HEATING ELEMENTS
About 5000 to 7000 furnaces for sintering zirconia are produced every year at the moment. The numbers are rising. There are two different heating element types that are installed in the dental furnaces on the market to achieve the extremely high temperatures, usually in excess of 1400°C (2552°F). By far the largest share of the furnaces on the market is built with molybdenum disilicide (MoSi2) heating elements. In some few cases, silicon carbide (SiC) heating elements will be used. These two element types differ in their properties in addition to the entirely different basic materials.
SiC heating elements are usually used up to a temperature of 1530°C (2786°F) as recommended by the furnace manufacturer. A firing cycle will take several hours. MoSi₂ heating elements can be used up to a temperature of 1750°C (3182°F), depending on the quality and furnace type. The maximum application temperature of these heating elements therefore is clearly above that of SiC heating elements. Additionally, the surface load, which means the power (W) that can be emitted per square centimeter (cm2) is more than twice that of SiC, at above 25 W/cm2. This permits much faster heating-up rates, to much higher application temperatures. Heating to 1550°C (2822°F) in less than 15 minutes is possible.
MolyCom®-Hyper 1800 (MoSi2) heating elements that have been used on the international dental market since 2005 have turned out to be much longer-lived than SiC elements in continuous tests and according to the experience of various furnace manufacturers. SiC elements usually need to be replaced after just a few hundred cycles due to the strong change of resistance, which corresponds to a service life of approx. 1-2 years at common use. MolyCom®-Hyper 1800 elements in contrast have been operated for more than 2500 cycles without any failure or need for exchange. Exchange of the defective element is usually sufficient in MoSi2 heating elements. In contrast to this, all parts of the SiC elements must be exchanged in one due to the strongly impaired resistance.