I use a rubber finger brush. It just fits over the end of your finger and you can direct it a lot better and nothing hard to hurt if they are a little uncooperative. They are like this one:
Dog Finger Toothbrush Dental Care Dog Health. Very inexpensive and easy to use.
Then I use any doggy toothpaste. I am not sure it is that important about the toothpaste itself, the physical brushing is what does the job.