Ledging and blockage of rootcanals during canal preparation:causes, recognition, prevention,management, and outcomesTHEODOROS LAMBRIANIDIS

Ledge formation, that is the iatrogenically created irregularity in the root canal that impedes access of instruments to the

apex, and canal blockage caused by packing dentin chips and/or tissue debris are the least-studied parameters of root

canal instrumentation. Variables associated with ledge formation and canal blockage by dentin chips and/or tissue debris

are presented. Emphasis is given to their most common causes, recognition, management, prognosis, and prevention.

Received 20 January 2008; accepted 8 June 2008.

Introduction

Several methods and principles have been developed for

cleaning and shaping the root canal system, and their

efficacy has been the subject of numerous studies. The

results are partially contradictory; therefore, no definite

conclusions can be drawn on the usefulness of hand and/

or rotary devices (1). There are various sources of

discrepancy among studies: experimental designs, meth-

odological considerations, evaluation criteria, number of

hand or rotary instruments analyzed, and/or techniques

evaluated. In the years of evidence-based dentistry, these

discrepancies, coupled with the immense development

of new technologies, instruments, and materials, do not

allow for a reliable comparison between the results of

different studies and particularly their correlation with

clinical procedural accidents.

Procedural accidents can interrupt the sequence of steps

during root canal treatment at any time and stage as all

steps are interdependent and equally susceptible to

iatrogenic errors. In most cases, these accidents are the

result of the dentist’s erroneous manipulation and

inattention to detail. In a few cases, they may be totally

unpredictable. Their management may require prolonged

chair time and effort from the dentist and sometimes can

be impossible. Procedural errors per se do not jeopardize

the outcome of the endodontic treatment unless a

concomitant infection is present. In these cases, their

impact is greater as they act as an impediment to the

necessary intra-canal procedures. Thus, when a procedur-

al accident occurs during the endodontic treatment of

infected teeth, there is always a potential for failure (2).

Occasionally, during root canal instrumentation,

instruments cannot be advanced to full working length

in a previously patent canal. This may be due to ledge

formation or canal blockage by foreign objects such as

restorative materials, separated instruments, cotton

pellets, paper points, remnants of calcium hydroxide

dressings, or packed dentin chips and/or tissue debris.

Ledge formation and canal blockage caused by packing

dentin chips and/or tissue debris are the least-studied

parameters of root canal instrumentation.

The aim of this paper is to present all aspects related

to ledge formation and canal blockage by dentin chips

and/or tissue debris with an emphasis on their most

common causes, recognition, management, prognosis,

and prevention.

Ledge formation

A ledge is an iatrogenically created irregularity (plat-

form) in the root canal that impedes access of

56

Endodontic Topics 2009, 15, 56–74All rights reserved

2009 r John Wiley & Sons A/S

ENDODONTIC TOPICS 20091601-1538

instruments (and in some cases irrigants) to the apex,

resulting in insufficient instrumentation and incom-

plete obturation (Fig. 1). 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 (3). In a prospective study among patients who

received root canal treatment performed in two visits

by undergraduate students using a step-back technique

by means of hand stainless-steel files, iatrogenic errors

were detected and ledge formation was found to be by

far the most frequently encountered error (4). Ledges

are formed either within the original canal path or by

creating a new false canal (Fig. 2). 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

apical constriction has been disrupted by resorption,

overinstrumentation, or apicoectomy with no root-end

filing, an apical plug with a plethora of materials (5),

preferably MTA (6–9), or modification of instrumen-

tation and obturation (5, 10) have all been proposed.

Modification of instrumentation involves re-determi-

nation of the working length and re-instrumentation in

order to intentionally create a ledge and thus a new

apical stop, approximately 1.5–2 mm coronal to the

original working length (Fig. 3).

The incidence of ledging and the factors associated

with its occurrence have not been studied adequately.

Overreporting of ledges that can result as short

obturations may be inadvertently included as such,

whereas underreporting can result due to the inherent

Fig. 1. Ledged root canal: characteristic cases.

Fig. 2. (a) Ledge formed within the original canal path asa result of skipping instrument sizes or erroneousworking length estimation. (b) False canal and a ledgeas a result of misdirection of files.

