PFM crown showing grey line from day 1, is it because dentist didn't push it up far enough?

This is a common occurrence in PFM crowns. The crown could have been designed to be slightly above the gumline, thus allowing you to notice this line of demarcation. Many dental professionals sometimes prefer this design based on the individual patient circumstances. 

Hi:
Unfortunately without a photo it is difficult to give you accurate advice.  Please post a photo the affected area.
Best,
Dr. Maddahi

Pfm crowns have been around for a long time and have a very good track record.  As far as being the “strongest” that is not true. We have a few options that are stronger such as a full gold crown or a full porcelain crown made from zirconia.  The gray line is where your tooth under the crown and your crown meet or the joint between the 2. Your underlying tooth shade is always darker than the crown. If the tooth has had a root canal  or has had a large amalgam (metal) filling for a long time the tooth will be much darker as well. I personally try to keep my restoration margins right at or slightly above the gum line for ease of cleaning. If all of the margins are above the gum line and you have a good fitting restoration you should have a better long term success rate for that restoration. If you do not want to see the margins than you need toplace them below the gum line but that will decrease the lifespan of the restoration. So long story short. If you do not like the esthetics of the restoration you should talk to the dentist that placed it.   Hope that helps

Joe