I always wondered why those medics and dentists say you must change your tooth brush after months. Can somebody explain me this. Do you have to change it becouse of some bacils? If yes this leads me to two questions: 1) Doesnt tooth paste suposed to kill bacils in my mouth and on tooth brush? 2) Or if the evil bacils are so bad why we are'nt suposed to change tooth brush everytime we use it? For me its a clear lobby for toth brush industy to make people spend their money.