most know what they do, some are bad and if you end up with a bad one you will know it your whole life. Mine was like: You have to brush your teeth more often then 2 times a day, else i will get cavities. When i brushed 3 times i got cavities everywhere, she said it is because i still only brush once a day....i was furrios as she just told me that i lie to her. Changed doctor as i did not wan't to go to a doctor telling me i am a liar. Doctor 2 knew what was going on, i was basically eating my own teeth everytime after brushing as then the protection layer is weak (weak against acids, string against sugar and stuff) and my saliva was just eating through them.