Yes cut the "needle" teeth within 48 hours, yes they do hurt the sows underline, the clue is in the name "needle teeth" The teeth can cause a variety of problems namely "ripping/scoring" your sows teats thus causing an infection and leading to mastitis very painful for all and leading to the sow losing the infected teats for future breeding, therefore reducing the number of working teats, or the worst sceniaro losing the sow all together.
To get some idea what it feels like for the sow, ask all the ladies on the site who have raised and breast fed children how they would have felt if there child/children was/where born with a full set of needle teeth!! I think you know the answer!!!