Can you keep your amalgam fillings
...without doing harm to yourself, others, or the environment?
Apart from the "amalgam" lobby who will swear on their grandmother's head that mercury and other serious toxins in dental amalgams are safe (after all, they have been used for 150+ years), interestingly, Ramiel Nagel, author of the self-help book Cure Tooth Decay maintains that as long as nutrition is good, amalgam fillings can be tolerated.
Perhaps this has a measure of truth on a purely personal level (also compare Are all amalgam carriers "doomed"?). But the following deserves consideration as well.
Until recently, it was assumed that the only thing that makes bacteria resistant to antibiotics was repeated administration of antibiotics (such as penicillin). Once the bacteria living in a person's body have become resistant to penicillin, they secrete so-called plasmids (small bubbles containing a piece of DNS or RNS, teaching the other bacteria in the environment how to become resistant to penicillin).
In a person carrying amalgam fillings, the oral bacteria (which also live in other parts of the body such as the intestines and the blood) become resistant to mercury, copper and the other metals contained in the mouth and simultaneously, become resistant to all antibiotics. In other words, bacteria which normally colonize our body will live in us happily ever after but won't respond to any antibiotic therapies. And more than that - each time we breathe out, we send millions of plasmids into our environment, teaching other bacteria how to also become resistant. In addition, at each outbreath (at least when speaking, coughing or yawning), we send mercury vapour into our surroundings.
So personally I certainly wouldn't advise keeping any amalgam fillings. For an enumeration of many serious reasons, see for instance the detailed information found in the article On the dangers of dental amalgam (mercury) "silver" fillings (including for the environment) and Dr. Dietrich Klinghardt on the dental toxicity issue. A pithy quote is owed to Dr. Hildegard Schreiber MD (public health official specialised in microbiology and the epidemiology of infectious diseases) who wrote about people carrying amalgam fillings, "During mastication, up to ... 700µg of mercury are released... if saliva were drinking water, one wouldn't be allowed to swallow it (translated from German by Healing Teeth Naturally)."