When I read this, I can only shake my head. People always come up with new ways to take money from others.
If you simply take 25 €/gram for dental gold, then you get just 16 grams of gold for 400 €, spread over 160 m². What is that supposed to achieve?
Also, I once saw a report where a gravel pit owner operates a plant to filter gold out of sand. So, there is apparently already gold naturally found in normal sand. So what is the additional gold supposed to do?