Are you sure it's toothache and not your sinuses? Not being funny but by OH suffered terrible facial pains at one time when he flew, and it was discovered that his facial sinuses were blocked - he had a small operation and has been 100% fine ever since. The sinuses underneath your eyes are quite close to the top teeth - could that be connected.
I don't want to cast aspersions on your dentist but what have fillings got to with it? The pressure in the cabin affects cavities in the head (i.e. sinuses) - if I was being cynical I could say that fillings earn your dentist money but might not cure your problem.
As your GP for a referral to an ENT consultant, or go privately as a one-off if the NHS wait is long.
Does the sinus thing sound possible - where does the pain occur?
OH said his was unbearable, he was in acute pain over about 4000 ft.