I brush my Scottie's teeth everyday to every-other-day. I use a human-baby toothbrush (one with the smallest and softest toothbrush head I could find) and Nylabone Tartar Control Toothpaste for dogs.
He used to hate it, but now he lets me brush, despite still not liking it one bit. I started by doing it for a few seconds every day. Now he'll let me brush for ~30 seconds. It takes a lot of patience and a lot of positive encouragement
The great news is that even though he had a tiny bit of plaque buildup on his back molars, since I started brushing, the plaque actually all chipped off!! I was amazed. His teeth are now plaque-less and all white
I highly recommend brushing your yorkies teeth!!! It's worth it to keep their breathe fresh and their health in good condition.