D.W.
If he needs a root canal you could also consult an endodontist. They specialize in root canals. The problem you are going to run into if he wants to be "out" as in completely sedated is you will need a doc who is licensed/certified to perform sedations. My hubby is and he had to take specialized training with anesthesiologists. An endodontist may use gas but most probably don't do heavier sedation. And a heavier sedation is going to cost far more $$.
Wanted to add too-oral surgeons don't do root canals. The general dentists can tackle some of them but I'd rather go to the specialist that spent an extra 3 years in school beyond the 4 in dental school to take care of a specialized problem.