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Effectiveness of Three Different Retreatment Techniques in
Canals Filled With Compacted Gutta-Percha or Thermafil: A
Scanning Electron Microscope Study
Chiara Pirani, DDS, MS, PhD,*Gian Andrea Pelliccioni, MD, DDS,
†
Silvia Marchionni, BS,*
Lucio Montebugnoli, MD, DDS,
‡
Gabriela Piana, MD, DDS,
§
and Carlo Prati, MD, DDS, PhD*
Abstract
Introduction: This study evaluated the root canal wall
morphology under scanning electron microscopy magni-
fication after removal of 2 types of root canal fillings by
using ultrasonic tips, nickel-titanium (NiTi) rotary instru-
ments, and hand K-files. Methods: Thirty-six extracted
roots were filled by using AH Plus (DeTrey-Dentsply,
Konstanz, Germany) as a sealer with Thermafil (Tulsa
Dental Products, Tulsa, OK) (18 roots) or warm vertically
condensed gutta-percha (18 roots). All fillings were
removed up to the middle third by using Gates Glidden
drills. The retreatment was completed by using K-files
(group 1), M-Two NiTi rotary instruments (group 2), or
ESI ultrasonic tips (group 3) in 12 roots each. Root canals
were irrigated by using 10% ethylenediaminetetraacetic
acid and 2.5% NaOCl. The samples were split longitudi-
nally and observed by scanning electron microscopy
(100–2000). The presence of smear layer, filling
debris, and the surface profile was evaluated in each
picture. Kruskal-Wallis (analysis of variance) and
Mann-Whitney tests were used to evaluate the differ-
ences between the obturation techniques, the 3 retreat-
ment methods, and the canal thirds (P< .05). Results:
Resin sealer tags were observed inside dentinal tubules.
No statistical differences (P> .05) were found among
the 3 retreatment methods. No statistical differences
were observed between Thermafil and vertically com-
pacted warm gutta-percha for each group or between
the coronal third used as control, middle, and apical
thirds. Conclusions: All retreatment techniques showed
similar performances in terms of smear layer
morphology, debris, and surface profile. None of them
completely removed filling debris from dentinal tubules
of apical third.
(J Endod 2009;35:1433–1440)
Key Words
Gutta-percha removal, K-files, Ni-Ti instruments, root
canal retreatment, Thermafil, ultrasonic tips
The clinical success rate of endodontic retreatments has been estimated to vary
between 50% and 90%, depending on the effective elimination of necrotic tissue,
bacteria, and infected obturation material such as gutta-percha and cements from
root canal (1–4).
Gutta-percha might be removed by using solvents, stainless steel rotary, manual,
heated endodontic and ultrasonic instruments (1, 5, 6). However, retreatment tech-
niques do not completely remove the obturation materials from the root canal (1, 6, 7).
The Thermafil (Tulsa Dental Products, Tulsa, OK) root canal obturation system
has greatly simplified root canal filling procedures but has probably made retreatment
procedures more difficult (7).In vitro, the Thermafil system produces a homogeneous
mass of gutta-percha in the canal (8). However, an oval-shaped canal might compro-
mise the quality of root fillings, even when using thermoplasticized techniques like
Thermafil or thermomechanical compaction (9). A radiographic study by Baratto-Filho
et al (7) showed that Pro-File nickel-titanium (NiTi) rotary instruments could not
completely remove the gutta-percha present in Thermafil root canal fillings.
The development of ultrasonic tips (10) and rotary NiTi instruments has modified
endodontic therapy. The ability of these new systems during retreatments has been
studied by in vivo investigations (11, 12). Other in vitro studies evaluating the use
of NiTi rotary instruments to remove root canal filling materials demonstrated that
they are timesaving but fail to remove all debris (7, 13–16).
Ultrasonic endodontic tips have been proposed for root canal instrumentation, the
removal of broken instruments, and cavity root-end preparation (10). Unfortunately,
no complete information is yet available regarding their ability to remove gutta-percha
and sealer from root canals.
The amount of gutta-percha remaining in root canals after retreatment with
manual files and solvents has been measured by using radiographs, dental operating
microscopes (17–21), and, more recently, by scanning electron microscopy (SEM)
observation (1, 5, 13, 15–23).
