Apply Vaseline on your teeth. While it may seem odd, applying Vaseline to the teeth is an old stage-hand trick, used to get dancers and other performers more enthusiastic about grinning. Vaseline prevents your lips from sticking to your teeth, and is a common preventative measure taken when applying lipstick. Done correctly, Vaseline can help avoid getting lipstick on the teeth.
Use caution and only apply a very small amount of Vaseline to your teeth. Nobody wants a mouthful of petroleum jelly.