Whats a simplified technique to preparing a tooth for a Zirconium crown?

 For years I have taught a simplified technique to dental students and residents for preparation of teeth for Zirconium crowns, using burs and diamonds commonly found in the NYUCD clinic or now at the Mountsinai General Practice Residency. 

First we start by using a 330 carbide bur. This bur has a cutting length of between 1.5- 2 mm (depending on the brand). This bur is used to make depth cuts along the occlusal surface by scribing the surface using the full length of the bur. Afterwards green or black diamond football bur is used to perform the occlusal reduction.

Then I use a one mm diamond to do reduction in the occlusal one Third of the tooth on the buccal and lingual of the tooth. Then a  # 012 or 014 diamond is used to create a shoulder or chamfer on the buccal and lingual of the tooth approximately .25 to .5 mm supragingivally,bringing the bur as far as possible into the mesial and distal embrasure without touching the adjacent tooth. There is no need to worry about the preps taper at this point.

Then using a tiny shoulder bur ( about .5 mm or a very short flame diamond, I prepare the inter proximal portion the preparation and use as small as available shoulder bur to prepare the interproximal shoulder and break the gingival contact. No real attempt is made to create taper yet and there is no need to constantly get rid of a wall that is slightly undercut relative to the other walls since this will be done in the final step before packing cord and taking an impression.

At this point the prep is a rough version of the final preparation and can now be refined using a one mm chamfer diamond (green) . On the bucclal the preparations should have two planes. A straight portion in the gingival 2/3 and an a second portion at the occlusal one third that tapers an rounds the occlusal one third ( more reduction is desirable in this portion of the prep) . If possible The ginvgival chamfer/shoulder can be made to be equigingival or slightly supragingival . If available I smooth the entire preparation using a one mm fine chamfer diamond. When done the chamfer or shoulder is checked with and endo explorer to make sure its continuous and without any steps. It should be at least .5 mm in depth ( the minimum thickeness that zirconium can be milled to) and a maximum of one mm.

The last step is to check the anguilation of the buccal and lingual walls to make sure they have a slight taper relative to each other and also check the proximal walls as well.  If the preparation looks good its time to pack cord and either take an elastomaric impression or scan the prepparation using a 3D scanner.

If used properly this technique will producre an excellent preparation for the lab to mill a well fitted zirconium crown.