My vet suggested wrapping guaze around your finger and putting doggie toothpaste on that, instead of a toothbrush. My boys tolerate that much better than the brush.
Also, we've had really really good results with this product:http://www.amazon.com/Proden-PlaqueOff-Dental-Care-Dogs/dp/B0047VWPNI/ref=sr_1_1?ie=UTF8&qid=1368628979&sr=8-1&keywords=dog+plaque
My big guy's back teeth were in such awful shape, brown and yellow and covered in tartar, I was afraid he'd have to have them pulled. But he's been using this for almost a month now and they look sooo much better, even the vet commented how much better his teeth look. And I was brushing my little guy's teeth regularly, but still couldn't get rid of the buildup on his back teeth. A couple weeks of adding this stuff to his food, and they're looking much whiter!