A severely damaged tooth can be restored without having to sacrifice healthy tooth structure using porcelain/resin onlays. An onlay is shaped to fit your tooth precisely and is cemented or bonded tightly to the healthy tooth structure that remains after defective or infected tooth structure is removed. Like a crown, an onlay strengthens and protects the tooth's biting surfaces, but unlike a crown, an onlay does not cover the entire tooth. An onlay has several advantages over a crown: The edges of an onlay end high up on the tooth, it does not butt up against the gums, like a crown does. This makes it easier to keep the tooth free of plaque along the gum line which helps keep the teeth and gums healthy. Less of the healthy tooth structure needs to be removed when prepping a tooth for an onlay as opposed to a crown, which preserves the tooth's strength. An onlay is generally bonded in place which creates a tighter seal and adds strength. Conclusion Onlays are a terrific option for restoring teeth that have suffered extensive decay; they add strength, protect the biting surface and are easy to maintain.