caused by:
1] large instruments out of sequence and
2] insertion of instruments short of working length or
3]use of inflexible instruments in a curved root canal
4]poor design access cavity prevent direct access to apical third of root canal
The access curvature in the coronal part of canal may prevent negotiation of an instruments through the apical curvature in a fine, tortuous canal and may result in ledge formation
ledges and blocked canals are recognized when the instrument cannot be reinserted to its established working length.
How to remove ledge
- Locate its position by inserting an instrument until it is blocked, verify the depth by the radiograph
- Once ledge is located, irrigate within sequence with sodium hypochlorite and EDTA.
- Explore ledge-take a small file 10 or 15 in which a severe curvature has been made from the tip extending about 1 to 3mm up the blade.
- When the ledge is reached, the instrument is retracted slightly and rotated to allow the curved tip to bypass the ledge and the instrument is teased apically past the obstruction
- Patiently try again if initial attempts are successful once the ledge is bypassed, do not remove the instrument rather start the circumferential filing of the canal to remove the ledge before witdrawing the instrument from the canal.
- Repeat the procedure with larger instrument and recapitulating with similar size until the ledge is filed away and desired enlargement at the established working length is made.
- If ledge cannot be bypassed, clean, shape and fill the RCto the level of obstruction.
- If the terminous of the filling is closed to the canal apex, monitor the toothfor healing and repair.
- If endo treatment is unsatisfactory consider an alternative treatment procedure such as retrograde amalgam surgery, hemisection or radisectomy, internal replantation or extraction.
