J.D.
I have a seven year old daughter who sucked her thumb until she was 5 1/2. I tried several things to get her to stop but to no avail. Her dentist kept telling me to leave her alone that she would stop on her own and as long as she did not have permanent teeth yet that the dental thing was not an issue. It worked. We left her alone and one month into kindergarten we noticed we were seeing less of the thumb sucking and asked her about it. She informed us she quit and that was the end. I wouldn't worry yet and if you can't help it, find a pediatric dentist and ask their opinion. By the way, she saw her dentist from 9 months on so he was aware of the situation the whole time. And today she has several permanent teeth, none of which are "damaged" from the thumb sucking. Good Luck!