The dentist files down or reduces your tooth's size, then makes an impression of it. The impression is sent to a lab that builds the crown by creating a metal casing to cover the tooth, then adds/builds porcelain on top of it until it will fit in your mouth.
My dentist had to grind mine down to accomodate my bite, and now the metal casing is showing on the surface -- it looks like I have a filling! It's preposterous to have a brand new crown that looks like it has a filling. I've decided what I'm going to do, and thanks for your response. I hope if anyone else has this happen, that they don't allow the dentist to get away with it. It may actually be the lab's fault for not making the crown correctly.