We go to the dentist every 6 months and the dentist always gives us brand new toothbrushes. My wife and kids leave their little bag from the dentist in the car or on the counter for months. I eventually pick them up and put them in the drawer near my sink. There must be 50 tooth brushes in there. I've never seen my wife buy new ones and non of them have ever asked for a new toothbrush even though, every time I go in that drawer, I mention to them that they need to be swapping out their toothbrushes and to get on from the drawer.

Of course, they have my teeth and mouth chemistry so they've never had a cavity even though they probably rarely brush their teeth. My wife skips a day brushing and she gets a cavity.