Unfavourable Outcomes in Older Adults with Oral Frailty: A Scoping Review

Introduction

Frailty is a biological syndrome characterized by a decline in physical status and activities, leading to increased vulnerability to adverse health outcomes.¹ Its social implications and associated factors, such as gender and daily functioning, vary across cultural contexts.² As the understanding of frailty evolves, oral frailty (OF) emerges as a specific type that underscores its significance in the health management of older adults.³ OF, a concept recently introduced in Japan, is now recognized as a key factor in dental and oral health policy. Measures to address OF have become a focus of Japan’s medical and welfare policies.⁴ OF is defined as

A series of events and processes that contribute to changes in oral conditions including number of teeth, oral hygiene and oral functions due to aging. These occurrences are accompanied by a decline in interest in oral health, reduced physical and mental capacity, and an increase in OF, leading to eating dysfunction and further declines in overall physical and mental functions.⁴

It is a comprehensive concept encompassing the diversity of oral functions.⁵ Functions such as chewing, swallowing, oral motor skills, and tongue pressure decline with age. This concept represents a state where multiple declines overlap.⁵

Global population aging is accelerating rapidly, with projections suggesting that by 2050, the number of people aged over 65 will approach 2 billion.⁶ Older adults also suffer from poor oral health due to diseases such as tooth decay, periodontal disease, and cavities. Compared to the general population, these issues accumulate throughout their lifetime and are exacerbated by frequent visits to oral health professionals.^3,7 Consequently, OF is more prevalent among the elderly. The prevalence of OF among the elderly varies by region and study population. A meta-analysis of pooled results indicated that the prevalence of OF and pre-OF was 24% and 57%, respectively.⁸ Increasingly, OF in the elderly is becoming a significant concern for overall health.

Factors associated with OF in old age, such as nutritional status and social aspects, are intricate.^9,10 One study shows OF predicted the risk of subsequent physical frailty, the need for long-term care, and mortality, suggesting that oral function may be a more accurate reflection of generalized frailty than physical function.^5,11 Additionally, older adults with OF have also reported poor gait performance,¹² malnutrition,^9,10 higher rates of eating alone,¹³ and lower food satisfaction.¹⁴ Furthermore, OF can initiate a negative spiral: food restriction and the selection of easier-to-eat food lead to further reduction in chewing ability, which in turn places individuals with OF at heightened risk of physical frailty and muscle loss.⁵ Hence, unfavorable outcomes of OF impact physical health, psychological well-being, social interactions, and overall quality of life (QoL) can be clearly observed.

Although numerous studies have focused on OF and its unfavorable outcomes, existing research is often limited by small sample sizes, variations in OF assessment methods, geographic differences, and inconsistent results across studies.^10,13,15 Thus, further evidence is needed to elucidate the relationship between OF and unfavorable outcomes in older adults. Therefore, this study aims to review the associated unfavorable outcomes of OF in elderly individuals comprehensively and systematically. Specifically, we will explore the definition of OF, assessment methods, and its association with generalized health. The findings of this study will enhance the development of targeted interventions, improve overall health outcomes, and reduce healthcare costs in elderly populations.

Methods

This review was conducted and reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis extension for Scoping Reviews (PRISMA-ScR) Guidelines.¹⁶ The protocol had been registered with Open Science Framework (OSF, https://osf.io/9mf 25).

Scoping Review Question

1. What are the assessment tools for OF in older adults?
2. What are the unfavorable outcomes of OF in older adults?

Inclusion/Exclusion Criteria

The review includes only studies with the highest quality from inception until March 31, 2024. The primary search included terms related to OF and older people.

The following were the inclusion criteria for this scoping review:

1. A cross-sectional or cohort study.
2. People aged ≥ 60 years.
3. Reported the relationship between OF and unfavorable outcomes.
4. Published in English.

Studies were excluded if they,

1. Had been published in other languages.
2. Reviews, meetings, conferences, or cases.
3. The full text cannot be obtained.

