stereomicroscopic evaluation of dentinal …

“STEREOMICROSCOPIC EVALUATION OF DENTINAL

MICROCRACKS CAUSED BY HAND, ROTARY AND RECIPROCATING

INSTRUMENTATION DURING ROOT CANAL PREPARATION”

By

Dr. S GYANANDRA PRATAP SINGH

Dissertation submitted to the

Rajiv Gandhi University of Health Sciences, Karnataka, Bangalore.

In partial fulfillment of the requirements for the degree of

MASTER OF DENTAL SURGERY

In the specialty of

CONSERVATIVE DENTISTRY AND ENDODONTICS

Under The Guidance Of

Dr. PRASANNALATHA NADIG

DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS,

KRISHNADEVARAYA COLLEGE OF DENTAL SCIENCES,

BANGALORE, KARNATAKA, INDIA

2013-2016

II

RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,

BANGALORE, KARNATAKA.

DECLARATION BY THE CANDIDATE

I hereby declare that this dissertation/thesis entitled “STEREOMICROSCOPIC

EVALUATION OF DENTINAL MICROCRACKS CAUSED BY HAND,

ROTARY AND RECIPROCATING INSTRUMENTATION DURING ROOT

CANAL PREPARATION” is a bonafide and genuine research work carried out

by me under the guidance of Dr. PRASANNALATHA NADIG, Professor,

Department of Conservative Dentistry and Endodontics, Krishnadevaraya college

of Dental sciences and Hospital, Bangalore.

Date:

Place: Bangalore.


P. G. Student,

Department of Conservative Dentistry and

Endodontics

Krishnadevaraya College of Dental

Sciences & Hospital, Bangalore.

III



CERTIFICATE BY THE GUIDE

This is to certify that the dissertation “STEREOMICROSCOPIC

EVALUATION OF DENTINAL MICROCRACKS CAUSED BY

HAND, ROTARY AND RECIPROCATING INSTRUMENTATION

DURING ROOT CANAL PREPARATION” is a bonafide research work

done by Dr. S GYANANDRA PRATAP SINGH in partial fulfillment of the

requirement for the degree of MASTER OF DENTAL SURGERY.

Date:

Place: Bangalore.

Dr. PRASANNALATHA NADIG,

Professor,

Department Of Conservative Dentistry

and Endodontics, Krishnadevaraya

College of Dental sciences & Hospital,

Bangalore.

IV



ENDORSEMENT BY THE HOD, PRINCIPAL/HEAD OF THE

INSTITUTION

This is to certify that the dissertation entitled “STEREOMICROSCOPIC

EVALUATION OF DENTINAL MICROCRACKS CAUSED BY

HAND, ROTARY AND RECIPROCATING INSTRUMENTATION

DURING ROOT CANAL PREPARATION” is a bonafide research work

done by Dr. S GYANANDRA PRATAP SINGH, under the guidance of

Dr. PRASANNALATHA NADIG, Professor, DEPARTMENT OF

CONSERVATIVE DENTISTRY AND ENDODONTICS.

Dr. A.A. PONNANNA.

Principal,

Krishnadevaraya College of

Dental sciences & Hospital,

Bangalore.

Date:

Place: Bangalore.

Date:

Place: Bangalore.

Dr. JAYALAKSHMI K.B.

Professor & HOD,

Department of Conservative Dentistry

and Endodontics



V

COPYRIGHT

DECLARATION BY THE CANDIDATE

I hereby declare that the Rajiv Gandhi University of Health Sciences, Karnataka

shall have the rights to preserve, use and disseminate this dissertation / thesis in

print or electronic format for academic / research purpose.

© RAJIV GANDHI UNIVERSITY OF HEALTH SCIENCES,

BANGALORE, KARNATAKA

Date:

Place: Bangalore.


