I completely closed the game and reloaded, and my scanner picked up 2 new teeth, which just happened to be how many I needed at the time.
I saved, quit, and reloaded and still the scanner was just showing that one tooth in the void and stalkers were still not dropping. Gave the stalkers metal to play with and heard the crunch repeatedly, but no teeth dropped. My Scanner Room saw nothing but one impossible to reach tooth under the ocean floor. Every Google search gave me the answers like the ones in this thread.
I was having this problem a few days ago. Have you tried completely re-loading the game (not just quitting, but actually closing the app)?
