Onlay
Pronunciation: ON-lay
An indirect intracoronal restoration that, unlike an inlay, extends to cover one or more cusps of a posterior tooth.
Full Definition
An onlay is an indirect tooth restoration that occupies the same internal cavity space as an inlay but additionally extends to cap and protect one or more weakened or missing cusps of the tooth. This design provides greater structural support than an inlay when significant tooth structure has been lost while avoiding the more extensive tooth preparation required for a full-coverage crown. Onlays are fabricated in gold alloy, ceramic, zirconia, or resin-based materials. In restorative dentistry and dental materials manuscripts, onlays serve as important study models for evaluating the effect of cusp coverage on stress distribution and fracture resistance. Editors frequently encounter confusion between 'onlay' and 'overlay', the latter sometimes used for full-occlusal-coverage restorations.
Usage
Usage note: An onlay always involves cusp coverage; an inlay does not. 'Overlay' is sometimes used as a synonym but is not universally accepted—query its use in manuscripts. Do not use 'onlay' and 'inlay' interchangeably.
In Context
- "Endodontically treated molars restored with ceramic onlays showed significantly higher fracture resistance than those restored with inlays." — In-vitro study, tooth fracture resistance
- "The editor cross-checked the operative notes against the figures to confirm whether the restorations described as 'onlays' included cusp coverage." — Copy-editing verification step, clinical case series