P. G. Student,

Department of Conservative Dentistry and

Endodontics



VI

ACKNOWLEDGEMENT

“The dream begins with a teacher who believes in you, who tugs and pushes

and leads you to the next plateau, sometimes poking you with a sharp stick

called “truth" ~ Dan Rather

With blessings of Almighty, I am immensely pleasured to pen down my

imprints of heartfelt expressions of gratitude for those who have played a

remarkable role in my dissertation and postgraduate course.

It is an honor to express my respect and gratitude to my guide

Dr. Prasannalatha Nadig, Professor, Department of Conservative

Dentistry and Endodontics, for her valuable guidance and encouragement

throughout my post graduation course. A fabulous advisor: sharp, cheery,

perceptive, and mindful of the things that truly matter. Her selfless perseverance

and attention to my work consistently found pearls among my heaps of data. I

respect her for standing strong for what she believes in.

I express my gratitude and profound indebtedness to Dr. K.B.

Jayalakshmi, Professor and Head of the Department, Department of

Conservative dentistry and Endodontics, who imparted her knowledge and

cheered the tensed hearts with her wit and constant encouragement.

VII

I express my gratitude with utmost sincerity to Dr. S.M. Sharath Chandra.

He is excellence personified with the highest of ideals and the deepest of

convictions, which have been truly inspirational to me and will continue to be in

future. It is indeed a privilege to have had the opportunity of being his student.

I am also grateful to Dr. Sujatha, Professor, Dr. Sridhar, Dr. Shibani, Dr.

Sahana, Dr. Manje Gowda, Readers, Dr. Revathi, Senior lecturer, Dr. Shobha,

Lecturer, Department of Conservative Dentistry and Endodontics, for their

constant guidance and help.

I take this golden opportunity to thank my beloved family, father Dr. Kartar

Singh Sisodia, mother Mrs. Vimal Sisodia, brother Nrapendra Sisodia,

grandparents Rambir Singh Sisodia, and Mrs. Vidya Sisodia for their sacrifices

throughout my life. It is their blessings and unconditional love that has helped me in

every aspects of my journey.

I would like to thank my fiancée Dr. Shalini Chauhan for her unconditional

love and support, and giving me a reason to smile every day.

A friend is one of the nicest things you can have, and one of the best things

you can be. ~Douglas Pagels.

I would like to thank my best friends Ruchita, Ankit, Shailesh, Raina,

Anchal, Shreya, Shilpa, Anuve and Nikhil for making my life worth living and

giving me memories that i’ll always cherish.

VIII

Words are inadequate in offering my thanks to my co-PG, roommate and best

friend Dr. Sivaji Kavuri for his unconditional support, and help in times of need. I

thank my colleagues, Dr. Punith Shetty, Dr. Roomani and Dr. Arpan Debnath,

for their support and wisdom in all walks of life.

I owe special obligation to all my seniors specially Dr. Hemalatha, Dr.

Shruthi, Dr. Rahul and Dr. Ameya for their constant support and motivation.

I thank my colleagues Dr. Vamsi, Dr. Vijay, Dr. Savithri, Dr. Rajisha, Dr.

Nalini, Dr. Vamsi Reddy, Dr. Charan Chanda, Dr. Mahesh, Dr. Pushkar, Dr.

Shreya, Dr. Pratyusha Chhava, Dr. Divya, Dr. Saketh, Dr. Hemanth, Dr.

Diganta, Dr. Manjunatha, Dr. Pratyusha, Dr. Shwetha, Dr. Prasanna, Dr.

Bharath, Dr. Sreenadh, Dr. Satya, Dr. Bharathi and Dr. Shruthi for their

constant support during my entire curriculum. I am deeply indebted to them for

their timely help, continuous co-operation, assistance and for giving me wonderful

memories and making this journey pleasant.

I thank Mr. K.P. Suresh for his contribution in statistical analysis.

I extend my humble thanks to our Principal, Dr. A.A.Ponnanna,

Krishnadevaraya College of Dental Sciences and Hospital, Bangalore, for allowing

me to utilize the facilities of the College.

Lastly, I want to thank Almighty for giving this great life full of opportunities.

