They do exist, but you have to look for them. The one we have is awesome. He is supportive of our extended breastfeeding and we are always with DD (22 months). He is older, but is very up-to-date with everything. My DD had some work done under GA, and although the anesthesiologist didn't want me back there, our dentist said there was no problem with it. Good luck!
eta- check out the AAPD
site, and the dentists websites. Usually you can find an office policies page that will say whether parents are allowed back or not.