In his book How To Prevent Dementia, Dr. Richard Restak (neurologist, neuropsychiatrist, author, and professor) shared that some signs of dementia can show up first in everyday tasks ― including brushing your teeth. 

“Four impairments underlie the outer expressions and inner experiences of the Alzheimer patient,” the doctor shared in his book. He called these the “four As.” 

One sign is amnesia, he says ― simply forgetting things. Then, there’s aphasia, which involves not being able to understand, find, or use the right words. 

“Neither amnesia nor aphasia in their milder forms is always abnormal,” Restak says. But “the third and fourth of the four A’s are always a sign something is amiss,” he adds. 

One of these is agnosia, or “an impairment of correctly understanding information provided by the senses of seeing, hearing, touching, smelling, and tasting.” For instance, someone might not be able to recognise a beloved family member by sight. 

The final one, apraxia, refers to an inability to perform “purposeful and highly practiced actions despite normal muscle strength and tone.” 

Brushing your teeth is a good example of where apraxia may show up

Source: https://www.buzzfeed.com/aglover/tooth-brushing-sign-of-dementia