Professionally whitening your teeth can be expensive, which is why many opt for at-home products such as teeth-whitening kits or whitening toothpastes. While these products do work, dentist Dr. Sandip Sachar says that it's important to be realistic with your expectations: "It should be noted that while whitening toothpastes can help remove surface stains and maintain brightness, they have limitations -- most won’t change the natural color of your teeth or treat deep discoloration." Why we like it: Colgate Optic White Pro Series toothpaste is one of the whitening toothpastes Dr. Fatima Khan, a dentist in Houston, Texas, recommends. Some of her reasons for recommending it include its trusted brand name and its 5% hydrogen peroxide whitening agent. Unlike other whitening agents that work by removing surface stains, hydrogen peroxide can penetrate the tooth, so it whitens intrinsically as well as extrinsically.…