Step 1 - Buy some pure fluoride toothpaste.
Step 2 - Mix Peroxide and baking soda and use on teeth as toothpaste.
Step 3 - After rinsing, lightly brush a small amount of the fluoride on your gums. Do not rinse or spit and don't eat or drink for half an hour.
Use once a week. For best results, buy a sonic brush.
My dentist said peroxide was better than lemon because lemon can be too acidic. It will taste like s**t though so I like to add clear flavor extracts like mint. Also, with any whiteners like this, it's always good to follow up with something like fluoride to restore the enamel.
Look for chewing gums sweetened with xylitol! Xylitol promotes your teeth's natural ability to repair themselves and reduces plaque.