For these reasons, further morphologic investigations are required to establish
whether NiTi and ultrasonic instruments are effective in removing debris from inner
dentin of previously filled root canals. M-Two (Sweden & Martina, Padova, Italy)
NiTi instruments have been studied and used in daily clinical practice. They present
positive rake angles, no radial lands, progressive blade chamber (pitch) in the
apical-coronal direction, and a noncutting tip. The M-Two cross-sectional design
resembles that of the S-File (24).
The aim of this study was to undertake an SEM investigation into the effectiveness of
3 different retreatment methods (ultrasonic tips, NiTi rotary instruments, and K-file
From the *Endodontic Unit,
†
Oral Surgery Unit,
‡
Oral Pathology Unit, and
§
Pediatric Dentistry, Department of Dental Sciences, Alma Mater Studiorum, University of
Bologna, Bologna, Italy.
Address requests for reprints to Dott. Chiara Pirani, Department of Dental Sciences, Alma Mater Studiorum–University of Bologna, Via San Vitale 59, 40125 Bologna,
Italy. E-mail address: chiara.pirani4@unibo.it.
0099-2399/$0 - see front matter
Copyright ª2009 American Association of Endodontists.
doi:10.1016/j.joen.2009.06.002
Basic Research—Technology
JOE —Volume 35, Number 10, October 2009 Effectiveness of 3 Retreatment Techniques 1433
manual instruments) in removing warm vertically condensed gutta-per-
cha or Thermafil filling material from previously in vitro filled root
canals.
Materials and Methods
Root Canal Preparation
Thirty-six single-rooted straight teeth of similar length extracted
for periodontal reasons were selected. The crowns were removed
with a diamond bur at cementoenamel junction level by using a high-
speed water-cooled handpiece. Two longitudinal grooves of 1-mm
depth were prepared with a diamond bur on the palatal and buccal
surfaces of each root to facilitate vertical splitting for microscopic
observation after retreatment.
The glide path was verified with a 10 K-file (FKG, La Chaux-
de-Fonds, Switzerland). Samples with 2 canals or calcification were
excluded from the study. Coronal thirds were enlarged with Gates Glid-
den 1-2-3 (Maillefer-Dentsply, Ballaigues, Switzerland), followed by
K-file 10-15-20-25-30-35-40-45-50 used in step-back sequence. The
apical gauging for each canal was set at 35 with K-files. Each sample
was irrigated with 5 mL NaOCl at 2.5% (Niclor 2.5; Ogna, Muggio
`, Italy)
and 5 mL liquid ethylenediaminetetraacetic acid (EDTA) at 10% (Tubu-
liclean; Ogna) during canal preparation. The root canals were dried
with sterile paper points (Mynol, Milwaukee, WI) and filled with vertical
condensation of warm gutta-percha with System B (Sybron Endo,
Orange, CA) (N = 18) or Thermafil (N = 18). AH Plus (DeTrey-
Dentsply, Konstanz, Germany) was used as sealer. Regardless of the
working length (WL) of each tooth, the extension of the root canal filling
was uniformly limited to 15 mm from the apical extension of the filling,
so that the volume of the gutta-percha was as equal as possible for all
teeth (1). Each root was covered with a pellet and Coltosol (Coltene,
Kostanz, Germany) and then immersed in tap water and stored for 2
weeks at room temperature in a test tube.
The samples were randomly assigned to 1 of 3 groups for retreat-
ment. Each retreatment group was composed of 12 elements, 6 filled
with AH Plus/Thermafil and 6 obturated with AH Plus/warm gutta-
percha vertically compacted with System B.
Retreatment Technique
Coltosol cement was gently removed by using ultrasound tips (Pie-
zon 5; Castellini, Bologna, Italy) in both filling groups (AH Plus-Ther-
mafil and AH Plus-gutta-percha). As first retreatment step, different
Gates Glidden 4-3-2 at 1000–1200 rpm were used in all 36 filled roots
for preliminary treatment of the coronal third and half of the medium
third to remove most of the gutta-percha up to half the length of the
root canals.
In the Thermafil group, the entire portion of the plastic carrier and
gutta-percha was easily removed with the Gates Glidden, and only small
plastic fragments were probably left inside the root canals.
Throughout the procedures, 5 mL of 2.5% NaOCl and 5 mL of 10%
EDTA were used to irrigate the root canals.