Fig. 3. Intentional creation of ledge in cases of destroyedapical constriction.

Ledges and blockages

57

limitation of radiographs to distinguish the canal

terminus. A study on 660 endodontic re-treatments

revealed that 25% of root canals were re-treated on the

basis of technical reasons and that 11% of root canals re-

treated due to osteitis were obstructed at the level of

the previous filling (11). Although the actual role of

ledging in these cases can only be speculated, it was

undoubtedly a major cause for these obstructions.

Tooth location, canal curvature, instrument design,

alloy properties, instrumentation techniques, and

operator experience are among the important factors

implicated in ledge formation.

In an attempt to identify the variables associated with

ledge formation in maxillary and mandibular first and

second molars treated by undergraduate students, it

was discovered that the main factor consistently related

to the presence of ledges was canal curvature (12). As

canal curvature increased, the number of ledges also

increased. Canals with a curvature o101 according to

Schneider’s scale (13) were rarely ledged, whereas

canals with a curvature 4201 were ledged over 56% of

the time (14). Canal location was also found to have

some effect on the incidence of ledging. The mesio-

buccal and the mesiolingual canals were more fre-

quently ledged than the distal, lingual, or distobuccal

canals (12). The decisive role of canal anatomy was also

verified in a micro-computed tomography study that

compared the effects on canal volume and surface area

of four preparation techniques using NiTi K-files,

Lightspeed instruments (Lightspeed Inc., San Antonio,

TX, USA), ProFile .04 (Dentsply Maillefer, Ballaigues,

Switzerland), and GT (Dentsply Maillefer) rotary

instruments in extracted human maxillary molars. A

strong impact of variations in canal anatomy was

demonstrated while very few differences were found

with respect to instrument type (15).

The clinical factors associated with ledging were

examined in teeth treated by undergraduate students

and endodontists (14). This study revealed that 51.5%

of the canals treated by students had been ledged

whereas the percentage was 33.2% in cases with intact

pulp cavities treated by endodontists and 40.6% in re-

treatment cases. Evaluation of 388 root-filled teeth

treated by undergraduate students (16) revealed that

the frequency of ledged root canals was significantly

greater (Po0.001) in molars than in anterior teeth. In

molars, 105 out of 270 root canals (38.9%) had been

ledged. The mesiobuccal, mesiolingual, and distobuccal

root canals were the most frequently ledged. Canal

curvature was found to be the most important factor

associated with ledges (16) (Tables 1 and 2). Determina-

tion of the shaping ability of Mity Roto 3601 (Loser,

Leverkusen, Germany) and Naviflex (Brasseler, Savan-

nah, GA, USA) rotary NiTi instruments using a step-

down approach in simulated canals of four different

shapes in terms of angle and position of curvature also

verified the importance of canal curvature (17). Statisti-

cally significant differences (Po0.001) between canal

shapes occurred in relation to the incidence of ledges. In

particular, ledges were more frequent in canals with 401

acute curves than 201 curvatures. The distance of ledges

from the end point of preparation was also significantly

Table 1. Percentages of ledged root canals in all teethaccording to canal curvature. From Eleftheriadis &Lambrianidis (16)

Curvature

Ledged

root canals

Number of

root canals Percentage

Straight 19 320 5.9a,b

Moderate 90 223 40.4c

Severe 45 77 58.4

Total 154 620 24.8

aStatistically significant difference (Po0.001) betweencanals with straight and moderate curvature.bStatistically significant difference (Po0.001) betweencanals with straight and severe curvature.cStatistically significant difference (Po0.05) betweencanals with moderate and severe curvature.

Table 2. Percentages of ledged root canals in molarsaccording to canal curvature. From Eleftheriadis &Lambrianidis (16)

Curvature

Ledged

root canals

Number of

root canals Percentage

Straight 11 72 15.3a,b

Moderate 69 157 43.9

Severe 25 41 61

Total 105 270 38.9

aStatistically significant difference (Po0.001) betweencanals with straight and moderate curvature.bStatistically significant difference (Po0.001) betweencanals with straight and severe curvature.

