Editorial
Masticatory Performance and Related Oral Functions: Novel Viewpoints of Oral Health
2024 Volume 31 Issue 12 Pages 1660-1661
Details
2024 Volume 31 Issue 12 Pages 1660-1661
See article vol. 31: 1664-1679
Indicators of oral health have traditionally been the prevalence of dental caries and periodontal disease, or the number of missing or remaining teeth. These items have a strong impact on chewing, the main oral function, so it is reasonable to set a national dental health goal (for example, the “8020 Campaign” by Japan Dental Association) of maintaining a certain number of teeth throughout one’s life. Looking back over the past 30 years, the number of teeth among older people in Japan has increased, and the proportion of older individuals with ≥ 20 teeth at 80 years old has increased dramatically from 10% to 50%1). However, the number of older people with few teeth has not decreased because of the approximately 3-fold increase in the number of people ≥ 75 years old. In addition, the number of older people with a reduced chewing function continues to increase regardless of the number of teeth due to various systemic diseases and the progression of frailty. This is a common problem not only in Japan but in other countries as well where the population is aging.
In this context, the concept of oral hypofunction syndrome (OHS) was established in 2018 to objectively evaluate the oral function as an indicator of oral health in older people from various perspectives and to capture it as a comprehensive pathological picture2). In OHS, seven items are evaluated as subsymptoms: oral hygiene, dry mouth, decreased occlusal force, decreased tongue pressure, a decreased tongue-lip motor function, decreased masticatory performance, and a decreased swallowing function. If a patient is positive for three symptoms, OHS is diagnosed and dental treatment and management are applied. The definition of OHS is based on the results of a cohort study (Kashiwa study) on the impact of a decreased oral function on the progression of frailty3). Of the seven subsymptoms, all except for a decreased swallowing function can be measured simply and quantitatively using testing equipment. The development and practical application of these testing equipment were carried out with the cooperation of industries, government, and academia, and their use is now a major characteristic of dental care in Japan. It is also important to note that these testing technologies are now being applied to clinical and epidemiological research, serving as a driving force for generating new evidence.
Takahara et al.4) conducted a 3-year follow-up observational study of 1,000 metabolic syndrome patients focusing on 2 subsymptoms of OHS (masticatory performance and the tongue-lip motor function) to investigate the impact of chewing function on the occurrence of adverse health events, such as all-cause mortality, onset/incidence of cardiovascular disease, fractures, malignant neoplasms, pneumonia and dementia. Masticatory performance was evaluated based on the concentration of soluble components (glucose) from the crushed test food (gummy jelly), and the tongue-lip motor function was evaluated based on the speed at which three types of single sounds (/pa/, /ta/, /ka/) were pronounced consecutively. During mastication, the tongue-lip motor function cooperates with other functional factors (bite force, tongue pressure, saliva secretion) to form a bolus. The condition for easy-to-swallow bolus is that the food is ground finely, which is evaluated as masticatory performance (Fig.1). Therefore, to determine the cause of impaired masticatory performance, it is necessary to evaluate individual functional factors.
In mastication, occlusal force contributes to breaking and crushing food (a), while tongue pressure, the lingual-labial motor function, and saliva secretion contribute to gathering small pieces of food and forming them into a bolus (b). Masticatory performance is an evaluation of the properties of the bolus based on the degree of fragmentation achieved by the integration of those functions (a, b). It affects the subjective difficulty of swallowing, which is assessed by a questionnaire in the diagnosis of oral hypofunction syndrome(c).
Chewing function indicators, such as masticatory performance and the tongue-lip motor function, are influenced by multiple oral local and systemic factors, so it cannot be assumed that they simply decline linearly with age or the number of teeth. Based on these characteristics of oral function indicators, Takahara et al. used a propensity score analysis to estimate the contribution of the chewing function decline to the occurrence of adverse health events by setting the decline in chewing function as the “exposure”. In their findings, the relationship between changes in both indicators and the risk of occurrence of events was visualized as a nonlinear model. As masticatory performance declines between 165-250 mg/dL, the risk of adverse health events gradually increases, and falling below the cutoff value for OHS of 100 mg/dL indicates the highest risk. In contrast, as the tongue-lip motor function declines between 4.7-6 times/second, the risk also increases, but a value of ≥ 6 times/second indicates the lowest risk. These differences in the nature of the cutoff values will be useful hints for exploring the relationship between OHS components and systemic health in future studies. It is expected that interdisciplinary medical and dental research utilizing oral function tests, such as this study, will lead to new proposals for health promotion.
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