When he did die, I was either too busy or too shy to bring the matter up to the mortician. For the next several decades I wondered in the back of my mind whether some mortuary assistant with a pair of pliers had enriched himself at our expense.
This year my question was answered. I had the opportunity to speak with a funeral director on an unrelated matter, and brought up the question that had been nagging at me for so long. He laughed and noted that he was uniquely qualified to address the question, not because of his mortuary experience, but because his father was a dentist.
During his father's dental career, it was common practice to extract teeth, many of which had metal fillings, including gold. Discarding the teeth into the environment was discouraged because of the heavy metals, so his father kept all the teeth he extracted in a large coffee can. Then one day the office building burned down. The family retrieved what they could from the office ruins, and in doing so found the coffee can with the organic material gone but the metal fillings fused into a solid mass. They took the block to a metalworking company and were rewarded with the princely sum of ... three dollars.
His explanation was that gold itself is too soft to be used as a filling on a grinding surface. "Gold" fillings are typically other amalgams colored with minuscule amounts of gold. They are offered to the public as a cosmetic enhancement, not as a financial investment.
I'm not sure whether the same applies to often rather striking "gold teeth" one can see on a Google image search.
A related post from last year: A concrete block filled with human teeth.
Photo credit: Myteethnvd's Weblog.