What a great site. I never realized what an inexact science dentistry was – it's scary! I just had a crown done, and if I understand you right where you said above “Crowns are suppose to be "supra gingival" which means the crown margin along the gumline should be at the gum, not underneath it.”, mine would seem to be placed right. However, this means that my tongue can feel the edge there at the tiny crack where they meet. What’s to stop food from getting into that crack & decaying what’s left of my real tooth? It sounds like it must be very difficult to get them to sit exactly right!