Associations of sex, age, and number of remaining teeth with performance on oral hypofunction tests

Introduction: Oral hypofunction comprises seven aspects of oral condition, including oral hygiene, oral dryness, bite strength, tongue-lip motor function, tongue pressure, masticatory function, and swallowing function. Each of these seven has a single diagnostic criterion; however, the use of a single indicator without consideration of sex, age, or other factors is controversial. The purpose of this study was to evaluate the association between the oral hypofunction test and sex, age, and number of remaining teeth. Methods: The study was conducted at 12 facilities by the members of the Japanese Society of Geriatric Dentistry during April to December 2019. The participants comprised 181 healthy older adults aged 65 years and over (56.9% female; age range 65–95 years) who regularly visited these facilities. All tests of oral function and oral status available in Japan were performed on the participants, and the association between these tests and sex, age, and number of remaining teeth was examined. Results: Sex differences were observed in masticatory function, bite force, lip closure force, jaw-opening force, oral diadochokinesis “ka,” and tongue coating index (p <.05). In men, age was weakly (r = 0.20–0.40) associated with masticatory function, jaw-opening force, maximum tongue pressure, oral diadochokinesis, and swallowing function. In women, the number of remaining teeth, masticatory function, jaw-opening force, and oral diadochokinesis “ta” and “ka” was also weakly associated with age. Conclusions: Performance on the oral hypofunction test differs by sex, age, and number of remaining teeth. This means that the current single criterion for evaluation requires caution in its interpretation.