When a large, defective filling needs to be replaced, porcelain inlays and onlays can be excellent ways to restore a tooth. An inlay is a very conservative restoration and usually is inserted into the area of the grooves of a tooth. An onlay is a little larger and is used in instances where the cusp of a tooth also needs to be covered. The porcelain used in inlays and onlays is harder and more durable than the white composite fillings. The inlay or onlay will be bonded or cemented to your tooth, creating a tight seal. Inlays and onlays also provide a more conservative restoration of a tooth than a full crown, therefore preserving more tooth structure.