Dr. Mauricio Grassi at Nancy's American Smile Clinic near Mercado 28. Their phone number is 887-4521. Hope you get right in, I've been in your shoes.
Did you look here? http://www.cancuncare.com/forum/viewtopic.php?t=25950 Or here? http://www.cancuncare.com/forum/viewtopic.php?t=7637
Mauricio is the man! Saved a tooth that other dentists all said needed a crown. He said "I can fix it in 20 minutes". I walked out with a perfect bite, and the tooth is happy. He speaks English, Italian, and some French too I think, and of course he's Mexican so he's got perfect Spanish. How many dentists in the States speak 4 languages?