As a CEREC user we understand the importance of preparation to creating long lasting restorations. 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.
![Disposable crown prep burs](../wp-content/uploads/2014/08/prep1-1024x682.jpg)
Step 1. Using the occlusal reduction bur cut grooves through the entire occlusal surface. This will ensure a uniform minimum reduction. I recommend the use of a 2.0mm depth reduction bur.
![2.0mm depth cutting bur to reduce occlusal](../wp-content/uploads/2014/08/prep2-1024x682.jpg)
Step 2. Using your thin coarse diamond go ahead and cut away the mesial and distal interproximal. Take your time to avoid dinging the neighboring tooth.
![interproximal walls removed](../wp-content/uploads/2014/08/prep3-1024x682.jpg)
Step 3. Using the same thin coarse diamond go ahead and reduce the occlusal depth grooves.
![reduce the occlusal grooves](../wp-content/uploads/2014/08/prep4-1024x682.jpg)
Step 4. Use the coarse diamond to make facial depth cuts. This bur is 1.4mm in width and burying it a bit more than half way will ensure a 1.0mm axial reduction. The rough prep is then completed.
![facial depth cuts to ensure axial reduction](../wp-content/uploads/2014/08/prep5-1024x682.jpg)
Step 5. Using the fine diamond go ahead and idealize your margin and smooth your preparation. A smooth preparation leads to better milling and fit. The fine diamond is an 856-021 which means the thickness is 2.1mm. Using a thicker fine diamond allows me to get a 1.0mm chamfer margin.
![preparation smooth and margin finalized with fine grit diamond](../wp-content/uploads/2014/08/prep6-1024x682.jpg)
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.
*** It is my preference to use disposable diamonds exclusively. One, it ensures a sharp cutting instrument which will reduce chatter and heat generation. Secondly, it is hygienic and clean. Currently (as of August 2014) I am utilizing Microcopy disposable diamonds.