Hi Maitry...have you done a search in the Appstore yet?
Not familiar with patient education and demos for Dentists...however, have you looked at the American Dentistry Association to see if they have a consumer section. Sometimes the Association websites will have a consumer section to view.
I think the app "Paper" by 53 might help to sketch down some stuff or create simple diagrams for your patients but other then that, I'm not familiar with Dentists apps.