EMPLOYEE WAS ENTERING THE CAB OF A CATERPILLAR 988F ENDLOADER. AS HE SAT HIS LUNCH BOX ON THE CAB FLOOR, HIS HARD HAT FELL OFF. HE ATTEMPTED TO CATCH THE HARD HAT WHILE BENDING OVER. HIS MOUTH CONTACTED THE SUPPORT GUARD SURROUNDING THE JOYSTICK CONTROL. THE CONTACT DAMAGED A FRONT TOOTH.