There are no codes to the doors in the Dental area. To get into Painless Dental (the room with the turret) just jump up on the chair next to the window while the turret is disabled. Then hop through the broken glass. To get into Chomper's Dental you need the Telekinesis Plasmid (which can be found in Dandy Dental) to grab the key hanging on a peg inside. It is visible through the broken window with a body hanging out of it.