My moler tooth have turned blue. Around 5 years back, I went to a dentist and she treated it with root canal. At that time I can feel/sense pain In my tooth, but as per her I shouldn't feel a thing as she has removed all the pulp and the tooth is basically disabled (in lack of better term to describe it). What's the treatment now, sometime there is pain in the tooth. It's an upper moler. What kind of testament is advised now.