Sintering Dental Zirconia and Temperature Measurement

The color, size and strength of dental parts made from zirconia are directly related to the temperature they are sintered.  The target temperature required to properly sinter Zirconia does not allow for much error.  Without proper control of the temperature, all of the detail and workmanship put into the parts can be ruined if placed into a poorly controlled furnace.  Control is achieved through the use of electronic temperature controllers, thermocouples and calibrated shrinkage products 

Electronic controllers are basically volt meters.  They convert the millivolt signal generated from the thermocouple into a temperature.  Extra computer logic is added along with some hardware to make the controller do some additional tasks to heat and cool the furnace on a programmed heating cycle. To perform properly, the electronic controller has to be calibrated.   This is not a one-time thing. Electronics degrade over time and require service to compensate for the degradation.  If not accounted for, a controller can easily misreport the actual temperature by as much as 50 degrees .  Check your owner's manual and contact your furnace supplier to find out how to calibrate the furnace according to their recommendations. 

Thermocouples are made from two dissimilar metallic wires that are welded together to form a bead.  When the bead is heated, a very small electrical signal is generated in the wires.  The electrical signal is on the order of millivolts and can be detected by connecting the ends of the wires to a volt meter (electronic controller).   Since the wire used to form a thermocouple degrades with each thermal cycle, the small electrical signal it generates will change as well.  Over time the signal will degrade to the point where the temperature read by the electronic controller will no longer be accurate.   The furnace readout will continue to display a temperature value, but the actual temperature can be off by over 100 degrees.