It would be better if you could post your x-ray in the forum, for a more conclusive and supportive suggestions. The possibilities could be many from a narrow calcified canal ( close to your interpretation of nerve blockage) to some pulp stones.

Hello there There seems to be a misinterpretation of the treatment,. There is nothing like nerve blockage... Is the root canal treatment completed, Or is it still underway, There can be stones in the pulp chamber (the place where you remove infected nerves), which can make negotiating and going deeper in the canals to clean them, whereby we keep some stone softening agent inside to help us go deeper at a later date... We sometimes wait to put a cap, if we need to see the response of root canaled treated tooth for any recurrence of pain or swelling, as it is still easier to go back to the tooth to treat then putting a cap and then face a situation like that... But that is rare... Hope this has helped you get more clarity Regards Dr Kaushal Shah

Hello..there might be pulp stone which causes blockage to approach the full length of canal.To dissolve pulp stone and to negotiate full length of canal dissolving solution is placed.wait for period of time,do not worry.It is nowhere related to thyroid as such.