3/4 crowns on four front teeth? (photos)

The most common reason that teeth shift in adults is gum disease.  Your dentist should be sure that your gums are healthy.  As for the pain, that concerns me.  The reason for the pain should be diagnosed and treated prior to doing crowns.   I am also concerned that your dentist is calling them 3/4 crowns.  I am concerned that he is doing veneers and calling them something else.  Veneers are great.  I have veneers and crowns.  It seems a bit sketchy to call veneers 3/4 crowns.

The more important question is "why are your teeth shifting?" Is there a periodontal (gum and bone support) problem or possibly an occlusal (the way your upper and lower teeth bite into each other) problem? Also, why is there pain and why are they turning grey? All of these questions should be addressed and answered BEFORE you agree to any treatment.

I'm not sure what the purpose of recommending 3/4 crowns is. There seems to be several issues that need to be addressed first before decoding on a course of treatment involving crowns. Number one would be to find out what is causing the exteme sensitivity and pain....are they abscessed and need root canals? Is there periodontal disease and bone loss going on? Is there an issue with your bite? Once these are addressed and handled then the need for crownsor not may become more apparent.