Some needles get dull from heat/friction when people used to do the "jab" the hair into the head thing (they didn't know any better). This usually doesn't happen if you root correctly. But like Tina W said... you usually are able to root many dolls with it. You should be able to tell after a while what the needle feels like rooting so you can tell if it seems dull. You'll get the hang of it :)
Barbed needles do not really get dull to the point that they do not work. German forked needles will, however. Even then, though, you can still do many dolls with the same needles.
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