Toothbrushes are important. You can make one by using a cattail/pussy willow; remove the downing head and you are left with a suitable toothbrush. A cedar bark tinder bundle tied to a stick and soaked in water can also be used. There is tannic in cedar, which tastes horrible, and ingesting too much of it will make you sick. Tannic acid however has been known to be effective against tooth decay.
Toothpaste can be made by stripping the inner bark from a birch, sassafras and spicebush twigs, and pounding it. Add a tad of water to turn it into a paste. Woodash also works wonderfully, just add a little water to make into a paste. To help with flavor, mix it with pine oil which can be made by boiling pine needles in water. (unless you are like me a deathly allergic to any evergreen)
Oak or cedar makes a great mouthwash. Boil the inner bark until the water is a reddish brown. Allow it to cool before using. Don't swallow, as it does contain tannic acid. These helps with toothaches and mouth cuts.