Help, Lost Teeth Panel

I got the first teeth panel in the manager's office, then got 2nd teeth panel in House of Mirrors, but when I go to put the teeth panels on the door of the House of Fears, one of the panels has disappeared from my inventory. I retraced my steps several times, thinking I must have dropped it or something. I even started the game over, but still the same result. Can anyone help me with this?