One of the most common questions I get asked is: “Which material should I use when restoring a patient with a worn dentition?”
I think the answer to this question has become easier as ceramics have evolved. Today, our selection mainly includes three materials: lithium disilicate, translucent zirconia and high-strength zirconia. The key to clinical success is knowing when and how to use different materials.
To begin, we first need to understand that we choose materials differently depending on where the restoration is in the mouth. In the posterior, the restoration needs to be strong, while in the anterior, the restoration needs to be esthetic Typically, the most esthetic restorations have at least the incisal 1/3 cut back and layered by hand. This creates a much more esthetic restoration, compared to just an external stain or glaze, as the technician can layer translucency and characterization into the incisal edge. In turn, layering the incisal edge will create the “weak link” of the restoration.
No matter how strong the base ceramic material is:
- Lithium disilicate = 500 MPa
- Translucent zirconia = 500-800 MPa
- High strength zirconia = 1000-1400 MPa
It is the veneering ceramic (approximately 89 MPa) that typically fails. In the posterior, where forces are higher and strength is important, it is preferable to use materials in their monolithic form – meaning the restoration is the same material through and through with no layered or veneering ceramic added.
In general, when choosing a material in the posterior it is important to remember that with less thickness, the strength of the material will need to be higher. But as the strength of the material goes up, the esthetics of the material goes down (Figs. 1- 2). In a worn dentition patient, I’m OK with sacrificing esthetics, since an opaque restoration is better than a fractured restoration.
However, if you want to enhance the esthetics of monolithic restorations, there are a few options. The restorations can be externally stained or glazed, milled with a multilayer block/puck (zirconia) or pressed with a multilayer ingot (lithium disilicate).
Greggory Kinzer, D.D.S., M.S.D., is a member of Spear Resident Faculty.