Emax (lithium disilicate) and zirconia are what we refer to as all porcelain crowns for the reason that there is no metal substructure to these restorations.  This allows them to look more life-like and translucent and there will not be that gray margin that may show on a porcelain fused to metal crown.  These all porcelain restorations are monolithic (one material), making them less likely to fracture porcelain.  These restorations are either made in-office on our Cerec milling unit or at our local lab in Palm Beach Gardens.