Inter-Proximal Reduction (IPR) is a method of gaining space in order to re-align teeth. This is sometimes done due to tooth size discrepancies or large amounts of crowding. The IPR is always limited to be no more that a quarter to half a millimeter of enamel and should never extent beyond enamel. Because only enamel is reduced there is almost never any discomfort following the IPR. Fluoride can be used to re-mineralize the exposed enamel rods and make sure they remain cavity free.
If your tooth is sensitive is may be for many reasons, go back to your dentist, this may not be related to the IPR or perhaps a small amount of root surface was abraded leading to transient sensitivity. Its best to get this checked out.