When treating all-ceramic, CAD/CAM owners will need to use hydrofluoric acid to create an etch pattern in order to create a surface to adhesively bond to. Different materials have different times to etch:
IPS Empress – 60 seconds with 5% hydrofluoric etch
IPS e.max – 20 seconds
Hydrofluoric acid “eats away” the glass matrix exposing crystals for bonding. In some cases, offices over etch IPS e.max, you can tell if the appearance is frosty white. IPS e.max does not look like it is etched, if it appears frosty it is over etched.
At this point, the best solution is to place in a ultrasonic cleaner for about 5 minutes to help clean the surface and remove loose crystals. Then the surface can be re-etched with hydrofluoric acid.
IvoCAD New, April 15, 2012