There's been some research lately that shows that the grains in dry dog food turn to sugar, in a dog's mouth, and thus into tartar. Apparently, dogs don't have the enzyme in their mouths that break them down. I've been told that if you'll put some water on the kibble, then put your hand over the bowl and dump the water back out, that little extra moisture helps prevent the tartar buildup.

I know that goes against everything we've ever heard, but for some reason, it makes sense to me.