Micro-computed tomographic assessment of dentinal microcrack formation in straight and curved root canals in extracted teeth prepared with hand, rotary and reciprocating instruments

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Micro-computed tomographic assessment of dentinal
microcrack formation in straight and curved root canals in
extracted teeth prepared with hand, rotary and reciprocating
instruments
International
endodontic
journal
2021
Presented by : DR.AJAY BABU G
IIYEAR PG
DEPARTMENT OF CONS AND
ENDO
J. C. L. G. D. Martins, B. P. Oliveira, D. A. Duarte, A. C. D. Antonino, C. M.
Aguiar&
A. C. Camara
1

 Various studies have investigated the effect of root canal shaping on the induction of dentinal defects as they are
likely to act as a starting point for vertical root fractures and, ultimately, tooth loss (Toure et al. 2011).
 However, reports from research data have been inconsistent concerning the incidence of dentinal cracks after
shaping of straight and curved root canals with either hand, rotary and reciprocating instruments, often generating
confusion and uncertainty on the part of practitioners who are seeking the safest technique.
 Most of the previous studies on the incidence of dentinal defects have used root sectioning and microscopy
analysis to assess the induction of microcracks.
 This methodology has several shortcomings, such as the possibility of producing dentinal defects by the
sectioning procedure itself and the impossibility of reliably identifying preexisting dentinal.
 On the other hand, recently, the introduction of a non-destructive high-resolution imaging technology, such as
micro-CT, has provided more reliable data on the formation of microcracks in roots
3

 Despite these advantages, even in studies that have used micro-CT analysis, the percentage of
microcracks created by nickel-titanium instruments in curved roots has ranged from 0% to 38%,
increasing the suspicion that root canal curvature may be one of the factors related to the development of
dentinal microcracks.
 It has been speculated that these contradictory findings reported in micro-CT research can be related to
differences in the methodological approaches used to assess the incidence of microcracks in each study,
such as scanning and reconstruction parameters, interpretation of defects and digital artefacts, and storage
conditions of teeth.
 Thus, micro-CT investigations in which straight and curved root canals are instrumented by different
techniques and analysed under similar experimental conditions are necessary to provide a better
understanding of the factors related to the development of dentinal microcracks.
4

 The aim of this study was to compare microcrack formation in roots of extracted teeth after shaping of
straight and curved root canals with hand, rotary and reciprocating files using micro-CT analysis. The
null hypothesis tested was that neither the canal curvature nor the root canal preparation technique has an
effect on microcrack formation.
6

Sample size calculation
Sample size calculation was performed using ANOVA test (G*Power 3.1 software; Heinrich Heine, University, Dusseldorf,
Germany), considering the effect size expected of 0.5, with a power of 0.80, a = 0.05 and 6 treatment groups. After
calculations, the sample size for each group was set at a minimum of 10 teeth.
Sample selection and preparation
120 mandibular incisiors & 150 mand 1st & 2nd molars
Steromicroscopic analysis
Mesiodistal and buccolingual radiographs for degree and radius of
curvature, and canal configuration
mandibular incisors with single straight root canals
(<5°), and mesial roots of mandibular molars with
two separate canals, severe curvature ranging from
25° to 40° and a radius of curvature smaller than 10
mm
Teeth with previous endodontic
treatment,calcifications,internal/external resorption
and root caries, non patient canals were discarded.
60 specimens
30 mandibular incisors and 30 mesial roots of mandibular molars 8

Roots of teeth decoronated 13mm from the apex
specimen was allowed to dry at room temperature (20 °C) for 2 h imaged with
at an isotropic resolution of 14 μm
Xrays were generated at 70 kV and 114 μA, and filtered with a 1-mm-thick
aluminium filter
Scanning was performed by 360° rotation around the vertical axis with a rotation
step of 0.12°, an exposure time of 500 ms and one frame per projection.
Roots of teeth decoronated 13mm from the apex
cross-sections of the internal structure of the roots
specimens were stored again in purified filtered water until use.
9