Group 1: NiTi Retreatment Group (N = 12)
A size 15 K-file was used to reach the preliminary WL. A size 40 M-
Two NiTi rotary instrument (Sweden & Martina) on a 16:1 reduction
handpiece powered by an electric motor (Tecnika Digital Torque
Control Motor; ATR, Pistoia, Italy) with a constant speed of 300 rpm,
and low torque was introduced into the root canal up to approximately
2.0 mm to the WL and gently used for 60 seconds. A size 20 (4%
tapered) M-Two rotary instrument followed by size 25 (6%)-30
(4%)-35 (5%)-40 (4%) M-Two at 250 rpm were used to the WL. A
rotary motion was alternated with the push-pull movement. A NiTi
Mtwo instrument size 40 was used, so that it was approximately 0.05
mm larger than the original preparation.
Group 2: K-Files Retreatment Group (N = 12)
A size 15 K-file was used to reach the preliminary WL. Retreatment
was carried out by K-files with a push-pull movement alternated with
a rotary motion. K-files of different sizes were used until the WL was
reached and the root was cleaned. A K-file 40 was used as last file at
the apex.
Group 3: Ultrasound Retreatment Group (N = 12)
A size 15 K-file was used to determine the WL of the root canals.
Ultrasound ESI tips of different sizes (15–35) mounted on a Piezon 5
(Castellini) were used in a circumferential motion until the WL was
reached. The master tip at WL was no. 35. A K-file 40 was then used
to finish apical thirds.
A final irrigation with 2.5 mL of NaOCl, 2.5 mL of EDTA, and 2.5 mL
of NaOCl concluded the retreatment procedure in the 3 groups.
The retreatment procedure in each group was considered
complete when apical file 40 fitted loosely in the root canal at full
WL, and no debris of materials was visible to the naked eye on the
file surfaces after removal from the canal (19).
SEM Preparation
The samples were fixed in a 4% glutaraldehyde 0.2 mol/L sodium
cacodylate buffer solution for 48 hours and then sectioned in half with
a chisel. Random halves were dehydrated in graded alcohol concentra-
tions, dried, and then gold-sputtered (Sputter Coater; SPI, Toronto,
Canada) and observed by SEM (JEOL 5200; JEOL, Tokyo, Japan).
After a general survey of the root canal walls, 3 SEM photos of each
third of the root canal were taken, 2 at a magnification of 2000to
score the smear layer and inorganic debris (coronal, middle, and
apical) and 1 at 75or 100to evaluate the surface profile.
The images were saved digitally with proprietary software (SemA-
fore; JEOL) and individually scored blind by 2 trained operators.
SEM Evaluation Methods
In selected SEM pictures the absence or presence of the smear
layer and filling debris was rated and scored by using a predefined scale
(24, 25) by an independent observer. The dentin surface profile was
assessed by evaluating the presence of grooves, pits, and predentin
areas (Table 1).
Each root canal was divided into 4 portions (coronal, coronal-
medium, apical-medium, apical), and each portion was evaluated sepa-
rately. The medium thirds were divided into 2 different portions
(coronal medium and apical medium) because the coronally placed
portion was instrumented with Gates-Glidden and only the apical part
with 1 of the 3 tested retreatment techniques. Coronal third and coronal
part of the middle third served as positive controls.
Statistical Analysis
Data analysis was performed by using the Kruskal-Wallis test (anal-
ysis of variance) to evaluate differences between the results of the 3
retreatment methods in the 4 different root canal portions. The
Mann-Whitney test was used to compare differences between the 2 obtu-
ration systems within each retreatment group. Box and whisker plots
were drawn for each single parameter, showing the differences between
the 3 retreatment instruments, the canal thirds, and the 2 obturation
systems. The length of the notch represents an approximate 95% confi-
dence interval for the median. Overlapping notches indicate no signif-
icant difference between the sample medians.
Basic Research—Technology
1434 Pirani et al. JOE —Volume 35, Number 10, October 2009
The level of significance in all tests was set at P<.05.
Results
Smear Layer
A small amount of smear layer compacted and spread only in
several portions of dentin root walls was observed in all retreatment
techniques. Smear plugs and debris covered the orifices of the dentinal
tubules in several areas so that they were not visible. In all groups smear
layer islands were found especially in the apical thirds. No statistical
differences (P> .05) were found between the 3 retreatment methods
or between the coronal (control), middle, and apical thirds (Figs.
1and 2). Ultrasound and M-Two retreatments created a smear layer
similar to that produced by manual K-files.