Date: Dr. S Gyanandra Pratap Singh

Place: Bangalore

IX

ABSTRACT

Background: The goals of endodontic instrumentation are to completely

remove microorganisms, debris, and tissue by enlarging the canal diameter and

create a canal form that allows a proper seal. At times, in the zeal of

biomechanical preparation of the canal, we inevitably end up damaging the root

dentin which becomes a gateway to dentinal cracks and minute intricate

fractures, thereby failure of treatment. Since the introduction of rotary Ni-Ti

instruments in 1988, there has been a growing shift from manual to rotary

engine-driven preparation. In spite of their obvious advantages, rotary files with

large tapers may cause significantly more complete and incomplete dentinal

cracks. The recently introduced single file nickel-titanium (Ni-Ti) reciprocating

systems are able to prepare canals with only one instrument, thereby requiring

even lesser time than rotary full-sequence system. It might be speculated that

when using only one instrument for complete preparation, more stress will be

generated during instrumentation as compared to full sequence rotary systems

that might result in increased incidence of dentinal defects. Hence there is need

for evidence regarding the behaviour of different instruments on root dentin

after endodontic preparations with hand, rotary and reciprocating file systems.

Aim: To compare and evaluate the incidence of dentinal microcracks caused by

hand, rotary and reciprocating instrumentation during root canal preparation.

Methodology: Eighty four freshly extracted human mandibular premolars of

similar sizes were randomly selected which met the inclusion and exclusion

X

criteria. To standardize canal instrumentation, teeth were decoronated by using

diamond disc, establishing a standardized root length of 15mm. Samples

selected were divided into seven groups with twelve teeth in each group. All

groups, except the Reciproc group, were first enlarged to a size 20 K- Flexofile

following which they were subjected to one type of instrumentation depending

upon the group. Group 1 served as control in which no further instrumentation

was done. In group 2, Ni-Ti hand K-files (Dentsply Maillefer, Ballaigues,

Switzerland) were used to enlarge the canals to size #40. In group 3, hand

ProTaper files (Dentsply Maillefer, Ballaigues, Switzerland) were used to

instrument the canals to F4, corresponding to size #40, 6% taper. In group 4, full

sequence rotary Mtwo files (VDW, Munich, Germany) were used to enlarge the

canals to size #40, 4% taper. In group 5, full sequence ProTaper rotary files

(Dentsply Maillefer, Ballaigues, Switzerland) were used to instrument the

canals to F4, corresponding to size #40, 6% taper. In group 6, single

reciprocating file, Reciproc R40 (VDW, Munich, Germany), corresponding to

size #40, 6% taper was used to instrument the canals and in group 7, canals were

enlarged by Single reciprocating large WaveOne file (Dentsply Maillefer,

Ballaigues, Switzerland), corresponding to size #40, 8% taper. In each group,

canals were irrigated with 2.5% sodium hypochlorite between each instrument

or after three pecks while using the reciprocating files, using a syringe with 27

G needle. After preparation, the specimens were rinsed with normal saline.

All the roots were then sectioned perpendicular to the long axis at 3, 6, and 9

mm from the apex and viewed under stereomicroscope for the detection of

dentinal cracks. Data obtained was subjected to statistical analysis. Chi-square

XI

test was performed to find the significance of study parameters between the

groups studied.

Results: Except for the Ni-Ti K-file group, all other samples showed the

presence of dentinal defects irrespective of the instrumentation used. Overall,

single file reciprocating systems, i.e. Reciproc and WaveOne resulted in

significantly more dentinal defects (P<.05) as compared to the other groups.

Although dentinal defects were detected at all the three levels, maximum

samples showed defects at 3mm from the apex.

Conclusion: All groups, except the Ni-Ti K-file group, induced dentinal defects

in the samples. Full sequence rotary systems caused less defects than the single

file systems, with Reciproc group causing significantly more defects as

compared to the other groups. Maximum samples showed defects at 3mm level

from the apex.

Keywords: Dentinal defects, Full sequence rotary systems, Reciprocation, M-

wire.

