I lived on Utila for 7 months and was recommended to see the dentist in main town (opposite Bush supermarket), Dr Ana Aguila. DO NOT under any circumstances open your mouth to this woman. My filling has fallen out and she pretty much destroyed most of the tooth underneath, she didn't file the other filling properly and the 'hole' in another tooth that she wanted to fix, didn't even exist my dentist here in Australia told me after some xrays.
Wait until you get home or go and visit the dentist in Nicaragua in a little town called Masaya, he is a legend there so ask absolutely anyone in the town and they will know who he is. My partner had his teeth fixed there and no problems.
Her email is even begins with 'odont', rather appropriate i think. Oh please don't!