Even though they contain sugar, many fruits are great for your teeth. Apples have been referred to as "nature's toothbrush," because the fibrous texture leaves your teeth feeling squeaky clean. Also, chewing an apple stimulates your gums and increases saliva flow. Saliva cuts down on the acidity in your mouth, which helps prevent tooth decay.
Citrus fruits, like oranges, grapefruits and tangerines are also important foods for oral health because they're chock full of vitamin C. If you're deficient in vitamin C, it can lead to bleeding and swollen gums, which affects the stability of your teeth. That said, citrus fruits also contain acids that can erode your teeth's enamel. Citric acid has been compared to stomach acid, whose main function is to help digest food, which explains why too much citric acid can contribute to tooth decay. This may send you running for your toothbrush after enjoying your morning grapefruit, but actually, that's exactly what you shouldn't do. Citric acid softens the enamel, so brushing on top of that will only serve to further weaken it. It's best to rinse your mouth with water after eating citrus fruits to get your saliva flow going. Saliva naturally neutralizes those acids in your mouth.