All Ceramic Confusion Part 3

The key to success on all ceramic restorations is undoubtedly the preparation. Most of us go into autopilot when preparing a tooth for a crown and do a cookie cutter prep for every type of restoration. This can get us into trouble. Let's review some of the preparation requirements for zirconia restorations.

Occlusal reduction: 1.8-2.0 mm. Obviously this can be difficult on a short tooth. My recommendation would be simple. Just don't use a zirconia restoration on a short tooth. There. That solves that.

Axial reduction: at least 1.5-1.8 mm. Part of the reason a doctor would chose to do a zirconia restoration is because of esthetics. So why not give the ceramist enough space to make the glass look like enamel? With less than 1.5 mm of reduction, this is difficult.

Finish line: Shoulder (1 mm depth). Beuer, et all did a study in Journal of Dental Materials that examined the fracture resistance of zirconia copings on teeth with different finish lines. Preps with a shoulder preparation far out preformed beveled shoulder, deep chamfer, and moderate chamfer. This means that the practitioner will have to reduce what appears to be a large amount of tooth structure to ensure maximum fracture resistance.

"Effect of preparation design on the fracture resistance of zirconia crown copings." Dent Mater J. 2008 May;27(3):362-7.