What metals are in porcelain fused to metal crowns?

Dr. Hall,
I have 6 porcelain-fused-to-metal crowns. I have two questions:

1) What are the usual metals contained in the metal shell?

2) Is the metal shell the thing that begins to show at the gumline, causing the black lines? (I have those black lines.)

Thank you for your information.
– Carolyn from New Jersey

Carolyn,
There are two basic types of metals that are used in porcelain-fused-to-metal crowns – precious or noble metals and base metals. Noble metals used are gold, platinum, and palladium. Base metals would be chromium and nickel. Dentists will classify these crowns as porcelain fused to high noble, porcelain fused to noble, or porcelain fused to base metal.

The noble metals have less tendency to corrode, provoke less sensitivity, and are made to a more accurate fit.

The metal can show at the gumline, and this is what causes the dark, sometimes it’s even black, line at the gumline. Dentists may try to hide this under the gum, but after several years, sometimes the gum recedes and this line is visible anyway. The dentist may ask the dental lab to cut back the metal at this front part of the gumline and leave this margin all in porcelain. This is called a porcelain butt margin. The dentist will pay an extra fee for this – about $30 to $40, and they generally pass this on to the patient. While this makes this line more subdued, it will usually still be present. The reason is that there is still a lot of opaquer that has to be used in the crown to mask the metal. The contrast between the opaque crown and the natural tooth structure makes it difficult to blend colors here, and creates the effect of the dark line.

Patients generally prefer the all-porcelain crowns, which will eliminate any dark line. And the general natural translucency of the crown without any metal is much more natural-looking. But be careful. I would never ask a dentist who is more comfortable doing a porcelain-fused-to metal crown to do an all-porcelain crown. Dentists who are good at all-porcelain crowns will far prefer them for front teeth. If your dentist suggests a porcelain fused to metal crown for a front tooth and you are concerned about the esthetics so that you want all-porcelain, take that as a signal that you are in the wrong practice. This dentist places a low priority on esthetics and if you try to nudge them out of their comfort zone, the results could be disastrous.
Dr. Hall

Follow-up – in a subsequent e-mail exchange, it came out that Carolyn is probably allergic to the metal in her porcelain fused to metal crowns. Read the posting on dental metal allergy.