Yeah, the clamp can cause some discomfort in the gums. A root canal can as well, because all the dental work inside the roots causes stress on the connective tissue that keeps your tooth in its socket. How long often depends on how the RC went and whether or not the tooth was abcessed or infected.
I usually have little post-RC pain and only on the day when they're pulling the nerve out. Though on my retreatment, my more painful post-appointment pain was when they were redoing the canals.
if you have increasing pain and swelling, you should contact your dentist, or if it doesn't lessen after3-4 days.
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Gum very painful after root canal 
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