Chewing Gum and Cognitive Function

Inclusion Criteria: * 60 to 79 years of age * All posterior teeth are evenly occluded on both sides, and those who have lost 4 or less teeth in the posterior teeth * Those who scored 50 points or less on the periodontal disease self-checklist * Meet the diagnostic criteria for subjective cognitive decline or mild cognitive impairment * Provide written informed consent Exclusion Criteria: * Those who have difficulty in chewing due to toothache, periodontal disease, temporomandibular joint disease, severe malocclusion, shaking teeth, etc. * Those who wear dentures on the upper or lower teeth * Dementia * Major psychiatric illness such as major depressive disorders * Other neurodegenerative disease (e.g., Parkinson's disease) * Other serious or unstable medical disease such as acute or severe asthma, active gastric ulcer, severe liver disease, or severe renal disease, or any medical conditions preventing to complete the study as judged by the study physician * Severe loss of vision, hearing, or communicative disability * Significant laboratory abnormality that may result in cognitive impairment * Any conditions preventing cooperation as judged by the study physician * Coincident participation in any other intervention trial * Those who are planning dental treatment such as preservation, prosthetics, and implants during the research period