The CEREC process for designing inlays and onlays is similar to the designing of a crown, only the function is different.
CEREC inlays are the superior versions of composite cavity fillings; superior due to the strength and aesthetics that the ceramic brings. Inlays milled from this ceramic material last far longer than any other cavity solution. They also behave most similarly to natural tooth enamel, in both appearance and feel.
Onlays (a.k.a. partial crowns) are the remedy to extensive cavity damage, covering a larger area of the tooth. In past cases, the weaker disposition of composite — or the porcelain restorations that contained metal — would require a full crown to be designed in order to maintain the tooth’s strength. Because CEREC onlays are so strong, one that is well-built will do everything it needs to do, causing minimal extra tooth damage and eliminating the need for a full crown.
Dr. Sperbeck, West Los Angeles