How can one determine if a crown is placed subgingivally or supragingivally

Can someone please confirm my understanding that a subgingival crown is a crown that is placed below the gingival margin. If a crown has been placed subgingivally for several years, it is common that inflammation results and that this inflammation attracts bacteria which increases pocket depths from within a normal tolerance (e.g. less than or equal to 3mm). That is, depths of 4mm or greater would result. A supragingival crown is one that is placed below the gingival margin. However, my understanding is that experienced practitioners place the crown slightly under the gingival margin in order to improve the esthetic of the crown to margin appearance. That said, how does one tell the difference between the 2 different placement techniques? Can someone tell me what type of crown placement a tooth that has an open margin on the lingual side and a crown that appears to be under the gingival margin would be considered? I am assuming that based on geometry, and no inflammation (e.g. pocket depths within normal limits) a that the crown placement would be considered supragingival. In addition, if a crown was placed subgingivally a radiograph should show a significant break in the gingival margin due to attenuation of the X-ray through the PFM material. Hence a solid white image would appear in the radiograph.  

[Ramin Mehregan, DMD]

Dear patient
A subgingival crown is a crown (usually PFM's) are placed below the gingival margin to hide the metal collar below the porcelain. Now if the crown is flush with the tooth it should not cause inflammation, but if there is a ledge it will lead to inflammation. An open margin can be detected with an x-ray and with a dental pick. Supragingival crowns are placed above the gingival margins (usually all porcelain or gold crowns, or depending on the tooth structure). It too can cause gingival irritation if there is an open margin or the crown margin is not flush with the tooth.
Hope this answers your question
If in doubt go for a second opinion