I have 11 crowns and every single one of them is slightly encased by the gumline...meaning that the gums actually healed tightly around them ever so slightly at the crownline. That's the way it should be.
In fact, once my dentist was concerned that my gum, which he had to do a lot of work on the tooth at the gumline so my gum over that tooth was quite a bit temporarily receded, wouldn't grow back down around the crown, and it did, quite nicely.
I don't know about actual millimeters, but crowns at the least should meet right at the gumline, if not slightly above, and the crownline should be covered by the gumline.
If the tooth presents a cosmetic concern then I think the margin of the crown should be placed 1/2 to 3/4 of a millimeter below the gum. There are crowns today made out of a very strong material(Zirconium) which extremely cosmetic and kind to the tissue.(Procera) I would ask your dentist about it.
the best scenario is for the margin (edge) of a crown to be supragingival, ie exposed and not covered by the gum tissue. The reason for this is that this way it can be easily cleaned, and it does not cause inflammation of the gum tissue, or recession of the gum tissue. When a crown margin is placed below the gumline, it is harder to clean, and can cause inflammation of the gum tissue and recession (which exposes the margin anyway). HOWEVER, since esthetics is an issue, most crowns are buried under the gum tissue, especially in the front. Personally, I try to make my margins above the gumline on the inside of a tooth, and above the gumline all the way around the tooth if it is in the back and wont be readily visible. Of course, I discuss all the risks and benefits with my patients before I begin work on a tooth. These are issues you should bring up with your dentist.
I have 11 crowns and every single one of them is slightly encased by the gumline...meaning that the gums actually healed tightly around them ever so slightly at the crownline. That's the way it should be.
In fact, once my dentist was concerned that my gum, which he had to do a lot of work on the tooth at the gumline so my gum over that tooth was quite a bit temporarily receded, wouldn't grow back down around the crown, and it did, quite nicely.
I don't know about actual millimeters, but crowns at the least should meet right at the gumline, if not slightly above, and the crownline should be covered by the gumline.
I have small teeth and a low gumline, so I can't help but show my gums even with the smallest smile, and you can't tell even one of my crowns from a real tooth.