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Article

Association Between Oral Hypofunction and Physical Frailty Among Korean Older Adults with Preserved Cognitive and Functional Status

by
Ha-Yeoung Kim
1,
Jiyoun Kim
2 and
Jun-Seon Choi
1,3,*
1
Department of Health Science, Graduate School, Gachon University, 191 Hambakmoero, Yeonsu-gu, Incheon 21936, Republic of Korea
2
Department of Exercise Rehabilitation, Institute of Human Convergence Health Science, Gachon University, 191 Hambakmoero, Yeonsu-gu, Incheon 21936, Republic of Korea
3
Department of Dental Hygiene, College of Medical Science, Gachon University, 191 Hambakmoero, Yeonsu-gu, Incheon 21936, Republic of Korea
*
Author to whom correspondence should be addressed.
Appl. Sci. 2026, 16(8), 3695; https://doi.org/10.3390/app16083695
Submission received: 10 February 2026 / Revised: 7 April 2026 / Accepted: 8 April 2026 / Published: 9 April 2026
(This article belongs to the Special Issue Oral Diseases and Clinical Dentistry—2nd Edition)
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Abstract

The oral cavity performs several functions that are essential for sustaining life and carrying out daily activities. Given the importance of maintaining functional abilities for healthy aging, exploration of the adverse health outcomes that may result from impaired oral function is needed. This cross-sectional study examined oral functional status in 176 community-dwelling older adults with preserved cognitive function and activities of daily living, and analyzed the association between oral hypofunction and physical frailty. Oral hypofunction was diagnosed using seven parameters. Frailty was assessed using the Korean version of the Fried Frailty Phenotype, which focuses on physical characteristics. Independent t-tests, one-way analysis of variance, the Kruskal–Wallis test, and multiple logistic regression analysis were conducted to examine the association between oral hypofunction and frailty. The prevalences of oral hypofunction and physical frailty were approximately 48% (n = 85) and 40% (n = 71), respectively. After adjusting for frailty-related factors, including sociodemographic and health-related characteristics, higher oral hypofunction scores were associated with an increased likelihood of physical frailty (odds ratio, 1.382; 95% confidence interval, 1.017–1.876). These findings suggest that maintaining the various functions of the oral cavity, including mastication, within normal ranges and restoring impaired oral abilities as early as possible may be relevant to healthy aging.

1. Introduction

Although life expectancy has steadily increased due to economic development, national health policy reforms, and medical technology advancements, gains in healthy life expectancy have lagged behind [1]. To address this, healthy aging, defined as a state of maintaining functional abilities while effectively managing diseases, has emerged as a major growing interest. The World Health Organization and the United Nations designated 2021–2030 as the “Decade of Healthy Aging,” proposing strategies to promote well-being and healthy aging among older adults worldwide [2]. Preventing frailty is of paramount importance in ensuring healthy aging [3]. Six major international societies, including the International Association of Gerontology and Geriatrics, define physical frailty as a “medical syndrome with multiple causes and contributors that is characterized by diminished strength, endurance, and reduced physiologic function that increases an individual’s vulnerability for developing increased dependency and death” [4]. When it comes to the changes in functional residual capacity with chronological aging, frailty represents an intermediate state between robust health and overt disability [5], which may increase the risk of falls, disability, hospitalization, and mortality, ultimately leading to declines in quality of life [6]. Importantly, since frailty is a potentially reversible state, early detection through active monitoring of middle-aged and older adults is essential [5,6].
Frailty is closely associated with multiple factors, including older age, depression, living alone, malnutrition, and lack of exercise [7,8]. Accumulating oral health problems may also affect the development or progression of frailty [9,10]. A study by Castrejón-Pérez et al. [11], which followed community-dwelling older adults for 3 years, demonstrated that a reduced number of teeth and severe periodontitis were associated with frailty. Older adults with edentulism [10], periodontal pockets deeper than 6 mm [12], poor oral hygiene [13] or self-reported masticatory dysfunction [8] have been reported to have a higher likelihood of frailty. However, most previous studies examining the association between poor oral health on frailty development have focused on the presence or severity of oral diseases. Unlike younger adults, older adults often have a high prevalence of chronic conditions and require systematic and comprehensive assessments of multiple bodily functions [14,15]. Functional assessments facilitate early detection of impaired or vulnerable areas, enabling timely and effective interventions to prevent irreversible disability and help older adults live healthier lives [14].
In recent years, interest in the oral functions of older adults has increased in the field of dentistry. The Japanese Society of Gerodontology proposed that oral hypofunction is not a morphological condition, such as caries, but a functional pathophysiological condition characterized by the concurrent deterioration of multiple oral functions and introduced seven parameters for diagnosing oral hypofunction [16]. Accordingly, it is necessary to comprehensively investigate indicators of oral functions that are vulnerable to changes in older adults that cannot be detected through existing oral disease-based assessments. Furthermore, the World Health Organization emphasizes considering the importance of developing and maintaining functional abilities for healthy aging, highlighting that it is essential to assess oral functional status and explore the adverse health outcomes that may result from declines in oral function. However, few studies have investigated the associations between oral functions and frailty after adjusting for frailty-related factors among community-dwelling older adults living independently. Therefore, this cross-sectional study examined the oral functions in community-dwelling older adults with preserved cognitive and functional activities of daily living, and investigated the association between oral hypofunction and physical frailty. This study was conducted based on the hypothesis that oral hypofunction and physical frailty may be associated.