Definition of of

OF, as defined by the Japanese Dental Association (JDA), covers the following main areas:⁴

1. Overall decline in oral function, including decreased chewing, swallowing, and articulation.
2. Deterioration of oral hygiene: As oral function declines, an individual’s oral hygiene may deteriorate, leading to an increased risk of oral disease.
3. Deterioration in the quantity and quality of teeth: loss or damage to teeth, periodontal disease, and other problems are prevalent.
4. Decreased salivary production leading to dryness of the mouth, affecting chewing, swallowing, and overall oral health.
5. Social and psychological impact: As a result of oral dysfunction, older people may face difficulties in eating, verbal communication, and social activities, which affects their mental health and social participation.

Definition of Unfavorable Outcomes

The definition of unfavorable outcomes may vary across healthcare settings and studies, but at its core, it refers to outcomes that negatively affect a patient’s health and QoL.¹⁷ It is a widely used term in the fields of medicine and healthcare management. These unfavorable outcomes may involve the worsening of the disease, failure of treatment, development of complications, medication side effects, dysfunction, death, etc.

Identifying Relevant Studies

A search was undertaken on PubMed, Web of Science, Embase, Cochrane Library, Scopus, and CINAHL using the Mesh terms from inception until March 31, 2024: “oral frailty”, “OF”, “oral frailty”, and “oral health” in combination with “aged”, “elderly”, “aging”, and “geriatric”, “old people”, “older adult”, “elder”. We also adopted a snowballing method to search the relevant literature. The search strategy is presented in Table 1.

Table 1 Search Strategy

Study Selection and Data Extraction

First, the articles collected by researchers (SR Zhu and WZ Tang) from various electronic databases were merged in Endnote, and duplicates were eliminated. Then, two independent reviewers screened the titles and abstracts of studies retrieved from the search. Studies that met the eligibility criteria underwent full-text review. Any disagreement was resolved by a third researcher (ST Mo).

A standardized data extraction template was independently filled out by two researchers (SR Zhu and WZ Tang) and crosschecked by another pair (Xiu-Juan Feng). Descriptive data for the study characterization included information on the first author, study design, sample size, assessment tools, and the unfavorable outcomes of OF identified from each article.

Collating, Summarizing, and Reporting Results

The results were presented in two formats. Descriptive numerical analysis was used to summarize the incidence of unfavorable outcomes of OF. Additionally, the key conclusions from the studies are outlined through a narrative summary, addressing the issues discussed in this review.

Assessment of Risk of Bias

Each study’s risk of bias was reviewed and assessed meticulously utilizing the Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies (QATOCCS).¹⁸ It was assessed independently by two researchers (SR Zhu and WZ Tang), any disagreement was resolved by a third researcher (ST Mo). Not all criteria are equally significant in assessing bias, and responses marked as “No”, “Cannot Determine (CD)”, or “Not Reported (NR)” are disregarded. Research is rated “good” if it has two or fewer demerits, “fair” if it has three to six demerits, and “poor” if it has more than six demerits. Criteria marked as “not applicable (NA)” do not count as demerit.

Results

Literature Selection and Results

The initial search identified 898 potentially relevant articles, of which 319 were removed as duplicates. Following a secondary screening of titles and abstracts, 65 articles were selected for full-text review. Twenty-eight articles were included after the full-text review. The literature screening process is depicted in Figure 1.

Figure 1 The literature screen flow chart.

Basic Features of the Included Literature

Among the final 28 studies published between 2017 and 2024, 20 were cross-sectional,^{3,6,9,10,12,15,19–32} and 8 were prospective cohort studies.^5,33–39 This scoping review included a total of 28,329 patients. Twenty-two studies were from Asia, covering countries/provinces with Japan,^{3,5,6,9,10,12,15,20,24,26–29,31,33,34,36,37,39} Singapore,²¹ India,¹⁹ and Taiwan,³² making up 78.57% of all Asian studies. America contributed three studies from Mexico,³⁸ Ecuador,^22, and Chile.²³ Additionally, one study was from Australia³⁰ in Oceania, and two studies from Europe, specifically from the United Kingdom³⁵ and Switzerland.²⁵ These included studies involved 20 different assessment tools for OF, identifying 15 unfavorable outcomes. The incidence of Unfavorable outcomes related to OF in older adults with ranged from 22% to 74%. The fundamental characteristics are detailed in Table 2.

