Simply put, we need to reduce the amount of sugar we're taking in. Sugar feeds the bacteria in the mouth, which subsequently produces an acid, which causes the tooth decay. So if we're reducing the amount of sugar that we're taking in, then we're not feeding that bacteria to produce the tooth decay. Having a good oral care regime will help as well. So there's fluoride in the majority of toothpaste, and that helps strengthen the teeth, but ultimately it comes down to how much sugar we're eating.