XII

TABLE OF CONTENTS

1. INTRODUCTION 1 - 4

2. OBJECTIVES 5

3. REVIEW OF LITERATURE 6 - 24

4. METHODOLOGY 25 - 38

5. RESULT 39- 46

6. DISCUSSION 47 - 57

7. CONCLUSION 58

8. SUMMARY 59 - 60

9. BIBLIOGRAPHY 61 - 70

10. ANNEXURE 71 - 72

XIII

LIST OF ABBREVIATIONS AND SYMBOLS

SL NO. ABBREVIATION MEANING

1 BMP Biomechanical preparation

2 mm

Millimeters

3 mL Millilitres

4 µ CT Micro Computed Tomography

5 Ni-Ti Nickel-Titanium

6 NaOCl Sodium Hypochlorite

7 VRF

Vertical Root Fracture

XIV

LIST OF TABLES

LIST OF GRAPHS

SL.No. TABLES PAGE

No.

1

COMPARISON OF COMPLETE CRACKS/FRACTURE

IN SEVEN GROUPS STUDIED

41

2

COMPARISON OF OTHER DEFECTS (INCOMPLETE

CRACKS/CRAZE LINES) IN SEVEN GROUPS

STUDIED

43

SL.No. TABLES PAGE

No.

1

PERCENTAGE OF COMPLETE CRACKS/FRACTURE

IN SEVEN GROUPS STUDIED

42

2

PERCENTAGE OF OTHER DEFECTS (INCOMPLETE

CRACKS/CRAZE LINES) IN SEVEN GROUPS

STUDIED

44

XV

LIST OF FIGURES

SL.No. FIGURES PAGE

No.

1

Eighty four single rooted human mandibular premolars 31

2 Decoronation using safe sided diamond disc 32

3 Standardizing root length to 15mm 32

4 Decoronated specimens 33

5 Armamentarium 33

6 Experimental hand Ni-Ti files used in the study 34

7

Experimental rotary Ni-Ti files used in the study 34

8 Experimental reciprocating Ni-Ti files used in the study 34

9 Canal instrumentation 35

10 Isomet low speed saw 35

11 Securing the instrumented specimen in holder for

sectioning 36

12 Sectioning using Isomet 36

XVI

SL.No. FIGURES PAGE

No.

13 Sections from 3mm, 6mm and 9mm from the root apex 37

14 Specimens stored in distilled water 37

15 Stereomicroscope 38

16 Specimen showing no dentinal defect 40

17 Specimen showing craze lines 40

18 Specimen showing complete crack or fracture 40

Introduction

Page 1

Endodontic diseases are associated with multiple bacterial infections, where

root canal therapy serves as a significantly effective treatment modality.1 Root

canal preparation is one of the most important factors in successful root canal

therapy that determines the efficacy of all subsequent procedures.2

As advocated by Schilder, the primary goal of endodontic instrumentation is to

completely remove microorganisms, debris and tissue by enlarging the canal

diameter and create a canal form that allows a proper seal.3 At times, in the zeal

of biomechanical preparation of the canal, we inevitably end up damaging the

root dentin.2

During biomechanical preparation, a canal is shaped by the contact between

instruments and dentin walls. These contacts create many momentary stress

concentration points in dentin. Such stress concentrations may induce dentinal

defects like microcracks or craze lines.4These localized defects may have the

potential to develop into vertical root fracture (VRF) 5-9 because subsequent

applied stresses caused by root canal obturation, retreatment and repeated

occlusal forces can be exponentially amplified at the tip of these defects and

therefore development of such defects should be prevented.

