Oral function improvement through oral exercise: gender differences in community-dwelling older adults

Abstract

Background

Older individuals with systemic diseases and disabilities face an elevated mortality risk, with oral functional decline further contributing to both oral and systemic health challenges. Given the rising prevalence of reduced oral function in older adults, this study aims to evaluate the effectiveness of oral exercise training on improving oral function and preventing functional decline. Additionally, the study examines potential gender differences in response to the intervention.

Methods

Seventy-seven community-dwelling older adults aged 65 and above participated in a six-week oral exercise program, performed before each meal. The study measured changes in oral function post-intervention, which including swallowing ability, salivary secretion, oral diadochokinesis and bite force. Pre- and post-intervention differences were evaluated using paired t-tests and Wilcoxon signed-rank test. The trial was registered on ClinicalTrials.gov (NCT06794814‖2025-01-16).

Results

Following six weeks of oral exercise training, significant improvements were observed in salivary secretion, swallowing ability (RSST), oral diadochokinesis, bite force, and quality of life (assessed by OHIP-14). Notably, female participants demonstrated statistically significant increases in stimulate saliva (p =0.013), bite force (p =0.016)  and Repetitive saliva swallowing test (RSST) scores (p = 0.021) post-training.

Conclusion

Although the scale of the present study was limited, its findings indicated that 6 weeks of oral exercise intervention could effectively improve oral function among older adults. Training improved swallowing ability and bite force increased mainly in females. Oral diadochokinesis significantly improved for /pa/, /ta/, and /ka/. Encouraging regular oral exercise, particularly before meals, may further optimize oral function and prevent oral hypofunction.

Introduction

Taiwan became an aging society in 1993, and aged society in 2018, and is projected to become a super-aged society by 2025 [1]. The increasing population of older adults has raised dependency rations, resulting in economic and caregiving pressures for younger generations. Some common causes of disability among older adults include hypertension [2], diabetes [3], depression [4], dementia [5], and frailty [6], all of which contribute to functional decline. Additionally, some studies have suggested that loss of masticatory function correlates with both disability and dementia [7–9]. For older adults, impaired chewing function can increase the likelihood of cognitive impairment and may result in malnutrition, muscle loss, frailty, and elevated mortality risk [10–12].

In recent years, oral hypofunction has gained increasing scholarly attention. Defined as a multi-factorial weakening of oral function caused by aging, diseasing, or other factors, oral hypofunction can progress to chewing and swallowing disorders, negatively affecting systemic health [13]. Both internal and external factors contribute to oral hypofunction and associated oral and systemic disease. One study highlighted higher susceptibility to oral hypofunction among women, finding that 39.0% of older men and 46.9% of older women were affected [13]. Muscle training through regular oral exercise can prevent oral hypofunction [14, 15]. Japan’s Kenko Taiso oral exercise program, originating from the 1989 “8020 Movement,” promotes oral function in older adults through movements like tongue stretching, cheek puffing, and phonation. Integrated into national health policy, it improves chewing, swallowing, and saliva flow, reducing aspiration pneumonia risk in community-dwelling elders [16, 17]. Oral health exercises have been found to significantly increase resting salivary flow [18], reduce tongue coating, decrease food debris, alleviate tongue dryness, and increase tongue pressure [19–21]. A 3-month oral exercise regimen, including tongue-strengthening exercises and oral diadochokinesis (ODK) exercises was found to improve tongue pressure and oral diadochokinetic movement in older adults with mild to moderate dementia [21].

The present study examined the effects of oral exercise on oral function among older adults in Taiwan, focusing on gender-related outcome differences.

Materials and methods

Study participants

A total of 119 Taipei city residents over the age of 65 were initially recruited. All participants were informed of the study objectives and procedures prior to commencement. By the end of the 6-week study period, 77 participants remained. Individuals who had incomplete data, failed to perform the assigned daily exercise, or were unable to adhere to the protocol and steps outline in the oral exercise video were excluded from the final analysis. The study was approved by the Ethics Committee of National Yang Ming Chiao Tung University, Taiwan (NYCU113040A). The trial was registered on ClinicalTrials.gov (NCT06794814‖2025-01-16).

