Hello, I'm Wes, and I'll be assisting you today.
The plastic tooth is part of the gear motor assembly that has broken off.
The bad part about that is the part will need to replaced and the cost is usually $50 to replace with parts and labor. It may be more cost effective to purchase a new printer.
Check first to see if you printer is under warranty that way it can re replaced instead.
Let me know if you need additional help and please rate my answer below.