Most zirconia disc manufacturers work hard to insure proper hue chroma and value of their zirconia. In a recent survey, many labs are exhibiting low value or gray results when working with the newer generation of anterior materials. That said, I would like to look more closely at why this occurs and how best to resolve it.
The nature of this generation of cubic zirconia materials requires more accuracy of the sintering process than any zirconia we have used in the past. All zirconia discs are shipped with an information for use (IFU) page in the packaging. Included on the IFU is the sintering cycle. For starters, it’s imperative to follow manufacturers’ instructions for sintering. Sintering cubic (or anterior) zirconia too hot or holding it too long at the top temperature will result in lowering the value or too gray.
Next step, let’s say you are using the manufacturer’s IFU for sintering and still having results that are gray and too low in value. Time to look at your sintering furnace. How long has it been since you calibrated the furnace? Did you calibrate the furnace correctly? The tendency of many sintering furnaces when they drift from the programmed top temp is to go higher or hotter. Hypothetically, you may have it programmed the top temp for 1450 degrees but the actual result could be as much as 100 degrees higher.
If you are using the IFU for sintering cycle and exhibiting low value gray results of any anterior zirconia have your furnace calibrated. Unfortunately, this is not a simple process (perhaps I will save this for another blog). With your next cycle, reduce the top temp by 40 degrees. If it’s still too gray, reduce the temperature by 25 degrees at a time until the value is right on. Once you have the correct value, you have likely achieved the proper sintering temperature. Please note, all zirconia becomes more opaque with lower temps.
Hope this helps all of you that have had gray looking zirconia.
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