You might try some baking soda and hydrogen peroxide.
Baking soda is a bad idea. It whitens teeth, but it does so by stripping away the enamel. This weakens your teeth, leaving them prone to cavities and other mouth horrors.
WARNING & DISCLAIMER:
SELECT AND USE OUTDOORS AND SURVIVAL EQUIPMENT, SUPPLIES AND TECHNIQUES AT YOUR OWN RISK. Information posted
on this forum is not reviewed for accuracy and may not be reliable, use at your own risk. Please
review the full WARNING & DISCLAIMER about information on this
site.