Space between crown and abutment: cause of bone loss?

The easiest way to remove the crown cemented to abutment if with tem-bond by bridge remover , if with final cem. By perforating the crown to screw out the abutment .

Without a film I would advise taking the perio advice over the labs advice. I don't get how an X-ray can be perfect yet one year later the crowns clinically are not fully seated?

Have you used a stock titanium abutment, a UCLA or a non-precious burn out abutment? How far is the crown margin from the implant head? Is it a bone level implant or a tissue level implant (tissue level would let you get away with more)? Did you do a probing depth charting? Whats the occlusion like? Is he parafunctioning? There probably more going on than just a small gap

It is to your advantage to post as much information as you can about the case you have questions about. A radiograph of the restored implant is really useful, and you are withholding necessary information for your colleagues to help you troubleshoot this complication. Also include as much information about the details of the case. Just like TRT said, whether the abutment was stock or custom, the margins of the crown were deep or shallow, the occlusion was checked and adjusted to be light when clenching, are there interferences in lateral or protrusive movements, do you see any redness or inflammation of the tissues? You can have a gap between the margin of the crown and the margin of a stock abutment that is placed too deep and still have a sealed margin if it is done on purpose, but most crowns are made to fit to the margin of the prepared abutment, so a gap usually indicates a poor fit, and that does not change in a year. In the absence of this information, I too would recommend you follow your periodontist's advise. Drill a hole through the occlusal of the crown to gain access to the abutment screw and remove the cemented crown. Assuming the abutment is worth salvaging, your laboratory can help you with that. Good luck!