Table 2 An Overview of the 31 Studies Included in the Scoping Review

Risk of Bias

For risk bias, 10 studies were rated as good quality^{5,6,12,19,34–39} and 18 were rated as fair.^{3,9,10,15,20–33} All high-quality studies clearly described the research question, defined the study population, had high participation rates, recruited participants in the same cohort of patients, and assessed key confounding variables. Among the 18 studies rated as fair quality, the main limitation is the report and assessment of exposure and outcome. Furthermore, no articles provided specific sample size justification or effect estimates.

Twenty articles were cross-sectional studies,^{3,6,9,10,12,15,19–32} that is, their assessments of exposure and outcomes were conducted over the same period; therefore, questions 6 and 7 were rated “No”. In addition, their follow-up measurement is not applicable to loss. The results are presented in Supplementary Table 1.

Operationalizing and Measuring of

Various OF assessment tools were utilized in older patients, with 20 different measures identified across the included studies. Most studies assessed OF based on the methods of Tanaka et al,^{9,10,12,19,27,31,34,39} and some studies used tools, namely OF Index-8,^24,25,36 OF 5-Item Checklist,^15,37 OF Checklist,³² Revised Oral Assessment Guide,²¹ Oral Health Assessment Test),³⁰ Kihon Checklist 6,³ and Tanaka’s 16 measure.⁵ A number of parameters have also been used in some studies to assess OF, such as oral hypofunction assessment with seven parameters,²² six subjective and objective parameters,²⁰ interview and clinical evaluation,²³ eight parameters for assessing oral hypofunction and the oral function questionnaire about Kion checklist,³³ oral examination and self-reported oral health,³⁵ seven parameters for assessing oral function,²⁹ determining oral health conditions using nine parameters,³⁸ oral function evaluation with seven parameters,⁶ and oral function evaluation with five parameters,²⁸ as presented in Table 3.

Table 3 Description of Oral Frailty Measurement Tools

The most common method for assessing OF is the method developed by Tanaka et al.⁵ This method categorizes the outcome into three groups: non-OF, pre-OF, and OF, based on the final score. Various assessment methods have since been developed based on Tanaka et al’s approach. These methods often modify the number of items or incorporate additional subjective items to evaluate the degree of OF.^10,20,33 Among the commonly used parameters commonly are teeth status, chewing ability, oral diadochokinetic rate, and tongue pressure. These assessments are typically conducted by well-trained dentists, dental hygienists, nurses, and allied health professionals. The simplest assessment tool contains four parameters: oral examination, masticatory performance, tongue pressure, and oral diadochokinesis. The most comprehensive assessment tool includes 24 objective and subjective parameters.

Identified Unfavorable Outcomes in Older Adults with of

Fifteen unfavorable outcome indicators were reported, with each study identifying between one and six of these indicators. The most frequently reported was the incidence of physical frailty, followed by malnutrition, low dietary variety, social withdrawal, disability, and low gait speed. Additionally, some unfavorable outcomes were reported in only one article each, including oral candidiasis, short stride length, short step length, wider step width, longer double support duration, higher stride time, lower urinary tract symptoms, mild cognitive impairment, and fall risk. Among these studies, one had a follow-up time of one year,³⁸ while three had a follow-up time of two years.^33,34 The follow-up time for one study varied between one and four years, depending on the outcome indicator assessed.⁵ Another study had a follow-up time of six years.³⁶ One study had a follow-up time of eight years,³⁵ and two studies reported a follow-up time ranging from one to nine years.^37,39

Physical Frailty Associated with of

Among the included articles, 19 studies assessed the effect of OF on physical frailty in older people.^{5,6,15,19,21–25,27–32,35,37–39} Tanaka et al (2018) found that poor oral condition is a significant predictor of future physical frailty.⁵ Another Tanaka et al (2023) reported that 39.3% of individuals with OF showed a significantly higher prevalence and new-onset rate of physical frailty.³⁷ Kimble et al (2023) highlighted that oral health issues, specifically tooth loss and dry mouth among older adults are linked to the development of frailty in later life.³⁵ Ayoob et al (2024) demonstrated that 74% of individuals faced an elevated risk of developing new-onset physical frailty.¹⁹

