I found this post on another unmentionable forum, and thought it may be helpful to you.
trimmed my 3 (1") SA puffs teeth & will probably have to do it again. It's hard to get them to eat enough snails. My gsps (5") & fahaka (8") get a regular diet of crablegs, shell-on shrimp, oysters, clams, mussels & crayfish, to keep their teeth nice & short.
I took my SAs & put them (1 at a time) in a large Coolwhip container, with tankwater. I held ther face under the water with a net (my hands were around the net & fish), so they wouldn't suck any air when they puffed. I clipped their teeth with sharp cuticle nippers. They deflated as soon as I let go. You have to clip quickly so as not to shatter their teeth. Be careful not to cut their mouth. A couple of them did crack, but it's still better than dying because they can't eat. I did a loose a puffer to long teeth.
I really hope that helps you. It's worth a try.