Oral hygiene management issues vary across types and clinical stages of dementia. We aimed to clarify the issues related to oral hygiene management in older adults with Alzheimer’s disease (AD) according to stages defined by the Functional Assessment Staging of Alzheimer’s Disease (FAST). In all, 397 records (45 men and 352 women; average age, 86.8 years; age range, 65–106) from older adults with AD were used for the cross-sectional study. We used data from a cohort of older adults (≥65 years old) who required long-term care and lived in the Omorimachi area of Yokote City, Akita Prefecture, Japan. Multilevel logistic regression analysis was conducted to examine the associations of the FAST stage, set as the exposure variable, with oral hygiene management parameters set as outcome variables. Compared to the reference category (combined FAST stage 1–3), FAST stages 6 and 7 had significantly higher odds ratios for refusal of oral health care, dependence in performing oral health care, and rinsing and gargling disability. FAST stages 4 and 7 were associated with dental plaque accumulation. Oral health care for older adults with AD should be planned appropriately according to dementia severity.

Oral function evaluation in older adults with dementia is important for determining appropriate and practical dietary support plans; however, it can be challenging due to their difficulties in comprehending instructions and cooperating during assessments. The feasibility of oral function evaluation has not been well studied. This cross-sectional study aimed to determine the feasibility of oral function evaluation in older adults with Alzheimer’s disease (AD) according to Functional Assessment Staging of Alzheimer’s Disease (FAST) stages. In total, 428 older adults with AD (45 men and 383 women; mean age: 87.2 ± 6.2 years) were included. Multilevel logistic regression models were used to examine the prevalence of participants who were unable to perform oral function evaluations, including oral diadochokinesis (ODK), repeated saliva swallow test (RSST), and modified water swallow test (MWST). In comparison to the reference category (combined FAST stage 1–3), FAST stage 7 was associated with the infeasibility of ODK (adjusted odds ratio, 95% confidence interval = 26.7, 4.2–168.6), RSST (5.9, 2.2–16.1), and MWST (8.7, 1.6–48.5, respectively). Oral function evaluation is difficult in older adults with severe AD. Simpler and more practical swallowing function assessments and indicators that can be routinely observed are required.