A lot of issues with zirconia restorations are related to sintering cycles and complexities. here are several components about your furnace and sintering zirconia that you need to know to get the best and most esthetic outcome of your final restoration.
1. What type of heating elements are in your sintering furnace?
Your furnace’s heating elements are likely either Molybdenum Silicide (MoSi2) or Silicon Carbide (SCi).
2. MoSi2 Heating Elements Require Special Care
If your furnace uses Molybdenum Silicide, it forms ceramic quartz on the outer surface of the restoration that interacts with green state colorants. Over time, the melting point of this quartz becomes lower than the top temperature of the sintering cycle and this creates pollution in the furnace chamber. As a result, these pollutants can cause greening or darkening of the restorations. In order to prevent this you should always use a covered crucible. This will reduce the likelihood of chamber pollution getting into the restoration.
3. Quartz Pollutes
The quartz pollution can have an effect on the thermocouple over time, about 6 to 12 months. The thermocouple will send lower temperature readings to the control panel resulting in firing temperatures of up to 100° higher than programmed.
4. Watch the Temp Throughout
From room temperature to 900°C, there is little effect on the restorations. The ramp rate from 900° to top temp, from top temp to hold time, consistency of temp through the hold, and then rate of cool back to about 900° are all critical.
5. Make Sure Colorants are Dry
Not adequately drying colorants added to green state colored zirconia prior to sintering will shorten MoSi2 heating element and add to the pollution problem in sintering furnaces.
For best results, you should always follow manufacturer’s instructions when sintering zirconia.
Have any tips about sintering zirconia or have any questions? Share them in the comments – we’d love to hear from you!