What does it mean if I have sensitivity to cold or sweets on a tooth after it has had a root canal?

Usually it means that the sensitivity is coming from an adjacent tooth and not the tooth that has had the root canal. For a tooth to experience these symptoms it must have vital pulp tissue and very few root canal teeth have any vital pulp tissue that remains. For that to be the case the tooth would need to have an extra root that was not compromised by the root canal treatment.

Usually the irrigants and medicament's that are used during a root canal will kill any vital pulp tissue. I have found that most people have a sensitivity that has a threshold of +or - one tooth, so that they often point to a tooth next to the one causing the symptom.

The best way for a dentist to pinpoint which tooth is causing cold sensitivity is to use an ice cube pr0be and place it on each tooth in a quadrant and see which tooth is the most sensitive to cold application.