In the, not too distant past, whenever you went to the dentist for a crown, it would be made strictly from metal. The combination of metals used was different. That would explain why some metal crowns were silver in color and others were gold. But, the color withstanding, all crowns were made purely of metal. These crowns worked wonderfully for many years. And to this day people still have metal crowns that are fully functioning in their own mouths.
Technology advanced and people started to demand crowns that looked more like teeth. people began to want function AND esthetics. Thus came the advent of the PFM (porcelain fused to metal) crown. The PFM crown seemed to be the cure all. It had a metal core for strength and was then overlaid with porcelain to give it the color real teeth.
Some problems began to pop up with the PFM crowns. Whenever 2 materials are fused together there is the chance for failure at the fusion point. Thus it is with the PFMs. We have found that the porcelain is beginning to fracture off of these crowns as they age. This doesn’t necessarily put the tooth at any risk due to the fact that the metal cores are staying intact. But, once the porcelain begins to chip off it makes the surfaces rough and again begins to show the metal underneath the crown.
Another problem is that PFM crowns show a black line, or ring, around the base of the crown near the gums. This is due to the fact that when porcelain is thinned out too far it becomes very brittle. And as the porcelain nears the gums it must become thinner. This dark line was also something that turned people off of these types of crowns.
Technology has now offered a solution to both of these problems. Dental labs are now able to use a material called Zirconia. Zirconia used in dentistry is actually Zirconium Oxide. That might not mean a lot to the average dental fan but let me give you what will mean a lot. The entire crown is made of the same material. What that means is that there are no pieces and parts that are fused together. Thus no parts to un-fuse.