I have lived with dogs all my life and can't remember us ever brushing their teeth. We've tended to give them bones and chews to do the job. Having said that, my little podenca Bebe came as a 6 year old with her teeth in a terrible state - from bad nutrition as a puppy according to my vet. But apart from having the 4 lower front teeth removed, the rest haven't caused problems and she is now 15 years old.
Here's a slide show of how to clean your dog's teeth.