2. Materials and Methods

2.1. Participants

This cross-sectional study was approved by the Institutional Review Board of Gachon University (IRB: 1044396-202412-HR-201-01) and was conducted in accordance with the World Medical Association’s Declaration of Helsinki. Participants were recruited from 20 senior welfare facilities with similar geographical and social environments in Yeonsu-gu, Incheon Metropolitan City, Republic of Korea. These facilities were selected through convenience sampling, considering their accessibility and willingness to participate in this study. The purpose, methods, and procedures of this study were explained to older adults aged ≥ 65 years who visited any of the 20 participating facilities between January 2025 and March 2025. It was explained in advance that individuals with pre-existing diagnoses of frailty, swallowing dysfunction, cancer, or dementia, as well as those with cognitive impairment and functional limitations in daily living would not be eligible to participate.
Written informed consent was obtained from 184 older adults who understood the study procedures and voluntarily agreed to participate. Two preliminary assessments were conducted to screen for functional and cognitive impairments. Functional disability was assessed using the Korean Activities of Daily Living scale [17]. Participants who reported needing assistance in at least one of the seven activities of daily living were excluded from the study (n = 4). Cognitive impairment was assessed using the Pre-screening Korean Dementia Screening Questionnaire, which is used in national health screenings in Republic of Korea [18]. Participants with scores ≥ 4, indicating the need for further testing, were excluded (n = 3). One participant who withdrew consent was also excluded, resulting in a total of 176 participants included in the final analysis.
The minimum sample size required for multivariate logistic regression analysis was calculated using G*Power software (version 3.1.9.; Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany), assuming an odds ratio of 2.1, a Pr(H0) of 0.140, an alpha level of 0.05, and a power (1 − β) of 0.90. The assumed odds ratio was derived from a previous study reporting an association between oral hypofunction and frailty [19], while the Pr(H0) was determined based on the reported prevalence of frailty assessed using the Fried Frailty Phenotype scale (FRAIL) [20]. The minimum sample size was calculated to be 162 participants. The flowchart of the participant recruitment process is presented in Figure 1.

2.2. Measurements

All assessments were conducted by a single trained examiner who underwent calibration prior to data collection to ensure measurement consistency. The collected data included sociodemographic characteristics (sex, age, education level, income level, and cohabitation status); health-related factors (smoking status, alcohol consumption, number of systemic diseases, risk of depression, number of meals per day, and body mass index); oral health-related factors (self-perceived oral health status, number of oral disease symptoms experienced over the previous 6 months, daily toothbrushing frequency, tongue cleaning, use of interdental devices, regular dental check-up, and regular dental scaling); oral functional status; and frailty status.

2.2.1. Health and Oral Health Related Factors

Height and weight were measured using a wireless ultrasonic height meter (HUK-2; HuBDIC Co., Anyang, Republic of Korea) and a digital scale (Ranix Smart Life Scale; Ranix Co., Anyang, Republic of Korea), respectively. Body mass index was calculated as weight (kg) divided by height squared (m2). The presence of 11 chronic diseases (hypertension, diabetes mellitus, hyperlipidemia, osteoporosis, osteoarthritis, heart failure, insomnia, stroke, gastritis and gastric ulcer, gastroesophageal reflux disease, and spinal stenosis) was assessed using a self-reported questionnaire. The risk of depression was assessed using the Patient Health Questionnaire-2, and participants with total scores ≥ 3 were considered at risk of depression [21]. Oral disease symptoms experienced over the previous 6 months were assessed using a self-reported questionnaire, including bleeding gums, swollen gums, receding gums, loose teeth, drifting teeth, sore gums, toothache, and bad breath [22,23]. The number of oral disease symptoms was calculated by summing the reported symptoms (range: 0–8).

