This is another way to make teeth-doors.  Thanks goes to Jaap Menist for writing this in the first place.

STEP 1: Create the following sectors. All are valid player space.

           +------------------+         +---------------+
           |                  |         |               |
           |                  +---------+               |
           |                  |  +---+  |               |
           |                  |  | d |  |               |
           |                  |  +---+  |               |
           |       A          |    C    |       B       |
           |                  |  +---+  |               |
           |                  |  | e |  |               |
           |                  |  +---+  |               |
           |                  +---------+               |
           |                  |         |               |
           +------------------+         +---------------+

          Sector 'A' and 'B' are the rooms, sector 'C' is the door and sectors 
          'd' and 'e' are the teeth in the door. 

STEP 2: Make all floors and ceilings equal height. (When the door is finished you may raise the ceiling of 'A' or 'B' if you like).

STEP 3: Now here's a nice one; The floors of sectors 'd' and 'e' have to be lowered, so holes appear. The amount you have to lower each sector can be calculated like this:

  ('PixelHeight of door' / 3) - 2

So you divide the door-height by 3 and subtract 2 from the result. This is the number of times you have to hit page-down when lowering the floor of sectors 'd' and 'e'. Weird eh? It looks as if the teeth move 3 times as fast as the door. Now you have two pretty deep holes where the teeth will sink into.

STEP 4: Put sector effectors in 'd' and 'e' and give them a low-tag of 22. Give them the same unique high-tag number. Put the effectors on the floor of 'd' and 'e'.

STEP 5: Lower the ceilings of 'd' and 'e' to their floors. In other words, put the teeth all the way down.

STEP 6: Give sector 'C' a low-tag of 29 and the same high-tag you issued for high-tags of the effectors in 'd' and 'e'. So sector 'C' high-tag is equal to the high-tag of the effectors in sectors 'd' and 'e'!

STEP 7: Lower the ceiling of sector 'C' to the ground and you're done !

STEP 8: You can put a music sprite in sector 'C' for a door sound and also an effector sprite to make the door auto-close. Now you have a door which is closed in the initial state, when it opens you see the teeth shoot up and if you stand in the doorway looking down into the holes, you get squished when the bastard shuts its mouth :)