These crowns are milled out of zirconium using cad cam technology-. Their fit can be checked prior to inserting using an acrylic version of the restoration also made either using either a digital or analog (silicone or polyether) impression. By trying in the acrylic temporary and, making adjustments on it, a dentist can insure that the zirconium version will fit without the need for any further adjustments. The adjusted acrylic temp can be sent back to the lab, rescanned and a perfectly fitting Zirconium copy made. Zirconium is a very hard material that can withstand forces that might shatter ordinary feldspar porcelain. Currently I recommend gold crowns for restoring Second molars that require a crown. All zirconium crowns appear to be a promising option for patients desiring a white shaded restoration. Although I personally have not fabricated one of these for any of my patients, a couple of my prosthodontist friends have, and they like the results so far!