2.2.2. Oral Functional Status

Oral hypofunction was diagnosed using seven parameters: oral hygiene, oral dryness, occlusal force, tongue–lip motor function, tongue pressure, masticatory function, and swallowing function [16]. Each parameter meeting its respective cut-off criterion was assigned 1 point, with a total score ≥ 3 indicating oral hypofunction [16]. Oral hygiene, one of the subcomponents of oral hypofunction, was assessed using the Tongue Coating Index [24]. For this, the tongue surface was divided into nine sections, each scored 0 to 2 points following visual inspection. Total scores were converted to percentages of the maximum possible score (18 points), with values above 50% classified as poor oral hygiene [16]. Oral dryness was measured three times using an oral moisture checker (Mucus; Life Co., Shinagawa, Japan), with median values < 27.0 indicating oral dryness [16]. Occlusal force was assessed according to the number of remaining natural teeth, with <20 teeth classified as reduced occlusal force [16]. In epidemiological studies, the number of remaining teeth has also been used as a practical proxy for occlusal force [25]. Tongue–lip motor function was evaluated using oral diadochokinesis [26], which evaluates the motor speed and dexterity of the tongue and lips [16]. Participants were instructed to repeat the syllables /pa/, /ta/, and /ka/ as quickly as possible for 5 s each. The number of syllables produced per second was measured using an automatic counter (Kenkokun Handy; Takei Scientific Instruments Co., Niigata, Japan). Based on the cutoff used in a previous study [27], rates < 6 syllables/s for all three syllables was classified as decreased tongue–lip motor function. Tongue pressure was measured using the Iowa Oral Performance Instrument (IOPI; IOPI Medical, Woodinville, WA, USA) [28]. A soft rubber pressure bulb was positioned longitudinally on the hard palate of participants just posterior to the alveolar ridge. Then, the participants were instructed to press the bulb with the front part of their tongue as strongly as possible for 2 s while keeping their lips slightly closed. Considering muscle fatigue, measurements were repeated three times with 30 s rest intervals, and a maximum value < 34 kPa was classified as reduced tongue pressure [29]. Masticatory function was assessed using the gummy jelly test (UHA Mikakuto Co., Osaka, Japan), where participants chewed 30 times as normal [30] and expectorated the chewed fragments into a disposable cup. The degree of fragmentation of the chewed gummy jelly was compared to a visual reference material, and scores ≤ 2 were classified as decreased masticatory function [31]. Swallowing function was assessed using the Eating Assessment Tool-10 (scores 0–40), with total scores ≥ 3 indicating a high risk of dysphagia [32].

2.2.3. Frailty Status

The Korean version of the FRAIL (K-FRAIL), applicable to community-dwelling older adults, was used to identify participants with physical frailty [33,34]. The scale comprises five components: exhaustion, weakness, slowness, low physical activity, and unintentional weight loss (≥4.5 kg, past 1 year). Each component was given a score of 1 point if present, resulting in a total frailty score ranging from 0 to 5. A total score ≥ 3 indicated physical frailty.

2.3. Statistical Analysis

Statistical analyses were performed using SPSS Software (v25.0; IBM Corp., Armonk, NY, USA). Independent t-tests, one-way analysis of variance with Scheffé post hoc analysis, and the Kruskal–Wallis test were used to examine differences in frailty scores according to participant characteristics. Post hoc comparisons following the Kruskal–Wallis test were conducted using the Mann–Whitney U test with Bonferroni correction. Multiple logistic regression was used to analyze the strength of the association between oral hypofunction and physical frailty after adjusting for factors associated with frailty. In the logistic regression models, the dependent variable was physical frailty (presence vs. absence) and the independent variables included all factors that showed statistical significance (p < 0.05) in the bivariate analysis. Among the independent variables, the total oral hypofunction score, calculated by summing the seven oral function items, was included in the model. Prior to logistic regression analysis, multicollinearity among independent variables was assessed using the variance inflation factor and tolerance values. Statistical significance was set at p ≤ 0.05.

3. Results

3.1. Sociodemographic Characteristics and Physical Frailty Scores

The mean frailty score was highest in female participants, participants ≥ 90 years of age, those with no formal education, and those living alone (p < 0.01, Table 1).

3.2. Health-Related Characteristics and Physical Frailty Scores

The mean frailty score was higher in participants with more than seven comorbid systemic diseases and those at high risk of depression than in their respective control groups. Among the systemic diseases, stroke and osteoarthritis were significantly associated with higher mean frailty scores compared to those without these conditions (p ≤ 0.05, Table 2).

