The oral health of older people is one of the very basic factors required for maintaining a healthy life. Oral functions, including chewing, swallowing, and pronunciation, are essential for maintaining social interactions as well as sound quality of life [1]. In particular, oral infection prevention and oral function improvements are necessary in order to masticate food, enjoy flavours, and display diverse expressions [2]. However, the mouths of elderly individuals often show substantial tooth loss due to oral infections that have accumulated throughout their lives [3]. Furthermore, remaining teeth are often worn out on the occlusal surface due to dental attrition, which results in lower cusps and decreased mastication [4]. In addition, decreased tongue strength, mobility and decreased saliva secretion due to salivary gland aging make swallowing difficult to the elderly [5]. With age-related decreased swallowing, the risk of aspiration (food or saliva entering the airway instead of the oesophagus) increases [6]. If these difficultes persist for a long time, the risk of aspiration pneumonia also increases [7]. Therefore, active efforts are required to improve the factors that negatively affect the quality of life for older people related to their oral health. These include conditions such as decreased chewing, dry mouth, and decreased swallowing [6,7].

The methods for improving the oral health of older people include oral health education, preventative assessments, and early treatment [8]. However, oral health education, which provides the basis for oral health motivation, is less effective due to fewer individuals carrying out the required behavioural changes. Care by experts, preventative assessments, and early treatment also is less effective because they require visits to the oral health centre [8,9]. Therefore, an oral exercise program that can be easily followed in daily life will effectively improve the oral health of older people [10].

In Japan, which has a high life expectancy, oral health improvement methods were added to oral health-related programs through oral health education [11]. Japan has an oral exercise policy for improving oral health [9] that has been reported to be very effective in improving the oral health of older people in an aging and super-aging society [9,11,12]. Furthermore, the recommended exercises can be continuously used by older people without complications, financial burden, or limitations of time or place [13].

An oral exercise program comprised of saliva-producing, chewing-strengthening, swallowing-strengthening, and speaking-strengthening exercises was also developed and applied in older people in facilities throughout Korea. As a result, this program has improved the level of oral health in elderly individuals with healthy oral functions [14]. The program promoted the active recovery, maintenance, and improvement of oral functions in elderly individuals with decreased oral functions. Altogether, it increased the quality of life and oral health of older people [15].

Furthermore, it has been reported that whole-body exercises have aging prevention and health improvement effects in older people [16,17]. These positive effects of whole-body exercises in older people include physiological and affective elements related to decreased depression and anxiety [18] as well as social interactions such as the maintenance of bonding with others. In this respect, whole-body exercises can be considered an essential activity in old age [19]. About 40% of people aged 60 years or older experience discomfort from dysphagia, and this is related to general muscle weakening [20]. Furthermore, whole-body muscle weakening affects muscles of the head and neck as well, and weakening of the tongue muscles is the root cause of dysphagia [21,22]. Therefore, whole-body exercise may have a positive effect on oral health improvements in older people. It is anticipated that oral function improvements will be greater in elderly individuals who perform oral exercises with whole-body exercises than in older adults who only perform oral exercises.

Therefore, an oral exercise program was selected as the oral function improvement methodology of this study. To differentiate our investigation from previous studies, we studied oral function improvements that result from oral exercise combined with whole-body exercise.

This study developed a program that combined whole-body exercises with existing oral exercises and identified related oral function improvements in elderly individuals. Scores of the OHIP-14 and GOHAI evaluations, which are the two representative indicators for measuring the relationship between oral health and quality of life, increased for the intervention groups, without statistical significance. This may be because the program was only five weeks in duration, which could have been too brief a period for individuals to consider that their quality of life improved as a result of their oral health. However, the participants’ behavioural changes could become significant when the program is continuously followed. Thus, further long-term measurements and evaluations are required in the future.

Saliva is responsible for keeping the mouth healthy by providing moisture to the oral mucous membranes and to prevent drying [5]. In the mouths of older people, the oral mucous membranes contract and saliva secretion decreases, resulting in xerostomia. Pain in the oral mucous membrane can decrease oral functions, such as mastication, deglutition, and pronunciation, and increase tongue coating, which leads to halitosis [6,7]. The findings of this study showed that the saliva flow rate did not change significantly in the control group, while the individuals in the intervention groups presented significant increases. In particular, the saliva flow rate of intervention group Ⅰ increased from 1.12 to 1.94, and this change was more pronounced than those of the other groups. Between-group comparisons also showed statistically significant differences. It has been reported that oral exercises are effective at improving xerostomia and increasing unstimulated saliva flow rates [14]. If appropriate, oral function exercises that are performed before further health deterioration and the functional decline in the salivary glands that accompanies aging and drug complications, can be modified [5]. In conclusion, increased saliva flow rates were found to result only from oral exercises, and it is thought that continuous oral exercise training among older people will have a positive impact on oral functional improvements.

