April 5, 2019 | Alexander Wünsche | General
There are so many factors and conditions that will affect the mechanical properties of a zirconia restoration. All the stages of creating the restoration must be carried out as not to create stresses and microdefects within the material. Mastering the sintering process is essential to a quality restoration. This blog will focus on my experience using the Sintra Plus furnace.
Check your parameters for each furnace, as results can vary between furnaces. Results can be influenced by different positions in the same furnace. It’s very important to regularly maintain these parameters, as the heating element can deteriorate over time, the controls may deregulate, or the interior of the furnace may be altered. Between different sintering furnaces, the accuracy, reliability and control can vary a lot.
After the substructures are created they must be placed in a sintering tray which usually has sintered beads that allow the restorations to move. One thing I appreciate about the Sintra Plus is the furnace comes with a beadless tray, which allows for better control of the sintering process. The beadles tray allows the substructures to move without the use of sinter beads. It’s very important the substructures can move freely since they are going to shrink to the required size during sintering. Any restrictions in movement can cause stress on the substructures and cause fractures or even breakage. It is essential that the different zirconia types are kept separate because they have different sintering temperatures. Sintering at the wrong temperature will compromise the microstructure, because sintering temperature determines the crystal size. Due to the temperature differences, each zirconia material has its own chemical composition. One other feature of the Sintra Plus that I appreciate is that you can stack sintering trays, and each sinter tray has a lid, so different zirconia brands can be kept separate without risk of cross contamination.
The Sintra Plus is fully programmable, with the max temperature of 1650°C. There are 30 programmable parameters, allowing for sintering of any dental material. I personally use three main programs. I use a seven-hour program for single unit substructures and small bridges. Due the smaller size of the restoration, the cooling time can be shortened since a shorter cool-down time won’t create the same stresses as with the long-span bridge. I use a 14-hour sinter program for long-span bridges. This allows the materials to dry out completely. The cooling after the sintering must be done very slowly, to prevent stresses in the restoration. Results from the Sintra Plus are highly satisfactory. Another sintering cycle I use often is the fast program, which is very useful for emergencies and cases that need to be done quickly. This cycle takes about two hours, but should be used with great caution. It’s important not to put many individual units in the sinter tray and no bridges. Due to the fast process, absolute control over temperature must be maintained, this gets harder with more units in the furnace. Using the Sintra Plus, I was able to successfully sinter ten units in 90-minute fast cycle program.
I really appreciate the hookup for compressed air with the Sintra Plus. Sintering restorations are very clean and results obtained are reliable. Compressed air offers control over cooling during sintering cycles and allows for degassing of the furnace. I use it when drying out colored zirconia or heating up at the beginning of every sinter cycle. Compressed air keeps the heating elements extremely clean and prevents oxidation which in turn helps lengthen the lifespan of the heating element. I use the Sintra Plus on a daily basis and I’m extremely pleased with the results. The furnace offers predictable results and can be programmable to the lab’s requirements. The additional features offered by Sintra Plus including the compressed air and beadless tray make the process functional and efficient.