I'm not sure bikerchickblonde, but if it's any help, I have just had a very troublesome wisdom tooth out, which was still completely inside the gum, by local anesthetic, and was in the chair for a total of 2 hours. Was not given a choice of any other methods, but still pleased with the dentist's work. Also I know that entonox is not available for childbirth here, so assuming it's also not available for dental work.