Crown and screw fell off! What do I do?

You should go to your dentist immediately and see if the crown and screw are intact. If so, the crown can  be placed back into its proper position, the screw tightened and then torqued to 32 or 35  n cm.  If this crew has broken, it will need to be removed and replaced with a new screw.  The crown  can then be repositioned and then the new screw can be tighten and torqued to hold the crown in position.  

From your description, it sounds like your implant crown/abutment has come loose.  This can sometimes happen.  Simply save all of the parts and pieces that came out of your mouth (crown, abutment, screw, etc.) and call your dentist.  He/she can likely put the abutment back onto the dental implant (with a new screw of course!) and then seat the crown back onto the abutment.  You may need to get a tiny bit of anesthetic to have this done as the gum tissue over your implant will have likely grown a bit with the abutment/crown out of the mouth.  A laser can remove the extra gum tissue very quickly and no sutures should be required.  I hope this helps!  Good luck!