Sinter Properly
The importance of proper protocols and maintenance for ovens
Jean Chiha, CDT
Over the course of evaluating more than 150 different zirconia materials at temperatures between 1,450°C and 1,600°C, I have learned that sintering protocols are always important in getting the best out of these materials. Laboratories need to evaluate what they need in a sintering oven—temperatures, programs, longevity, and maintenance—before starting their research.
Latest Developments in Sintering Ovens: In 2020, most new sintering ovens can be connected to a computer, whether wired or via Wi-Fi, allowing updated sintering programs to be downloaded directly into the oven.
There also have been improvements in software programs for sintering zirconia based on the temperatures and times needed for optimal output. Most oven manufacturers use two companies for white boards and heating elements, so the real difference comes down to software. Zirconia manufacturers have gotten smarter with their recommended sintering programs, knowing that slower times are required for grain growth, which produces translucency—though it is also important to note that excessive translucency can appear gray in the mouth, requiring microlayering of the incisal edge in some situations.
Another feature I find useful in some new models is that they use 220 V power, making them slightly faster than ones with 110 V.
What to Know When Purchasing: Cost-effective can be is expensive. If you buy a cheap sintering oven, you are not going to have good results; the same goes for off-market options.
Laboratories need to monitor the temperatures at which they need to sinter. What is the maximum temperature capability of the heating element compared to the maximum programmable temperature? For example, if the maximum programmable firing temperature is 1,500°C, then using an oven with a heating element that has a maximum temperature of 1,530°C is not ideal. Running at 97% capacity puts a lot of stress on the oven. The heating elements can wear quickly, increasing the margin for error when operating.
Consistent firing for repeatable results is the goal. Regular maintenance is necessary to keep that consistency, and some expenses are associated with that. Laboratories that have been using the same sintering oven for years but not maintaining it should consider purchasing a new one. Those with heavy use should be replaced about every 3 years to ensure the utmost consistency and reliability. Sintering ovens do hard work and their parts have limitations. Taking care of them and even replacing them regularly is the only way to help ensure consistent performance and results.
How to Get the Most Out of Your Oven: The first and most important thing to do with a new sintering oven is to follow the manufacturer instructions for use and maintenance. You must follow protocol.
So many laboratories all over the world do not pay attention to those details. They do not use the tabs to check the temperatures, so they do not know how well their ovens are reaching and maintaining the temperatures needed. Calibrate temperatures regularly—including the very first sintering cycle. Following instructions is critical even for the tabs used to detect temperatures. You cannot take a tab and just throw it in an oven. The manufacturer authorized you to use this tab based on a certain process so you can detect the temperature.
The same is true of oven cleaning and maintenance. I follow a protocol when testing new zirconia in my laboratory. I purge my oven first, clean everything (including the heating element), and use a tab to check the temperature. I run one cycle after, and then I test the product. After I finish, I repeat the process before the next test.
With heavy use, heating elements typically must be replaced after approximately 3 years. When that time arrives, always consider replacing with original parts.
Key Takeaway
Buy based on what this oven can do for you. It should help you provide a consistent end product.
About the Author
Jean Chiha, CDT, is the owner of North Star Dental Laboratories and Milling Center in Santa Ana, California.
