good brushing is technique independent of time if you brush for 2 minutes but don't get enough passes over each square mm of surface area, you have done a bad

good brushing is technique independent of time if you brush for 2 minutes but don't get enough passes over each square mm of surface area, you have done a bad job of brushing instead of watching the clock, imagine each of those surface areas and make sure you hit them plus gums, tongue, roof of mouth, etc.