Fracture susceptibility of an endodontically treated tooth depends primarily on

the final canal shape, the extent of canal enlargement and the elimination of

irregularities, which are the stress concentration sites.7 Thus, different

instrumentation techniques and systems, with different cutting blades and tip

Introduction

Page 2

designs and tapers, lead to different types and degrees of dentinal damage to the

root canal wall.10-12

Traditionally, root canal preparation was carried out using stainless steel

endodontic files manipulated by hand. Significant changes in the endodontic

instrumentation have occurred over the last 10 years. Paramount among these

being the introduction of nickel-titanium (Ni-Ti) rotary instrumentation that

have led to new design concepts and techniques for canal preparation.13

Most of the clinicians prefer these systems because of their obvious advantages

such as time saving 14-15, better cutting efficiency16, increased cleanliness, better

shaping ability and less canal straightening, apical transportation and

perforations.17-18

However, rotary instrumentation results in significantly more rotations of the

instruments inside the canal14 that may cause more friction between the files and

canal walls. Also rotary files with large taper result in more dentin removal and

may cause significantly more complete and incomplete dentinal cracks.19

In 2008, a novel canal preparation technique with only the F2 ProTaper

instrument used in clockwise and counter clockwise movement was described.20

The concept of using a single NiTi instrument to prepare the entire root canal is

interesting because the learning curve is considerably reduced as a result of

technique simplification. Moreover, the use of a single NiTi instrument is more

cost-effective than the conventional multifile NiTi rotary systems. Added

benefits include reduced cross contamination and reduced instrument fatigue.

Introduction

Page 3

The recently introduced single file nickel-titanium reciprocating systems

(Reciproc and WaveOne) are able to prepare canals with only one instrument,

thereby requiring even lesser time than full sequence rotary system.21These

reciprocating files are made of a special nickel-titanium alloy called M-wire 22

that provides increased flexibility and improved resistance to cyclic fatigue of

the instruments.23-24

The reciprocating motion is based on the “Balanced Force” concept. It is

claimed to relieve stress on the instrument by special counter clockwise (cutting

action) and clockwise (release of instrument) movements, and it is assumed that

this movement reduces the risk of cyclic fatigue caused by tension and

compression.25-27 These files also have the advantage of creating less invasive

root canal preparations by increasing canal centering.28-29

The angle of counter clockwise cutting direction is greater than the angle of the

clockwise direction. Due to this fact, it is claimed that the instrument

continuously progresses towards the apex of the root canal. The angles of

reciprocation are specific to the design of the particular instruments and are

programmed in an electronic motor. The angles of reciprocation are smaller than

the elastic limit of the files in a single reciprocating movement, but not when

multiple clockwise/anticlockwise movements are made and the tip of the file

binds in the canal.1

It might be speculated that when using only 1 instrument for complete

preparation, more stresses will be generated during mechanical instrumentation

compared with canal instrumentation by using full sequence systems. Thus, it

Introduction

Page 4

might be assumed that the incidence of dentinal defects might be increased

compared with preparations by using full sequence rotary systems.

Hence, the present study was undertaken to evaluate and compare the incidence

of dentinal microcracks caused by hand NiTi (NiTi K files and Hand ProTaper),

rotary NiTi (Mtwo and Rotary ProTaper) and reciprocating (Reciproc and

WaveOne) instrumentation during root canal preparation.

Aim and Objectives

Page 5

AIM OF THE STUDY:

To evaluate the incidence of dentinal microcracks caused by hand, rotary and

reciprocating instrumentation during root canal preparation.

OBJECTIVES OF THE STUDY:

To compare the incidence of dentinal microcracks caused by hand (NiTi K-files

and ProTaper hand files), rotary (Mtwo and ProTaper rotary files) and

reciprocating (Reciproc and WaveOne) instrumentation during root canal

preparation.

To determine the incidence of dentinal microcracks at different levels from the

apex.

