Influence of Root Canal Preparation on Formation of Dentinal Microcracks: A Systematic Review

Valle, Alânia Dalla; Dotto, Lara; Morgental, Renata Dornelles; Pereira-Cenci, Tatiana; Pereira, Gabriel Kalil da Rocha; Sarkis-Onofre, Rafael

doi:10.1590/0103-6440202002652

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Review Article • Braz. Dent. J. 31 (3) • May-Jun 2020 • https://doi.org/10.1590/0103-6440202002652 copy

Influence of Root Canal Preparation on Formation of Dentinal Microcracks: A Systematic Review

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The effect of root canal preparation technique on microcrack initiation is a controversial issue. This systematic review aimed to assess the role of root canal preparation techniques with different kinematics (manual, rotary, reciprocating, adaptive, self-adjusting file) on microcrack initiation. In vitro and in situ studies comparing the influence of at least two different root canal preparation techniques on the initiation of dentin microcracks were searched in PubMed/MEDLINE and SCOPUS up to June 5, 2018 without language and period restriction. Two authors independently reviewed all identified titles and abstracts for eligibility. Tables were generated to summarize the included studies, and the included studies were assessed for bias. Fifty-four (n=54) articles met the eligibility criteria. The results were classified according to the method used for microcrack evaluation, and most studies that used micro-computed tomography showed no formation of new cracks after root canal preparation. In general, the instrumentation techniques induced microcrack formation when the methods were destructive, irrespective of kinematics. In relation to the apex region, when the preparation working length was set as the root canal length subtracted of 1 mm, the risk of microcrack initiation reduces. The majority of the included studies had low risk of bias for all assessed domains. Our results seem to indicate that the various root canal preparation techniques considered in this study will not cause damage to the dental structure when adequately employed and the proper methodology is applied.

Key Words:
endodontic treatment; dentinal microcracks; micro-computed tomography analysis; root canal preparation; systematic review

Reference	Method of microcrak evaluation	Comparison tested	Root canal irrigation	Teeth used
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Karatas, E., et al. (2016). «Incidence of dentinal cracks after root canal preparation with ProTaper Gold, Profile Vortex, F360, Reciproc and ProTaper Universal instruments.» Int Endod J.	Destructive/Stereomicroscope	Rotary, Reciprocating	2% NaOCl	90 human mandibular central incisor teeth with mature apices and straight canals, single canal, mature apices and single apical foramen
Karatas, E., et al. (2015). «Incidence of Dentinal Cracks after Root Canal Preparation with Twisted File Adaptive Instruments Using Different Kinematics.» J Endod 41(7): 1130-1133.	Destructive/Stereomicroscope	Hand, Twisted File Adaptive	NaOCl	105 human mandibular central incisors with single canals and similar lengths
Kesim, B., et al. (2017). «Evaluation of dentinal defects during root canal preparation using thermomechanically processed nickel-titanium files.» Eur J Dent 11(2): 157-161.	Destructive/Stereomicroscope	Hand, Rotary, Reciprocating, Twisted File Adaptive	1% NaOCl	150 human mandibular premolars with mature apices and a root canal curvature<5°, one straight canal
Kfir, A., et al. (2017). «Incidence of microcracks in maxillary first premolars after instrumentation with three different mechanized file systems: a comparative ex vivo study.» Clin Oral Investig 21(1): 405-411.	Destructive/Dental Operating Microscope	Rotatory, Reciprocating, Self Adjusting File	3% NaOCl	80 human maxillary first premolars with two separate root canals, straight roots and closed mature apices
Khirtika, S. G. and S. Ramesh (2017). “Comparative evaluation of dentinal cracks and detachments after instrumentation with hand and rotary files at various instrumentation lengths: An in vitro study.” J Adv Pharm Technol Res 7(3): 236-239.	Destructive/Dental Operating Microscope	Hand instrumentation, Rotatory	1% NaOCl	36 human mandibular central incisors, single root and single canal
