Zpacks has a good one, nice and short. A full tube of travel tooth paste and the brush come in at .7oz.
Could I go lighter? Yes I could use the paste that comes in the Zpacks kit, but it's only good for two or three nights and I would have the hassle of refilling it often etc. Some people dehydrate it! Clean teeth are important to me, and me sticking my hands deep in my mouth just to save 1 gram does not appeal to me.