A decade-long Japanese study of nearly 1,400 adults found that bleeding gums were associated with a 61% higher risk of Alzheimer's disease and 56% higher risk of all-cause dementia, while receding gums and deep tooth-gum gaps also showed elevated dementia risk. The findings suggest that oral inflammation and pathogens may contribute to neurological damage through systemic inflammation or direct brain colonization, though the observational study cannot prove causation.