INSTRUMENT SEPARATION ( Common in rotary files )
a) At apex
 Can leave it there if BMP almost done – if its tightly sealed at apex – if no periapical lesion – Good prognosis
 Cant leave – if did only minimal canal enlargement ie. BMP had only started – then complete RCT up to the file breakage – then do apicocectomy + retrograde filling.
b) At furcation / middle / coronal 3rd
 Poor prognosis

LEDGE FORMATION
 Ledge is a nick formed on the wall surface of a root canal, especially at the curves that prevent the instrument going further towards the apex- because it gets stuck there.
 Caused when instrument that is not pre-curved is inserted into the canal with excessive pressure
 Take a small size file – apply EDTA & do circumferential filing for long time- it will help smoothen out the ledge by cutting away excessive dentine.
 Thereby bypass the ledge
 EDTA helps dissolve & soften the area - chelation property
 After correction of ledge & bypass, the wall becomes very thin, therefore chances of perforation - most important complication