ヘルスサイエンス・ヘルスケア

Volume 21，No.2（2021）

EDITORIAL

Evidence-based conceptual pathway of oral function decline
Ageing is a major health issue being confronted simultaneously by all nations of the world. This problem is
now affecting not only high-income countries but also in middle- and low-income countries. Extension of life
expectancy represents a celebrated achievement of a goal that humans have long desired, but at the sametime it poses a monumental challenge. With age, an individual becomes more susceptible to disease, and thisleads to a decline in the functions of life (intrinsic capacity and functional ability).
The 2015 World Report on Ageing and Health defines the goal of healthy ageing as helping people todevelop and maintain the functional ability that enables well-being 1）. Functional ability is defined as thehealth-related attributes that enable people to be and to do what they have reason to value . Functional
ability consists of the intrinsic capacity of the individual, the environment of the individual and theinteractions between them. Intrinsic capacity is the composite of all the physical and mental capacities thatan individual can draw on . In order to delay functional decline and support people s health and well-being, it
will be necessary not only to provide medical care and long-term care insurance for all, but also to integratethese care systems into a larger social infrastructure that promotes healthy behavior and removes barriers.
Oral functions such as eating, talking and smiling are essential life functions that are deeply dependent onoral health 2）. As such, access to oral health care must be recognized as a fundamental and universal humanright. To that end, communities and governments have an obligation to maintain a health care system inwhich all persons can access the education, prevention, treatment and care necessary to maintain oral healththroughout the life course.
Oral function is a complex, multifaceted system of interacting parts and movements. It consists of several
higher-order functions essential to daily living and survival such as eating, talking and smiling. These
functions are supported by a number of lower-order (physiological) components: teeth, saliva, lips, tongue andoral-facial muscles. As people age, they experience a changing oral environment accompanied by a decline inoral functions including motor function (lips and tongue movement), masticatory function and swallowing
function. In Figure 1, I propose a novel conceptual pathway of the complex array of factors related to oral
function decline. This visual representation places oral function in the center and depicts the various factorsthat contribute to and are affected by it. The main risk factors that directly cause oral function decline areoral diseases and symptoms such as caries, periodontal disease, tooth loss, and pain. However, this conceptual
pathway shows that a variety of other factors related to general health and well-being also contribute to oral
function decline. The figure also reflects the growing recognition that there are complex reciprocal
relationships between the various factors and oral function. Furthermore, the three central components ofthe pathway (oral diseases, oral functions, and systemic health) are themselves in a state of interaction
with larger social and biological factors such as socioeconomic status, behavior, psychosocial status, andenvironment (including health services). All of this occurs in the context of and as an integral part of
the ageing process.
The relationship between ageing and oral function decline, as well as the effect of oral function decline on
systemic health, are supported by empirical evidence. For example, the proportion of community-dwelling
independent older people in Japan at risk of dysphagia is reported to be 25.1% 3）. The decline in oral functionthat occurs during aging reduces the diversity of food intake, resulting in insufficient nutrients and leading tonutritional impairment. In addition, a large-scale longitudinal study of elderly people living in Japan has
shown that minor oral dysfunction increases the risk of sarcopenia, dependence on long-term care and̶ 37 ⑴ ̶EDITORIAL

Figure 1. Conceptual pathway of oral function declinedeath 4）.
With an eye to preventing oral function decline, the Japanese Geriatric Dental Association has
already proposed an oral function assessment (screening) program that would expand traditional dental
assessment, attempting to measure even slight decreases in components of oral function such as
tongue function, lip function, saliva production, and eating and swallowing functions 5，6）. These assessments
still require improvement, particularly in terms of reliability and validity, but it is clear that person-centeredassessment of oral function in conjunction with multi-sectorial correspondence based on such assessments
are essential approaches for maintaining oral health in the later stages of life.
The oral function improvement interventions that would accompany such screening programs can take anumber of different forms, many of which have already been researched. Such interventions may include:
health education (e.g., the role of the oral cavity, the role of saliva, how to prevent aspiration pneumonia); oralhygiene guidance; oral function maintenance exercises (e.g., facial and tongue exercises, saliva gland massage,
pronunciation practice, breathing training) 7−9）. These interventions can be performed by a wide variety ofhealthcare professionals, including dental hygienists.
The number of research reports on the effects of interventions designed to improve the oral function ofcommunity-residing elderly persons is increasing. However, there have not yet been any systematic reviews
or meta-analyses of this body of research, so a strong claim of the effectiveness of such interventions cannotyet be made 10）.
Healthy longevity and health equity are the right goals, and they resonate with people in all walks of life
and of all races and cultures. They therefore have the potential to unite humanity across our multitudinous
divisions. The factors contributing to healthy longevity are numerous, complex, and interrelated, requiring
creative, interdisciplinary, intergenerational and global approaches. Prevention of oral function decline is an
important part of that picture, and person-centered approaches such as community-based, muti-sectorial
screening programs are practical, effective, and pose a low economic burden on society.
Kakuhiro Fukai, D.D.S., Ph.D.
Director, Fukai Institute of Health Science̶ 38 ⑵ ̶ヘルスサイエンス・ヘルスケア

Volume 21，No.2（2021）

References
1）World Health Organization. World report on ageing and health, Geneva, 2015
2）FDI. FDI s definition of oral health, https://www.fdiworlddental.org/fdis-definition-oral-health3）Igarashi K, Kikutani T, Tamura F. Survey of suspected dysphagia prevalence in home-dwelling older people using the10-Item Eating Assessment Tool (EAT-10)PLoS One. 2019；14（1）：e0211040.
4）Tanaka T, Takahashi K, Hirano H, et al. Oral frailty as a risk factor for physical frailty and mortality in communitydwelling elderly. J Gerontol A Biol Sci Med Sci. 2018；73（12）：1661-7.
5）Minakuchi S, Tsuga K, Ikebe K, et al. Oral hypofunction in the older population: Position paper of the Japanese Societyof Gerodontology in 2016. Gerodontology. 2018；35（4）：317-24.
6）Tanaka T, Hirano H, Ohara Y, et al. Oral Frailty Index-8 in the risk assessment of new-onset oral frailty and functional
disability among community-dwelling older adults. Arch Gerontol Geriatr. 2021；94：104340.
7）Sakayori T, Maki Y, Hirata S, et al. Evaluation of a Japanese Prevention of Long-term Care project for the improvement in oral function in the high-risk elderly. Geriatr GerontolInt. 2013；13（2）：451-7.
8）Ohara Y, Yoshida N, Kono Y, et al. Effectiveness of an oralhealth educational program on community-dwe11ing olderpeople with xerostomia. Geriatr GerontolInt. 20l5；15（4）：48l-9.
9）Iwao Y, Shigeishi H, Takahashi S, et al. Improvement of physical and oral function in community-dwelling older people
after a 3-month1ong-term care prevention program including physical exercise, oral health instruction, and nutritional
guidance. Clin Exp Dent Res. 2019；5（6）：611-9.
10）Dent E, Morley JE, Cruz-Jentoft AJ, et al. Physical Frailty: ICFSR International Clinical Practice Guidelines for Identification and Management, J Nutr Health Aging 2019；23（9）：771-87.
Received date：10 November 2021
Accepted date：1 December 2021

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