Onlays and a dental crown is a single-tooth restoration and restores the affected tooth. Inlays and fillings do not treat the area that an Onlay and dental crowns do. A major difference between Inlay and Onlay is, inlay covers the affected area of the teeth, the Onlay covers the cusp of the teeth. The shape and size of the inlay after fixing into the teeth may differ and create gaps or space that forms bacteria or cavities. Onlay once designed correctly fits into the affected area, the procedure does not fail most of the time. Onlays are appealing than others and do not shrink for a long time.