Do you have trouble matching those difficult C and D shade cases? They can be very tough. We have some great blocks out there like Vita's Real Life block and the Sirona C In block that have a dentin shaded core and then more translucent enamel to help with this, but not everyone has these blocks in stock. What can one do in a case when you do not have those blocks? Here is a trick I have done for years and it really seems to work well in my hands.  I generally do this on teeth in the esthetic zone and it can only be done with the multi shaded blocks like Vita Triluxe, Empress Multi or the Sirona PC blocks. Here is the workflow:

This case was a premolar tooth on a patient with C2 shade. I did not have any C2 blocks, but my Easyshade from Vita told me that I could use a 2M2 shade also. This was the block in the milling preview initially with the Triluxe option selected. 

Notice that the block was probably a size 12 selected and the sprue is on the lingual. This will need to be changed.

The first thing I do is check the size of the block. I like to change the block size to the largest option to I can have the most maneuverability of my restoration within that block, so I change it to a 14/14.

The next step that must be done it to move the sprue to the interproximal. I know that many don't like to have to remove the sprue, but 1) it is not hard to do and 2) it is the only way to allow the next step I will show to happen. 

I will then activate the move tool and I will rotate the block 90 degrees so that the translucent zone is now on the facial. I can manipulate the translucent area so there is a bit of the middle layer at the gingival 1/3 and I can still get a multi layer effect. The advantage of rotating the block like this is that the darker dentin from the C or D shaded dentin will much more readily shine through the translucent portion of the block and we'll get a very nice match. You may need to do a bit of characterization to dial in the final touches, but this really works great and makes a difficult task of ours a bit easier.