Root canal procedure
 The canal length was measured by inserting a size 10 K-file into the canal until its tip became visible at the apical foramen. The working
length was established by subtracting 1 mm from this length. To simulate the periodontal ligament space, the surfaces of the roots were
coated with a thin film of silicone based impression material and embedded in acrylic resin.
 The teeth were numbered and randomly divided into 6 experimental groups (n = 10) according to the technique used for the root canal
preparation and the canal curvature evaluated. Hand, rotary and reciprocating files were tested: Pro-Taper Universal for Hand Use
(Dentsply Sirona), HyFlex EDM (Coltene-Whaledent, Altst€atten, Switzerland) and Reciproc Blue (VDW, Munich, Germany). The
instrumentations were performed in different canal curvatures: mandibular incisors (straight canals), and mesiobuccal and mesiolingual
canals of mandibular molars (severely curved canals).
 The glide path was performed using a size 15 K-file up to the working length. ProTaper Universal for Hand Use files were employed in the
following sequence: Sx prepared the coronal portion of the canal, and subsequently, S1, S2, F1 and F2 (size 25, .08 taper) were used until
the working length was reached. HyFlex EDM files were employed in a crowndown sequence by using: size 25, .12 taper (two thirds of the
working length), size 10, .05 taper, and size 25, variable taper (the full working length). The R25 Reciproc Blue (size 25, .08 taper) was
used in a reciprocating slow in-and-out pecking motion of approximately 3 mm in amplitude with a light apical pressure until the working
length was reached.
10

 Instrumentation with HyFlex EDM and Reciproc Blue instruments was carried out with a low-torque motor (X-Smart Plus;
Dentsply Sirona) according to instructions set by the manufacturer of each system. All root canal preparations were carried out
by a single operator, and each instrument was used to prepare 4 canals only. Irrigation was performed using a total of 15 mL
1% sodium hypochlorite per canal, administered with a syringe and a 30-gauge needle (Ultradent Products Inc, South Jordan,
UT, USA) between the use of each instrument or after 3 pecking motions. Final irrigation was performed using 5 Ml 17%
EDTA and 5 mL distilled water.
 After instrumentations, the specimens were removed from the acrylic resin and imaged again with micro-CT (post-
instrumentation scan) using the aforementioned parameters. Thereby, the pre- and post-instrumentation images were produced
and, subsequently, assessed using the same parameters.
11

Microcrack evaluation
 Micro-CT cross-sectional images generated before and after the root canal preparation (n = 111.480) were
evaluated blindly by three examiners, who were endodontic specialists, to detect the presence of microcracks in
the roots.
 A microcrack was defined as any incomplete crack (line extending from the canal wall into the dentine without
reaching the outer surface of the root), complete crack (line extending from the root canal wall to the outer
surface) or craze line (other lines that did not reach any surface of the root or extend from the outer surface into
the dentine but did not reach the canal wall) observed in the root dentine.
 If a post-instrumentation image exhibited a microcrack, the pre-instrumentation corresponding cross-section
image was also inspected to check the preexistence of microcracks.
 The images were reassessed after an interval of 4 weeks. In case of discrepancy amongst the observations, the
slices were examined again, and the examiners discussed the findings until they reached an agreement.
12

 From a total of 111 480 slices, 18 451 (17%) had microcracks. Instrumentation of mandibular incisors had 3446 (19%),
1996 (11%) and 4182 (23%) crosssectional images with dentinal microcracks when canals were prepared with ProTaper
Universal for Hand Use, HyFlex EDM and Reciproc Blue, respectively. When instrumentation was performed in mesial
roots of mandibular molars, dentinal microcracks were present in 2860 (15%), 2902 (16%) and 3065 (17%) cross-
sectional images when canals were prepared with ProTaper Universal for Hand Use, HyFlex EDM and Reciproc Blue,
respectively.
 All microcracks detected after root canal preparation had already existed before instrumentation. Thus, independent of
the canal curvature or the technique used for the root canal preparation, no new microcrack was generated. Because there
were no new dentinal defects, statistical analysis was not performed.
14

