What is the difference between the OLD dental Crowns that have been used and the new glass crowns? (procera)?

I am trying to figure out the difference-- and what makes them better to have. There are all these new glass crowns on the market and what makes them so much better-- actually what makes the Old crowns not a durable?

What is the difference between the OLD dental Crowns that have been used and the new glass crowns? (procera)?
The Procera crowns are not made out of glass, it is all porcelain. I think what you mean by older crowns, are the Porcelain fused to metal (PFM). They still have porcelain on them but underneath that is a metal substructure %26amp; this is why they are more durable. I ALWAYS recommend a PFM crown on patients second molars (the very last tooth in your mouth). But on any other tooth, you can use the all porcealin ones. You definetly need the all porcealin on front teeth, because they look much more natural %26amp; PFM crowns will cause a gray line next to the gumline, which you wouldn't want in your smile. Hope this answers your questions. Good luck!