I had a fifteen year old lab that never got a tooth brushed or a cleaning. I knew knew you had to. We had dogs on the farm that lived outside forever without teeth cleaning. In fact when I first saw a TV commercial for cleaning a dogs teeth, I had a good laugh. Until I talked to the vet that is. And she told me some dogs are worse then others, and it depends on what they are fed. His teeth were fine according to the vet. But he ate dry dog food, and would chew on a old hard cow knuckle (we called them) all the time, and would get the occasional pig ears, and stuff that helped him clean his teeth naturally. His teeth were a little discolored I admit, but seemed good and healthy. Maybe I was just lucky.