Review of Literature

Page 6

Wilcox LR, Roskelley C and Sutton T in 1997 conducted an in vitro study to

assess the effect of lateral condensation forces on the development of vertical

root fracture (VRF) in teeth after controlled internal root reduction. Thirty four

maxillary anterior teeth were prepared with the step-back method so that the

canal width was 20% of the total root width and obturated. 24 hours after

obturation, the teeth were examined by transillumination for VRF. Teeth not

exhibiting VRF were tested after gp removal and further canal enlargement to

30%, 40%, and 50% of the root width. The teeth were then sectioned and

examined under stereomicroscope. No VRF occurred at 20% or 30%; five teeth

fractured at 40% and seven at 50%. Craze lines were developed in all seventeen

of the remaining unfractured samples.5

An in vitro study was undertaken by Bier CAS, Shemesh H, Filho MT,

Wesselink PR and Wu MK in 2009 to compare the incidence of dentinal

defects after canal preparation with different nickel-titanium rotary files in two

hundred sixty mandibular premolars. Forty teeth were left unprepared. The other

teeth were prepared with manual Flexofiles (Dentsply Maillefer), ProTaper

(Dentsply Maillefer), ProFile (Dentsply Maillefer), SystemGT (Dentsply

Maillefer), and S-ApeX (FKG Dentaire). Roots were then sectioned at 3mm,

6mm and 9 mm from the apex and observed under a stereomicroscope. No

defects were found in the unprepared roots and those prepared with hand files,

whereas S-ApeX. ProTaper, ProFile, and GT preparations resulted in dentinal

defects in 16%, 8%, and 4% of teeth, respectively.19

Adorno CG, Yoshioka T and Suda H in 2010 evaluated the effects of working

length and root canal preparation technique on crack development in the apical


Page 7

root canal wall. Seventy mandibular premolars were mounted in a resin block

with simulated periodontal ligaments. The crown was removed 2 mm above the

proximal cementoenamel junction to ensure straight line access and provide a

reference point. The apical 2-3 mm of the root was exposed to allow

intraoperative image recording. The teeth were randomly divided into seven

experimental groups (n=10) according to preparation technique and working

length: group A, step back preparation with stainless steel files with working

length set at the apical foramen and defined as root canal length(CL); group B,

same as for A, except that the working length was CL-1mm; group C, crown

down preparation with Profile instruments followed by an apical enlargement

sequence with CL as working length and group D, same as for C, except that the

working length was CL-1mm. Groups E, F and G served as controls. Groups E

and F were prepared only with the crown down sequence up to CL and CL-

1mm, without further apical enlargement, and group G was left unprepared.

Digital images of the apical root surface (AS) were recorded before preparation,

immediately after instrumentation and after removing the apical 1mm (AS-

1mm) and 2mm (AS-2mm) of the root end. It was observed that working length

significantly affected crack development at AS (p < 0.05). Preparation technique

significantly affected crack development at AS-1mm (p < 0.05).At AS-2mm,

there was no significant difference between preparation technique and working

length in terms of crack development on dentin wall. It was concluded that root

canal preparation alone, regardless of the technique used, can potentially

generate cracks on the apical root canal wall as well as apical surface. Working

1 mm short of the apical foramen might produce fewer cracks in the apical

region.11


Page 8

Kim HC et al in 2010 performed an in vitro study to compare the stress

conditions during rotary instrumentation in a curved root for three NiTi file

designs using finite element (FE) analysis. FE models of ProFile (Dentsply

Maillefer), ProTaper Universal (Dentsply Maillefer), and LightSpeed LSX

(Lightspeed Technology,Inc, San Antonio,TX) were rotated within a curved

root canal. The stress and strain conditions resulting from the simulated shaping

action were evaluated in the apical root dentin. ProTaper Universal induced the

highest stress concentration in the root dentin and had the highest tensile and

compressive principal strain components at the external root surface.

LightSpeed generated the lowest stresses. It was concluded that the stiffer file

designs generated higher stress concentrations in the apical root dentin during

shaping of the curved canal, which raises the risk of dentinal defects that may

lead to apical root cracking.30

Yoldas O, Yimaz S, Atakan G, Kuden C and Kasan Z in 2012 conducted an

in vitro study to compare dentinal microcrack formation while using hand files,

four brands of nickel-titanium (NiTi) rotary files and the self-adjusting file in

mesial canals of mandibular molars. One hundred forty mandibular first molars

were selected. Twenty teeth were left unprepared and served as control, and the

remaining one hundred twenty teeth were randomly divided into six groups:

