How to Control the Firing Process of Layered Ceramics for Optimum Esthetics

Jim Emmons, CDT, FNBC, discusses how his efforts to control the heat zone led to the development of the Wonder Z-Ring and offers advice on managing the firing process.

The process demands of 21st century ceramics are greater than we have experienced in the past 50 years (yes, I was there and remember it well). Compared to feldspathic PFM restorations, layered lithium disilicate and milled zirconia are even more susceptible to the effects of thermal stress caused by uneven heat patterns.

In order to achieve the best firing results for lithium disilicate and zirconia—as well as any type of layered ceramic—the technician has to accurately control the Ceramic Thermal Conductivity (CTC). Unlike the CTE, the CTC relates to the heat absorption rate of the restorative material as the units are fired to maturation and then cooled down.

It’s critical to keep the vertical and horizontal thermal heat patterns on the firing tray constant. Due to the way conventional...