Revision Emax crowns turning gray after being cemented with Block-out. What is the protocol to block out dental shade?

Sorry to here you are having difficulty with your crowns.  eMax crowns are not so much designed to “block out” the underlying discoloration of the tooth but to compensate for the discoloration internally.  This is why a lab needs a “stump shade” of the prepared tooth so they can compensate for the discoloration.  If there is still an issue with the dark underlying tooth discoloring the final eMax crowns there might be a need to switch to a different type of crown (such as a porcelain fused to zirconia) that would actually block out the tooth discoloration and then correct the shade to what you desire.  The other issue with leaking under the crown could happen with the incorrect cement or not silinating the internal of the eMax crown prior to cementing.  I have never used BlockOut cement and am not confident on its application.  If it is a veneer cement then it is most likely light curable or dual cure and there is a possibility that the cement is not fully cured through a thicker eMax crown. 

Hi:Sorry to hear about your situation.  I normally use Variolink Opaque cement to block out the gray color of teeth when using the emax crowns.Best,Dr. Maddahi