I’d check with your endo about the situation.  We’ve never had dental work done beyond cleanings (yet).  General anesthesia can cause heart failure in a CAH patient, it should never be given without a stress dose and under the endo’s supervision.  I don’t know much about happy gas, so don’t know chemically what that is.  We had ingrown toenails, several times, locals were given in the area, and our endo advised a double oral stress dose for those.