Lambrianidis

58

affected (Po0.01) by canal shape (17). On the contrary,

superimposition of projected radiographs taken in

buccolingual and mesiodistal views before and after

preparation using traditional and flexible stainless-steel

hand instruments with three different handpieces com-

bined with stainless-steel files and sonically and ultra-

sonically powered instruments in extracted human roots

with straight, apically curved, and entirely curved canals

suggested that ledge formation as well as coronal

transposition of the apical stop, uneven wall contour,

and incidence of zips were independent of root canal

morphology (18).

The roles of the instrumentation technique and the

type of instruments have also been investigated in relation

to ledge formation. Comparison of the reaming and filing

instrumentation techniques in a study of 520 roots

treated by supervised dental students showed a 10%

incidence of lateral deviations. The incidence of ledging

and instrument breakage was more frequent with the

reaming technique whereas root perforation and over-

filling occurred more often with the filing technique (19).

An ex vivo comparative study of 51 curved canals in

human teeth instrumented with K-files and a step-back

technique, K-files and a crown-down technique, sonic

instrumentation with Shaper-Sonic files (Medidenta

International Inc., Woodside, NY, USA), and the

NiTiMatic (N.T. Co., Chattanooga, TN, USA) system

revealed no difference between step-back and crown-

down techniques in terms of straightening while crown-

down and sonic techniques produced more ledges and

NiTiMatic did not produce any ledges (20). Ledging has

also been described with ultrasonic instrumentation (21).

It is worth noting that root canal preparation using laser

irradiation techniques might result in more ledge

formation than conventional hand techniques with K-

type files (22) or rotary instrumentation (23).

The material and the design of the instrument also

seem to affect the incidence of ledge formation because

the shaping ability of an instrument, i.e. the centering

ability (maintenance of the original canal path), and the

prevention of aberrations depends on the alloy type, the

type of cutting tip, the geometry of the cross-section, the

taper, and the size (24). Studies, mostly on acrylic blocks,

regarding the creation of zips, elbows, perforations, and

ledges revealed fewer errors with NiTi than with

stainless-steel instruments (25–29). Ciucchi et al. (30)

reported that the use of modified instruments eliminated

the ledging and transportation effects seen with

conventional rotating instruments used in curved canals.

Tip design has a strong impact on the final canal shape

and affects the ease with which a canal can be

instrumented. When three differently designed file tips

were compared, specifically pyramidal (sharp transition

angles and a forward-cutting ridge on the face), conical

(sharp transition angles and a smooth face), and biconical

tips (reduced transition angles and dual-guiding faces),

ledges were more frequently found with pyramidal-shaped

tips while biconical tip files produced the least transporta-

tion and no ledges (31). Changing the tip design of

Quantec NiTi instruments (Tycom Dental, Irvine, CA,

USA) from non-cutting to ‘safe-cutting’ increased the

prevalence of canal transportation, zipping, elbows,

ledges, and perforations (32, 33). Incorporation of an

active, simple, triangular, and cross-sectional geometry

instead of the more passive U shape did not seem to

predispose canals to the creation of zips, perforations, or

ledges (34) whereas a more convex, triangular, and cross-

sectional geometry tended to straighten curved canals

(35). Increasing the taper and especially the adoption of a

variable taper along the shaft (36–41), as well as increasing

the size (diameter) of NiTi files, resulted in increased

stiffness (42, 43), leading to canal aberrations in curved

canals, and thus their use fails to provide any advantage

compared with the use of stainless-steel files (44).

Comparison of the shaping effects of instrumenta-

tion using a torque-control, low-speed engine in a

crown-down technique with ProTaper, K3, and RaCe

NiTi rotary instruments in simulated canals with an

S-shaped curvature also revealed the importance of the

instrument used. A tendency to ledge or zip at the end

point of preparation was found with ProTaper files as

opposed to the less tapered, more flexible K3 and RaCe

instruments (45).

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 (Fig. 4).

It must be remembered that most canals are curved

in at least one plane and conventional radiographs

detail mesiodistal but not buccolingual curvatures

(46). Approximation of curvature of the file to that

of the canal reduces iatrogenic errors.

� Incorrect length determination of the root canal

(Fig. 2).

