Few questions I need to ask you.
1.If the Rct treated teeth was restored with crown(cap)?
2.suddenly you have started feeling pain or sensetivity?
3.Did u chew any hard substance and from than your pain has started?
4.do you see any visible metal exposed from your crown?(if restored with crown)?
For reliving pain instatanly you can take any analgesic drug.But don't wait if you see you pain still persist.
Next Steps
immediately go to your nearby dentist and go for an x ray.
there may be fractured, poor quality of Root canal which may lead to a infection .
or secondary caries under the restoration.
Health Tips
you have to be very cautious if you see any sign symptom of swelling or difficult in chewing or feel pain when you close the mouth and your teeth come in contact.
Don't do any self medication with out any appropriate consultation.