Peritubular and intertubular erosions were present especially
in the coronal and middle thirds (Fig. 3a). Dentinal tubules
appeared enlarged and with a funnel entrance. In the middle thirds
excessive erosion often led to the conjunction of 2 or more tubular
orifices.
Fractured resin tags were visible in several samples. Many dentinal
tubules were found to be filled by sealer resin tags and gutta-percha
tags. Many other tubules were partially obturated by smear plugs
(Fig. 3b). More tubules remained partially filled in the apical thirds,
despite the lower number of tubules that is a normal feature of the apical
part of the root canal compared with the middle and coronal parts.
Lateral branches were visible in the dentinal walls of each retreatment
group especially in the apical third (Fig. 3c).
Dentin surface morphology was similar in the 3 retreatment
groups, irrespective of the obturation system used (AH Plus/Thermafil
versus AH Plus/warm gutta-percha).
Filling Debris
Virtually all samples presented superficial sparse dentinal and
filling debris (Fig. 4). The debris particles, probably constituted by
TABLE 1. Scale of Values Assigned to the 3 Different Parameters Evaluated
1234
Smear layer Smear layer absent,
more than 75% of
tubules exposed and
free from smear layer.
Tubules completely
opened.
Present in limited areas,
less than 75% of
tubules uncovered.
Tubules partially
opened.
Present, tubules visible
in limited areas and
partially closed. Less
than 50% of dentinal
tubules visible.
Homogeneous smear
layer present above
all dentin. Dentinal
tubules not visible.
Filling debris Absent Minimal presence.
Present in less than
25% of the area.
Often present Present everywhere and
covering dentin
surface.
Surface profile Absence of irregularities Isolated irregularities
and grooves
Partially irregular, with
limited
noninstrumented
areas
Irregular with grooves,
areas of
uninstrumented
dentin
Figure 1. Box and whiskers plots for the retreatment groups. Smear layer, surface profile, and filling debris parameters. (manual K-file, M2 NiTi rotary instru-
ments, ultrasounds ESI).
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JOE —Volume 35, Number 10, October 2009 Effectiveness of 3 Retreatment Techniques 1435
sealer, had a diameter of 5–6 mm and were located on the inner dentin
surface (Fig. 4a). Gutta-percha debris was occasionally noted with frag-
ments of a diameter up to 100 mm but more frequently was represented
by small fragments of 20–30 mm.
There were no significant differences between K-files, M-Two, and
ultrasound retreatment groups.
Coronal, middle, and apical thirds showed similar quantities of
debris in both filling groups (Fig. 4). No statistical differences were
Figure 2. Box and whiskers plots for each retreatment group. Smear layer parameter. Coronal third (positive control) = 1; coronal part of medium third = 2;
apical part of medium third = 3; apical third = 4.
Figure 3. Smear layer evaluation (original magnification, 2000). Dentin (coronal third) resulted completely free from smear layer and no debris obturated
tubules (A). (B) Several dentinal tubules (apical third) appeared partially or completely obliterated by the presence of smear layer and smear plugs. After retreat-
ment, debris can be seen in the middle third, with peritubular enlargement of several tubules (C). Lateral branches are well-displayed in the micrograph (original
magnification, 2000) and were funneled probably by the double action of EDTA and NaOCl.
Basic Research—Technology
1436 Pirani et al. JOE —Volume 35, Number 10, October 2009
observed between AH Plus/Thermafil and AH Plus/warm gutta-percha
for each retreatment group considered (Fig. 5).
Surface Profile
No statistical differences were found between the 3 retreatment
groups (Fig. 1b). The canal walls of the samples showed smooth
surfaces and were free from irregularities such as pits or grooves
(Fig. 6a, b).
The 3 retreatment groups showed similar canal morphology, irre-
spective of the 3 thirds of the canals (Fig. 7). Predentin was observed in
limited uninstrumented areas with grooves (Fig. 6c).
Discussion
During root canal retreatment, the removal of gutta-percha and
sealer is essential to allow the endodontic irrigants to contact and
reduce the bacteria contained in the root canal space and dentinal
tubules (26).
The present study used high-resolution SEM images to evaluate the
effectiveness of the retreatment techniques used on the inner root canal
dentin morphology. SEM observation is the only technique available to
observe the smear layer and organic and filling debris in a re-treated
root canal. The resolution of all other possible techniques (including
micro–computed tomography) is insufficient to detect these features.
