What crown prep margin did my dentist use?

[swatkins]

I just got a full gold crown in the upper jaw on the second molar from the back not counting the wisdom tooth that can't be seen. From looking at the mold the dentist got back from the lab, it looks similar to a Feather Margin or Knife edge but at the gum line instead of being any kind of shoulder what so ever, the dentist cut a groove that encircles the tooth near the gum line. I can't find a photo or diagram this type margin anywhere online.

What type margin prep this is? Post a link to an image? Is it recommended for a full gold crown? Seems like it could weaken the tooth with the groove cut encircling the base at the gums since this reduces more of the tooth body? What was the purpose of the groove at this location?

 

[Bertram Boniface]

The diagram of the tooth preparation laboratory model shows a knife edge preparation.
The groove is cut in the model by the technician (not in tooth by the dentist) to make it easier for him to see where the preparation ends when he is waxing up the crown for casting. There is no groove in your tooth!
You do not need to worry.