Throbbing pain under crown, with root canal already done

[JuliaB121]

I had root canal done on my four front teeth 8 years ago. They were capped with fused-to-metal crowns. Two months ago I decided to change them to all porcelain crowns. The dentist installed posts in all four teeth in order to make them stronger.
Three weeks ago one of the teeth began throbbing. It is not painful. It comes and goes, but I am very concerned. He wants me to see an endodontist and have the root canal redone, which would require a surgery because I now have a post in that tooth. I am very scared; I am not sure it is really failing root canal. The pain would have been much stronger and more persistent.  Do you think the surgery will help? what could cause this throbbing?

[JuliaB121]

I forgot to mention that my cosmetic dentist did an x-ray, which showed neither infection nor a crack in the tooth, as far as he could tell.

I am currently wearing temporary crowns and the dentist does not want to proceed until the problem is solved.
Has anyone had a similar problem?

[scottma]

Some endodontists are trained to differentiate Endodontic origin pain and non odontogenic pain.if your endodontist can rule out Endodontic pain, he or she may refer you to Orofacial pain specialist.