Shopping for toothpaste is like shopping for anything these days: You walk down the drugstore aisle and are bombarded by a range of choices, all promising multiple things--whiter teeth, better breath, cavity protection, and much, much more.
Looking at the ingredients can be overwhelming, too. There are flavorings, silica, water, moisturizers, and more. One ingredient that toothpaste SHOULD contain is fluoride, which strengthens tooth enamel and makes it more resistant to bacteria.
But while most toothpastes contain sodium fluoride, they don't all contain the better cavity-fighter: stannous fluoride. Stannous fluoride is a more effective at killing off bacteria, which produce the acids that cause cavities. And it can better protect you against the effects of sugary foods and drinks better too--which bathe your teeth in cavity-producing acids for five minutes after you eat them.
So check to see if your toothpaste contains STANNOUS fluoride as well as sodium fluoride, especially if you take medications like antidepressants and statins that dry out your mouth. Saliva neutralizes acids, so less saliva makes you more prone to decay.