Hi!
First I sympathize. I'm finishing my Masters myself and was accepted at the PhD level but I was able to obtain an additional delay because of my health problems.

My advise is [color:"blue"] get the amalgam out ASAP [/color] but get the dentist to write a letter in which he or she explains the situation in details, including mercury poisoning and the fact that you can't just detoxicate in 2 days, that it is a long process and normally, the University should grant you an additional delay.

Good luck !