ledging and blockage of root canals during canal ......limitation of radiographs to distinguish the...
TRANSCRIPT
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.
References
1. Hulsmann M, Peters OA, Dummer PM. Mechanicalpreparation of root canals: shaping goals, techniquesand means. Endod Topics 2005: 10: 30–76.
2. Siqueira JF Jr. Aetiology of the endodontic failure: whywell-treated teeth can fail. Int Endod J 2001: 34: 1–10.
3. Southard DW, Oswald RJ, Natkin E. Instrumentationof curved molar root canals with the Roane technique.J Endod 1987: 13: 479–489.
Fig. 19. (a) The discontinuation of canal space is due toits blockage by dentin chips after instrumentation. (b)SEM original magnification � 35.
Table 3. Number of canals with blockages. FromAI-Omari & Dummer (62)
Technique Blockages
Standardized (n 5 26) 1
Step-back with reaming (n 5 25) 1
Step-back with circumferential (n 5 26) 16
Step-back with anti-curvature filing (n 5 27) 19
Double-flare (n 5 26) 11
Step-down (n 5 25) 2
Crown-down pressureless (n 5 26) 1
Balanced-force (n 5 27) 0
Fig. 20. Forceful introduction of endodontic instru-ments in efforts to negotiate a blocked canal may leadto new iatrogenic error(s) such as a ledge, perforation, orinstrument separation.
Ledges and blockages
71
4. Oikonomou IA, Spanaki-Voreadi AP, Georgopoulou
MK. Procedural errors during root canal treatment
performed by undergraduate students in Athens: a
prospective study. Int Endod J 2007: 40: 982 (ESE
abstract R1.9).5. Lambrianidis T. Risk Management in Root Canal
Treatment. Thessaloniki: University Studio Press,
2001: 75–83, 176, 181–182.6. Giuliani V, Baccetti T, Pace R, Pagavino G. The use of
MTA in teeth with necrotic pulps and open apices. DentTraumatol 2002: 18: 217–221.
7. Al-Kahtani A, Shostad S, Schifferle R, Bhambhani S.
In vitro evaluation of microleakage of an orthograde
apical plug of mineral trioxide aggregate in permanent
teeth with simulated immature apices. J Endod 2005:
31: 117–119.8. Pace R, Giuliani V, Pini Prato L, Baccetti T, Pagavino G.
Apical plug technique using mineral trioxide aggregate:
results from a case series. Int Endod J 2007: 40:
478–484.9. Simon S, Rilliard F, Berdal A, Machtou P. The use of
mineral trioxide aggregate in one-visit apexification
treatment: a prospective study. Int Endod J 2007: 40:
186–197.10. Glickman GN, Dumsha TC. Problems in canal cleaning
and shaping. Prevention, identification and manage-
ment. In: Gutmann JL, Dumsha TC, Lovdahl PE,
Hovland EJ, eds. Problem Solving in Endodontics, 3rd
edn. St Louis: Mosby, 1997: 110.11. Bergenholtz G, Lekholm U, Milthon R, Heden G,
Odesjo B, Engstrom B. Retreatment of endodontic
fillings. Scan J Dent Res 1979: 87: 217–224.12. Greene KJ, Krell KV. Clinical factors associated
with ledged canals in maxillary and mandibular
molars. Oral Surg Oral Med Oral Pathol 1990: 70:
490–497.13. Schneider SW. A comparison of canal preparations in
straight and curved canals. Oral Surg Oral Med OralPathol 1971: 32: 271–275.
14. Kapalas A, Lambrianidis T. Factors associated with root
canal ledging during instrumentation. Endod DentTraumatol 2000: 16: 220–231.
15. Peters OA, Schonenberger K, Laib A. Effects of four
Ni–Ti preparation techniques on root canal geometry
assessed by micro computed tomography. Int Endod J2001: 34: 221–230.
16. Eleftheriadis G, Lambrianidis T. Technical quality of
root canal treatment and detection of iatrogenic errors
in an undergraduate dental clinic. Int Endod J 2005:
38: 725–734.17. Thompson SA, Dummer PM. Shaping ability of Mity
Roto 3601 and Naviflex rotary nickel–titanium instru-
ments in simulated root canals. Part 2. J Endod 1998:
24: 135–142.18. Nagy CD, Bartha K, Bernath M, Verdes E, Szabo J. The
effect of root canal morphology on canal shape
following instrumentation using different techniques.
