onlay

An onlay is a type of indirect dental restoration designed to repair a damaged or decayed tooth while preserving as much of the healthy tooth structure as possible. It is manufactured outside the mouth and then cemented onto the tooth, covering one or more cusps and extending onto the chewing surfaces and adjacent sides. Onlays are distinct from inlays, which fit within the grooves of the tooth without covering cusps, and from crowns, which encase the entire visible portion of the tooth.

Indications for an onlay include moderate to extensive decay, small fractures, or after root canal treatment where a direct filling would not provide sufficient strength. They are commonly used on molars and premolars where occlusal forces are high and where conservative restoration is preferred. Materials range from gold and porcelain-fused-to-metal to all-ceramic and resin composites, including CAD/CAM-made options.

The typical process involves preparing the tooth, taking an impression or digital scan, fabricating the onlay in a dental laboratory or with chairside equipment, and cementing it with adhesive resin cement or glass ionomer cement. Advantages include conservation of tooth structure, enhanced strength compared with direct fillings, and the availability of aesthetic ceramic options. Limitations include higher cost, multiple visits (though some systems allow single-visit CAD/CAM fabrication), and the need for adequate remaining tooth structure. Onlays offer an intermediate choice between inlays and crowns, balancing durability with tooth preservation.