Hand files (Dentsply Maillefer), HERO Shaper (Micro-Mega), Revo-S (Micro-

Mega), Twisted file (Sybron Endo), ProTaper (Dentsply Maillefer), and Self-

adjusting files (ReDent Nova). After canal instrumentation, roots were

sectioned at 3mm, 6mm and 9 mm from the apex and observed under a

stereomicroscope for the presence of dentinal microcracks. Results revealed that

the control, hand file and self-adjusting file groups did not show any


Page 9

microcracks. In roots prepared with the HERO Shaper, Revo S, Twisted file and

ProTaper, dentinal microcracks were observed in 60%, 25%, 44% and 30% of

teeth respectively. There was a significant difference between the control/ hand

file/ self-adjusting file group and the four NiTi rotary instrument groups (p <

0.0001). However, no significant difference was found among the four NiTi

rotary instruments (p > 0.005). It was concluded that all rotary files created

microcracks in the root dentin, whereas the self-adjusting file and hand

instrumentation presented with satisfactory results with no dentinal

microcracks. 31

Milani AS et al in 2012 conducted an in vitro study to evaluate the effect of

root canal preparation on the development of dentin cracks. Fifty seven

mandibular incisor teeth were selected for this study and were randomly divided

into 2 experimental and one control group (n=19). The teeth in the experimental

groups were prepared using hand ProTaper (Dentsply Maillefer) and rotary

ProTaper instruments (Dentsply Maillefer), whereas the teeth in control group

were left unprepared. The teeth were then sectioned horizontally 3 mm and 6

mm from the apex and viewed under dental operating microscope for various

dentinal defects. The hand and rotary ProTaper group demonstrated

significantly more defects than the control group (p = 0.001). However, there

was no significant difference between the experimental groups (p > 0.05). The

authors concluded that canal preparation, whether hand or rotary, produced

structural defects in dentin. The ProTaper rotary system when used according to

the manufacturer’s instruction, tends to produce fewer cracks and can be

considered a safe preparation technique.32


Page 10

An in vitro study was undertaken by Liu R, Hou BX, Wesselink PR, Wu MK,

Shemesh H in 2013 to compare the incidence of root cracks observed at the

apical root surface and in the canal wall after canal instrumentation with three

single-file systems and the ProTaper system. One hundred mandibular incisors

were selected. Twenty control teeth were coronally flared with Gates-Glidden

drills and no further preparation was made. The other 80 teeth were mounted in

resin blocks with simulated periodontal ligaments and the apex was exposed.

They were divided into 4 experimental groups(n = 20); the root canals were first

coronally flared with Gates-Glidden drills and then instrumented to the full

working length with the ProTaper (Dentsply Maillefer), OneShape (Micro-

Mega), Reciproc (VDW) and the Self-Adjusting File (ReDent Nova) . The

apical root surface and horizontal sections 2, 4, and 6 mm from the apex were

observed under a microscope to evaluate for the presence of cracks. No cracks

were found in the control teeth and teeth instrumented with Self adjusting file,

whereas cracks were found in 50%, 35% and 5% of the teeth after canal

instrumentation with the ProTaper, One Shape and Reciproc files respectively.

The difference between the experimental groups was statistically significant (p

< 0.001). The authors concluded that the Self-adjusting file and Reciproc files

caused less cracks compared to the ProTaper and OneShape file.33

Burklein S and Schafer E in 2013 performed an in vitro study to evaluate the

incidence of dentinal defects after root canal preparation with reciprocating

instruments and rotary instruments. One hundred human mandibular central

incisors were randomly assigned to 5 groups (n = 20). The root canals were

instrumented by using the reciprocating single-file systems Reciproc (VDW)


