When does the screw need replacing?

Screws can be used over fifty times.

Screws with a blunt thread should only be used for thick-walled root fragments with firm dentine.

Finger test for checking the screw thread:

         Hold the screw head with your thumb/index finger.
         Grip the thread with your opposing thumb/index finger.
         If you exert tension on a blunt screw your fingers will slip over
         the thread.  

Important tip:
Keep a new screw separately* and use it only for extrusion treatment and for situations where luxation is not possible and/or the root fragment has a thin wall.

* in the Benex set are always two screws:
         a little used / newer (no marking)
         and an older one (marked with a diamond on the screw head).
The newer is used only for delicate roots and during extrusion.
The older one is used usually, until it no longer cuts, then it is replaced with a new one and the remaining screw is marked as "older"