Causes of Grey Lines on Veneers 1 Year Post Op?

Without knowing the history of your case it is hard to be 100% sure. However, I would agree that it is probably a bonding issue most of the time. Where you gums bleeding when the temporaries were take off?? How long where you wearing the temporaries?? It is possible that some blood or saliva contaminated the bonding procedure, and that the gray lines are showing that. Have any of the teeth had root canals?? Sometimes after a root canal the root can turn dark and give the tooth a gray appearance. If your veneers are over contoured at the gum line and rough, it may be possible to have the dentist recontour them, and see if that helps?? Do you smoke?? It could be possible the gray is staining of the resin cement used  due to smoking. I would recommend recontouring them at  the gum line first. However, be prepared if you do not get the results that you like, you may need to have them redone.

If the cause is  only the "bulkiness" of the margins, resulting in bacterial build-up, then it would be worth trying to polish the margins "razor-thin", and see if that helps. If the cause is "poor bonding technique", however, then you have no choice but to remove the veneers and begin again. You really have nothing to lose (except time and a few dollars) trying to "thin - out) the margins first, unless it's obviously a poor bonding.