dog health

My dog is a pretty healthy dog but i have a lot of ?'s...he is a 5 year old labrodor retriever. so..Heres my questions.
   
1) Do dog tooth brushes and tooth paste really work? If so, What kind?
   
2)What type of daily active vitamins for my dog would you prefer?
   
3)My dog use to (like 5 months ago and all before) eat like he had never eaten before when we went to feed him, now when we feed him he doesnt eat but about 2 bites of it? I just dont understand?
   
4)what kind of good active dog food would you prefer for my dog?