When we discuss all ceramic restorations we can chose between a champfer or modified shoulder margin design. Both fill the bill of only rounded preparation features and adequate thickness of material given that we create proper tooth reduction. When I talk to dentists and technicians alike, most have a preference but there science supports that they work equally well.
The biggest difference is in the choice of burs and how to utilize the correct diameter diamond to get the desired outcome. When preparing a tooth with a champfer margin the curve of the design is accomplished with half the diameter of the diamond. If you cut to a depth that goes beyond the half way point due to the curve of the cutting tip you will create a lip of unsupported enamel at the margin. For a prep with .8mm of reduction at the margin chose a champfer diamond with a diameter at the tip of 1.6mm.
When preparing a tooth with a modified shoulder margin design chose a modified shoulder diamond. The cutting tip of the diamond will have a rounded transition from the tip to the sides of the bur. The bur can be used to 75% of it’s diameter at the cutting tip to create the margin. Using a diamond with a diameter at the tip of 1.6mm you can create 1.2mm of reduction at the margin.