Khoshbin, E., et al. (2018). «The effect of canal preparation with four different rotary systems on formation of dentinal cracks: an in vitro evaluation.» Iran Endod J 13(2): 163-168.	Destructive/Stereomicroscope	Hand, Rotary, Reciprocating	Reciproc (3 mL of saline); Control groups (2.5% NaOCl)	110 human single-rooted, single-canal human teeth with no apical root curvature
Kumari, M. R. and M. M. Krishnaswamy (2016). «Comparative analysis of crack propagation in roots with hand and rotary instrumentation of the Root Canal -An Ex-vivo Study.» J Clin Diagn Res 10(7): Zc16-19.	Non-Destructive (apex)/ Stereomicroscope	Hand, Rotatory	None	70 human premolars with complete apices and single, straight root and root canal
Li, M. L., et al. (2018). «A micro-computed tomographic evaluation of dentinal microcrack alterations during root canal preparation using single-file Ni-Ti systems.» Exp Ther Med 15(1): 494-499.	Non-destructive/µCT	Hand, Rotary, Reciprocating	5.25% sodium hipochloryte	100 human mandibular first molars with completely separated roots
Li, S. H., et al. (2015). «Occurrence of dentinal microcracks in severely curved root canals with ProTaper Universal, WaveOne, and ProTaper Next File Systems.» J Endod 41(11): 1875-1879.	Destructive/Stereomicroscope	Rotary, Reciprocating	1% NaOCl	60 human molars, each with at least 1 curved root and root canal
Liu, R., et al. (2013)a. «Incidence of apical root cracks and apical dentinal detachments after canal preparation with hand and rotary files at different instrumentation lengths.» J Endod 39(1): 129-132.	Destructive/Stereomicroscope (apex)	Hand, Rotatory	2% NaOCl	240 human mandibular incisors with straight roots and single canal
Liu, R., et al. (2013). «The incidence of root microcracks caused by 3 different single-file systems versus the ProTaper system.» J Endod 39(8): 1054-1056.	Destructive (sections) Non-destructive (apex)/Stereomicroscope	Rotatory, Reciprocating, Self Adjusting File	2% NaOCl	100 human mandibular incisors with straight roots, single canal
Milani, A. S., et al. (2012). «The effect of root canal preparation on the development of dentin cracks.» Iran Endod J 7(4): 177-182.	Destructive/Dental Operating Microscope	Hand, Rotatory	1% NaOCl	57 human mandible incisor teeth.
Monga, P., et al. (2015). «Comparison of incidence of dentinal defects after root canal preparation with continuous rotation and reciprocating instrumentation.» Singapore Dent J 36: 29-33.	Destructive/Stereomicroscope	Hand, Rotary, Reciprocating	3% NaOCl	150 human mandibular premolars with mature apices and single straight root canals with single apical foramen
Pedulla, E., et al. (2017). «Effects of 6 single-file systems on dentinal crack formation.» J Endod 43(3): 456-461.	Destructive/Stereomicroscope	Rotary, Reciprocating	3% NaOCl	64 human mandibular central incisors with mature apices single rooted teeth with a single straight canal
Pop, I., et al. (2015). «Synchrotron light-based µCT to analyse the presence of dentinal microcracks post-rotary and reciprocating NiTi instrumentation.» Clin Oral Investig 19(1): 11-16.	Non-destructive/µCT	Rotary, Reciprocating	1% NaOCl	14 human mandibular and maxillary first molars with mature apices
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Author	Preparation technique	System	Results
Author	Preparation technique	System	Microcracks on baseline	Instrumentation inducing, forming or propagating cracks
Bayram et al., 2017	Rotary, Self-Adjusting File	ProTaper Universal (rot), ProTaper Gold (rot), Self-Adjusting File, XP-endo Shaper (rot)	Yes	No
Cassimiro et al., 2017	Rotary, Reciprocating	ProTaper Next (rot), K3XF (rot), WaveOne Gold (rec)	Yes	No
Ceyhanli et al., 2016	Rotary, Reciprocating	ProTaper Universal (rot), RaCe (rot), Safesider (rec)	Yes	ProTaper Universal (Rot) system generated more post-instrumentation dentinal microcracks than the RaCe system (Rot)
de Oliveira et al., 2017	Manual, Rotary, Reciprocating	ProTaper Universal for Hand Use (manual), HyFlex CM (rot), Reciproc (rec)	Yes	No
De-Deus et a., 2015	Rotary, Adaptive	ProTaper Next (rot), Twisted File Adaptive (TFA)	Yes	No
