Don't let anyone yell at you or try to put you down. You fed him and that was the better choice at the time. Now is time to take care of his teeth, and that is what you expect from him. Keep your chin up. You have been a good mother and now is his turn to be a good dentist and do his job.
When DS was 9 we spent a week in NYC. he packed his toothbrush in my suitcase. Before we left I noticed that it was still there. As it turned out, he never brushed his teeth all the time we were there. I assumed he knew he had to do it, and he just forgot. The day after we came home he had a dentist appointment and I asked the Dr to yell at him for not brushing. He took a look and came back to me. I asked if he said something to him and he said: "I can't do that. His teeth are perfect. I have nothing to use against him". I had a good laugh at this one. Here I was so upset at him. Poor kid.