The key to Chompers' Dental in the Medical Pavilion is acquired by using 
Telekinesis through the broken window to the left of the door. There should be a 
corpse hanging over the broken window. The key should be grabbed with 
Telekinesis because it is hanging on a wall on the other side of the window. You 
can get Telekinesis in an area near here. You will need to get that first, but 
do not follow the arrow back to the rubble that you need to get rid of until you 
explore Chompers' Dental. There is a safe and other good items inside. Note: 
Both Telekinesis and Chompers' Dental are near where you find the shotgun.