S.W.
I spent 20 years working in the pediatric dental field and insurance can be tricky no matter what your coverage. Most plans (private, large group, etc) do not cover sedation of any kind, including nitrous oxide - laughing gas, let alone oral sedation. One avenue you may want to pursue, is to check with your case worker to see if you might qualify for temporary medicaid coverage just to get the dental work completed. I have advised this for parents in the past and some were able to get medicaid on a temporary basis, others were not so successful. However, if you are able to qualify for medicaid, you may have to switch dental offices since not all providers accept it.
As one other person suggested, you may even be able to have the sedation covered under the medical portion of CHIP. Not a guarantee, but worth a shot (pardon the pun). If the administrative staff at your dentist is willling to go the extra mile, they can write a letter to explain medical necessity to your medical plan. Good luck to you! I know the cost can be very overwhelming if you cannot get it covered, but at least you will have peace of mind knowing you tried.