Why do some old people seem to be chewing on nothing, and they often have an underbite?

Question

It looks like they have a collapsed jaw and they are chewing on their gums. It is kind of distrubing. Do you know what this is and can you give me a name for this problem.

Answer 1

Its the skin around teh mouth that looses its elasticity and the jaw heights drop so they look like their bite is off