Ask for advice from some of the parents you meet who have older children with the same disability as your child. See how long they have been going. Ask what techniques the dentist uses and if they like the dentist. Most severely disabled people need some type of special help to cooperate. In the US now this is very safe and the anesthesia is usually kept at low levels for general dentistry.
Oral surgeons can safely do general anesthesia in their offices.
Anesthesiologists are better than nurse anesthetists. All anesthesia personnel are aware that special needs people present more risks than non-disabled people and they take this into consideration when they recommend anesthesia. If you are skeptical about this, discuss risks with them far in advance of the procedure. Call the hospital and make a special trip just to have your child prescreened by the anesthesiologist if you are worried, we do. Many states require a special permit to do this.