Int Endod J 1997: 30: 133–140.
19. Stadler LE, Wennberg A, Olgart L. Instrumentation of
the curved root canal using filing or reaming technique
– a clinical study of technical complications. Swed Dent J1986: 10: 37–43.
20. Luiten DJ, Morgan LA, Baumgartner JC, Marshall JG.
A comparison of four instrumentation techniques on
apical canal transportation. J Endod 1995: 21: 26–32.21. Fogarty TJ, Montgomery S. Effect of preflaring on
canal transportation. Effect of ultrasonic, sonic and
conventional techniques. Oral Surg Oral Med OralPathol 1991: 72: 345–350.
22. Ali MN, Hossain M, Nakamura Y, Matsuoka E,
Kinoshita J, Matsumoto K. Efficacy of root canal pre-
paration by Er,Cr:YSGG laser irradiation with crown-
down technique. Photomed Laser Surg 2005: 23:
196–201.23. Radatti DA, Baumgartner JG, Marshall G. A compar-
ison of the efficacy of Er,Cr:YSGG laser and rotary
instrumentation in root canal debridement. J Am DentAssoc 2006: 137: 1261–1266.
24. Peters OA. Current challenges and concepts in the
preparation of root canal systems: a review. J Endod2004: 30: 559–567.
25. Bishop K, Dummer PM. A comparison of stainless steel
Flexofiles and nickel–titanium NiTiFlex files during
the shaping of simulated canals. Int Endod J 1997: 30:
25–34.26. Bryant ST, Thompson SA, Al-Omari MA, Dummer
PM. Shaping ability of ProFile rotary nickel–titanium
instruments with ISO sized tips in simulated root
canals: Part 1. Int Endod J 1998: 31: 275–281.27. Bryant ST, Thompson SA, Al-Omari MA, Dummer
PM. Shaping ability of ProFile rotary nickel–titanium
instruments with ISO sized tips in simulated root
canals: Part 2. Int Endod J 1998: 31: 282–289.28. Thompson SA, Dummer PM. Shaping ability of ProFile
.04 Taper Series 29 rotary nickel–titanium instruments
in simulated root canals: Part 2. Int Endod J 1997: 30:
8–15.29. Thompson SA, Dummer PM. Shaping ability of Hero
642 rotary nickel–titanium instruments in simulated
root canals: Part 2. Int Endod J 2000: 33: 255–261.30. Ciucchi B, Cergneux M, Holz J. Comparison of curved
canal shape using filing and rotational instrumentation
techniques. Int Endod J 1990: 23: 139–147.31. Ponce de Leon Del Bello T, Wang N, Roane JB.
Crown-down tip design and shaping. J Endod 2003:
29: 513–518.32. Griffiths I, Bryant S, Dummer PM. Canal shapes
produced sequentially during instrumentation with
Quantec LX rotary nickel–titanium instruments:
a study in simulated canals. Int Endod J 2000: 33:
346–354.33. Griffiths I, Chassot A, Nascimento M, Bryant S,
Dummer PM. Canal shapes produced sequentially
during instrumentation with Quantec SC rotary nick-
el–titanium instruments: a study in simulated canals.
Int Endod J 2001: 34: 107–112.
Lambrianidis
72
34. Rangel S, Cremonese R, Bryant S, Dummer PM.
Shaping ability of RaCe rotary Ni–Ti instruments in
simulated root canals. J Endod 2006: 32: 61–65.35. Yun H, Kim S. A comparison of the shaping abilities of
4 NiTi rotary instruments in simulated root canals.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod2003: 95: 228–233.
36. Bergmans L, Cleynenbreugel J, Beullens M, Wevers M,
Meerbeek B, Lambrechts P. Progressive versus constant
tapered shaft design using NiTi rotary instruments. IntEndod J 2003: 36: 288–295.
37. Javaheri H, Javaheri G. A comparison of three Ni–Ti
rotary instruments in apical transportation. J Endod2007: 33: 284–286.