Different techniques have been proposed to measure the amount
of debris, gutta-percha, and sealer on the root inner dentin surface (6,
11, 12, 27). Many recent studies used light microscopy, visual inspec-
tion, and/or other techniques such as clearing (22) and optical evalu-
ation (12). Hence, the results of the present study can only be compared
with previous radiographic (7), stereomicroscopic (13), and light
microscopic studies (5, 17).
Other recent studies measured the area of remaining obturation
material on the inner dentin surface by using a computer image analysis
program after root decalcification (22) or a photo micrographic
method by epiluminescence (28). SEM allowed observation of smear
layer morphology, the presence of debris inside dentinal tubules and
root canal orifices, and the morphology of intertubular dentin (29).
The techniques previously used failed to detect dentin and debris
morphology at high magnification.
The present SEM analysis demonstrated that only 2 samples
(5.6%) were completely free from smear layer and filling debris
after endodontic retreatment. Similar amounts of smear layer and
filling debris were found in each canal third, irrespective of the
root filling and retreatment techniques adopted. These results
suggest that gutta-percha/sealer traces are almost impossible to re-
move from the canal in accordance with previous investigations
(12, 19). Hence, our study demonstrated that the apical third could
only be partially cleaned, leaving a small amount of smear layer and
sealer debris.
The morphology of re-treated dentin differs from that of dentin
commonly observed at the end of the first endodontic treatment (24,
25), whereas sealer debris was observed on the dentin surface. Erosion
of dentinal tubules was observed in several samples, possibly as a result
of continuous irrigation with EDTA during retreatment. EDTA was found
to be effective in removing peritubular dentin, thereby increasing the
diameter of dentinal tubules (24).
Figure 4. In several samples dentinal tubule orifices were obturated by gutta-percha and resin sealer material (A; original magnification, 2000). These fractured
resin tags obliterated the orifices of dentinal tubules and remained in place after the retreatment. A similar morphology was observed in all 3 retreatment techniques
used. These resin tags (AH Plus) were probably created during canal obturation (B; original magnification, 2000), and the deeper side of the ‘‘resin tail’’ remains
blocked in dentinal tubules after the retreatment. Several tubules contained debris (C; original magnification, 5000) pushed inside the orifices during the instru-
mentation phases. The use of EDTA probably contributed to the removal of much of this debris, but in several samples at medium-apical third the debris (probably
a sort of artificial smear layer) remained packed inside tubules. EDTA and NaOCl probably failed to solve and remove the debris from the tubules because of its
artificial composition (resin and gutta-percha).
Basic Research—Technology
JOE —Volume 35, Number 10, October 2009 Effectiveness of 3 Retreatment Techniques 1437
All the root canals in the present study were filled with AH Plus as
the sealer. Material resin tags were seldom found inside dentinal tubules
in any of the 3 groups. AH Plus proved to be a very difficult material to
remove from dentinal tubules, as suggested by a recent investigation in
which Epiphany was readily removed (22). AH Plus penetrates 10–80
mm into the dentinal tubules when the smear layer is removed (29), but
penetration of the sealer tags into the dentinal tubules is not associated
with higher bond strength (30). Considering that the retreatment instru-
mentation probably removes at least 40–80 mm, this explains why
dentinal tubules were partially free from resin tags. Debris and tags
Figure 5. Box and whiskers plots for each retreatment group. Filling debris parameter. Coronal third (positive control) = 1; coronal part of medium third = 2;
apical part of medium third = 3; apical third = 4.
Figure 6. Surface profile in the middle third of a sample obturated with AH Plus/Thermafil (A; original magnification, 75). Different layers of partially instru-
mented dentin surface with a ‘‘tree-bark’’ configuration (B; original magnification, 2000). Underinstrumented dentin surface (C; original magnification, 500)
with a well-visible area of predentin and dentinal groove. No smear layer is present. Another area of dentin (on the left) was instrumented. The middle of the picture
shows an area with filling debris spread and immersed in the thickness of the smear layer.
Basic Research—Technology
1438 Pirani et al. JOE —Volume 35, Number 10, October 2009
were observed at the orifices of dentinal tubules that appeared partially
patent if not with erosion aspects.
It is obvious that EDTA and NaOCl were not able to remove resin
(AH Plus) and gutta-percha tags. The presence of a new ‘‘artificial’’
smear layer (resin sealer–gutta-percha and dentin debris) created by
instruments did not prevent the irrigant solution from removing debris
in all the retreatment groups. Only larger apical size and canal diameter
after retreatment created the conditions to remove tags. The use of EDTA
during the first instrumentation of root canal removed the smear layer
and probably increased the number of dentinal tubules filled with resin
sealer and gutta-percha (27, 28, 31). The presence of a smear layer
might reduce the penetration of resin sealer into dentinal tubules.
