"Grant Erwin" wrote: (clip) I seem to recall hearing that Coca-Cola actually dissolves teeth. Is that
^^^^^^^^^^^^^^^^^^ It must be pretty slow--else most of the population would be toothless. I suggest tap-tap-tap with a small hammer. Or leave the tooth in, and have a jeweler add a small ring, so you can wear it on a chain around your neck. :-)
Melt it out with a propane torch. Improvise a casting crucible by grinding and compressing bentonite clay (hidden in the grocery store disguised as the cheapest unscented store-brand kitty litter). Or from silicate furnace cement.
Gold dealers will give you about half the bullion value of the gold scrap. They're in it for a profit. Likely no more than $50 or $100 cash for an old crown, so it may not even be worth the trouble. But you could play with the jewelry style of metalworking, say casting and finishing a finger ring.
Dilute HCl, .1 N dissolves Hydroxyapatite. In the absence of nitrate, this will not dissolve the gold, though it may extract alloying metals such as copper from the surface, leaving a frosty surface. You can speed this up in a beaker floating in an ultrasonic cleaner. This cavitates the organic materials as well as speeding up the dissolution of the HA.
Coke will not work because it is a very dilute solution of phosphoric acid, which gave rise to stories about it removing rust from bumpers.
Gold crowns are not made from amalgams. Gold amalgams are used for fillings. Silver amalgam fillings are always removed before a tooth is crowned.
The reason that an amalgam filled tooth gets a crown in the first place, is mostly, that there is new decay around or even under the filling, so the tooth has to be cleaned and the amalgam is removed to make place for either an inlay, overlay or a full crown. You cannot prep a tooth properly for a crown, with the amalgam still in place.
It not necessary to put a torch to a tooth with a crown still on it. Since the tooth has already been extracted, it will have become brittle rather rapidly, because it is no longer fed by blood vessels and nerves. Just take a pair of pliers to it, and it'll break in pieces quite easily.
BTW, before I became a goldsmith, I spent three years in dental school at the university of Amsterdam trying to become a dentist.
I don't doubt that you have described how it is supposed to be. But the world isn't perfect, and there is no cost to being a little cautious while heating the gold alloy. It might be contaminated if the dentist didn't get all the amalgam out.
This is almost impossible. However, in the unlikely event, that this was the case, the work was done by an exceptionally bad dentist.
Getting old silver amalgam fillings out, is quite easy, since the moment they are touched with a drill, they pretty much crumble and get ripped out. The pieces fly in all directions (inside the mouth of course), because of the characteristics of the material once it has been in a tooth for some time.
It is also very likely, that if in fact there was still some silver amalgam left under the crown, the patient would have developed new decay and with it quite a severe toothache. The crown would have failed, have to be removed, the tooth would have to be cleaned again, and a new crown would have to be made and placed.
Also, if he did choose to heat it, the cement with which the crown is affixed to the tooth would decompose long before the gold would melt.
And lastly, even if there were a silver amalgam filling under the crown, heating it would most likely be harmless. It is unlikely that he is going to get hurt from "Mercury vapors" from a single silver amalgam filling.
A mouthful of silver amalgam fillings is a lot more dangerous to a person's sustained health, than heating one that is no longer in a mouth.
Before the advent of electroplating, precious metal smiths used the extremely poisonous technique of "fire gilding" to gold plate silver objects. This was done with gold amalgams.