3.3. Oral Health-Related Characteristics and Physical Frailty Scores

The mean frailty score was higher among participants who reported 4–8 perceived oral disease symptoms, those who never used interdental cleaning devices, and those who did not receive regular dental check-ups, compared to their respective control groups (p < 0.05). Although the mean frailty score also tended to be higher among those who brushed their teeth twice a day and those who did not receive regular dental scaling, these differences were not statistically significant (p = 0.078 and 0.054, respectively; Table 3).

3.4. Oral Hypofunction and Physical Frailty Scores

The mean frailty score was higher among participants with oral dryness, reduced occlusal force, decreased tongue–lip motor function, reduced tongue pressure, impaired masticatory function, and deteriorated swallowing function (p < 0.05). In addition, participants with oral hypofunction (≥3 reduced components of oral functions) had a higher mean frailty score than the group with normal oral function (p < 0.05; Table 4).

3.5. Strength of Association Between Oral Hypofunction and Physical Frailty

The multiple logistic regression results are presented in Table 5. In Model 1, which only included oral health-related factors, the odds ratio for frailty significantly increased with a higher oral hypofunction score (odds ratio [OR] = 1.468, p = 0.005). In Model 2, in which all factors associated with frailty were adjusted for, the association between oral hypofunction and frailty remained significant (OR = 1.382, p = 0.038). In addition, female sex and a higher number of perceived oral disease symptoms were associated with a greater likelihood of frailty (p < 0.05). In contrast, the use of interdental cleaning devices was significantly associated with a lower likelihood of frailty (p < 0.05), whereas regular dental check-ups showed a similar association but was not statistically significant (p = 0.058). All independent variables showed variance inflation factor values < 5 and tolerance values > 0.20, indicating that multicollinearity was not a concern. The Nagelkerke R2 values were 0.287 for Model 1 and 0.422 for Model 2. The Hosmer–Lemeshow test results indicated good model fit for both models (p > 0.05).