Ledges and blockages

59

� Use of non-precurved stainless-steel instruments in

curved root canals (Fig. 4). Prebending the file

according to the canal curvature may minimize the

risk of iatrogenic errors. However, overcurved

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 (Fig. 2). The novel technique proposed by

Yared (47) 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 (Fig. 5).

� Re-treatment (Fig. 6). 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 (Fig. 7).

� An attempt to negotiate a calcified or a very narrow

root canal (Fig. 8).

� During post-space preparation after the completion

of root canal treatment (Fig. 9).

Fig. 4. Ledge formation in a curved root canal. (a)Pre-operative X-ray. (b) Insufficient access cavity pre-paration, combined with the use of non-precurvedinstruments, led to ledge formation.

Fig. 5. Ledge formation in both mesial canals of a mandi-bular molar during efforts to by-pass and retrieve aseparated instrument from each canal. From Lambrianidiset al. (48).

Fig. 6. Ledge formation during re-treatment. (a) Incom-plete obturation with the presence of materials with twodifferent opacities in the middle of the root canal in thepre-operative X-ray. A distance of 0.5 mm between thematerials can be seen. (b) Failure to retrieve or by-passboth segments of the material ‘diverted’ the instrumentsfrom the root canal and led to ledge formation. FromLambrianidis (5).

Lambrianidis

60

Recognition

Ledge formation is easily recognized because the

endodontic instrument can no longer be inserted into

the canal to the full working length. At the same time,

the characteristic tactile sensation of the instrument

reaching the narrowest end of the root canal is lost.

This feeling is supplanted by that of an instrument

hitting against a solid wall.

A radiograph taken with an instrument placed against

the ledge provides additional information and verifies

its formation when the instrument tip is directed away

from the canal lumen. Special attention is required so

that the central X-ray beam is directed perpendicular to

the area where the instrument is placed.

In cases of previously endodontically treated teeth,

the existence of a ledge may be suspected when the

filling material is at least 1 mm shorter than the

expected root end or deviates from the natural canal

space, especially in teeth with curved roots (12, 14,

16). Angulated radiographs are also helpful in verifying

the presence of ledges (48) (Fig. 10).

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 (Fig. 11).

Fig. 8. Ledge formation and excessive removal of dentalstructure during efforts to explore a calcified/narrowroot canal. From Lambrianidis (5).

Fig. 9. (a) Pre-operative radiograph where a ledge at the apical end of the post can be seen. (b) Removal of the post andnegotiation of the canal to the desired length. (c) Obtutration of the canal space. Note filling material at the ledge/falsecanal caused during post-space preparation.

Fig. 7. Ledge found after removal of a separatedinstrument.

Ledges and blockages

61

� 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. Analysis of 10 different

pathfinder-type files with respect to the dimensional

characteristics, pitch, rigidity, efficiency, and wear

revealed that pitch, taper, cross-section, heat temper-

ing, metal type, tip geometry, and operator skill can all

influence efficiency (54).

� 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 (55). 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 (56) or GT hand files precurved

with Endo Bender pliers (Analytic Endodontotics,

Orange, CA, USA) (57) have also been advocated

to reduce or eliminate the ledge. The greater taper

of these files quickly smooths the ledge.

Fig. 10. (a) There is uncertainty regarding the presenceof a ledge in the orthodontic exposure. (b) Ledge appearsclearly in the angulated radiograph. From Lambrianidiset al. (48).

Lambrianidis

62

� Root canal obturation follows (Figs. 12 and 13).

Even if the canal is fully prepared, it is important to

test that the selected master gutta-percha cone can

reach the working length. Gutta-percha cones are

soft materials and they sometimes fail to by-pass the

ledge. Precurving the cone to match the canal

curvature can be helpful.

The effort required to by-pass a ledge is related to the

size of the instrument responsible for its formation and

the size of the canal apical to the ledge. Early detection

of ledge formation will allow its management. A ledge

created by large instruments is much more difficult to

by-pass because the ‘platform’ created is more likely to

prevent further penetration into the root canal. The

Fig. 11. Correction of ledge. (a) Diagrammatic representation of the radiographic location of the ledge with the help of asmall-sized endodontic instrument. Detail of the ledge (b) with and (c) without the instruments that caused it. (d–g)Pre-enlargement of the canal coronal to the ledge and initial by-passing of the ledge with a precurved size #8 K-file,followed by instrumentation up to the established working length with precurved file sizes #10 and #15.Instrumentation with stainless-steel and/or rotary NiTi instruments incorporating the ledge (h) into the canalpreparation and (i) obturation.

