As a CEREC user we understand the importance of preparation to creating long lasting restorations. Â A proper preparation makes marking the margin easier, makes design easier, and ensures enough reduction for material strength.
I wanted to take an opportunity to outline my step by step method of crown preparation.
Here is a photo of the basic burs that I use for a crown prep.  Essentially it’s 3 burs – occlusal depth reduction bur, coarse rough prep bur, and a fine diamond to finalize the prep.

Step 1. Â Using the occlusal reduction bur cut grooves through the entire occlusal surface. Â This will ensure a uniform minimum reduction. Â I recommend the use of a 2.0mm depth reduction bur.

Step 2. Â Using your thin coarse diamond go ahead and cut away the mesial and distal interproximal. Â Take your time to avoid dinging the neighboring tooth.

Step 3. Â Using the same thin coarse diamond go ahead and reduce the occlusal depth grooves.

Step 4. Â Use the coarse diamond to make facial depth cuts. Â This bur is 1.4mm in width and burying it a bit more than half way will ensure a 1.0mm axial reduction. Â The rough prep is then completed.

Step 5. Â Using the fine diamond go ahead and idealize your margin and smooth your preparation. Â A smooth preparation leads to better milling and fit. Â The fine diamond is an 856-021 which means the thickness is 2.1mm. Â Using a thicker fine diamond allows me to get a 1.0mm chamfer margin.

An extra tip….  We utilize electric hand pieces in our office.  When finalizing our margin I go to 50% speed and I have full control over location and thickness of margin.
*** Â It is my preference to use disposable diamonds exclusively. Â One, it ensures a sharp cutting instrument which will reduce chatter and heat generation. Â Secondly, it is hygienic and clean. Â Currently (as of August 2014) I am utilizing Microcopy disposable diamonds.