Case by Case

 A tooth can sure go through a lot of different treatments before a "FINAL" filling or crown is placed.
First, you have to start with a tooth that shows radiographic and clinical decay around an old filling:

We gave him an injection, and then started to remove the "old" filling.

         The old filling is removed  and LOOK, there is a huge crack down the middle of the pulp floor along with some decay.  This seems to happen more times than not lately, and in order to not SPLIT the crack more, we have to put in some sort of covering that won't the tooth break apart = gold crown.
And just so you know, a gold crown is THE LONGEST LASTING CROWN there is.  Seriously.  Nothing will be here longer in this guy's mouth than a gold crown.

Next, we have to fill the tooth with something so we have a nice strong base to put the crown onto.  One of the strongest we can use is another amalgam filling.
The tooth is filled up, shaped to look like a tooth, and then the patient is sent home.  We had to wait a couple of weeks to make sure the tooth did not flare up in pain because of the big crack and the fact that we were using a drill in the middle of his tooth.

 I shaped that tooth to fit a crown and then took an impression of the tooth.  Then, in the laboratory, I make a new crown out of wax on a stone model of the tooth.  The wax is turned into gold by a very long process, and then I cement that gold crown back into the patient's mouth.  Here is the crown on the model, and here is the crown in the mouth.

Gold crown in mouth after cementation