Definitions: Dementia and Demented: [View all]

Dementia is not a specific disease but is rather a general term for the impaired ability to remember, think, or make decisions that interferes with doing everyday activities. Alzheimer's disease is the most common type of dementia. Though dementia mostly affects older adults, it is not a part of normal aging.

Demented is an adjective describing behavior that is crazy, unhinged, or insane.

The terms clearly differ.