There is several 'dental' treats out on the market but I am unaware of their effectiveness. There's also a food made by Science diet called T/D that is designed to help control tartar build up. You can get that at your veterinarian.
As far as getting him used to brushing his teeth you have to take it slow and have a lot of patience because this is a new experience for him and he's probably wondering what the hell you're trying to do to him.
I found this article at healthypet.com. I hope it will be of some use to you.
Try to clean your pet's teeth and gums once a day, if possible, and preferably after he eats. The most important area to focus on is the gum line, where bacteria and food mix to form plaque. To customize a fearful Fido or timid Tabby to the idea of dental care, start slowly and gradually. Dip a finger into beef bouillon (for Fido) or tuna water (for Tabby), and gently rub along the gums and teeth. Focusing on the gum line, start at the front of the mouth, then move to the back upper and lower teeth and gum areas. Once your pet is okay with a little bit of touching, gradually introduce gauze over your finger, and rub the teeth and gums in a circular fashion.
When your four-legged friend can handle that, try it with a toothbrush specially designed for pets, or a very soft, ultra-sensitive toothbrush designed for people. Gradually add special dog/cat toothpaste (flavored with meat or fish), but never use people toothpaste or baking soda, as both will upset your pet's stomach. The entire process should only take a minute or two. If Fido or Tabby continue to resist, try gently wrapping them in a large bath towel with only the head out. Above all, avoid overstraining and keep sessions short and positive. With plenty of praise and reassurance, your dental sessions can bring the two of you closer---a closeness that won't be marred by the perils of dog breath