I believe it would be a nearly perfect world if the only type of margin I ever cut was supragingival. No retraction issues, no worries about tissue management and margins that any patient can clean with a toothbrush in addition to always bonding to enamel at the margin. Unfortunately I don’t get to always do supragingival margins, but more and more these days I can. In the early years of my practice when my esthetic restoration was a porcelain fused to metal crown with metal margins we placed the margins as far subgingival as possible without violating the biology. Why, to hide the ugly metal ring of the restoration. Today, all ceramic restorations have become esthetic enough that we no longer have to hide our work.
The advantages of supragingival margins are clear, but what are the limitations? The first is contour change of the final restoration, If we are attempting to alter the rotation of a tooth or close a black triangle supragingival margins do not allow enough running room for the technician. Next, we have to consider color changes. If we are closely approximating the final color to the existing color it works great. Most of our all ceramic materials are translucent enough to allow the natural tooth color to create beautiful effects and a contact lens effect at the margins if we do thin veneers. If we are lightening the final restorative color more than one shade we need to place the margins at least equigingival if not subgingival to mask the old tooth color. Lastly, for patients with risk of acid erosion or high caries risk we may chose to place the margins subgingival to take advantage of the sulcular fluid to bath and protect the margin. Certainly int he posterior I am leaving more and more of my margins above tissue and utilizing materials that can be bonded and adhesive techniques for retention.