The differences between sintering furnaces go beyond just brand and price. Heating elements, the number of programs, heating chamber structure, sintering speed, and even the size of the equipment all vary. So, which sintering furnace is best for your dental laboratory?
The driving force behind the development of new furnace designs and performance improvements stems from the increasing variety of zirconia materials and the sintering parameters they require.
Most zirconia materials sinter at 1550°C or lower, with a slow heating rate (4°C to 10°C per minute). Some zirconia manufacturers recommend lower temperatures, while others recommend higher temperatures.
Appropriate Temperature
It's worth noting that recent research indicates that zirconia achieves maximum strength when fired at approximately 1500°C to 1550°C (the exact temperature depends on the furnace temperature accuracy), and even a temperature difference of only 150°C above or below the recommended temperature can lead to reduced strength due to grain growth.
One specific study showed that the strength of zirconia decreased from approximately 1280 MPa at 1500°C to approximately 980 MPa at 1600°C, and only about 600 MPa at 1700°C.
Excessively high temperatures can lead to decreased stability and uncontrolled transformations, causing the zirconia to crack. This is just a change in physical properties.
For this material, excessively high temperatures also lead to reduced translucency. Higher temperature is not always better! As long as the manufacturer is reputable, their recommended sintering program must be strictly followed.
Most yttria-partially stabilized zirconia materials achieve their ideal physical, mechanical, and aesthetic properties at approximately 1550°C.
Furnace Features
If you use multiple types of zirconia, or if you want to achieve different results depending on factors such as the patient or the location of the restoration in the mouth, you will likely need a furnace that offers multiple programs, multiple program stages, and control over the cooling rate of the zirconia restoration.
Program Stages
The program stage function allows you to adjust the temperature, delayed start time, heating rate, and holding time to optimize the final result.
Since most sintering cycles are quite long, you may want to increase the heating rate from ambient temperature to the sintering start temperature, and then decrease the heating rate in subsequent stages to optimize translucency. Why not utilize the heating phase, before any material changes occur, to save time?
Capacity
Depending on the laboratory's production needs, furnace capacity is another important factor to consider. Some furnaces can only use one sintering tray per cycle; many can accommodate two trays, but the ideal furnace should be able to stack 6 trays vertically, allowing for the processing of more than 60 parts, or even a full arch of zirconia.
Safety
Of the many features of a zirconia sintering furnace, safety is perhaps the most important. After all, these furnaces heat up to extremely high temperatures and maintain those temperatures for extended periods, and require high current to operate.
If you care about the safety of your employees and laboratory, be sure to purchase and use a sintering furnace that meets safety certification standards.
This means that independent testing laboratories have confirmed that the equipment will operate safely even in the event of a malfunction (such as temperature runaway, etc.). There are many good options available on the market.
When you are ready to purchase a zirconia sintering furnace, please refer to this article when selecting a high-quality, efficient, and safe sintering furnace for your laboratory.