An onlay is a custom restoration that rebuilds part of the biting surface of a tooth and extends over one or more cusps — the raised points that do the work of chewing. It is sometimes described as a partial crown, which captures the idea well: it protects the vulnerable parts of the tooth while leaving the sound walls untouched.
When an onlay is recommended
Your dentist at Parkway Dental will suggest an onlay when a cusp is cracked, undermined by decay, or so thin after an old filling is removed that it would likely fracture under normal chewing. Covering that cusp protects it. Because the remaining walls of the tooth are left in place, an onlay conserves significantly more natural tooth than reducing the whole tooth for a crown.
Materials and fit
Onlays are usually made from porcelain, high-strength ceramic, or gold alloy. Porcelain and ceramic match the surrounding tooth closely and are the usual choice where the restoration may be visible. Gold is exceptionally durable and gentle on the opposing tooth, which suits heavy chewing forces at the back of the mouth.
What to expect
The tooth is numbed, decay and any old restoration are removed, and the affected cusps are reduced to make room for the onlay. An impression or digital scan is taken, a temporary is fitted, and the onlay is made to fit precisely. At the second visit the fit, contacts and shade are checked, the onlay is bonded with resin cement, and the bite is adjusted so pressure is distributed evenly.
Afterwards
Expect some cold or pressure sensitivity for a week or two. Because the bonded onlay holds the cusps together rather than wedging them apart, it reduces the risk of the kind of fracture that can otherwise split a heavily filled tooth. Clean the margins thoroughly — the tooth beneath remains susceptible to decay even though the onlay itself does not.