I had a fiil in a month ago. now my tooth is sensitive to hot and cold foods. why is this happening??
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To put it in simple terms: the nerve of the tooth is getting used to a new material. Give it time and as the nerve recedes away from the filling, the sensitivity will go away. Sometimes this takes up to 6 months or so. Use sensodyne or any other sensitivity toothpaste for up to 4 weeks at a time. If the sensitivity gets worse, or if throbbing occurs, please contact your dentist.

Source(s):
I'm a dental hygienist and this is common