The sintering process required to harden Zirconia requires much higher temperatures than are required to harden typical ceramics. Laboratories often have mixed results from their sintering effort depending on the systems and technologies employed to do the sintering. Unlike a traditional dental radiant heat furnace, a microwave oven sinters copings and frameworks through direct application of energy on the dental ceramics, and not solely by heating the surrounding materials and air chamber. Due to significant speed and quality advances, we believe that in the future, all sintering ovens will be microwave based.

There are many reasons to use a microwave sintering furnace, chief among them being to create stronger dental substructures in a quicker turn-around time while saving energy costs. Because a traditional oven heats the substructures from the outside inward, uniformity of the crystalline microstructures cannot be fully realized via radiant sintering.

Below is a list of some of the components of a microwave dental furnace and the role that these components play in the sintering process:

Microwave Transparent Crucible - In a mircowave furnace, the crucible is made of a light insulating material that is transparent to microwaves allowing the waves to pass through unimpeded to the zirconia. Unlike traditional furnaces which have hardened ceramic crucibles, the material used to create our microwave crucible must be low density and have very low dielectric loss. Our crucible design is also speckled with silicon carbide granules which act as a susceptor, helping to rapidly increase the heat inside the crucible. The purpose of the crucible is to evenly and inwardly focus the heat energy created by microwave and the susceptors so that the fastest ramp-up times can be achieved, and that energy will not be wasted heating the entire chamber.

Susceptor Plate - Zirconia and most other ceramics do not absorb (couple with) microwaves at room temperature, so a susceptor is used to heat the zirconia to the point where it absorbs microwaves. For zirconia, at about 1000°C, the dielectric loss is high enough so thatzirconia couples directly with microwave. The purpose of the suceptor plate (and the susceptor granules in the crucible) then, is to increase the zirconia temperature to a point where coupling can take place. Copings and spans are placed on a silicon carbide susceptor plate designed to fit in the bottom of the crucible. Our plates are laser-etched with a lettered and numbered grid allowing the operator to easily track the substructures through the sintering process.

infrared pyrometer - Whereas traditional furnaces measure the temperature of the air inside the heat chamber to monitor and manage their programs (if they have programs), our newest generation of sintering furnaces uses an infrared pyrometer to directly measure the temperature of the zirconia material by measuring the infrared heat energy coming off of the zirconia. The pyrometer maintains focus on a small spot of zirconia and reads the infrared heat energy from a distance calculating the temperature based upon a formula that incorporates the Stefan-Boltzmann constant and the emissivity of zirconia material.