hello and welcome to hcm forum,
i would like to inform you that your oral surgeon is right when he/she says that its a TMJ
related problem, sometimes post cementation of the crown over the RCT treated tooth, TMJ problems have been noticed , this occurs due to improper cementation of crown. or there may be a problem in the tooth itself which has undergone RCT, i would have appreciated if you would have send in your tooth x-ray, i assume that RCT has been performed correctly.
For treating TMJ problem you need to visit an oral surgeon, he/she will prescribe you muscle relaxants, and suggest you a few facial exercises.
also, itching over the area is not associated with TMJ problem.
i wish you good health,