Malnutrition Associated with of

Three studies indicated that OF increases the risk of malnutrition among the elderly.^9,21,34 One study indicated that the likelihood of experiencing more severe malnutrition, as assessed by the MNA^®-SF score, rose by 36% with each additional OF component.⁹ Another study reported that individuals with poor oral health had a 2.76 times higher risk of malnutrition.²¹ Additionally, a study demonstrated a significant correlation between OF and declining nutritional status, with 12.4% of participants showing worsening nutritional conditions.^33,34

Low Dietary Variety Associated with of

The relationship between low dietary variety and OF in the elderly has been explored in three studies.^5,10,15 Among older adults, one study found a significant correlation between the severity of OF and dietary variety scores. Specifically, the absence of daily consumption of meat, eggs, and soybean products differed markedly depending on the severity of OF.¹⁰ Another study identified a significant indirect association between OF and physical frailty through low dietary variety.¹⁵ Furthermore, participants diagnosed with OF were notably more prone to experiencing decreased meal volumes and decreased meat intake.⁵

Social Withdrawal Associated with of

Research from two studies has examined the relationship between social withdrawal and OF.^15,33 Iwasaki et al (2024) demonstrated that the indirect effect of OF on physical frailty, mediated by social isolation, was significant.¹⁵ Furthermore, Hasegawa et al (2020) discovered that oral hypofunction was linked to increased social withdrawal among older adults. The study identified several factors significantly linked to increased social withdrawal: the number of remaining teeth, gingival condition, occlusal force, masticatory efficiency, and issues related to swallowing and dry mouth.³³

Disability Associated with of

Three studies assessed the impact of OF on disability in the elderly.^5,36,37 Tanaka et al (2018) found that poor oral condition significantly predicted future disability, with OF being related to a 2.3-fold higher risk of disability.⁵ In a later study, Tanaka et al (2021) found that each one-point increase in the OFI-8 score corresponded to a 1.3-fold higher risk of new-onset OF and a 1.1-fold increased risk of disability.³⁶

Low Gait Speed Associated with of

Two studies explored the connection between low gait speed and OF.^12,27 Iwasaki et al (2021) found inverse linear correlations between the number of OF components and gait speed, stride length, and step length.¹² Similarly, Komatsu et al (2021) reported a notable correlation between gait speed and OF.²⁷

Others

Baba et al (2022) demonstrated that the presence of C. albicans and C. glabrata in saliva samples is linked to OF.²⁰ Iwasaki et al (2021) noted that participants with OF exhibited slower gait speeds, shorter stride and step lengths, wider step widths, longer double support durations, and greater variability in stride and step lengths.¹² Yoneyama et al (2024) demonstrated that the risk of OF independently correlates with lower urinary tract symptoms.³ Nagatani et al (2023) discovered significant correlations between a reduction in remaining teeth, low tongue pressure, and difficulty eating tough food with the onset of new mild cognitive impairment. Additionally, they discovered that individuals experiencing oral and physical frailty had an increased risk of mild cognitive impairment.³⁹ Kamide et al (2023) showed that OF was significantly linked to an increased risk of falls, independent of other potential confounding factors.²⁶

Discussion

This study aimed to explore the relationship between oral frailty and unfavourable outcomes in elderly patients and summarize their findings to provide an overview of the evidence. 20 oral frailty assessment tools were summarized. Then the evidence collected and analyzed in this review shows that the most common adverse outcomes in older patients with oral fragility are physical frailty, malnutrition, limited dietary variety, social isolation, disability, and reduced gait speed. The following findings were revealed.

