Everyone who has had an angry member of the family thrown a porcelain plate at him will raise an eyebrow when told that his crown is going to be made with porceelain. In the past, porcelain had to be backed with a metal core if the crown is to last more than a couple of years in function. These crowns were known as porcelain fused to metal (PFM) crowns. While they were strong and lasted for many years, PFM crowns posed aesthetic challenges. This is because metal will impart an ugly greyish colour to porcelain. To mask this greyish colour, an opaque layer must be painted on the metal. This is why many PFM crowns look flat. Light does not penetrate it like it does a natural tooth. A black line also appears at the gum margin after a while as wear and tear sets in.
Of course, there were patients who insisted on having metal-free crowns. Full porcelain jacket crowns (PJC) were done, but these crowns never lasted for than a few years as unreinforced porcelain just isn’t strong enough to withstand chewing forces.
Some years back, a new material called Empress came into the market. Like glass, Empress can be made to mimic the translucency of natural teeth. Like glass which can be made bullet proof, Empress can be made stronger than conventional porcelain. The fracture strength is about 200MPa. In spite of the increased strength, many Empress crowns and bridges fractured within a few years.
About 4 years ago, the same manufacturer that gave us Empress brought in a new, improved material called emax. Just as aesthetic as Empress, emax is even stronger, with a strength of 400MPa. With emax around, there is now no reason to make PJCs or PFMs for front teeth.
The patient wants to straighten his lateral incisors
The teeth to be rearranged were trimmed down
Completed emax crowns fitted. Teeth look straighter now.