It can be a drain - so that the pus can drain from the sac in the jaw and the open tooth (canal) with food does not "burn". if this is the case, then during the next treatment, the dentist pulls out the rods, cleans the canal again and seals the crown (or re-drains it). But it can also be a pin (strengthening the root of the tooth) - it remains in the tooth. : o Why didn't you ask the dentist ???