Ceramics
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.
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#1 by KonstantinMiller on July 7th, 2009
Hello. I think the article is really interesting. I am even interested in reading more. How soon will you update your blog?
#2 by admin on July 7th, 2009
I’ll update sooner if I get more genuine comments.
#3 by lu bu on July 18th, 2009
Very informative, Dr Chan.
I’m surprised perfect tooth structures were removed though.
#4 by Joanne on August 7th, 2009
Hi,
I had a root canal done on my front teeth and thereafter a metal porcelain crown on it about 8 years ago. After the crown was placed, there was slight swelling and bleeding around the gum above this crown (esp after i floss/brush). This persisted for years, until recently the affected gum area seems to turn a bit dark pink / grey and seems to have receded a little bit.
I’m not sure of the cause of this. But is it too late to “save” my gum now? If not too late, what can be done? Should i do a recrown with a full porcelain crown? Would this help?
What is the cost of a full porcelain crown? Thanks.
#5 by admin on August 7th, 2009
Joanne,
From the way you described it, yours is certainly a challenging case. If the root of your tooth has turned darker in colour and the discolouration is showing through the gums, the treatment will be quite complicated. Your gums are probably very thin. The first thing that needs to be done is to thicken your gums by a procedure called connective tissue grafting. Some gum tissue is taken from the roof of your mouth and tucked into the gum area overlying your crowned tooth.
After this is done, your old crown will be removed. The discolouration inside must then be properly masked to prevent it from showing through the ceramic. After this is done, impressions are taken for your new full ceramic crown.