Our dogs have baby toothbrushes but the veterinary dental clinic recommends a cat toothbrush and they say you can do a more thorough job with it. We use that one and we also use just a baby soft toothbrush. Here's the link to the cat toothbrush and the toothpaste it comes with can be used for dogs as well.
Amazon.com: C.E.T Cat Toothbrush: Pet Supplies