Inside Dental Technology
July/August 2013, Volume 4, Issue 8
Published by AEGIS Communications
Dependable Zirconia Sintering
Testing Whip Mix’s Infinity ZR Furnace to the limit
With the number of the zirconia products available today, it is important that laboratories use a furnace flexible enough to meet all of their sintering requirements. The furnace is not only used to achieve the material’s ideal density, shrinkage, and translucency, but it is also critical to changing the material from a weak monoclinic state to the much stronger, self-healing tetragonal phase. This is accomplished by taking the zirconia to a minimum transitional temperature of approximately 1,000°C. The final temperature for most zirconia is critical and, with many furnaces, is at approximately 1550°C. When the zirconia reaches this temperature, it will have finalized its transformation to the tetragonal phase and will be idealized for use in the mouth.
Most zirconia researchers agree that temperatures higher than 1550°C can cause deleterious effects such as low temperature degradation. This is represented by a return to the weaker monoclinic phase.
Unfortunately, many technicians think that the higher the temperature, the greater the translucency of the zirconia. This is only true to a point. The maximum translucency of zirconia is actually determined by a combination of the product’s chemistry, the amount of strengthening agents (ie, alumina) used, and the time/temperature of sintering parameters, which may be altered to fit the needs of individual zirconia products. This is because the temperature ramp (speed) and the soak periods at various temperature plateaus also influence the physical properties of the material. In many cases, a slower climb to the high temperature produces not only idealized strength properties, but desirable translucency as well.
To accomplish the recommended parameters for zirconia, Whip Mix’s Infinity ZR Furnace offers the laboratory complete flexibility and control over the sintering process. Thirty individual programs give the technician the ability to fire any material on the market, and four programmable stages allow for an optimization of firing programs. For instance, technicians may want to increase the rate rise from ambient to the point where the crystal formation begins, then lower the ramp rate in a subsequent stage to optimize the translucency. The programming itself is extremely easy and the furnace’s high accuracy is the result of being pre-calibrated to +/- 3°C tolerance specification.
Unique Thermal Web Technology
The Infinity ZR’s muffle and door insulation is constructed of the highest purity alumina fiber insulation and its heating elements have been selected for long life and their low replacement cost. But what makes the furnace stand out among available dental sintering furnaces is that it has exclusive patented thermal web grooves in the insulation. These grooves increase the surface area and allow for off axis re-radiation, which serves to further homogenize the heat dispersion. A similar example would be overhead fluorescent tube lights. You rarely see a naked fluorescent bulb because diffusers between the bulb and the room make the light output more even. As the insulation takes on and stores heat, the thermal webbing then re-radiates the heat. It literally smooths out hot spots created by the direct radiation of the heating elements.
The six robust silicon carbide heating elements, when combined with the thermal control technology, produce a constant and even heating of the zirconia units within the tray. The uniquely designed sintering tray features legs that allow an even heat circulation around the entire tray when the trays are stacked. Technicians may stack up to three trays, allowing them to sinter up to approximately 60 units simultaneously.
Of all of the features offered by the Infinity ZR furnace, probably the most important is enhanced safety. Unlike most of the competitive furnaces on the dental technology market, this furnace is UL safety certified to the UL 61010 standard. This means that an independent testing laboratory has confirmed the unit will fail-safe.
Whip Mix’s well-deserved reputation for making top-of-the-line, versatile, and dependable dental laboratory products has been proven again with this new sintering furnace.
Disclaimer: The preceding material was provided by the manufacturer. The statements and opinions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Inside Dental Technology.