Inlays and onlays are often referred to as partial crowns. They are used to strengthen a tooth, restore its shape, and prevent further damage without having to cover the entire tooth, as with a crown. An inlay is done when there is no damage to the cusps of the tooth and can be placed in the tooth. An onlay is used when damage is a little more extensive and part of the tooth needs to be covered. Inlays and onlays are chosen over regular fillings when the tooth requires more strength and protection than can be offered by a filling, but when the tooth doesn't require full coverage, as with a crown.