 Bier et al. (2009) and Shemesh et al. (2009) reported a relationship between canal preparation and microcrack formation in roots of
extracted teeth, and since, then various studies have described a contradictory and worrisome incidence of microcracks generated by
hand, rotary and reciprocating instruments.
 For instance, the incidence of dentinal microcracks after canal preparation with hand files has ranged from 0% to 50%, whereas
preparation with ProTaper Universal system caused cracks in 0% to 80% of the sample. Root canal preparation with Reciproc R25
instrument produced cracks in 0% (De- Deus et al. 2014, de Oliveira et al. 2017b) to 75% (Pedulla et al. 2017) of specimens.
 This discrepancy of results can be explained by differences in the methodologies used to assess dentinal microcracks. The
accumulated body of evidence correlating canal preparation to the development of microcracks in roots is mostly based on root
sectioning methods by which, after root canal preparation, the specimens are sectioned at various levels from the apex, and the
resulting slices are observed through a stereomicroscope.
 In recent years, this technique has received severe criticism due to its deficiency in detecting pre-existing microcracks, which, when
added to those produced by the sectioning procedure, might induce false-positive results (Versiani et al. 2015).
 In contrast, with micro-CT methodology, high-resolution images are provided in all three dimensions without sectioning the
samples, enabling the assessment of dentinal defects before and after root canal shaping on the same tooth. Thus, in this method,
pre-existing microcracks can be reliably detected, and each sample serves as its own control (Versiani et al. 2015). 17

 Under this micro-CT technology, the current study revealed that no microcrack could be attributed to root canal
instrumentation with either the ProTaper Universal for Hand Use, the HyFlex EDM or the Reciproc Blue. This result agrees
with previous investigations that also showed a lack of relationship between microcrack formation and biomechanical
preparation with hand, rotary or reciprocating instruments by using micro-CT analysis.
 Although micro-CT is a reliable, highly accurate and non-destructive experimental imaging method, recently, several micro-
CT studies have reported that root canal preparation produced microcracks in mandibular molars. These findings increased
the suspicion that root canal curvature may be one of the factors related to the creation of dentinal defects.
 In the present study, biomechanical preparation did not cause microcracks, even in root canals with severe curvature (25°–
40°) or in straight canals, regardless of the technique used to prepare the canals. Therefore, the null hypothesis was accepted,
agreeing with previous findings.
 These conflicting findings reported in micro-CT studies can be related to different methodological approaches used. Some of
these are as follows: scanning and reconstruction parameters, interpretation of defects and digital artefacts, number of cross-
sectional images assessed and, mainly, the conditions of samples storage. Concern has been raised that dehydration of
extracted teeth may induce spontaneous cracking or may affect the biomechanical response of root dentine to
instrumentation, and so, decrease teeth resistance to the fracture.
18

 In addition, it has been demonstrated that the moisture content of dentine influences the visibility of microcracks on micro-CT images,
and scanning of samples after 2 h dry time significantly improved the identification of microcracks compared to wet specimens.
Consequently, in this study, in order to ensure a more reliable identification of dentinal defects, the teeth were allowed to dry for 2 h
before pre- and post-instrumentation scans. Even so, the same microcracks that were detected in the post-instrumentation images were
detected in the pre-instrumentation images. This result agrees with R€odig et al. who also concluded that drying of specimens for 2 h did
not induce new microcracks.
 It is important to point out that, in this study, the extension and width of the microcracks were not evaluated, which is a limitation of this
investigation. Further research is required for more detailed evaluation of changes in the morphology of microcracks.
 In the present study, the roots were encapsulated with an elastomeric impression material and acrylic resin to mimic the periodontal
ligament during the root canal preparation.
 According to Soros et al. (2008), there is no artificial material capable of absorbing the forces on teeth similarly to the natural
periodontal ligament. Thus, the absence of natural periodontal structures may have been a limitation. However, a micro-CT investigation
performed under almost ideal conditions using an in situ fresh cadaver model with an intact periodontal ligament and bone also found
that root canal preparation with ProTaper Universal and Reciproc systems did not induce the formation of dentinal microcracks.
 Therefore, further studies are needed for the establishment of ideal methodological approaches to evaluate the presence of dentinal
microcracks and, thus, provide a better understanding of the factors related to the development of this worrisome entity. 19