4. Discussion

This study evaluated oral health and functional status in community-dwelling, independently living older adults with preserved cognitive and functional activities of daily living, and analyzed the association between oral hypofunction and physical frailty. This study applied the oral health criteria proposed by the Japanese Society of Gerodontology because they evaluate oral functions using multiple functional parameters and primarily assess physiological oral functions. As such, they are less influenced by population differences and can be easily and conveniently implemented in clinical settings.
The prevalence of physical frailty in this study, defined as a K-FRAIL score of ≥3, was 40% (n = 71), which was substantially higher than the 11.2% reported by Kim et al. [35], who also used the same scale. This discrepancy may be attributed to the slightly older age of participants in the present study (mean age: approximately 82 years). Alternatively, the use of convenience sampling may have resulted in the selection of senior welfare facilities frequented by relatively less active older adults. Furthermore, as a result of analyzing the association between the seven parameters of oral functions and physical frailty, six of these, excluding oral hygiene status, were associated with a higher mean frailty score. Even after adjusting for factors associated with frailty, such as systemic diseases and depression (Model 2), the odds of frailty increased with a higher oral hypofunction score, although the association was of moderate strength (OR = 1.382). In other words, the more impaired oral functions were, the higher the likelihood of frailty occurring. This finding is consistent with a previous study reporting that older adults with oral hypofunction were more likely to be in a pre-frail or frail state [19]. Another study reported that oral hypofunction was associated with comprehensive frailty even after adjusting for sarcopenia but was not associated with frailty status that reflected only physical function [36]. This study suggested that, because oral functions affects social aspects such as communication and aesthetics, a decline in oral function may influence psychological and social well-being [36]. Similarly, another study reported that poor oral health was associated with frailty, sarcopenia, and disability in community-dwelling older adults [37]. In addition, a study using the same instrument used herein found that swallowing function showed the strongest association with frailty among oral function items [19]. However, frailty itself may also lead to deteriorations in oral functions. Nevertheless, our findings suggest that impaired oral functions may be associated with the development of frailty. Therefore, maintaining comprehensive oral cavity function as much as possible with aging and restoring impaired functions as early as possible may help to prevent or delay the onset of physical frailty.
In this study, 50% of older adults exhibited oral hypofunction. Given the high incidence and accumulation of oral diseases at older ages, the prevalence of oral hypofunction is substantially high in this population. A study using the same tools used herein also reported oral hypofunction in approximately 53% of participants [36]. These findings show that older adults, caregivers, and healthcare professionals should recognize oral hypofunction as a prevalent condition among community-dwelling older adults and pay close attention to related adverse health outcomes. Encouragingly, since oral hypofunction is reversible when appropriate oral care is provided in a timely manner [16], our findings suggest that the surveillance of oral functions should be reinforced in older adults beyond a certain age to enable early identification of high risk. Oral health professionals should identify modifiable areas and areas requiring intensive management to plan and deliver personalized oral care based on oral functional assessment findings.
Evaluation of the parameters of oral functions revealed that the most impaired ability among participants was oral hygiene (which was low in 52% of participants), followed by tongue–lip motor function (48%), occlusal force (46%), swallowing function (36%), tongue pressure (32%), oral dryness (30%), and masticatory function (22%). Bivariate analysis demonstrated that swallowing function, tongue pressure, and masticatory function, in particular, were strongly associated with a higher mean frailty score (p < 0.05). This aligns with a previous study showing that dysphagia was associated with the development of frailty, irrespective of the presence of neurodegenerative disease and the number of chronic diseases or pharmacological medicines used [38]. Similarly, Iwai et al. [39] reported that older adults ≥ 75 with poor chewing and swallowing function were more likely to need support or care after 3 years. Reduced tongue pressure can impair regular food consumption, potentially leading to complications such as malnutrition, dehydration, and aspiration pneumonia [40]. The tongue is a complex muscular organ that works in harmony with the lips, mandible, and pharynx to perform various functions vital for life, such as mastication, swallowing, and speech [16]. Specifically, the tongue elevates and positions food over the teeth for easier chewing and subsequently propels the food bolus from the oral cavity toward the pharynx [41]. Consequently, reduced tongue pressure may impair both masticatory and swallowing functions, leading to weight loss and reductions in physical function, ultimately accelerating frailty progression. These findings underscore the need for early identification of older adults with low tongue pressure and for providing effective interventions for improving tongue pressure (e.g., mastication exercises using chewing gum [42]).
