It is impossible for a tooth to still be sensitive to cold after a root canal if the procedure has been completed properly because the tooth is now nerveless. The only exception is if the root canal was incomplete and there are still nerves in the tooth.
If it is neither of the above, the only other possibility would be you confusing the cold sensitivity with another tooth. Yes, we're saying that a different tooth may be bothering you.
Cold sensitivity after root canal is impossible
After a root canal has been completed, it is physically impossible for the tooth to be cold sensitive since the nerve has been completely removed. The procedure takes the entire tooth nerve out of the canals, thus leaving it nerveless.
Therefore without any nerves inside of the tooth, it should not be sensitive to cold nor other temperatures for that matter. Basically you have a hollow tooth with no nerves and no blood supply inside of it.
The only reason that your tooth can feel changes in temperature is because of the nerve inside of it. Imagine if you had nerve damage in your hand, it would be permanently numb because it can't feel anything. The same can be said for your tooth. The root canal permanently damages the nerve by taking it out.
In summary, a tooth that has undergone a root canal procedure should not be sensitive to cold afterwards at all.
Incomplete root canals can be cold sensitive
The one exception to when a tooth with a root canal can still be sensitive to cold is if the procedure was incomplete.
Situations with incomplete root canals:
Your dentist wasn't done with the root canal.
Your tooth has extra nerves that was missed.
Perhaps you were mistaken and you thought the root canal was finished but in reality, it is still in process. Patients sometimes think that the root canal is one appointment and that it is done in one visit. While that may be true in some situations, there are others where the procedure requires multiple visits for it to be complete.
Most notably teeth with large tooth abscesses may require multiple treatment visits before it is considered complete. This condition actually requires your dentist to place an antibiotic inside of the canal for at least 1-2 weeks before they can finish it by filling the canals. The root canal isn't finished until you return for that second visit to get the root filling.
If this is your situation and you're walking around with antibiotics inside of your tooth, the procedure is not complete. It wouldn't be unusual for you to have some residual cold sensitivity. However that should go away once you complete it during the second visit.
Alternatively your tooth could still be sensitive to cold after a root canal if it had extra nerves that were missed. It is not unusual for your tooth to have additional nerves inside that your dentist was not expecting.
A prime example would be molar teeth which often have 3 nerves inside but can have 4 nerves 50% of the time. However there are rare situations where it can have even more than 4 nerves!
Did you potentially have a missed nerve inside your root canal tooth? If that is the case you may need to return to your dentist to have them remove the missed one.
Referred cold sensitivity
Last but not least, one of the most common situations for cold sensitivity after a root canal is referred sensitivity. In other words, that cold sensation that you're feeling is NOT coming from your root canal tooth but rather from an adjacent tooth.
We get this situation a LOT, where a patient comes in and points to a tooth saying it has cold sensitivity. We look at the x-ray and the tooth has already had a root canal done so that is simply impossible.
Nonetheless, we begin to conduct cold tests on the teeth and the results are what we would expect.
Tooth with root canal has no response to cold.
Tooth adjacent to the root canal one responds to cold.
Essentially, the patient is mixing up the signals for which one is actually feeling the cold. They "think" it is the one that had the root canal but it is actually the adjacent tooth! We typically have to give the patient a mirror and do the cold test in front of them to prove it to them.
The image above shows a tooth with gum recession. If you have a tooth like this next to the endodontically treated tooth, you may mistake the sensitivity coming from it.
The root canal procedure removes the nerve from the tooth so it should be impossible for it to feel any cold afterwards. However if you're still feeling a cold sensation, it could be a complication such as a missed nerve or the procedure is simply incomplete but you thought it was. Both of those situations would require a visit back to the dentist.
Although in our experience the most likely scenario is that an adjacent tooth is having cold sensitivity and not the root canal treated one. You're just mixing up the signals. Also, if it is the adjacent tooth, just because it is cold sensitive it doesn't mean it needs a root canal.