Solution? Yes. Heat the toothbrush up, without letting it get so hot that it drips plastic. Bend the heated plastic onto itself, like when forging a katana, and hammer the air bubbles out of the plastic while it's still hot. you can forge by holding it very close to a candle until the plastic is bendy. Bend it over and repeat the process. Bend and hammer such that you end up with the handle (which you were holding through the whole process) on one end, and a rectangular, thicker piece at the other end. Then make the partial denture.