What kind of adhesive is used to bond a milled zirconia framework to the layered porcelain in an all-ceramic restoration?

After the zirconia has been milled and sintered, a very thin, even layer of porcelain should be applied to the zirconia surface. This slurry or wash coat should be fired at a temperature of at least 50 deg. C higher than the normal firing temperatures, with a one-minute hold under vacuum. The porcelain must obtain a glassy appearance. The key factors are a uniform layer and over-firing the porcelain to enhance the mechanical bonding of the zirconia substructure and the overlying porcelain.