some people think that they will use their teeth on other pigs (or you!). we raised feeder pigs and did NOT do anything with their teeth. nor did we cut their tails. our pigs did not injure each other nor did they chew on each others tails. however they were raised on pasture so they had plenty to do.
When a gilt or sow has a large litter, you often need to clip the "needle" teeth. There are 4 needle sharp teeth on both the top and bottom jaws on each side. If they are not clipped, the piglets will sometimes injure their siblings on either side when they nurse. The injured pigs will often get an infection from these injuries and stop nursing. They then starve out. Baby pigs stake a claim to their own individual nipples, and will fight anything that is on either side. They will stay with their own nipple till weaning.