This might be important for the elimination of bacteria from the dentinal
tubules (4). In fact, bacteria might easily grow in canal debris and cause
the retreatment to fail. Recent studies demonstrated that bacteria such
as Enterococcus faecalis might survive for a long time inside the root
canals (32, 33).
No solvent was used to help remove the root canal filling materials.
This was done to minimize the number of variables involved in the study.
According to Wilcox and Juhlin (34), the use of solvents results in the
deposition of a thin layer of filling material on the root canal walls that is
difficult to detect and remove. This layer attenuates the action of intra-
canal antibacterial medicaments and might impair the adaptation of the
subsequent filling material to the root canal walls (21, 31).
The number and diameter of dentinal tubules were very limited in
the apical area. Few tubules were present in the apical third, and only
intertubular dentin was seen in several areas in which the amount of
debris was modest and the tubules (when present) were free from
debris and clearly visible.
Considering previous light microscopy investigations, Betti and
Bramante (17) found no differences between each canal third by
comparing retreatments with ProTaper and K-files, whereas Hu¨lsmann
and Bluhm (5) observed that the apical third was the area with the most
gutta-percha debris. No statistical differences were observed in the
present study between rotary NiTi, manual instruments, and ultrasonic
tips in terms of removing gutta-percha, in agreement with earlier studies
comparing hand files with NiTi rotary instruments (5, 18).
The quality and the quantity of debris left in the canal system and
the morphology of debris inside dentinal tubules in the AH Plus/Ther-
mafil group were similar to those of the other group. The presence of
the plastic carrier means that a different technique might be used in the
preliminary step of the retreatment, but the morphology obtained at the
end is similar. Smear layer morphology and resin tags were similar in
both groups.
Ultrasonic tips are outstanding tools in the coronal half of root
canal systems, but in curved canals they could compromise the
apical half of a canal’s anatomy; hence, they should only be used
above canal curvatures. For this reason, only straight teeth were
selected in the present study. They have not been used in in vitro
studies on retreatments of root canals filled with Thermafil, so few
studies have evaluated retreatment on Thermafil obturated roots
in vitro (7, 34).
Wilcox and Juhlin (34) observed that the adequacy of Thermafil
retreatment is related more to the ability to remove the carrier than
to the technique of gutta-percha removal. Our study found no carrier
debris inside the root canals.
As regards the technical procedures applied in this study, we
presume that the use of Gates-Glidden to remove the coronal position
of root canal filling created adequate conditions for the preliminary
removal of the plastic Thermafil carrier. Hence, the removal of the
coronal portion of filling materials permits the correct insertion of
NiTi and ultrasound instruments.
Figure 7. Box and whiskers plots for each retreatment group. Surface profile parameter. Coronal third (positive control) = 1; coronal part of medium third = 2;
apical part of medium third = 3; apical third = 4.
Basic Research—Technology
JOE —Volume 35, Number 10, October 2009 Effectiveness of 3 Retreatment Techniques 1439
Conclusion
SEM is an extremely efficient means of observing the morphology
of residual root filling material. Apical instrumentation with a no. 40 is
probably insufficient (4) for complete removal of filling debris plugs
present in all the dentinal tubules. The complex morphology of the
inner dentin root might increase the risk of insufficient sealer debris
removal from dentinal tubules, as confirmed by the presence of several
fractured resin tags.
All retreatment techniques showed similar performances in terms
of smear layer morphology, amount of debris, and surface profile. None
of them completely removed filling debris from the dentinal tubules of
apical third. Retreatment techniques for teeth filled with AH Plus/Ther-
mafil produce a dentin morphology similar to that obtained with AH
Plus/warm condensed gutta-percha. Thermafil-filled teeth might be
re-treated with different techniques.
No differences were observed in the root dentin morphology of
teeth filled with AH Plus/Thermafil and with AH Plus/warm condensed
gutta-percha.
Acknowledgments
This study was supported by ‘ex 60% RFO’ grants from the
University of Bologna (funds for selected research topics).
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Basic Research—Technology
1440 Pirani et al. JOE —Volume 35, Number 10, October 2009
