There are also corrosion issues, which is why I got rid of my amalgam fillings 15 years ago. For a small cavity, a big hole has to be drilled in order to get the amalgam in. And all it does is fill the hole. So the area between the tooth material and the amalgam sometimes gaps (due to some corrosion taking place) and cavities form in the hole. The newer bonding materials work much better, since it actually binds to the tooth material. Small cavity found early, less drilling. There is a drawback however with bonding material and large fillings (such as replacing amalgams). There is a long term curing process (over a span of years) outside of the initial curing where the material shrinks and places stresses on the tooth material which it is bound to. Thus causing cracks, and necessitating crowns.
There are also corrosion issues, which is why I got rid of my amalgam fillings 15 years ago. For a small cavity, a big hole has to be drilled in order to get the amalgam in. And all it does is fill the hole. So the area between the tooth material and the amalgam sometimes gaps (due to some corrosion taking place) and cavities form in the hole. The newer bonding materials work much better, since it actually binds to the tooth material. Small cavity found early, less drilling. There is a drawback however with bonding material and large fillings (such as replacing amalgams). There is a long term curing process (over a span of years) outside of the initial curing where the material shrinks and places stresses on the tooth material which it is bound to. Thus causing cracks, and necessitating crowns.
Actually, the preparation for an aamlgam filling should be no larger than the periphery of the decay, as long as the remaining tooth structure is not unsupported.
The gap you speak of is actually filled in by the process of corrosion, which is in opposition to the inability of resin fillings which are notorious for sensitivity because of shrinkage during the polymerization process which results in microleakage. The resins are designed to bond to the tooth structure... if done properly. That requires absolutely no contamination from moisture. These are done with a rubber dam, right??
There is no long term curing process. What you may be confused about is the continuous process of thermal expansion, whereby amalgam again is favored as it will expand and contract at a rate closer to that of the tooth material than reinforced resin.