What can be done about my upper anterior crowns that are suddenly shifting after 15 years?

  Hello. Yes, you can replaced it but is a metal crown over implant for the next crown do one in Zirconia that is more esthetic. 

Yes, that is possible through orthodontic treatment to extrude posteriors. I advise visiting an orthodontist to check cephalometric values and how much correction is required and whether is it possible through brace treatment.

I would take the guard to the dentist and have them adjust it in the area of the front teeth. Sometimes a night guard will fit so tightly, it will cause discomfort in some of the teeth.

Yes, it can be possible. Go to one specialist to value if will be durably, esthetic and functional and get the best option the doctor proposed you. 

There are a number of different factors that go into the decision of crowning vs. extracting your wisdom tooth. The pertinent clinical findings that only your dentist can determine gives her the unique ability to make this call. I can, however, tell you that removing your wisdom tooth will not ...

A well prepared tooth and a properly made crown, should NOT REQUIRE so much adjustment as to expose 50% of the underlying metal. You should consult with that Dr. and express your concern. You should also know that there are crowns that can be made today that do not have ANY metal, and are strong...