18 month dental visit

This morning I took Braydon to his 18 month dental visit.  It only involved the dentist brushing his teeth and putting some "vitamin" paste on his teeth.  He cried during the whole procedure. The Dentist basically told me I do not brush my son's teeth properly.  I do the best I can considering he is a child and doesn't want me to go near his mouth, nose or ears.  Braydon has all eight teeth on top and has one more molar on the bottom coming in and then it will be time for his two year old molars to come in. The Dentist also mentioned that I should try to break his habit of sucking his thumb.  Really, you expect me to be able to curb that when my own parents had a hard time doing that with me?  Plus isn't 18 months a little too early to expect him to be over that?