De-Deus et a., 2017	Rotary, Reciprocating	Reciproc (rec), ProTaper Universal (rot)	Only in ProTaper Universal group	No
Jamleh et al. 2015	Rotary, Reciprocating	ProTaper (rot), WaveOne (rec)	No	WaveOne (Rec) showed a trend of introducing fewer microcracks than ProTaper (Rot)
Li et al., 2018	Manual, Rotary, Reciprocating	WaveOne (rec), OneShape (rot), Reciproc (rec), K-file (manual)	Yes	The OneShape system (Rot) resulted in increased microcracks
Pop et al., 2015	Rotary, Reciprocating	ProTaper (rot), WaveOne (rec)	Yes	Both systems induced microcracks
Stringheta et al., 2017	Rotary, Reciprocating	Reciproc (rec), ProTaper Next (rot), WaveOne Gold (rec), ProDesign Logic (rot)	Yes	No
Zuolo et al., 2017	Rotary, Reciprocating, Self-Adjusting File	TRUShape (rot), Self-Adjusting File, BioRace (rot), Reciproc (rec)	Yes	No

Author	Preparation technique	System	Non-prepared teeth as baseline comparison	Results
Author	Preparation technique	System	Non-prepared teeth as baseline comparison	Microcracks on baseline	Instrumentation inducing, forming or propagating cracks
Arias et al., 2014	Hand, Reciprocating	Profile GT (hand), WaveOne (rec)	Yes	Yes	No indicatives of formation of microcracks in comparison to non-instrumented teeth
Aydin et al., 2015	Reciprocating, TFA	Reciproc (rec), WaveOne (rec), TFA (adaptive motion)	Yes	No: non instrumented teeth show absence of microcracks	Formation of microcracks regardless of instrumentation system used.
Ashwinkumar et al., 2014	Hand, Rotary, Reciprocating	NiTi K-files (manual); ProTaper (manual); ProTaper (rot); WaveOne (rec)	Yes	No: non instrumented teeth show absence of microcracks	ProTaper rotary files were associated with significantly more microcracks than ProTaper hand files and WaveOne Primary reciprocating files. Ni-Ti hand K-files did not produce microcracks at any levels inside the root canals.
Bahrami et al., 2017	Hand, Rotary, Reciprocating	Stainless steel K-Flexo files (hand), TRUShape (rot), WaveOne Gold (rec)	Yes	Yes	No indicatives of formation of microcracks in comparison to non-instrumented teeth. (There was no relationship between the shaping kinematics (hand preparation, WaveOne reciprocation, and rotary TRUShape) and the frequency of microcracks)
Bier et al., 2009	Hand, Rotary	Flexofiles (hand), ProTaper (rot), ProFile (rot), SystemGT (rot), S-ApeX (rot)	Yes	No: non instrumented teeth show absence of microcracks	Hand instrumentation and rotary instrumentation with S-ApeX system show absence of microcracks. However, the use of other rotary NiTi instruments resulted in formation of microcracks.
Borges et al., 2018	Hand, Rotary, Reciprocating	Stainless steel K-files (hand), ProTaper Universal (rot), ProTaper Next (rot), ProFile (rot), Reciproc (rec), WaveOne (rec)	Yes	No: non instrumented teeth show absence of microcracks	All instruments lead to the formation of microcracks, regardless of the enlargement or not of the cervical portion.
Burklein et al., 2013	Rotary, Reciprocating	Mtwo (rot), ProTaper (rot), Reciproc (rec), WaveOne (rec)	Yes	No: non instrumented teeth show absence of microcracks	Formation of microcracks regardless of instrumentation system used. (At the apical level of the canals, reciprocating files produced significantly more incomplete dentinal cracks than full-sequence rotary systems)
Cassimiro et al., 2018	Rotary, Reciprocating	ProTaper Next (rot), Reciproc (rec), WaveOne Gold (rec)	Yes	No: non instrumented teeth show absence of microcracks	Formation of microcracks regardless of instrumentation system used. (The Reciproc file generated the lowest incidence of defects, and the highest incidence occurred 6 and 9 mm from the root apex)
Çiçek et al., 2015	Hand, Rotary, Reciprocating	Stainless steel K-Flexo files (hand), ProTaper Universal (rot), ProTaper Next (rot), WaveOne (rec)	No	No: hand instrumented teeth show absence of microcracks	All instruments caused microcracks except for hand file. (The highest percentage of microcrack was recorded in 3 mm section for all groups)
Coelho et al., 2016	Rotary, Reciprocating	ProFile (rot), TRUShape (rot), WaveOne Gold (rec)	Yes	Yes	No indicatives of formation of microcracks in comparison to non-instrumented teeth.
