Ledging and blockage of root canals

Ledge formation

A ledge is an iatrogenically created irregularity (plat- form) in the root canal that impedes access of

instruments (and in some cases irrigants) to the apex, resulting in insufficient instrumentation and incom- plete obturation. Thus, ledges frequently contribute to ongoing periapical pathosis after root canal treatment. Ledging of curved canals is a common instrumentation error that usually occurs on the outer side of the curvature due to exaggerated cutting and careless manipulation during root canal instrumenta- tion. Ledges are formed either within the original canal path or by creating a new false canal.Occasionally, even skilled and meticulous clinicians may create a ledge within a root canal while treating teeth with unsus- pected aberrations in their anatomy. In cases where the Intentional creation of ledge in cases of destroyed apical constriction.

Causes of ledge formation

The most common causes of ledge formation are:

• 􏰀 Incorrect or insufficient access cavity preparation that does not allow adequate and unobstructed
• access to the apical constriction.
• 􏰀 Incorrect assessment of root canal direction.
• It must be remembered that most canals are curved in at least one plane and conventional radiographs detail mesiodistal but not buccolingual curvatures.Approximation of curvature of the file to that of the canal reduces iatrogenic errors.
• 􏰀 Incorrect length determination of the root canal 􏰀 Use of non-precurved stainless-steel instruments in curved root canals. Prebending the file according to the canal curvature may minimize the risk of iatrogenic errors. However, over curved instruments may also lead to ledge formation.
• 􏰀 Failure to use the instruments in a sequential order (use of large-sized instruments without having previously used smaller instruments in the same root canal). Skipping sizes during instrumentation and erroneous length determination are the most com- mon causes of ledge formation within the original canal path. The novel technique proposed by Yared where the canal is negotiated to the working length with a size #8 hand file and then the canal preparation is completed with an F2 ProTaper instrument used in a reciprocating movement needs to be investigated as it is the first technique that does not follow a sequential order of instruments.
• 􏰀 An attempt to retrieve or by-pass a fractured instrument or a foreign object (pin, post, etc.) from the root canal.
• 􏰀Occasionally, after removal of pre-existing filling materials or fractured instru- ments from the root canal, dentists may encounter ledges that had already been formed by previous attempts to negotiate the canal.

Management

When a ledge is suspected, root canal instrumentation should immediately cease and efforts should be con- centrated on regaining access to the apex using small- sized hand stainless-steel instruments.

 For this purpose:

• 􏰀 A high-quality radiograph is obtained with the instrument that created the ledge in place to verify it and reveal its location.
• Copious irrigation with sodium hypochlorite and frequently replenished chelating agents is required throughout the procedure.
• 􏰀 Pre-enlargement of the canal coronal to the ledge is obtained by removing any curvature or obstruc- tions. This is crucial as it will enhance the tactile sensation needed for the manipulations to follow.
• 􏰀 The ledge is first probed with a precurved K-file ISO size 08 or 10. Hand instruments provide a better tactile sensation and are thus preferred to rotary instruments. The properties of NiTi instru- ments allow them to remain more centered and preserve the root axis significantly better than stainless-steel instruments when used either manu- ally (25, 49–51) or in a rotary mode (52, 53), but these instruments appear less efficient when by- passing ledges. In order to by-pass the ledge and gain access to the apex, the shortest instrument that can reach the level of the ledge should be used in a ‘watch-winding’ and gentle ‘picking’ motion of a short amplitude to look for a catch. Shorter instruments provide more stiffness and allow the clinician’s fingers to be positioned closer to the tip, resulting in a greater tactile sensation and control over the instrument. Directional tear-shaped rub- ber stops can be used on the file in order to orient its curvature. If the instrument progresses apically in the canal, it is prudent to stop the instrumenta- tion and take a working radiograph in order to verify its direction. This will provide valuable information about the position of the instrument in relation to the canal and will prevent additional iatrogenic errors such as transportation and per-
• foration.
• The use of endodontic pathfinders and C-files that
• have originally been introduced for the initial instru- mentation of the root canal can be very helpful when attempting to by-pass a ledge. However, there is no scientific documentation available regarding the com- parative efficacy of pathfinders to negotiate narrow root canals and cut dentin walls.
• 􏰀 Once the file used for ledge probing and by- passing, or a longer instrument if the length of the short instrument is not adequate, reaches the desired length, a radiograph is taken with the file in place to re-confirm and re-determine the work- ing length. This can also be easily, accurately, and preferably done with the use of an electronic apex locator, particularly in cases where a working radiograph was obtained earlier.
• 􏰀 Root canal instrumentation follows. Filing is performed under copious irrigation with short vertical strokes pressing the blades against the ledged area and always keeping the file tip apical to the ledge. 
• Chelating agents are also very useful. After the K-file reaches the estimated working length freely, a larger file is then used in a similar manner. Instead of proceeding to the next size, the use of the same file after cutting off 1 mm of its tip has also been recommended.This approach needs to be used with caution as the new ‘active tip’ of the instrument has difficult-to-smooth edges and may lead to new ledge formation. Intermediate file sizes are now available and can be helpful. Instrumentation is completed with anti-curvature filing in an effort to blend the ledge into the canal preparation. Once the canal has been fully nego- tiated with stainless-steel hand files of ISO sizes 15– 20, rotary NiTi instruments can be used for further canal enlargement. A NiTi instrument such as a manual ProTaper F1 precurved with orthodontic birdbeak pliers  or GT hand files precurved with Endo Bender pliers (have also been advocated to reduce or eliminate the ledge. The greater taper of these files quickly smooths the ledge.

Canal blockage

Blockage by dentin chips and/or tissue debris is an obstruction in a previously patent canal that prevents access and complete disinfection of the most apical part of the root canal system. 

The blocked canal may contain:

• 􏰀 compacted dentinal mud (most frequently)
• 􏰀 residual pulp tissue.
• 􏰀 remnants of filling materials (in cases of re-
• treatment).

Management

Canal blockage is corrected by instrumenting the root canal. 

For this purpose, 

• A precurved hand stainless-steel K-file ISO size 08 or 10 is inserted into the canal under copious irrigation with NaOCl and chelating agents and rotated circumferentially to detect a weak ‘sticky’ spot in the mass of the debris. Once this is detected, the file is carefully rotated passively in a ‘watch-winding’ motion with simultaneously small in-and-out strokes until it reaches the desired working length. This is followed by circumferential motion of the same file and is repeated with larger sizes until optimum enlarge- ment. If the blockage occurs at a curve or a bend of the root, gently precurving the instrument to redirect it is also effective. Caution must be exercised in these cases as a ledge or a lateral perforation can be caused, particularly if large sizes of Endodontics instruments are used.
• If the canal cannot be renegotiated to its desired working length due to canal blockage, it is obturated and then reviewed periodically. In case of an existing periapical lesion or if one develops post-operatively, surgical endodontics might be considered. The timing and type of surgical intervention follows the same strategy as with ledges.

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