The present study also identified a significant association between objectively measured masticatory function and frailty. This is consistent with earlier research reporting an association between chewing difficulty and frailty, although this previous study relied on self-reported chewing ability [43]. Recently, studies have emphasized the importance of masticatory ability in preventing negative health outcomes such as frailty, sarcopenia, and malnutrition [44]. The number of remaining natural teeth is a key determinant of masticatory function [43,45], and fewer remaining teeth leads to diminished masticatory function, which increases the risk of poor nutritional status [46]; this, in turn, is directly linked to functional disability, dementia, and mortality [47,48]. Okuyama et al. [49] showed that partial or complete loss of occlusion led to a decrease in leg extensor power and balance function, suggesting that maintenance of dental occlusion is an important factor in maintaining activities of daily living in older adults. Consistent with these findings, a systematic review reported that a low number of teeth was associated with frailty [50]. Similarly, Zhang et al. [51] found that the risk of frailty was approximately twice as high in individuals with fewer than 20 remaining teeth. Komiyama et al. [52] emphasized the importance of preserving natural teeth for healthy aging as the use of dentures did not slow the progression of frailty. Therefore, as tooth loss can cause not only impaired masticatory ability but also malnutrition and a decline in physical function, oral health interventions should be provided early so that functional natural dentition can be kept for as long as possible. Notably, there may be a bidirectional relationship between periodontal disease, the prevalence of which increases substantially with age, and frailty [53]; thus, more attention should be paid to periodontal care from middle age onward. In addition, since aging itself may adversely affect masticatory performance [54], factors that influence this ability, including tooth loss, reduced salivation, or muscle atrophy, should be monitored comprehensively at an early stage.
In the present study, no significant association was observed between poor oral hygiene assessed using the Tongue Coating Index and physical frailty. This is consistent with a previous study reporting that oral hygiene, among the seven components of oral hypofunction, was not associated with frailty or sarcopenia [55]. Unlike functional factors such as swallowing or chewing abilities, oral hygiene is an indicator of oral care status rather than physiological oral function. Therefore, it may have little or no direct association with frailty, which reflects a decline in systemic function. Nevertheless, the tongue harbors about two-thirds of the microorganisms present in the oral cavity, and tongue cleaning plays an essential role in preventing oral diseases that cause tooth loss [56]. Bacteria on the tongue surface may be transported to the pharynx via saliva, thereby increasing the risk of aspiration pneumonia [57]. Therefore, future studies should clarify the association between an individual’s ability to maintain oral hygiene and frailty.
Additionally, in this study, female sex was identified as the factor most strongly associated with physical frailty, reaffirming it as a major predictor of frailty (OR = 4.900). This may be explained by the fact that women have lower baseline muscle mass and strength than men, making them more susceptible to sarcopenia and frailty [58]. Therefore, older women require closer monitoring of frailty risk factors, including sarcopenia and systemic diseases, as well as interventions aimed at maintaining muscle mass and strength, particularly through moderate-intensity exercise.
This study has several limitations. First, its cross-sectional design makes it difficult to establish a causal relationship between oral hypofunction and frailty development. Although this study focused on associations between oral hypofunction and physical frailty, their relationship may be bidirectional. Second, as data were collected using questionnaires for several variables, including health behaviors, the findings may have been subject to social desirability bias. Although the data were obtained in face-to-face interviews, participants’ responses relied on recall, further introducing the possibility of memory-related errors. Third, while various factors that may influence frailty development were adjusted for in the final regression model, there may be risk factors or confounding factors for frailty that were not considered. Because only variables that were statistically significant (p < 0.05) in the bivariate analysis were included in the final regression model, some potentially important variables may have been omitted. Fourth, since no gold standard currently exists for the diagnosis of frailty [59], the K-FRAIL scale was used herein. Although this screening tool has high sensitivity (81.7%) and specificity (82.5%) [34], it cannot provide a definitive diagnosis of frailty. Fifth, the IOPI was used to assess tongue muscle strength. Variations in measurement tools may contribute to differences in the reported prevalence of oral hypofunction. However, given that the IOPI has high reliability and validity [60] and that a total score combining the clinical signs/symptoms of oral hypofunction was used in the final regression model rather than dichotomous classification (presence or absence), this limitation is unlikely to have substantially affected the main findings. Sixth, two subcomponents of oral hypofunction, tongue muscle strength and tongue–lip motor function, were related to the tongue, resulting in potential redundancy in assessment, even though the two represent distinct functional domains of swallowing and tongue/lip motor function [16,61,62]. Furthermore, occlusal force was assessed using the number of remaining natural teeth (<20), but this method may not fully reflect functional occlusal performance. Further research is needed to develop standardized oral functional assessment tools that address these limitations. Finally, this study recruited participants using convenience sampling, which may have introduced selection bias. In particular, there were more female than male participants, resulting in an uneven sex distribution. This may partly reflect the demographic characteristic that women have a longer life expectancy than men. Although sex was adjusted for in the regression model, sex-specific differences were not examined and thus cannot be ruled out. Consequently, the sample may not fully represent the general older adult population, limiting the generalizability of the findings. Future studies should incorporate both objective tools and self-reported measures to increase the validity of data and minimize bias. Longitudinal studies employing diagnostic tools and accounting for a broader range of frailty risk factors in larger populations are also warranted to elucidate the influence of oral hypofunction on frailty development more definitively.

