[The surface conditioning of pressed ceramics and its effect on the bond strength to composites]

After removal of the investment material, unpolished surfaces of pressed glass ceramics (Empress) are covered by a layer containing magnesium and phosphorus. This layer most likely results from the contact with the investment material during pressing. Following short-time conditioning with 5% HF-gel the superficial layer stays amorphous. After etching for 120 s most of the surface layer is removed revealing the fine grained etching pattern characteristic for this type of ceramics. Shear strength of composite luted to unetched pressed ceramic samples was rather low. After etching for 60 s bond strength was considerably higher, but only following 120 s of etching shear strength reached a level comparable to that of ground pressed samples and ground ingots after 60 s of etching. Since mechanical removal of the surface layer by grinding is not recommended, pressed glass ceramics should be etched for 120 s or longer to achieve an optimal bond strength to the luting composite.