Is developing inappropriate facial expressions a symptom of dementia?

Possibly... If one has dementia, that could explain such symptoms; otherwise, emotional, neuropsychological and/or organic factors would need to be explored.
Facial expressions. Facial expression is so important in all animals and humans. As a normal part of communication we look for visual clues in facial expression. When someone is suspected of showing signs of dementia facial expression may reflect feelings of anxiety, depression, agitation or bewilderment. The person's facial expression may be inappropriate.