You can find a whole variety of shapes and sizes on the internet or in the pet store, but I find an old human toothbrush usually does the trick. (doorbellvet.com)
When he will accept this type of touching calmly, get him a doggie toothbrush, either one that looks like a smaller human toothbrush or one that fits over your finger. (animalbehaviorcollege.com)
Brushing your canine friend's teeth has the same health implications as that of human toothbrushing. (mypetneedsthat.com)