Assessment of Oral Frailty

In current research on oral frailty in elderly patients, a variety of assessment parameters are employed, but no unified standard has been accepted yet. Among the 20 tools identified, the following three were used most frequently: assessment according to the methods of Tanaka et al, the Oral Frailty Checklist, and OFI-8 (a simplified version of Tanaka’s 16 measures). The first assessment method is based on the following six criteria, which are also important parameters of oral frailty: the number of present teeth, masticatory function, tongue pressure, oral diadochokinesis, difficulty swallowing, and difficulty chewing. This assessment method combines subjective and objective indicators but requires trained professionals to conduct the measurements.⁹ The second tool, the Oral Frailty Checklist, is a simple and easy-to-use subjective questionnaire that has been validated for assessing oral frailty and is widely used for screening oral frailty among the Japanese population.^40,41 The third tool, OFI-8, is designed to screen older adults at risk of oral frailty in community settings.¹¹ This eight-item subjective questionnaire evaluates tooth loss, diminished oral function, oral health-related behaviors, and reduced social participation. It includes two types of cut-off values, indicating the need for a dental check-up and the level of risk associated with oral frailty among older adults.¹²

We found that the assessment of oral function in studies is widespread. However, healthcare and dental services, as well as insurance systems, vary between countries. Additionally, most tools have been developed in Japan, so there is a need to enhance the external reliability and effectiveness of these tools to increase their applicability. In the future, combining subjective and objective structured assessment tools will help monitor oral frailty in elderly patients, taking into account cultural backgrounds and demographic characteristics.

Physical Frailty, Reduced Gait Speed and Disability Associated with Oral Frailty

The connections and pathways between oral frailty with frailty, reduced gait speed and disability have been extensively discussed. To elaborate, oral frailty is a strong predictor of physical frailty and disability and is associated with various factors, such as dental issues (tooth loss and the need for dental prostheses), periodontal disease, reduced occlusal force, decreased masseter muscle thickness, and oral motor dysfunction.^42–44 This dysfunction is often measured by the ability to accurately repeat a series of rapid, alternating sounds.

Additionally, interrelationships between oral hypofunction and dysphagia may contribute to frailty and disability through common pathways like changes in muscle function. These changes can affect the strength and coordination of swallowing muscles, including the geniohyoid muscle and tongue,⁴⁵ leading to impaired mastication, inefficient bolus transport, and increased aspiration risk.⁴⁶ Moreover, the relationship between oral frailty and physical frailty is likely to be bidirectional. Individuals with impaired physical function often have limited self-care abilities and restricted access to oral healthcare. Conversely, oral frailty is linked to sarcopenia, a precursor to overall frailty.⁵ Another possible mechanism linking oral frailty and physical frailty is through diet, as individuals with poor oral health tend to consume fewer healthy foods, leading to overall physical weakness.⁴⁷

Another study noted that participants with oral frailty exhibited poor gait performance, mirrored by slower gait speeds, shorter stride and step lengths, wider step widths, longer double support durations, and greater variability in stride and step lengths.¹² Firstly, oral diseases can cause occlusal interference and alter the position of the mandible. These changes can subsequently affect the posture of the head and neck, ultimately resulting in disturbances in overall body posture control and balance.¹² Then dental occlusion can adversely affect muscle tone, which is connected to knee muscular performance and ultimately influences gait.⁴⁸ Importantly, a study demonstrated a significant link between masticatory performance and gait speed, revealing that this relationship was mediated by protein intake.⁴⁹ Furthermore, oral frailty was significantly linked to an increased risk of falls, as gait impairment is a well-established risk factor for falls in older adults.⁵⁰ These findings emphasize the importance of a multidisciplinary approach to managing oral frailty, with dental care being a crucial component.

