Pain in left lower molar tooth. , why?

I have consulted twice but NOT satisfied , Why ? I have a pain in capped left lower root canaled molar tooth w/o swelling , done 6 years ago, but whenever I have cold that tooth starts paining The area near my left ear also pains. This happens only at the time of cold attack. I read in the net that it may be due to sinus. But two dentists say that no sinus attack is possible in lower teeth. Fortunately one of my friends who contacted me shared his experience which runs contrary to the opinion of dentists. He also has the same issue and his dentist told that it is due to sinus (lower molar capped root canaled tooth) and refused to remove the tooth.After taking treatment for sinus the pain vanished . His teeth are intact but the dentist I consulted in Chennai ask me to remove the tooth and say iy is not due to sinus !