Crown for molar: gold alloy versus lithium disilicate, zirconium, etc.

[dentalquestion]

I have a molar with a large 30+ year old amalgam filling, and there now appear to be cracks in it (a known risk of amalgam filling metal expansion from heat). It may eventually need a crown...

For crowns, my understanding is that gold alloy is generally the longest lasting and requires the least removal of tooth material. Are there any disadvantages of gold alloy versus other crown materials besides appearance (which is not a concern for me for a molar, since no one else outside a dental office will see it)? Is there any difference in how likely it is to fall off? Are other crown materials less opaque to X-rays, and does that make any difference in the usefulness of X-rays to detect problems under the crown?

 

[MattKW]

1. Firstly, let's dispel the myth that amalgam causes cracking. It certainly doesn't cause it from heat expansion. It can weaken teeth more than composite because amalgam doesn't bond (glue) to teeth and sometimes need more tooth structure removed than a composite. As a teacher in clinical dentistry, I encourage students to try amalgam in selected cases; it is sometimes much better than amalgam; unfortunately it is grey!
2. Gold alloy is my preference for 2nd molars. Minimal preparation and has similar wear characteristics to enamel of opposing teeth. Monolithic zirconia (not layered zirconia) can also be used in a similar fashion. but... crowning a tooth causes indirect damage and there is ~8% chance of the nerve dying. If that happens, then it is easy to cut through gold alloy and do an RCT, and keep the crown. If you cut through zircionia (really tough!), then you will have to replace the crown. If I ever need a crown, it will be a gold alloy.
3. The glue that holds either a gold crown or a zirconia is about the same amount of grip. The glue should not be the determining factor in holding on a crown. With special treatment it is possible to get a better grip on zirconia than gold, BUT the preparation of the crown with fairly parallel sides is more important. Most crowns I have seen come off have been where they were over-prepared (too tapered).
4. Radio-opacity doesn't really matter. If you develop decay under any crown, it will be at the margin where the crown meets natural tooth. Decay will go under the crown and also below the crown onto the root surface. So, it will be visible on the root surface anyway, and that's enough reason to assume the same amount is under the crown, and requires the removal of the crown.

 

[dentalquestion]

Would lithium disilicate be similar to zirconia in the above (and similarly less desirable than gold alloy for molar crowns)?

 

[MattKW]

Lithium disilicate should not be used for molars, only up to 2nd premolars. It has a better translucency and "look" than gold or zirconia, but much weaker.