Ledges and blockages

63

smaller the width of the platform, the easier the

negotiation of the canal to the full working length.

However, in order to regain access to the apex, the

most important factor is not the actual size of the

instrument that created the ledge but the difference in

diameter between the instrument and the width of the

canal apical to the ledge. Thus, ledges caused with even

small-sized instruments into uninstrumented narrow

canals are very difficult to negotiate as opposed to

ledges caused by wider instruments in already-prepared

canals. Occasionally, regardless of the caution exercised

and the regular radiographs obtained during the effort

to negotiate them, new iatrogenic errors that include

formation of a new ledge, instrument separation, or

perforation (Fig. 14) can be caused.

If ledge by-passing is not possible, and the patient is

asymptomatic, the root canal is instrumented up to the

ledge and irrigated with copious amounts of sodium

hypochlorite and chlorhexidine, as it may still be

possible for irrigants to penetrate beyond the ledge.

The canal is dressed with calcium hydroxide for at least

a week (58, 59) and is then obturated. In these cases, it

is preferable to obturate the ledged canal with

techniques that use warm gutta-percha because part

of the softened gutta-percha may flow beyond the

ledge and fill, although not tightly seal, part of the

apical portion of the root canal. The patient is informed

about the guarded prognosis, the need for regular

follow-up (Figs. 15 and 16), and the possible future

treatment options, which include surgery, replantation,

and even extraction.

Surgery is performed immediately or at a later stage.

It is done immediately when:

� There are acute clinical symptoms, and obturation

alone under these circumstances (incomplete in-

strumentation because of a ledge far short of the

apex) will aggravate these.

� There is pre-operative periapical radiolucency. If

there are no clinical symptoms, these cases may also

be re-assessed, particularly if the ledge is close to the

root apex. Surgery may be performed after an

observation period if this is deemed necessary.

� Prosthetic restoration that includes the ledged

tooth is required or an implant(s) will be placed

adjacent to it. Thus, in order to prevent possible

esthetic implications of surgical intervention after

the completion of prosthetic rehabilitation, it is

preferable to proceed to the surgery immediately.

Even in these cases, a long-term temporary

restoration can be placed and the case can be re-

considered after an observation period.

Surgery is performed at a later stage (Fig. 17) when

clinical and radiographic findings indicate that a

periapical lesion has developed or that the size of the

pre-existing lesion has increased.

Regardless of the timing, the type of surgical

treatment depends on:

� the tooth and canal location;

� several anatomical parameters and esthetic consid-

erations;

� the existence, size, and location of periapical

pathosis;

� the condition of the periodontium;

� the experience/dexterity of the surgeon; and

� the distance of the ledge from the apex.

When ledging has occurred very short of the apex

in single-rooted teeth, removing the untreated portion

of the root will result in an undesirable crown : root

ratio. In these cases, curettage combined with root-end

preparation and filling of the apical 3 mm of the

canal is recommended (60). If the ledge is located only

slightly short of the apex, the unfilled portion

of the root is removed and the canal is root-end filled

in both single- and multi-rooted teeth. In the latter,

Fig. 12. (a) Pre-operative and (b) post-operative radiograph. Note the presence of filling material in the ledged area.From Lambrianidis (5).

Lambrianidis

64

where apical surgery is usually more challenging

because of anatomical parameters, amputation and

hemisection can be considered as alternative treatment

options.

Intentional replantation (61) is usually reserved as

the last alternative treatment when all routine methods

are contraindicated or have failed and conventional

surgical intervention would be extremely hazardous or

impossible (Fig. 18). In this case, the portion of the

canal apical to the ledge is treated either by reverse

filing procedures and root-end filling or by root-end

resection and root-end filling with the extra-oral period

kept as short as possible.

Prognosis

When the ledge has been by-passed and blended into

canal instrumentation, it has no effect on the prog-

nosis. In cases where the ledge cannot be by-passed, the

prognosis is determined by:

� the pre-operative status of the pulp and the

presence and extent of periapical periodontitis;

� the distance between the ledge and the root apex;

and

� the size of the instrument that had instrumented

the root canal up to the desired length before ledge

formation. This allows an assessment of how ‘clean’

the root canal may be before the formation of the

ledge.

