This procedure is performed when dental fillings are not enough to solve the problem such as in cuspal fracture. Capping a damaged tooth unnecessarily with a dental crown removes more tooth structure than needed. But a large dental filling can weaken the remaining structure of the tooth, causing the tooth to break, crack or eventually need a root canal.
It is an indirect restoration which incorporates a cusp or cusp by covering or onlaying the missing cusp
An onlay is sometimes also referred to as a partial crown. It is made by a professional dental laboratory and is permanently cemented onto the tooth by your dentist.