5. Conclusions

This cross-sectional study demonstrated that higher oral hypofunction scores were associated with an increased likelihood of physical frailty among community-dwelling older adults with preserved cognitive and functional activities of daily living, even after adjusting for frailty-related factors. These findings suggest that early identification of individuals at high risk of oral hypofunction through periodic oral function assessments, followed by personalized oral health interventions based on the assessment results, may have implications for strategies aimed at preventing or delaying physical frailty. Given that this study did not address causal relationships between oral hypofunction and physical frailty, future studies with larger sample sizes and longitudinal designs are warranted to confirm and extend these findings.

Author Contributions

Conceptualization, H.-Y.K., J.K. and J.-S.C.; methodology, H.-Y.K., J.K. and J.-S.C.; software, H.-Y.K.; formal analysis, H.-Y.K. and J.-S.C.; investigation, H.-Y.K. and J.-S.C.; data curation, H.-Y.K. and J.-S.C.; writing—original draft preparation, H.-Y.K. and J.-S.C.; writing—review and editing, H.-Y.K. and J.-S.C.; visualization, H.-Y.K. and J.-S.C.; supervision, J.K. and J.-S.C.; project administration, H.-Y.K. All authors have read and agreed to the published version of the manuscript.

Funding

This study did not receive any financial support.

Institutional Review Board Statement

This study was approved by the Institutional Review Board of Gachon University (approval no: 1044396-202412-HR-201-01, approval date: 17 January 2025) and all involved procedures were performed in accordance with the World Medical Association Declaration of Helsinki.

Informed Consent Statement

Informed consent was obtained from all participants involved in the study.

Data Availability Statement

The data presented in this study are available on request from the corresponding author due to privacy restrictions.