38. Loizides A, Kakavetsos V, Tzanetakis G, Kontakiotis E,
Eliades G. A comparative study of the effects of two
nickel–titanium preparation techniques on root canal
geometry assessed by microcomputed tomography.
J Endod 2007: 33: 1455–1459.39. Schafer E, Florek H. Efficiency of rotary nickel–titanium
K3 instruments compared with stainless steel hand
K-Flexofile: Part 1. Int Endod J 2003: 36: 199–207.40. Peters OA, Peters CI, Schonenberger K, Barbakow F.
ProTaper rotary root canal preparation: effects of
canal anatomy on final shape analysed by micro CT.
Int Endod 2003: 36: 86–92.41. Yang G, Zhou X, Zhang H, Wu H. Shaping ability of
progressive versus constant taper instruments in simu-
lated root canals. Int Endod J 2006: 39: 791–799.42. Kuhn W, Carnes D, Clement D, Walker W. Effect of tip
design of nickel–titanium and stainless steel files on root
canal preparation. J Endod 1997: 23: 735–738.43. Camps J, Pertot W, Levallois B. Relationship between
file size and stiffness of nickel–titanium instruments.
Endod Dent Traumatol 1995: 11: 270–273.44. Marsicovetere ES, Burgess JO, Clement DJ, del Rio CE.
Torsional testing of the Lightspeed nickel–titanium
instrument system. J Endod 1996: 22: 681–684.45. Yoshimine Y, Ono M, Akamine A. The shaping effects
of three nickel–titanium rotary instruments in simu-
lated S-shaped canals. J Endod 2005: 31: 373–375.46. Cunningham CJ, Senia ES. A three-dimensional study
of canal curvatures in the mesial roots of mandibular
molars. J Endod 1992: 18: 294–300.47. Yared G. Canal preparation using only one Ni–Ti rotary
instrument: preliminary observations. Int Endod J2008: 41: 339–344.
48. Lambrianidis T, Molyvdas I, Mazinis E. Radiography inEndodontics. Thessaloniki-Athens: Odont Vima, 2007:
233 [in Greek].49. Coleman C, Svec T, Rieger M, Suchina J, Wang M,
Glickman G. Analysis of nickel–titanium versus stainless
steel instrumentation by means of direct digital
imaging. J Endod 1996: 22: 603–607.50. Gambill J, Alder M, del Rio C. Comparison of nickel–
titanium and stainless steel hand-file instrumentation
using computed tomography. J Endod 1996: 22: 369–
375.
51. Song Y, Bian Z, Fan B, Fan M, Gutmann J, Peng B. A
comparison of instrument-centering ability within the
root canal for three contemporary instrumentation
techniques. Int Endod J 2004: 37: 265–271.52. Glossen C, Haller R, Dove S, del Rio C. A comparison
of root canal preparations using Ni–Ti hand, Ni–Ti
engine driven, and K-Flex endodontic instruments.
J Endod 1995: 21: 146–151.53. Schafer E, Schultz-Bongert U, Tulus G. Comparison of
hand stainless steel and nickel titanium rotary instru-
mentation: a clinical study. J Endod 2004: 30: 432–435.54. Allen MJ, Glickman GN, Griggs JA. Comparative
analysis of endodontic pathfinders. J Endod 2007: 33:
723–726.55. Weine FS, Healey HJ, Gerstein H, Evanson L. Pre-
curved files and incremental instrumentation for root canal
enlargement. J Can Dent Assoc 1970: 36: 155–157.56. West J. Endodontic update 2006. J Esthet Restor Dent
2006: 18: 280–300.57. Roda RS, Gettleman BH. Nonsurgical retreatment. In:
Cohen S, Hargreaves KM, eds. Pathways of the Pulp, 9th
edn. St Louis: Mosby, 2006: 993–994.58. Bystrom A, Sundqvist G. The antibacterial action of
sodium hypochlorite and EDTA in 60 cases of
endodontic therapy. Int Endod J 1985: 18: 35–40.59. Shuping GB, Ørstavik D, Sigurdsson A, Trope M.
