Same-Day Indirect Ceramic Polymer Inlays/Onlays

An inlay is an indirect restoration constructed of cast metal, porcelain/ceramic, or composite/resin that neither supports nor replaces a cusp (or cusps) of a tooth. The inlay restoration is nothing more than a centric stop in that it provides no protection for the cusp tip as concerns lateral and/or protrusive masticatory forces in excursions.
The onlay component of an inlay/onlay restoration is another story. The onlay component replaces the cusp tip (or tips). The onlay entirely replaces the cusp tip so as to maintain and/or restore the vertical dimension in the preparation. When the cusp tips are sound (Figures 3, 6, and 8), the original vertical dimension is not altered.
The coding sequence provides for a single code number to identify an inlay with an associated onlay component. As we all know, it is a technical impossibility to construct an onlay without first identifying the surfaces of the inlay. Hence, the descriptions are currently somewhat misleading.
With regard to third-party reimbursement, few if any benefit plans consider an inlay in the absence of an onlay component to be a contractual benefit. Since an inlay is nothing more than a centric stop that adds little or no strength to the remaining natural tooth structure, it is traditionally reimbursed at the level of a traditional, direct restoration.
Inlay restorations (Figures 6, 7, and 9) are optional benefits when the tooth can be restored adequately with a similar direct restoration. An allowance is generally made for that similar material, and the patient is responsible for the difference in cost.