Some Native Americans used to pound the ends of hardwood twigs to fray the ends so the twigs could be used as a toothbrush. Oak and Maple are good tree choices to consider when selecting a twig to make your toothbrush. Certainly there are many other good choices. I name these because they are easy to identify and readily available.
Making a toothbrush from a small branch is easy. All you have to do is cut a green twig about the diameter of a pencil. Cut it 8 to 10 inches long or however long you like actually. Length is just personal preference. I like to whittle away the bark where I want the bristles to be. You can disregard this step if you don't have a knife or just don't want to.
Take a hammer or even a rock and start smashing the end of the twig. Make sure that the rock or hammer is very clean or it will transfer to the twig and render it useless. After it has broken up a good bit chew on the end until a bit until the frayed twig starts to get soft and resembles a toothbrush. That is it!