Dementia Tooth Pain Symptoms?

I brought mother to dentist yesterday and was told she needed a root canal.
Omg.
A deep cavity had formed under an old filling.
It was this or remove her only molar up there.
 I could tell he was hitting near the nerve area while he was drilling because mom's foot would move.
Unfortunately she cannot hear when told "open/close" and they get impatient.
This and she has a growth on her palate and tiny mouth making xrays practically impossible.

My mother has been complaining of food from refrigerator being too cold,
 leaving fruits, yogurt, everything on the counter to "warm up".
 Also, she has been sticking her finger in there picking around.
I have  found her to be ' flushed ' with no fever sometimes.
The flushed thing seems to be an overall indication that something is wrong.

apparently, you dont need to have an infection to need one-
just the area be exposed
http://www.animated-teeth.com/root_canal/t3_root_canal_reasons.htm