Reduction of intracanal bacteria using nickel–titanium
rotary instrumentation and various medications.
J Endod 2000: 26: 751–755.60. Kim S, Kratchman S. Modern endodontic surgery
concepts and practice: a review. J Endod 2006: 32: 601–
623.61. Deves G, Kosidou G, Lambrianidis T. Intentional
replantation, a clinical case. 11th BaSS Congress,Sarajevo, Bosnia and Hersegovina, May 11–14, 2006.
62. AI-Omari MAO, Dummer PM. Canal blockage and
debris extrusion with eight preparation techniques.
J Endod 1995: 21: 154–158.63. Kfir A, Rosenberg E, Zuckerman O, Tamse A, Fuss Z.
Comparison of procedural errors resulting during root
canal preparations completed by senior dental students
in patients using an 8-step method versus serial step-
back technique. Oral Surg Oral Med Oral Pathol OralRadiol Endod 2004: 97: 745–748.
64. El Deeb ME, Nguyen TTQ, Jensen JR. The dentinal
plug: its effect on confining substances to the canal on
the apical seal. J Endod 1993: 9: 335–339.65. Jacobsen EL, Bery PF, BeGole EA. The effectiveness of
apical dentin plugs in sealing endodontically treated
teeth. J Endod 1985: 11: 289–293.66. Tronstad L. Tissue reactions following apical plugging
of the root canal with dentin chips in monkey teeth
subjected to pulpectomy. Oral Surg Oral Med OralPathol 1978: 45: 297–304.
67. Pitts DL, Jones JE, Oswald RJ. A histologic comparison
of calcium hydroxide plugs and dentin plugs used for
the control of gutta-percha filling material. J Endod1984: 10: 283–293.
Ledges and blockages
73
68. Torabinejad M, Owen R, Danforth RA, Howell RE.
Periapical tissue response to dentin and vitreous carbon
plugs in apical perforations of dogs’ teeth. Endod DentTraumatol 1985: 1: 17–21.
69. Brady JE, Himel VT, Weir JC. Periapical response to an
apical plug of dentin filling intentionally placed after
root canal overinstrumentation. J Endod 1985: 11:
323–329.70. Holland R, Souza V, Nery MJ, Bernabe PFE, Mello W,
Otoboni FJA. Apical hard-tissue deposition in adult
teeth of monkeys with use of calcium hydroxide. AustDent J 1980: 25: 189–192.
71. Briseno BM, Sonnabend E. The influence of different
root canal instruments on root canal preparation: an invitro study. Int Endod J 1991: 24: 15–23.
72. Clauder T, Baumann M. ProTaper NT system. DentClin N Am 2004: 48: 87–111.
73. Hsu Y, Kim S. The ProFile system. Dent Clin N Am2004: 48: 69–85.
74. Mounce R. The K3 rotary nickel–titanium file system.
Dent Clin N Am 2004: 48: 137–157.75. Versumer J, Hulsmann M, Schafers F. A comparative
study of root canal preparation using ProFile .04 and
Lightspeed rotary Ni–Ti instruments. Int Endod J2002: 35: 37–46.
76. Buchanan LS. Management of the curved root canal.
Calif Dent Assoc J 1989: 17: 40–47.77. Lambrianidis T, Kosti E, Boutsioukis C, Mazinis M.
Removal efficiency of various calcium hydroxide/
chlorhexidine dressings from the root canal.
The role of the patency file. Int Endod J 2006: 39:
55–61.78. Gutierrez JH, Brizuela C, Villota E. Human teeth with
periapical pathosis after overinstrumentation and over-
filling of the root canals: a scanning electron micro-
scopic study. Int Endod J 1999: 32: 40–48.79. Lambrianidis T, Tosounidou E, Tzoanopoulou M. The
effect of maintaining apical patency on periapical
extrusion. J Endod 2001: 27: 696–698.80. Tinaz AC, Alacam T, Uzun O, Maden M, Kayaoglu
G. The effect of disruption of apical constriction
on periapical extrusion. J Endod 2005: 31: 533–
535.81. Goldberg F, Massone EJ. Patency file and apical
transportation: an in vitro study. J Endod 2002: 28:
510–511.
Lambrianidis
74