The tongue is a stomatognathic structure that is comprised of various intrinsic and extrinsic muscles [27]. Extrinsic muscles play a role in changing the location of the tongue through protrusion, retraction, depression, and elevation, while intrinsic muscles play a role in changing the shape of the tongue [28]. These muscles cooperate during the deglutition process by regulating the mastication, formation, and manipulation of food in the mouth, and they are also involved in breathing and language [29]. Furthermore, cheek muscles reside in the lower interior location, and the buccinator muscle is the agonist muscle that plays a role in ensuring that food is not left between the teeth and gums (i.e. sulcus lateralis) through continuous contraction during mastication [26]. In this study, the tongue and cheek strength measured with the IOPI showed that anterior tongue strength increased significantly and posterior tongue strength and cheek strength increased without statistically significant differences in intervention group I. However, in intervention group Ⅱ, anterior tongue strength, posterior tongue strength, and cheek strength significantly increased, and the between-group comparisons showed statistically significant differences. In relation to this, previous studies have also implied that oral exercise can improve oral strength, including mastication, the buccinator muscle, and the root of the tongue, due to movement of the oral muscles [26]. Prior studies have also showed that long-term participation in oral exercises with physical activities can inhibit the deterioration of oral functions in older people and contribute to the maintenance of oral health [11]. Tongue and cheek strength were found to significantly improve in this study as well as being partially in line with the findings of previous studies [26]. Furthermore, although it was difficult to clearly hypothesize the reason for the more significant increase in oral strength when whole-body exercises were performed with oral exercises, it may be that relaxation of the body and tense muscles through whole-body exercises can increase blood flow to the brain [30] and increase the effects of oral exercise. Therefore, it is necessary to identify the cause for the observed improvements through future studies.

The findings of this study showed that the saliva flow rate increases with oral exercise alone and that improvements in the saliva flow rate and oral strength were observed when whole-body exercises and oral exercises were performed in parallel. However, because the duration of the study was five weeks, there was not enough time to test the effects of oral exercise with whole-body exercises, and this likely contributed to the lack of large differences between the two groups. Previous research has implied that whole-body exercise with oral exercise contributes to oral function improvements [11]. Considering these findings, it is anticipated that the long-term application of an oral exercise program with whole-body exercise will lead to large oral function improvements.

Although there have been many studies focused on oral exercises as methods for preventing xerostomia in older people, no investigations have used an oral exercise program in combination with whole-body exercise to improve oral functions. Furthermore, no studies have measured the oral strength using IOPI. Thus, there are difficulties with directly comparing the findings of this study to those of prior studies. This study is significant in that it pioneered an investigation of oral functional improvements for older adults with insufficient prior research. This study also compared the differences in the oral functional improvements of regular oral exercise with oral exercise in combination with whole-body exercise. It is thought that an oral exercise program with whole-body exercise will increase the oral health related quality of life of older people and contribute to oral health improvements. This combined program will benefit an aging society.

To evaluate the impact of an oral exercise program with whole-body exercise on the oral function of older people. The participants (aged ≥65 years) were divided into three groups: intervention group Ⅰ (only oral exercise), intervention group Ⅱ (oral exercise with whole-body exercise), and control group. Before and after the program, the oral health status, saliva flow rate, and oral muscle strength were measured. Analyses were performed to compare the three groups and to identify changes in the three groups before and after the program.

1. Saliva flow rate increased in intervention group Ⅰ and in intervention group Ⅱ. These increases were statistically significant.

2. In oral strength measurements using the IOPI, anterior tongue strength increased significantly in intervention group I. In this group, posterior tongue and cheek strength increased; however, these differences were not statistically significant.

3. In intervention group Ⅱ, anterior tongue, posterior tongue, and cheek strength increased, and these changes were statistically significant.

The oral exercise program with whole-body exercise was found to have positive effects on increasing the saliva flow rate and oral strength. No significant differences were observed in the quality of life related to oral health. Therefore, in subsequent studies, repeated studies are needed to confirm changes in oral health quality of life through long-term measurement.