I second what everyone has said about the importance of diet, specifically not eating sugar and grains (and starches in general?) I think its a good idea to brush and floss in general, though, regardless of what one is eating - although with a pure paleo diet I doubt any toothpaste-type stuff would be necessary, although still helpful. And flossing is generally a very good idea, since I notice that it makes a BIG difference in the level of unhealthy mouth bacteria, and the health of gums generally. I remember hearing that flossing adds years to your life, something about the stress of the body constantly having to combat unhealthy bacteria, that are "poisoning" the system so to speak.
Although brushing and flossing need not be plastic toothbrush + store-bought toothpaste + manufactured floss! Sinew is obviously excellent as floss, and I'm sure various plant fibers would work as well. Traditional cultures would often chew the end of a twig (I've heard about cottonwood/poplar in N America, and neem in India) and brush with the fibrous part, most often not using anything substances other than the natural antibacterial properties of the wood.
Nowadays, I use calendula infused in olive oil on a toothbrush, along with a tooth powder I made of myrrh, neem leaf, and cinnamon (frankincense was also recommended, but is harder to find). In the morning, because it has fresh-tasting peppermint oil and just to change it up (because I believe that bacteria quickly adapt to something that's used continuously), I like to use a toothpaste made by the company Uncle Harry's - one of the only toothpastes I've ever found that doesn't have glycerin (bad because it coats the teeth), or abrasive baking soda. Instead it is based on clay (that particular healthy kind), and has colloidal silver (antibacterial) + trace minerals that help the remineralization of tooth enamel.