Garg et al., 2015	Hand, Rotary	Stainless steel K-files (hand), ProTaper (rot), K3 (rot), Easy RaCe (rot)	Yes	No: non instrumented teeth show absence of microcracks	No indicatives of formation of microcracks using hand files. Indicatives of formation of microcracks using rotary instruments with intensity dependent on the system (ProTaper> K3 > Easy RaCe).
Harandi et al., 2017	Rotary, Reciprocating	ProTaper Universal (rot), Neolix (rot), SafeSider (rec)	Yes	No: non instrumented teeth show absence of microcracks	Formation of microcracks regardless of instrumentation system used.
Helvacioglu-Yigit et al. (2015)	Hand, Reciprocating	Stainless steel K-files (hand), WaveOne (rec), Reciproc (rec)	Yes	No: non instrumented teeth show absence of microcracks	Formation of microcracks regardless of instrumentation system used.
Hin et al., 2013	Hand, Rotary, SAF	Stainless steel K-Flexo files (hand), ProTaper (rot), Mtwo (rot), SAF (5000 in-and-out vibrations per minute)	Yes	No: non instrumented teeth show absence of microcracks	Instrumentation of root canals with SAF, Mtwo, and ProTaper results on damage to root canal dentin. (SAF has a tendency to cause less dentinal cracks as compared with other files)
Jain et al., 2017	Hand, Rotary	Stainless steel K-files (hand), Hero Shaper (rot), OneShape (rot)	No	Yes	All instruments results on formation of microcracks, whereas hand files induced lesser amount.
Jalali et al., 2015	Rotary, Reciprocating	Mtwo (rot), PTU (rot), Reciproc (recip)	Yes	No: non instrumented teeth show absence of microcracks	All three engine-driven systems created dentinal defects, whereas Reciproc caused less cracks.
Kansal et al., 2014	Rotary, Reciprocating	ProTaper (rot), ProTaper F2 file (rec), WaveOne (rec)	Yes	No: non instrumented teeth show absence of microcracks	Dentinal cracks are produced irrespective of motion kinematics, whereas reciprocating motion introduced less defects.
Karatas et al., 2015	Hand, TFA	K-files (hand), TFA (adaptive motion), TFA (rot), TFA (rot/rec)	Yes	No: non instrumented teeth show absence of microcracks	All the kinematics used caused dentinal crack formation. (TFA with rotary and reciprocating motion under specific parameters (210CW-30CCW) and hand files introduced statistically less defects)
Karatas et al., 2015a	Rotary, Reciprocating, TFA	ProTaper Universal (rot), ProTaper Next (rot), WaveOne (rec), TFA (adaptive motion)	Yes	No: non instrumented teeth show absence of microcracks	All the kinematics used caused similar dentinal crack formation.
Karatas et al., 2016	Rotary, Reciprocating	ProTaper Universal (rot), ProTaper Gold (rot), ProFile Vortex (rot), F360 (rec), Reciproc (rec)	Yes	No: non instrumented teeth show absence of microcracks	All systems produced dentinal cracks where F360 introduced less defects been statistically similar to non-instrumented teeth.
Kesim et al., 2017	Hand, Rotary, Reciprocating, TFA	Stainless Steel K-files (hand), K3XF (rot), ProTaper Next (rot), Reciproc (rec), TFA (adaptive motion)	No	Yes	Hand files, K3XF and Reciproc introduced statistically fewer defects.
Kfir et al., 2017	Rotary, Reciprocating, SAF	ProTaper (rot), WaveONe (rec), SAF (5000 in-and-out vibrations per minute)	Yes	Yes	Rotary and Reciprocating systems lead to microcrack formation. (SAF was not statistically different from non-instrumented teeth which show a small occurrence of microcrack)
Khirtika and Ramesh, 2017	Hand, Rotary	Hand instrumentation (hand), ProTaper Universal (rot), Protaper Next (rot), Mtwo (rot)	No	Yes	All groups show microcrack formation, whereas the least defects were observed in canals with hand instrumentation.
Khoshbin et al., 2018	Hand, Rotary, Reciprocating	Stainless steel K-files (hand), ProTaper (rot), Mtwo (rot), Reciproc (rec), Neolix (rot)	Yes	No: non instrumented teeth show absence of microcracks	Hand instrumented teeth show no microcrack formation. All rotary systems created dentinal cracks whereas Neolix caused the least number of cracks.