Intervention period

The study flow chart showed in Fig. 1. The dental hygienist demonstrated the oral exercises for participants, who were asked to perform the exercise daily before meals for 6 weeks [22, 23]. The study was conducted over three time periods: from October to November 2022, from April to May 2023, and from May to July 2024.

Fig. 1.

Flow chart of the study

Oral exercise protocol

The oral exercise protocol [24] included several physical components, namely neck and shoulder stretching, cheek puffing exercises, tongue exercises, salivary gland massage, and oral diadochokinesis. Participants were instructed to follow along with an oral exercise video to perform the exercises, in accordance with the following instructions.

(Link: https://www.youtube.com/watch?v=hfBcGSH83HA&ab_channel=%E8%94%A1%E6%B3%95%E6%85%88)

Neck and shoulder stretching

Stretching in multiple directions activates and relaxes the muscle surrounding the neck. To perform the exercise, slowly count to five for each motion. Begin with a gradual upward head tilt, then return to a neutral position. Next, lower the head before returning to neutral. Follow by turning the head slowly to the right and left, returning to center after each movement.

Cheek puffing exercises

This exercise simulates mouth rinsing to maximally engage the facial muscles on both sides. To perform the exercise, first inflate the right cheek, then the left, and finally both cheeks simultaneously.

Tongue exercise

Tongue agility is essential for effective food mastication and bolus formation and can be trained through the following excises: (Step 1) extending the tongue forward, (Step 2) curling it backward, (Step 3) lifting it upward toward the nose, (Step 4) extending it downward toward the chin, (Step 5) stretching it to the left, (Step 6) stretching it to right, and (Step 7) making circular motions in both clockwise and counterclockwise directions.

Salivary gland massage

1. Parotid gland massage: Rotate the fingers forward and then backward on the parotid area in a circular motion for approximately 30 s in each direction.

2. Submandibular gland massage: Gently massage the submandibular tissue at the underside of the jaw for approximately 5 s.

3. Sublingual gland massage: Apply gentle upward pressure on the floor of the mouth with the thumbs, repeating approximately 5 times.

Oral diadochokinesis

During vocalization exercises, produce sounds with abdominal support, which concurrently strengthens core muscles. The following sounds should be practiced:/pa/,/ta/,/ka/,/ra/.

Oral functional assessment

Oral function was assessed as follows:

1. Repetitive saliva swallowing test (RSST) [25]: Participants were instructed to swallow saliva as frequently as possible while seated for 30 s. During this time, the number of clear palpations of the laryngeal prominence and elevations of the hyoid bone were recorded, with fewer than three occurrences considered indicative of dysfunction.

2. Saliva secretion measurement [26, 27]: Saliva secretion was measure by placing a pre-weighted 2 g piece of gauze (7.5 cm x7.5 cm) in the participant’s mouth for 2 min. After chewing, the gauze was re-weighted, and the difference in weight indicated the volume of saliva produced. An increase of less than 2 g was noted as possibly indicating xerostomia, given that healthy individuals typically produce over 5 g of saliva during the same period. Minor discrepancies in results may have arisen due to variations in gauze type and size.

3. Bite force measurement [28]: Bite force was measured using the Bite Force Analyzer (GC Corp., Tokyo, Japan) and specialized testing device. Participants were instructed to bite down on the films for three seconds, leaving a red mark, which was subsequently analyzed with software to determine the bite force in Newtons (N).

4. Oral diadochokinesis [29]: Participants were instructed to articulate the syllables/pa/,/ta/,/ka/, and/ra/as quickly as possible for 5 s. The number of repetitions per second was calculated to assess the speed of syllable production.

