The Chompers Dental key in the Medical Pavilion is acquired by using Telekinesis through the broken window to the left of the door. There is a corpse hanging over the broken window. The key must 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 exploring Chompers Dental. There is a safe and other good items to be found inside. Note that both Telekinesis and Chompers Dental are near where you find the shotgun.