Removing the pulp tissue of a tooth dries it out and weakens it. All posterior teeth that have been root canaled need a crown to prevent the tooth from splitting. Anterior teeth should get a crown or composite filling to strengthen the tooth. Silver fillings are not an option for a tooth that has a root canal.
What is filling normally used .They normally do filling and then they put a cap .
What should the composite filling be (what material).I read and understood there seems a big debate between potential hazards of using Silver amalgam fillings .
The so called potential hazards you read about is a controversy that has been going on for decades, with almost no proof at all. I would not worry about silver fillings from that perspective.
Normal depends on the office, some use more amalgam, some more composites. When I say composite, thats what the filling is called. There are only two main types of fillings, white composites and silver amalgams.
You are correct, most crowns require a buildup, which is basically a filling under the crown. What material does not matter much. Amalgams are a little stronger, and under a crown would not pose any problem even according to the group that claims they are hazardous. But newer composites are almost as good.