These three factors are closely interrelated. Ledges

formed relatively close to the apical foramen after

instrumentation to the desired length with the appro-

priate instrument size are more favorable than ledges

formed well short of the foramen before complete

instrumentation of the apical portion, particularly if

there is no periapical lesion as opposed to the existence

of periapical pathosis in the latter. Additionally, ledges

formed close to the apex usually offer more surgical

options in unfavorable outcomes.

Prevention

Ledges can be prevented if:

� accurate, high-quality diagnostic pre-operative

radiographs are obtained and carefully interpreted

before initiation of the treatment;

� the practitioner is fully aware of the typical root

canal morphology and its variations;

� adequate access cavity is prepared in order to elimi-

nate all obstructions coronal to the apical constric-

tion;

� precurved instruments are used under copious

irrigation, in sequential order without skipping

any sizes and without applying undue force; and

Fig. 13. (a) Pre-operative radiograph where a ledge canbe seen in an incompletely obturated mandibularpremolar. (b) Immediate post-obturation radiographfollowing instrumentation up to the desired length. (c)Six-month recall radiograph.

Ledges and blockages

65

� frequent recapitulation is performed, that is, re-

introduction of previously used instruments,

throughout the instrumentation procedure.

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 in-

fected); and/or

� residual pulp tissue; and/or

� remnants of filling materials (in cases of re-

treatment).

The type of blockage is related to the instrumenta-

tion technique used. Assessment and comparison of

canal blockages by dentin debris during canal shaping

with eight preparation techniques revealed that they

varied significantly among techniques (Po0.001).

Blockages occurred most frequently in canals prepared

with step-back techniques with anti-curvature and

circumferential filing and occurred least when the

balanced-proof technique was used (62) (Table 3). In a

clinical study, procedural errors that occurred in

patients during root canal preparation by senior dental

students using a new eight-step method with standar-

dized K-files or rotary NiTi instruments were com-

pared with the traditional serial step-back technique

with stainless-steel K-files. Results suggested that the

new eight-step method resulted in no obstructions as

opposed to the traditional serial step-back technique,

where 8% of the canals had obstructions (63).

Accidental canal blockage should not be mistaken with

the intentionally placed apical plug with autogenous

dentin chips. In this technique, the apical 1 mm of the

root canal is filled with dentin chips to provide a barrier

against the extrusion of filling material. The chips are

produced with Hedstroem files or Gates-Glidden drills

from the coronal third of the root canal after completion

of instrumentation and drying of the root canal. Chips

are then pushed apically with a small premeasured

plugger. There are contradictory views in the literature

regarding the sealing ability (64, 65) and the biological

consequences of this technique (66–70). Given the

reported controversy, but most importantly because of

the inability to control the sterility of dentin chips and

the increased risk of forcing dentinal chips into the

periapical tissues during the packing procedure, this

method should be avoided or used with great caution.

Fig. 14. (a) Pre-operative radiograph where a ledge can be seen at the apical extent of the silver cone. (b) Inabilityto negotiate the ledge following removal of the silver cone. (c) Immediate post-obturation radiograph revealingperforation caused during efforts to negotiate the ledge and extrusion of filling material to periapical tissues. Courtesy ofDr. D. Christacoudi.

Lambrianidis

66

Causes of canal blockage

Canal blockage is caused when:

� pulpal tissue is packed and solidified in the apical

constriction by the use of instruments;

� instrumentation is not accompanied by copious

irrigation; or

� instruments are not cleaned before their reinsertion

into the canal. In a study of instrumentation by nine

file types, researchers observed little debris along

the canals of plastic blocks if the files were removed

and the flutes were cleaned periodically (71).