Li et al., 2015	Rotary, Reciprocating	ProTaper Universal (rot), ProTaper Next (rot), WaveOne (rec)	Yes	No: non instrumented teeth show absence of microcracks	All 3 NiTi files can cause dentinal microcracks. The ProTaper Next system induces lesser defects.
Liu et al., 2013	Rotary, Reciprocating, SAF	OneShape (rot), ProTaper (rot), Reciproc (rec), SAF (5000 in-and-out vibrations per minute)	Yes	No: non instrumented teeth show absence of microcracks	SAF instrumented teeth show no microcracks. Reciproc produced less dentinal defects than ProTaper and OneShape.
Liu et al., 2013	Hand, Rotatory	K3 (rot), ProTaper (rot), Flex K Files (hand)	Yes	Not reported	Rotary instruments caused more dentinal defects than hand instruments
Milani et al., 2012	Hand, Rotary	Stainless steel K-Flexo files (hand), ProTaper Universal (rot)	Yes	No: non instrumented teeth show absence of microcracks	Hand instrumentation lead to more crack formation.
Monga et al., 2015	Hand, Rotary, Reciprocating	Stainless steel K-files (hand), ProTaper (rot), K3XF (rot), WaveOne (rec)	Yes	No: non instrumented teeth show absence of microcracks	Hand instrumented teeth show no microcracks. Continuous rotating and reciprocating instruments produce dentinal crack formation, whereas reciprocating movement introduced less defects.
Nasr and Kader, 2014	Rotary, Reciprocating	WaveOne (rec), ProTaper (rot), ProTaper (rec)	Yes	No: non instrumented teeth show absence of microcracks	Wave one system introduced less defects than ProTaper.
Pedulla et al., 2017	Rotary, Reciprocating	One Shape (rot), F6 SkyTaper (F6ST) (rot), HyFlex EDM (rot), WaveOne (rec), Reciproc (rec), WaveOne Gold (rec)	Yes	No: non instrumented teeth show absence of microcracks	Instrumentation lead to microcrack formation whereas HyFlex EDM caused less defects.
Priya et al., 2014	Hand, Rotary, Reciprocating	Stainless steel K-file (hand), ProTaper (rot), ProTaper (rec), ProTaper Next (rot), ProTaper Next (rec), OneShape (rot), OneShape (rec), Reciproc (rot), Reciproc (rec)	Yes	No: non instrumented teeth show absence of microcracks	Least defects were seen in canals with hand instrumentation. (Among engine driven instrumentation ProTaper Next files showed least cracks when set in rotary or reciprocating motion. Full sequence systems showed less cracks than single file systems and reciprocating motion was found to be better for both full sequence and single file systems)
Rose & Svec, 2015	Hand, Rotary, Reciprocating	WaveOne (rec) ProTaper (rot), GT files (hand)	Yes	No: non instrumented teeth show absence of microcracks	No formation of microcracks
Saha et al., 2017	Rotary, SAF	Mtwo (rot), ProTaper Next (rot), SAF (5000 in-and-out vibrations per minute)	Yes	No: non instrumented teeth show absence of microcracks	Instrumentations lead to microcrack formation whereas SAF introduced fewer defects.
Shori et al., 2015	Hand, Rotary	Hand Files (hand), ProTaper Universal (rot), Hero Shaper (HS) (rot), ProTaper Next (rot)	No	Yes	Hand files lead to the lower microcrack formation than rotary systems. (ProTaper Netx rotary system induce less dentinal defects than ProTaper and Hero Shaper)
Ustun et al., 2015	Hand, Rotary, Reciprocating	Stainless steel K-Flexofile (hand), ProTaper F2 (rec), Reciproc (rec), ProTaper (rot), ProTaper Next (rot)	Yes	No: non instrumented teeth show absence of microcracks	All experimental groups showed microcrack formations in statistically similar intensity.
Yoldas et al., 2012	Hand, Rotary, SAF	Hand file (hand), Hero Shaper (HS) (rot), Revo-S (RS) (rot), Twisted File (TF) (rot), ProTaper (PT) (rot), SAF (5000 in-and-out vibrations per minute)	Yes	No: non instrumented teeth show absence of microcracks	Hand and SAF instrumented teeth show no microcracks. Other NiTi instruments tend to induce various degrees of dentinal damage during root canal preparation.
Zhou et al., 2015	Rotary, Reciprocating, TFA	Protaper Universal (rot), Twisted File (TF) (rot), WaveOne (rec), TFA (adaptive motion)	Yes	No: non instrumented teeth show absence of microcracks	TFA instrumented teeth show no microcracks. TF system introduced fewer defects than ProTaper Universal and WaveOne.

