Replacing amalgams should be done carefully over time. I had 7 replaced(I still have many more) and developed nasty candida infections in my mouth. There is something between traditional fillings and crowns. I am talking about inlays and onlays. These are usually porcelain. They also last much longer than composite fillings but are much more expensive. Some dentists can do these in a single visit(using a Cerac machine) while others use a temporary filling while an outside lab custom makes the inlay or onlay. The cost for dental work varies tremendously based on location. The US average cost is around $800 each, but the price in the US probably varies from around $400 to $2,200 each. Composite fillings are not very good for large cavities. An inlay or onlay is usually less expensive than a crown, and preserves much more of the natural tooth. My dentist wanted to replace many of my amalgams since they are old(average around 30 years old). Replacing amalgam fillings will expose you to plenty of mercury.