Tooth fillings usually last for many years before they need to be replaced. But tooth fillings can wear out over years of chewing. If you clench or grind your teeth, you may need to have tooth fillings replaced sooner. If you notice signs of wear on your tooth fillings, such as cracks or worn areas, see your dentist to have the filling replaced as soon as possible. Continuing to chew with a damaged filling can cause the tooth to crack and require additional repair that is more expensive and more complicated than a simple cavity filling. If additional tooth decay develops around a filling, whether or not the filling is damaged, your dentist may choose to repair the tooth with a crown instead of a second cavity filling.