Author	Preparation technique	IL	System	Methodology for microcrack detection	Results
Author	Preparation technique	IL	System	Methodology for microcrack detection	Microcracks on baseline	Instrumentation inducing, forming or propagating cracks
Adorno et al., 2009	Hand, Rotary	RCL, RCL-1mm	Stainless steel files (hand), Profile (rot)	NDM: visual inspection of photographs of apex surface on a digital microscope at 100´ before and after instrumentation	No	Crack formation on apex surface was associated with the IL and not the instrumentation technique. IL equal to RCL resulted in more more cracks.
Adorno et al., 2010	Hand, Rotary	RCL, RCL-1mm	Stainless steel K-files (hand), Profile (rot)	Mixed analysis (DM and NDM): visual inspection of photographs of apex surface on a digital microscope at 100´ before and after instrumentation. Then, slices were made to evaluate 1 mm deep and 2 mm deep the integrity of root surface)	No	Crack formation on apex surface was associated with the IL and not the instrumentation technique. IL equal to RCL resulted in more more cracks.The rotary technique produced more cracks prolonged into root canal surface up to 1mm deep (<2 mm deep).
Devale et al., 2017	Hand, Rotary	RCL, RCL-1mm	Stainless steel K-files (hand), RaCe (rot), K3 (rot)	NDM: visual inspection of photographs of apex surface on a stereomicroscope at 100´ before and after instrumentation	No	There was no significant significance between stainless steel hand files and rotary files for crack formation. IL had a significant effect on crack formation when rotary files were used but not for hand files.
Kumari and Krishnaswamy, 2016	Hand, Rotary	RCL, RCL-1mm	Stainless Steel files (hand), ProTaper Universal (rot), ProTaper Next (M wire) (rot)	DM: apex surface was polished, photographed and images were examined on a stereomicroscope at 20´ before and after instrumentation	No	All samples depict crack formation after instrumentation. Hand files caused more cracking than rotary files, the smallest number of cracks for ProTaper Next. When the IL was set 1 mm short, all systems showed fewer cracks
Liu et al., 2013	Rotary, Reciprocating, SAF	RCL	OneShape (rot), ProTaper (rot), Reciproc (rec), SAF (5000 in-and-out vibrations/min)	NDM: visual inspection of photographs of apex surface on a stereomicroscope at 20´ before and after instrumentation	No	Only instrumentation with Protaper system showed apex microcrack formation.
Liu et al., 2013a	Hand, Rotary	RCL, RCL-1mm, RCL-2mm, RCL+1mm	Stainless Steel K-flexo files (hand), K3 (rot), ProTaper (rot)	DM: visual inspection of photographs of apex surface on a stereomicroscope at 20´, instrumentation, re-evaluation and sectioning for checking microcrack extension	No	Rotary instruments caused more dentinal defects than flexible hand instruments; instrumentation short of RCL educed the risk of dentinal defects.
Rose and Svec, 2015	Hand, Rotary, Reciprocating	RCL-1mm	Profile GT (hand), ProTaper Universal (rot), WaveOne (rec)	DM: instrumentation was performed in teeth of pigs still positioned in the hemisected jaws with preservation of whole surrounding tissues. Thereafter, tissue was removed and the apex was exposed, sectioned and examined under dental operating microscope	No	No crack formation was found for non-instrumented teeth or teeth instrumented with different systems. In situ periradicular tissue supporting the roots may prevent cracking or dentinal damage.
Zhou et al., 2015	Rotary, Reciprocating, TFA	RCL-1mm, RCL+1mm	Protaper Universal (rot), Twisted File (TF) (rot), WaveOne (rec), TFA (adaptive motion)	DM: Apex surface was observed with a stereomicroscope to confirm absence of cracks. After instrumentation, the apical region was sectioned and examined by scanning electron microscopy at 50 and 100×)	No	There were no significant differences among the conditions studied regarding apex microcrack formation, although small canals predisposed more crack formation than larger canals and RCL+1mm led to more defect introduction.

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[1] Correspondence: Dr. Rafael Sarkis-Onofre, Rua Senador Pinheiro, 304, 99070-220 Passo Fundo, RS, Brasil. Tel: +55-54-3045-6100. e-mail: rafael.onofre@imed.edu.br