Demographic information, quality of life, and swallowing ability questionnaire

Information on basic demographic characteristics, including gender, age, living situation, and educational level, was collected for all participants. The Oral Health Impact Profile (OHIP-14) [30] was used to assess the influence of oral health on quality of life over the month prior to study participation, specifically examining whether mouth, teeth, or denture concerns affected physical or psychological well-being. The OHIP-14 questionnaire encompasses seven domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap. Additionally, the Eating Assessment Tool (EAT-10) [31] was used to evaluate swallowing function, with scores ranging from 0 to 4 for no swallowing problems (score = 0), occasional problems (score = 1), moderate problems (score = 2), frequent problems (score = 3), and severe difficulty (score = 4). A total score of 3 or higher suggests the presence of a potential swallowing disorder.

Statistical methods

Demographic characteristics, including age, gender, existing medical conditions, and oral health status, were summarized using descriptive statistics. Data were analyzed with SPSS Statistics for Windows version 24.0 (IBM, New York, NY, USA). The distribution of data was tested using the Shapiro-Wilk test. Variables that were normally distributed were analyzed using paired t-tests, while non-normally distributed variables were analyzed using the Wilcoxon signed-rank test. A significance level of p < 0.05 was set to assess the effect of oral exercise intervention.

Result

Participant demographics

A total of 77 older adults living in Taipei city participated in the study, including 19 men and 58 women. The overall average age of all participants was 72.35 years, with female participants averaging 71.82 years and male participants averaging 73.95 years.

Among the participants, 17 had at most a junior high school education or below, 24 had at most high school education, and 36 had a university or graduate school degree. None of the participants were smokers, and only one reported a history of betel nut chewing (Table 1).

Table 1.

Participant demographic characteristics

	Total (N = 77)	Male (N = 19)	Female (N = 58)
Age
65–69	23	4	19
70–79	48	12	36
≧ 80	6	3	3
Education level
Junior high school or below	17	5	12
Senior high school	24	4	20
University or above	36	10	26
Smoke
Current	0	0	0
Never	77	19	58
Betel-nut chewing
Current	1	1	0
Never	76	18	58
Numbers of natural teeth
Less than 20 teeth	10	2	8
More than 20 teeth	67	17	50

Effects of oral exercises on salivary secretion, repetitive saliva swallowing test (RSST), and bite force

The results of total participants revealed no statistically significant difference in salivary flow before and after the intervention (median = 3.16 mL, IQR = 2.22 vs. median = 3.30 mL, IQR = 2.00; p = 0.076). In contrast, a significant improvement was observed in swallowing frequency, increasing from a median of 8.00 (IQR = 7.00) to 10.00 (IQR = 9.00; p = 0.007). Similarly, bite force significantly increased from a median of 665.00 N (IQR = 632.70) to 719.30 N (IQR = 607.80; p = 0.007) following the intervention.

Significant improvements in oral functions were observed after the intervention among the female participants. Salivary flow increased from a median of 2.94 mL (IQR = 2.15) to 3.30 mL (IQR = 2.13), with a statistically significant difference (p = 0.013, Wilcoxon signed-rank test). Swallowing frequency also showed a significant increase, from a median of 7.5 (IQR = 6.25) to 9.5 (IQR = 9.00) (p = 0.021). Additionally, bite force improved significantly from a median of 542.25 N (IQR = 508.90) to 679.60 N (IQR = 602.07), with a p-value of 0.016.

Among male participants, the result indicated no statistically significant differences in oral function outcomes following the intervention. Specifically, salivary flow slightly decreased from a median of 3.23 mL (IQR = 1.70) to 2.98 mL (IQR = 1.60), with a p-value of 0.615. Swallowing frequency increased from a median of 8.00 (IQR = 7.00) to 10.00 (IQR = 7.00), but the change was not statistically significant (p = 0.139). Similarly, bite force showed a decrease from a median of 1039.70 N (IQR = 809.30) to 929.10 N (IQR = 698.30), with no significant difference observed (p = 0.117). (Table 2).

Table 2.

