Hard-shelled foods will keep his teeth trimmed--there is nothing you can feed him to file his teeth down. Once the teeth are overgrown you will have to hand-trim yourself.
http://www.**************.com/forum/library/hospital/dentistry/
http://www.**************.com/forum/library/feeding/feeding-your-puffers/
like just about all puffers they need to be feed hard foods or there teeth will over grow and will stop it from eating and them you would have to clip them which is hard to do and its not fun at all puffer teeth are pretty sharp