Gosh I had this exact same problem with Zoe,
First, I suggest you trying fingerbrushes to start off with, although I find them rather large for the tiny dogs. Zoe fused and fused and would even bite down on my fingers. Put your baby on your lap, on his back and get them used to the toothbrush in their mouth. It used to take me 30 min to brush her teeth because of all the fighting involved and the resistance. Now, it is like night and day, she doesn't like it but tolerates it and we are done in 2 minutes! Keep at it until they get used to it. I personally like buying plain baby/kids tooth brushes at walmart for about $3 rather than a fancy pet toothbrush. I look for the softest bristles. If you must, you might need assistance, one person holds their mouth open while the other brushes. Also, as suggested, treat them and rave and make a big deal if he has a good session. Same with the brushing, they will get used to it. Also, as suggested above, try petzlife, it's an awesome product, helps with bad breath, keeps the teeth white, and will for sure prevent tartar. We have a really good package deal at
www.sassypup.net The great thing is they carry a spray that helps, or if at the end, if your dog does not and will not tolerate brushing, they have suggestions to either put the gel in their toy to chew on, place it on their lip to lick and distribute in their mouth, or mix it with a favorite item like peanut butter.