In dentistry, an onlay is an indirect restoration consisting of a solid substance (such as gold or porcelain) fitted to a chamber of a tooth, extending to replace one or more cusps, and is cemented into place. The chamber of the tooth is the area where there use to be tooth decay, and the destroyed cusp is gone by either an extension of the decay or by trauma. Whereas an inlay is the same as an onlay, except that it does not extend to replace any cusp. Crowns are onlays which completely cover all surfaces of a tooth.

A tooth would need an inlay or an onlay when the decay or fracture is so extensive that a direct filling such as amalgam or composite, would compromise the structural integrity of the restored tooth or provide substandard opposition to biting forces. In such situations, an indirect gold or porcelain inlay restoration may be indicated. When an inlay is used, the tooth-to-restoration margin may be finished and polished to such a super-fine line of contact that recurrent decay will be all but impossible. While these restorations might be ten times the price of direct restorations, the superiority of an inlay in terms of resistance to occlusal forces, protection against recurrent decay, precision of fabrication, marginal integrity, proper contouring for gingival (tissue) health, and ease of cleansing offers an excellent alternative to the direct restoration.


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  2. Medical dictionary by Farlex (

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The masculine gender may have been more used in the article, but without prejudice, to make reading easier.

Category Treatments