It is standard practice to use toxic levels of mercury in fillings, it doesn't really matter that it's lower weight than the other metals. Mercury is detrimental to human health in small amounts, whereas something like silver actually has antimicrobial properties in the body.
That's a great point that metal fillings can indeed crack the teeth, because they are unable to compress under pressure (like in biting), and the force is distributed to the surrounding tooth. They are really not a valid solution for protecting or activating health.
Composites may come down in price as more and more consumers learn about the dangers of mercury and demand an alternative.
Sure, any amount of mercury is pretty toxic. I'm not defending them. Haha
I really hope that the price doesn't come down because man, $200 a filling is killing me! Haha
If you ever need dental work done get it all done in Mexico. Its WAY cheaper so much so u can often afford a plane ticket and a hotel and food for the same price as getting it done locally. Plus you then get to have some fun in mexico!