Effects of oral exercises on salivary secretion among male, female, and all participants based on repetitive saliva swallowing test (RSST) and repetitive saliva swallowing test results. *p < 0.05 of Wilcoxon signed-rank test

	Pre-intervention median (IQR)	Post-intervention median (IQR)	p value
Stimulate saliva (mL/min)
Total	3.16 (2.22)	3.30 (2.00)	0.076
Male	3.23 (1.70)	2.98 (1.60)	0.615
Female	2.94 (2.15)	3.30 (2.13)	0.013*
RSST (times)
Total	8.00 (7.00)	10.00 (9.00)	0.007*
Male	8.00 (7.00)	10.00 (7.00)	0.139
Female	7.50 (6.25)	9.50 (9.00)	0.021*
Bite force (N)
Total	665.00 (632.70)	822.42 (607.80)	0.259
Male	1039.70 (809.30)	929.10 (698.30)	0.117
Female	542.25 (508.90)	679.60 (602.07)	0.016*

Effects of oral exercises on oral diadochokinesis

Gender-stratified analysis revealed that prior to intervention, female participants articulated the sounds/pa/21.79 times,/ta/22.69 times,/ka/23.72 times, and/ra/23.78 times in 5 s. Post-intervention, these frequencies increased to 22.83, 23.86, 24.74, and 24.47 times for/pa/,/ta/,/ka/, and/ra/, respectively. For male participants, the mean phonation frequencies prior to training were 19.05 times for/pa/, 20.47 times for/ta/, 21.00 times for/ka/, and 22.11 times for/ra/. Their post-training frequencies increased to 21.89, 23.05, 23.43, and 24.11 times for/pa/,/ta/,/ka/, and/ra/, respectively. For all participants combined, mean phonation frequencies prior to intervention were 21.12 times for/pa/, 22.14 times for/ta/, 23.05 times for/ta/, and 23.36 times for/ra/. Post-intervention, these frequencies increased to 22.60, 23.66, 24.42, and 24.38 times for/pa/,/ta/,/ka/, and/ra/, respectively. Oral diadochokinesis significantly improved for/pa/,/ta/, and/ka/. These results suggest that 6 weeks of oral exercise intervention significantly enhanced specific phonatory functions (Table 3).

Table 3.

Effects of oral exercises on oral diadochokinesis among male, female, and all participants. *p < 0.05 of paired t- test

	Pre-intervention average value	Post-intervention average value	p value
Total (N = 77)
/PA/	21.12	22.60	0.049*
/TA/	22.14	23.66	0.026*
/KA/	23.05	24.42	0.028*
/RA/	23.36	24.38	0.085
Male (N = 19)
/PA/	19.05	21.89	0.093
/TA/	20.47	23.05	0.146
/KA/	21.00	23.43	0.085
/RA/	22.11	24.11	0.190
Female (N = 58)
/PA/	21.79	22.83	0.218
/TA/	22.69	23.86	0.097
/KA/	23.72	24.74	0.143
/RA/	23.78	24.47	0.258

Effects of oral exercises on oral health impact profile (OHIP-14) and EAT-10

Among male participants, the median OHIP-14 score decreased from 6 (IQR = 14) to 2 (IQR = 4), and the EAT-10 score declined from 1 (IQR = 4) to 0 (IQR = 2) post-intervention, indicating potential improvements in oral health-related quality of life and swallowing function, though neither change reached statistical significance (p = 0.053 and p = 0.133, respectively). In contrast, no significant changes were observed in the total participant group, as the median OHIP-14 score remained at 6 (IQR = 10 vs. 11; p = 0.885), and the EAT-10 score increased slightly from 1 (IQR = 3.5) to 2 (IQR = 3; p = 0.889), suggesting limited overall effect of the intervention. Among female participants, the median OHIP-14 score rose from 6.5 (IQR = 10) to 8.0 (IQR = 10.25; p = 0.324), and the EAT-10 score increased from 1.0 (IQR = 3.25) to 2.0 (IQR = 2.25; p = 0.369), with neither result achieving statistical significance. (Table 4).

Table 4.