Recognition

Canal blockage by dentin chips and/or tissue debris is

recognized because the instruments can no longer be

advanced to the working length. In some cases, this is

also evident during obturation of the root canal as the

gutta-percha cone cannot be introduced to the desired

length. Canal blockage needs to be differentiated from

ledge formation. This is very easily done as the tactile

feedback in these two cases differs considerably. When

the root canal is blocked, there is a characteristic tactile

sensation of the small-sized endodontic instrument

Fig. 15. (a) Ledge formation in a calcified root canal. (b) Immediate post-obturation radiograph. Post-treatmentfollow-up radiographs in (c) 3 months, (d) 6 months, (e) 12 months, and (f) 60 months. From Lambrianidis (5).

Ledges and blockages

67

reaching an almost solid but ‘penetrable wall’ as

opposed to the instrument hitting a solid wall in cases

of ledge formation. Radiographically, canal blockage

may appear as the absence of canal space in an

otherwise patent canal (Fig. 19).

In cases of root canal-treated teeth, it is difficult to

identify the cause of short obturations based only on

the radiographic appearance. The absence of canal

space apical to the filling material might be a sign of

blockage but it can also be a calcified canal or simply the

result of superimposition.

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 endodontic instruments are

used (Fig. 20).

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.

Prognosis

Often canal blockages can be corrected, particularly

when they are recognized early during the course of

instrumentation. In these cases, canal blockage has no

effect on prognosis. When the blockage cannot be

negotiated, the hardened debris may jeopardize the

outcome, particularly in infected cases, as micro-

organisms can remain embedded in debris.

Prevention

Canal blockage can be prevented if instrumentation

adheres to guidelines. Of particular importance is the

need for copious frequent irrigation, preferably ultra-

sonically activated, wiping of instruments before their

reinsertion into the canal, and recapitulation during

the entire instrumentation procedure.

The use of rotary NiTi instruments, due to their

innovative design (features) such as grooves around the

shaft, variable helical angle, and variable pitch, seems to

promote debris removal coronally while the instrument

rotates clockwise (72–74) and thus prevents canal

blockage (33, 41, 75).

The passive use of a flexible, small patency file 1 mm

longer than the canal terminus to effectively prevent

blockages and at the same time clean and disinfect the

most apical part of root has been proposed (76).

Fig. 16. (a) Immediate post-obturation radiograph. (b)Six-month recall radiograph. From Lambrianidis (5).

Lambrianidis

68

Patency filing also facilitates removal of most of the

calcium hydroxide dressings from the apical third of the

root canal (77). Thus, the foramen remains unblocked

and patent. However, the concept of apical patency is

considered controversial because of the differences in

the amount of extruded material found in cases with

and without patency filing (78–80). If a patency file is

used, the smallest file size possible should be used as it

was found that more material was extruded apically as

the diameter of the apical patency increased (80).

When a #20 file was used as a patency file, the possi-

bility of transporting the apical foramen increased (81).

In conclusion, ledges and blockages can be prevented

if accurate, high-quality diagnostic pre-operative radio-

graphs are obtained and carefully interpreted before

initiation of the treatment to verify the prerequisite,

Fig. 17. Surgical treatment of ledge formation. (a) Pre-operative radiograph. (b) Inability to by-pass the ledge duringre-treatment and thus instrumentation and obturation of the root canal up to the ledge followed. (c) Periapicalradiolucency is evident in the 6-month recall radiograph. An apicoectomy was performed. (d) Recall radiograph 3months following apicoectomy. From Lambrianidis (5).

Ledges and blockages

69

Fig. 18. Intentional reimplantation. (a) Pre-operative X-ray and (b) X-ray showing ledge formation as provided by thereferring general dental practitioner. Note the proximity of the root with the antrum and the fracture in the cervical area.(c) Extraction of the tooth and retrograde preparation. (d) Repositioning of the tooth and (e) immediate post-reimplantation X-ray. Recall X-rays at (f) 3 months, (g) 6 months, (h) 12 months, and (i) 18 months. From Deveset al. (61).

Lambrianidis

70

that is, the thorough knowledge of the morphology

and its variations in the tooth to be treated. Instru-

mentation with copious irrigation adheres to the

guidelines. Among the several factors associated with

the occurrence of ledges and blockages, the canal

curvature, instrumentation technique, and instru-

ments used seem to be the most important.

Acknowledgements

I thank Dr. M. Mazinis for the drawings and Assistant

Professor L. Vasiliadis for his help with the SEM Fig. 19.

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