 Within the limitations of this laboratory study, the instrumentation of straight and curved root canals in extracted teeth with
ProTaper Universal for Hand Use, HyFlex EDM and Reciproc Blue systems did not produce microcracks in roots.
21

MICRO-COMPUTED TOMOGRAPHIC EVALUATION OF DENTINAL MICROCRACK
FORMATION AFTER USING NEW HEAT-TREATED NICKEL-TITANIUM SYSTEMS
 Introduction: The aim of the present study was to evaluate the frequency of dentinal microcracks observed
after root canal preparation with HyFlex CM (Coltène/Whaledent, Altstätten, Switzerland), HyFlex EDM
(Coltène/Whaledent), Vortex Blue (Dentsply Tulsa Dental Specialties, Tulsa, OK), and TRUShape (Dentsply
Tulsa Dental Specialties) systems using micro-computed tomographic (micro-CT) analysis.
 Methods: Forty human mandibular incisors with 1 and straight root canals were randomly assigned to 4
experimental groups (n = 10) and 1 control group for root canal preparation: group 1, HyFlex CM; group 2,
HyFlex EDM; group 3, Vortex Blue; and group 4, TRUShape. The specimens were scanned using high-
resolution micro-CT imaging before and after root canal preparation. Afterward, preoperative and
postoperative cross-sectional images of the teeth were screened to identify the presence of dentinal
defects. The number of microcracks was determined as a percentage for each group.
 Results: Before and after canal preparation, 36,152 cross-sectional images were examined. Four thousand
four hundred fifty-two (12.31%) dentinal defects were observed. No new microcracks were observed after
root canal instrumentation with the tested systems.
 Conclusions: Root canal preparation with the HyFlex CM, HyFlex EDM, Vortex Blue, and TRUShape
systems did not induce the formation of new dentinal microcracks on straight root canals of mandibular
incisors.
22

DENTINAL MICROCRACK FORMATION AFTER ROOT CANAL
INSTRUMENTATION BY XP-ENDO SHAPER AND PROTAPER
UNIVERSAL: A MICROCOMPUTED TOMOGRAPHY EVALUATION
Aim
 To evaluate dentinal microcrack formation on root canals instrumented, continuously in the body temperature, with XP-endo shaper (XPES) and
ProTaper Universal (PTU), by means of microcomputed tomographic (micro-CT) analysis.
Methodology
Nineteen mesial roots with two separate canals (Vertucci Type IV) of extracted mandibular molars were used in this study. The root canals (N = 38) were
divided into 2 groups. Group 1 (n = 19): all MB canals were instrumented with XPES. Group 2 (n = 19): all ML canals were instrumented with PTU. All
roots were scanned with micro-CT before and after instrumentation. Two precalibrated examiners evaluated the cross-sectional images of each sample
with DataViewer program. The dentinal microcracks (complete and incomplete) were counted in each third of the root for the preinstrumentation and the
postinstrumentation images. Wilcoxin signed-rank and Mann–Whitney U tests were used for statistical analysis at a significance level of P < 0.05.
Results
The number of microcracks increased significantly (P < 0.05) after instrumentation with XPES in the middle and cervical thirds. The number of
microcracks increased significantly (P < 0.05) after instrumentation with PTU in the cervical third only. There was no significant difference between the
groups in the cervical and apical thirds. In the middle third, the XPES induced more incomplete microcracks than PTU (P < 0.05).
Conclusion
Within the limitations of this study, there was no significant difference in the dentinal microcrack formation between XPES and PTU in the apical and
cervical thirds of the root. However, XPES instrumentation induced more incomplete microcracks than PTU in the middle third of human roots.
23

Micro-computed tomographic assessment of dentinal microcrack formation in straight and curved root canals in extracted teeth prepared with hand, rotary and reciprocating instruments

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Micro-computed tomographic assessment of dentinal microcrack formation in straight and curved root canals in extracted teeth prepared with hand, rotary and reciprocating instruments