Acknowledgments

The authors are grateful to all the subjects who participated in this study.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
IOPIIowa Oral Performance Instrument
K-FRAILKorean version of the Fried Frailty Phenotype
SDstandard deviation
KRWKorean won
CIconfidence interval
ORodds ratio

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Applsci 16 03695 g001
Figure 1. Flowchart of participant recruitment process.
Figure 1. Flowchart of participant recruitment process.
Applsci 16 03695 g001
Table 1. Frailty scores according to socio-demographic characteristics.
Table 1. Frailty scores according to socio-demographic characteristics.
VariablesnFrailty ScoreStatisticp
SexMale391.49 ± 0.99t = −4.056<0.001
Female1372.28 ± 1.34
Age (years)65–79481.48 ± 1.16 aF = 8.856<0.001
80–891032.28 ± 1.33 b
≥90252.60 ± 1.11 b
Education levelNo education542.46 ± 1.22 aF = 9.416<0.001
Primary school772.26 ± 1.41 a
≥Middle school451.42 ± 0.96 b
Income level ≤290,0001202.08 ± 1.31t = −0.3630.717
(monthly KRW)≥300,000562.16 ± 1.33
CohabitationLiving alone822.38 ± 1.32 aF = 4.8280.009
Living with spouse501.66 ± 1.33 b
Living with child(ren)442.11 ± 1.12 ab
Analyzed using the t-test or one-way analysis of variance (ANOVA), with t and F denoting the corresponding test statistics. All values are expressed as mean ± standard deviation. a,b Same characters denote no significant differences assessed using Scheffe’s multiple comparison at α = 0.05.
Table 2. Frailty scores according to health-related characteristics.
Table 2. Frailty scores according to health-related characteristics.
VariablesnFrailty ScoreStatisticp
Smoking statusNon-smoker1512.15 ± 1.33t = 1.3570.351
Former and current251.88 ± 1.16
Alcohol consumption Yes341.79 ± 1.27t = 1.5650.122
No1422.18 ± 1.13
Systemic disease +Yes122.83 ± 1.03Z = −2.0910.037
(stroke)No1642.05 ± 1.32
Systemic disease +Yes512.39 ± 1.34Z = −1.9580.050
(osteoarthritis)No1251.99 ± 1.29
No. of systemic 0–2821.95 ± 1.30 ax2 = 8.2250.042
diseases3–4612.13 ± 1.33 ab
5–6292.28 ± 1.25 ab
≥743.75 ± 0.50 b
Risk of depressionNormal (≤2)1501.99 ± 1.25t = −2.8310.005
(score)High risk (≥3)262.77 ± 1.50
No. of meals ≤2262.27 ± 1.28t = 0.6760.500
(day)≥31502.08 ± 1.32
Body mass indexUnderweight (<18.5)61.17 ± 1.16x2 = 3.1240.210
(kg/m2)Normal weight (18.5–22.9)352.17 ± 1.56
Overweight or obesity (≥23)1352.13 ± 1.24
Analyzed using the t-test, Kruskal–Wallis test, or Mann–Whitney U test, with t, χ2, and Z denoting the corresponding test statistics. All values are expressed as mean ± standard deviation. + Among the 11 systemic diseases, only two showed a significant association with frailty. a,b Same characters denote no significant differences assessed using Scheffe’s multiple comparison at α = 0.05 or using the Mann–Whitney U test (with Bonferroni correction).
Table 3. Frailty scores according to oral health-related characteristics.
Table 3. Frailty scores according to oral health-related characteristics.
Variables nFrailty ScoreStatistic p
Self-perceived oral Good331.85 ± 1.06F = 0.8570.426
health statusNormal942.14 ± 1.36
Poor492.22 ± 1.37
No. of oral disease 0–31311.98 ± 1.28t = −2.2780.024
symptoms4–8452.49 ± 1.35
Daily toothbrushing 0–1 231.74 ± 1.21F = 2.5950.078
frequency2 932.31 ± 1.27
≥3 601.93 ± 1.37
Tongue cleaningNever292.34 ± 1.47t = 1.0610.290
Sometimes and always1472.06 ± 1.28
Use of interdental Never1142.28 ± 1.34t = 3.3040.001
cleaning devicesSometimes and always491.55 ± 1.17
Regular dental check-upYes1241.44 ± 1.22t = 4.589<0.001
No522.39 ± 1.30
Regular dental scalingYes501.76 ± 1.34t = 1.9380.054
No1132.19 ± 1.30
Analyzed using the t-test or one-way analysis of variance (ANOVA), with t and F denoting the corresponding test statistics. All values are expressed as mean ± standard deviation.
Table 4. Frailty scores according to the seven parameters of oral hypofunction.
Table 4. Frailty scores according to the seven parameters of oral hypofunction.
ParametersVariablenFrailty Scoretp
Oral hygienePoor 922.14 ± 1.280.3510.726
Normal842.07 ± 1.16
Oral mucosal moistureDry 542.43 ± 1.31−2.1900.030
Normal 1211.96 ± 1.28
Occlusal forceReduced 812.35 ± 1.27−2.2390.026
Normal951.91 ± 1.32
Tongue–lip motor functionDecreased 842.33 ± 1.40−2.1950.031
Normal921.90 ± 1.20
Tongue pressureDecreased562.48 ± 1.36−2.6570.009
Normal 1191.92 ± 1.26
Masticatory functionDecreased 392.56 ± 1.29−2.4820.014
Normal1351.98 ± 1.30
Swallowing functionDeteriorated 632.63 ± 1.33−4.147<0.001
Normal1131.81 ± 1.21
Overall oral functions≥3 (Oral hypofunction)852.47 ± 1.35−3.657<0.001
(score)≤2 (Normal)911.77 ± 1.18
Analyzed using t-test. All values are expressed as mean ± standard deviation.
Table 5. Strength of associations between oral hypofunction and frailty in multiple logistic regression analyses.
Table 5. Strength of associations between oral hypofunction and frailty in multiple logistic regression analyses.
VariablesModel 1Model 2
Adjusted
OR		95% CIp *Adjusted
OR		95% CIp *
Regular dental scaling, yes (ref.no)2.3020.810–6.5420.1181.9430.574–6.5730.285
Regular dental check-up, yes (ref.no)0.2050.071–0.5880.0030.3050.089–1.0430.058
Interdental cleaning devices, yes (ref.no)0.2880.114–0.7240.0080.2300.081–0.6540.006
No. of oral disease symptoms1.3081.050–1.6300.0171.2871.021–1.6240.033
Oral hypofunction score1.4681.121–1.9230.0051.3821.017–1.8760.038
Sex, female (ref. male) 4.9001.317–18.2210.018
Age 1.0440.960–1.1350.317
Education level, no education (ref. ≥ middle) 1.4460.357–5.8530.605
Education level, primary school (ref. ≥ middle) 2.0400.576–7.2270.269
Living alone (ref. with child) 1.9540.750–5.0900.170
Living with spouse (ref. with child) 1.8810.554–6.3800.311
Stroke 2.2650.434–11.8340.332
Osteoarthritis 1.7020.704–4.1180.238
No. of systemic diseases
(excluding stroke and osteoarthritis)		 1.1100.852–1.4470.438
High risk of depression 1.4720.494–4.3900.488
* Multiple logistic regression analysis. Dependent variable: physical frailty (presence, absence). Independent variables: sex (male, female); age (continuous); education level (no, primary school, ≥middle school); cohabitation (living alone, living with spouse, living with children); stroke (presence, absence); osteoarthritis (presence, absence); no. of systemic diseases excluding stroke and osteoarthritis (continuous); risk of depression (normal, high risk); no. of oral disease symptoms (continuous); interdental cleaning devices (no, yes); regular dental check-ups (no, yes); regular dental scaling (no, yes); oral hypofunction score (continuous). Model 1 included only oral health-related variables associated with frailty in the bivariate analysis in this study. Model 2 included all variables associated with frailty. CI, confidence interval; OR, odds ratio.
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Kim, H.-Y.; Kim, J.; Choi, J.-S. Association Between Oral Hypofunction and Physical Frailty Among Korean Older Adults with Preserved Cognitive and Functional Status. Appl. Sci. 2026, 16, 3695. https://doi.org/10.3390/app16083695

AMA Style

Kim H-Y, Kim J, Choi J-S. Association Between Oral Hypofunction and Physical Frailty Among Korean Older Adults with Preserved Cognitive and Functional Status. Applied Sciences. 2026; 16(8):3695. https://doi.org/10.3390/app16083695

Chicago/Turabian Style

Kim, Ha-Yeoung, Jiyoun Kim, and Jun-Seon Choi. 2026. "Association Between Oral Hypofunction and Physical Frailty Among Korean Older Adults with Preserved Cognitive and Functional Status" Applied Sciences 16, no. 8: 3695. https://doi.org/10.3390/app16083695

APA Style

Kim, H.-Y., Kim, J., & Choi, J.-S. (2026). Association Between Oral Hypofunction and Physical Frailty Among Korean Older Adults with Preserved Cognitive and Functional Status. Applied Sciences, 16(8), 3695. https://doi.org/10.3390/app16083695

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