Wilcoxon signed-rank test analysis of oral health impact profile (OHIP-14) and EAT-10 scores before and after oral exercise intervention among male, female, and all participants. *p < 0.05

	Pre-intervention median (IQR)	Post-intervention median (IQR)	p value
OHIP-14 Score
Total (N = 77)	6 (10)	6 (11)	0.885
Male (N = 19)	6 (14)	2 (4)	0.053
Female (N = 58)	6.5 (10)	8 (10.25)	0.324
EAT-10 Score
Total (N = 77)	1 (3.5)	2 (3)	0.889
Male (N = 19)	1 (4)	0 (2)	0.133
Female (N = 58)	1 (3.25)	2 (2.25)	0.369

Discussion

This study represents the first investigation in Taiwan examining sex differences in outcomes following oral exercise interventions. The intervention protocol was adapted from the Japanese model [15, 17], incorporating a structured routine administered three times daily. Although certain variables did not reach statistical significance, post-intervention improvements were evident. The six-week oral exercise program demonstrated overall effectiveness, with differential effects by sex—female participants showed greater improvements compared to males. These sex-related differences may be associated with disparities in health awareness and behavior [32, 33]. Females consistently demonstrate higher levels of engagement in health-related behaviors and health information seeking compared to males, indicating a stronger orientation toward preventive health. These gender-based differences manifest early in life and persist across various health domains, highlighting the importance of incorporating gender-sensitive approaches in public health interventions [34–36]. In this study, the dropout rate was higher in the male group compared to the female group. Accordingly, promoting health consciousness and adherence to daily oral exercises among older men may enhance intervention outcomes. The duration required for oral exercise interventions to be effective varies, the present findings align with prior research indicating the effectiveness of oral exercises within a six-week period [37, 38]. While short-term benefits were observed, longer intervention durations may further enhance oral function in community-dwelling older adults.

Although assessment scores generally increased from pre- to post-intervention, these differences were not statistically significant. However, these increases suggest that oral exercises may have positively stimulated saliva secretion, which is consistent with prior research indicating the effects of oral exercise on saliva production among older adults [38, 39]. A non-significant increase in swallowing frequency among participants in the present study reflected previous finding related to a 3-month swallowing training program for older adults [29].

Participants in the present study exhibited a statistically significant improvement in phonation frequency, especially for the sounds/pa/,/ta/, and/ka/. This finding aligns with research from Japan demonstrating that oral exercises effectively strengthened lip and tongue muscles in older adults [29].

Bite force significantly increased post-intervention, which aligns with the finding of a prior study indicating a bite force increase among older adults following a similar exercise program [15]. Notably, female participants exhibited a greater improvement in bite force, suggesting that the exercises had a potentially stronger effect on this group.

Compared to female participants, male older participants showed decreased outcomes following the exercise intervention. This may be attributed to the higher average age of the male participants compared to the females. Finally, oral health impact profile (OHIP-14) scores indicated a trend toward improved quality of life post-intervention, though these changes were not statistically significant. This finding aligns with prior findings suggesting that oral exercise interventions can enhance quality of life related to oral health [24]. The limitation of this study was the unequal distribution of male and female participants.

Conclusion

Although the scale of the present study was limited, its findings indicated that 6 weeks of oral exercise intervention could effectively improve oral function among older adults. Training improved swallowing ability and bite force increased mainly in females. Oral diadochokinesis significantly improved for/pa/,/ta/, and/ka/. Encouraging regular oral exercise, particularly before meals, may further optimize oral function and prevent oral hypofunction.

Authors’ contributions

FT and ML contributed to conception, design, data acquisition and interpretation, drafted and critically revised the manuscript. WR contributed to design, data acquisition and interpretation, performed all statistical analyses, drafted and critically revised the manuscript. FW, MT contributed to data acquisition and interpretation. All authors gave their final approval and agree to be accountable for all aspects of the work.

Funding

This work was supported by the Project for Oral Exercise in Wenshan District Health Center, Taipei City.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the Ethics Committee of National Yang Ming Chiao Tung University, Taiwan (NYCU113040A) and conducted in accordance with the Declaration of Helsinki. All participants in this study provided informed consent and completed the signing process.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.