oral health but also the overall quality of life. Poor chewing ability in the elderly can decrease their ability to perform daily activities, thus worsening their quality of life and increasing the occurrence of mental illnesses such as depression [30]. And Miyake et al. [31] reported that chewing attenuates morphologic changes and stress-induced functional in the hippocampus. Therefore, it is necessary to overcome the discomfort in chewing function.

This study was based on the National Health and Nutrition Survey to represent the elderly in Korea. However, because this study is a cross-sectional study, it can’t explain the causal relationship whether the chewing level is uncomfortable due to high stress, or whether it is more stressed due to the uncomfortable chewing level. And even after adjusting covariates the value was increased seems that there was a difference in the number of subjects. In addition, there were limitations because it was investigated using subjective measuring tools for stress and chewing level.

Therefore, more objective measurement tools need to be utilized and more in-depth follow-up studies are needed.

This study was examined their stress level and chewing ability from elderly people over 65 years old using the 2nd and 3rd year (2014-2015) of the 6th Korea National Health and Nutrition Examination Survey data. The results are below.

1. The degree of stress according to the general characteristics was significantly different in age, gender, education, smoking, drinking, and chewing level (p<0.05).

2. The chewing level according to general characteristics was significantly different in age, income(home), education, and stress (p<0.05).

3. The stress in the elderly is related to the chewing level. When there was a lot of stress, The odds ratio of poor chewing level was 2.67 times, and the risk ratio was 2.74 times after adjusting age, sex, residence types, economic activity, home income, education, smoking, drinking, hypertension, diabetes.

We hope to improve the overall quality of life of older adults by exploring various methods to reduce the stress of the elderly and also focusing on oral health as well as general health. This study is expected to be a useful resource for improving mental health and oral health in the elderly.