A CEREC restoration is a CAD/CAM (computer aided design & manufacturing) that is custom made for the patient.
CEREC is a same day porcelain restoration. CEREC software converts the digital image into a 3-dimensional virtual model on a computer screen. Your dentist then uses his or her dental expertise to design the inserting block into the milling chamber restoration using the CEREC 3D computer program.
An inlay or onlay is a restoration that partially covers a tooth where as a crown is a restoration that fully covers and both protects a tooth that has been damaged by: decay, breakage, existing filling.
An inlay or onlay is a very conservative way to repair only the bad part of the tooth and not take away anymore tooth structure.
A crown, instead of an inlay or onlay is placed on a tooth that cannot be partially covered due to a bigger fracture/breakage.