I had a root canal about 3 years ago and have not had  a crown put on.  I just notice it has turned dark near the top of the tooth.  I do not have any tooth pain but the last two days have had blisters in the roof of the mouth and sore glands in my throat.  Not sure this is related or if the tooth is infected or dead.  Just does not look the same.
Whenever a root canal of a tooth is done it is always advisable to get a crown for that tooth done after finishing your root canal as prolong it without a crown can cause fracture of teeth or reinfection of teeth so get a X-ray done for your teeth again as u suggesting blackish discoloration of teeth there could be secondary caries or infection check the present condition of your teeth if the root canal is all done well and there is no secondary infection or caries of the tooth than just get a crown done for your teeth or else the secondary caries can be restored, and after that crown can be given. Regards Chat Doctor. 