Problems encountered during instrumentation :
Problems Encountered during Instrumentation

Loss of working length due to a blockage of the canal system
Ledging (shelf formation)
Breakage of instrument
Deviation from the normal canal anatomy
Zipping (elliptication)
Stripping/lateral wall perforation
Inadequate canal preparation
Overinstrumentation (beyond apical constriction)
Over preparation (excessive removal of tooth structure)
Under preparation (insufficient canal preparation)
Ledging.
Stripping / lateral wall Perforation .
Zipping.
All of the above.