Malnutrition and Low Dietary Variety Associated with Oral Frailty

The accumulation of oral frailty increases the risk of low dietary variety and has a dose-response relationship with deteriorating nutritional status.⁵¹ Specifically, poor dentition can exacerbate anorexia, leading to a loss of pleasure in eating and making individuals more prone to dietary changes.^52,53 Edentulous individuals (including those with dentures) may also have more difficulty chewing than those with natural teeth.^54,55 Additionally, one study found that edentulous subjects, regardless of whether they had a prosthesis, consumed fewer fruits and vegetables. This group also exhibited decreased intake of protein and micronutrients, particularly in individuals with fewer than 21 teeth.⁵⁶

Biologically, OF, characterized by impaired chewing and swallowing, leads to the avoidance of foods that are difficult to chew, such as meats, vegetables, and fruits.⁵⁷ This avoidance can result in low dietary variety and poor diet quality.^58–60 Moreover, a complex condition related to OF, sarcopenic dysphagia, is characterized by a loss of muscle mass and strength in the swallowing muscles, leading to impaired swallowing and potentially resulting in malnutrition through multiple pathological mechanisms.⁶¹ A previous study stated that older adults who experience chewing and swallowing impairments, often have insufficient intake of fiber, linoleic acid, potassium, calcium, magnesium, zinc, selenium, vitamins D, E, and K, folate, biotin, and molybdenum.⁶²

Furthermore, among these pathophysiological mechanisms contributing to malnutrition, poor oral hygiene may play a crucial role by increasing the risk of progressive periodontal disease and dental decay.^55,63 Therefore, oral health screening for older adults is of great significance for improving overall health.

Social Withdrawal Associated with Oral Frailty

Previous studies have demonstrated that oral frailty is associated with social withdrawal.^64,65 The mouth is a crucial tool for social interaction, and individuals with oral frailty face difficulties in communication and social engagement due to impaired verbal motor skills.^65,66 Additionally, older adults with severe tooth loss often feel embarrassed and avoid face-to-face social activities, such as smiling, talking, and eating.⁶⁷ This avoidance can lead to reduced social engagement.^65,68 Furthermore, social outings often include eating and drinking. Studies have shown that individuals with oral frailty face dietary restrictions due to eating and swallowing disorders and may need to pause frequently during meals. This can create a psychological burden, making them reluctant to dine with others, reducing communication skills, and potentially worsening social withdrawal.³³ However, social withdrawal heightens the risk for experiencing loneliness in older adults, making them more vulnerable to both mental and physical health conditions.⁶⁹ Therefore, medical staff should screen oral function and develop personalized management measures related to oral frailty, which is crucial in preventing the worsening of social withdrawal.

Strengths and Limitations

This scoping review has some strengths. First, to the best of our knowledge, this is the first scoping review on the topic that highlights the importance of oral frailty in older adults and be available to researchers and healthcare providers. Second, our study adopted a robust method to guide and report the results of the scoping review framework based on the established range, including study identification and selection, and data synthesis.

While it is important to consider several limitations that may impact the generalizability of our findings. For instance, some studies may have methodological flaws, such as small sample sizes, lack of control groups, or potential biases in data collection and analysis, which can undermine the overall strength of the evidence. Additionally, variations in study design, patient populations, outcome measures, and definitions of oral fragility leads to heterogeneity in the data, complicating the process of drawing definitive and cohesive conclusions.

Future Research and Recommendations

Future research can expand to meta-analysis, allowing for a quantitative synthesis of existing studies to strengthen the evidence’s persuasiveness and applicability. Additionally, developing standardized assessment tools that are culturally adaptable will help optimize OF risk stratification and better identify varying degrees of OF in the elderly. Moreover, future research can compare the manifestations, causes, and effects of OF in older adults across cultures, helping to identify culture-specific factors and their impact on health outcomes. Furthermore, to reduce the prevalence of OF, future research should explore using Lean Thinking to optimize the collaborative processes of multidisciplinary teams (eg, dentistry, dietetics, nursing, social work) for the systematic identification and management of OF.⁷⁰

Conclusion

The current scoping review highlights the unfavorable outcomes linked to OF in older patients. The evidence collected and analyzed in this review suggests that physical frailty, malnutrition, low dietary variety, social withdrawal, disability, and low gait speed are the most common unfavorable outcomes in older patients with OF. Identifying these unfavorable outcomes is crucial because it significantly impacts the health and quality of life of the elderly. Furthermore, it aids in the development of public health policies, the optimization of healthcare resource allocation, and the enhancement of overall societal well-being. Future research should explore cross-cultural differences in the prevalence and impact of these unfavorable outcomes to enhance understanding and improve public health interventions.