They could be correct. I was a dental nurse for seven years and this sort of thing was fairly common. When removing an old filling, particularly a deep one, there is always a risk that the root will be irritated and, once this occurs, it will continue to happen (even though flare-ups can sometimes be a long way apart) The best way of fixing it is to remove the nerve and fill in the root canal - this is usually successful but isn't 100% reliable (chances of success are worst in molars). In some circumstances the tooth has to be extracted in the end. If you can afford it, keeping the tooth is always worth going for as, once the tooth is removed, the bone around it shrinks away which can have a knock-on effect on the stability of the surrounding teeth. Root filled teeth are more brittle after the procedure so Mr Roach's dentist might suggest a crown over the top of the tooth for strength.