When using resin cements, do you need to etch the ceramic restoration or use silane primer?

Most laboratories will etch the intaglio surface of porcelain crowns and therefore it is unnecessary to etch a second time unless the crown is exposed to saliva during try-in. A silane primer is not necessary for crowns with zirconia cores (Lava Crowns and Bridges, 3M ESPE; Crystal, Dental Laboratory Milling Supplies) but is necessary with silica-based ceramic restorations (3G All Ceramic System, Pentron Ceramics; IPS Empress CAD, Ivoclar Vivadent; IPS e.max CAD, Ivoclar Vivadent).