Page 11

and WaveOne (Dentsply Maillefer) and the full sequence rotary Mtwo (VDW)

and ProTaper instruments (Dentsply Maillefer). One group was left unprepared

as control. Roots were sectioned horizontally at 3, 6, and 9 mm from the apex

and evaluated under a microscope by using 25-fold magnification. No defects

were observed in the controls. Instrumentation with Reciproc was associated

with more complete cracks than the full sequence files. Although both

reciprocating files produced more incomplete cracks apically (3mm) compared

with the rotary files, no statistically significant differences were obtained

concerning the summarized values of all cross sections (p > 0.05). The authors

concluded that root preparation with both rotary and reciprocating instruments

resulted in dentinal defects. However, at the apical level of the the canals,

reciprocating files produced significantly more incomplete dentinal cracks than

full sequence rotary systems.34

Ashwinkumar V, Krithikadatta J, Surendran S, Velumurugan N in 2013

conducted an in vitro study to evaluate the effect of reciprocating file motion on

microcrack formation in root canals. One hundred and fifty mandibular first

molars were selected. Thirty teeth were left unprepared and served as controls,

and the remaining one hundred twenty teeth were divided into four groups

(n=30). Ni–Ti hand K-files (Dentsply Maillefer), ProTaper hand files (Dentsply

Maillefer), ProTaper rotary files (Dentsply Maillefer) and WaveOne Primary

reciprocating files (Dentsply Maillefer) were used to prepare the mesial canals.

Roots were then sectioned 3, 6 and 9 mm from the apex, and the cut surface was

observed under scanning electron microscope (SEM) and checked for the

presence of dentinal microcracks. The control and NiTi hand K- files were not


Page 12

associated with microcracks , whereas there was a significant difference

between control / NiTi hand K-files group and ProTaper hand files / ProTaper

rotary files / WaveOne primary reciprocating file group (p < 0.001) with

ProTaper rotary files producing the most microcracks.35

An in vitro study was undertaken by Hin ES, Wu MK, Wesselink PR and

Shemesh H in 2013 to compare the incidence of cracks in root dentin after canal

preparation with Self-adjusting file (ReDent Nova), Mtwo (VDW) and Protaper

(Dentsply Maillefer). One hundred extracted premolars were divided equally

into five groups (n=20). Group 1 was left unprepared. All other canals were then

enlarged upto size 20K-Flexofile. Group 2 was further prepared with K-

Flexofile, Group 3 with Protaper files, Group 4 with Mtwo file and Group 5 with

Self-adjusting file. Roots were then sectioned and observed under a microscope.

Results showed no cracks in the control group and canals prepared with K-

Flexofile, whereas, Protaper, Mtwo and Self-adjusting files caused cracks in

35%, 25%, and 10% of the teeth respectively. It was concluded that

instrumentation of the canals with Self-adjusting file, Mtwo, and ProTaper could

cause damage to the root canal dentin. However, Self-adjusting file has a

tendency to cause less dentinal cracks as compared to Protaper or Mtwo.12

Kansal R, Rajput A, Talwar S, Roongta R and Verma M in 2014 compared

the formation of dentinal cracks with instruments working in continuous rotation

and reciprocating motion. One hundred twenty extracted human mandibular

premolars were selected for the study. Thirty teeth served as controls, and the

remaining 90 teeth were divided into 3 groups depending on the root canal


Page 13

preparation technique (n=30). Group 1 samples were treated with WaveOne

primary files (Dentsply Maillefer), group 2 samples with single F2 ProTaper

(Dentsply Maillefer) working in reciprocating motion, and group 3 samples

were prepared with sequential ProTaper until F2, working in continuous rotation

motion. Roots were then sectioned at 3, 6, and 9 mm from the apex, and the cut

surface was observed under a stereomicroscope for the presence of dentinal

microcracks. The control group and WaveOne, single F2 ProTaper in

reciprocating motion, and continuous rotation ProTaper groups caused cracks in

0%, 15%, 26% and 53% of the samples respectively. A statistically significant

difference was found between two reciprocating file groups (WaveOne and

single F2 ProTaper in reciprocating motion) and the continuous rotation

ProTaper group (p < 0.05). However, no significant difference was found

amongst the two reciprocating file groups (p >0.05). The authors concluded that

dentinal cracks were produced irrespective of the motion kinematics. However,

such incidences were less with instruments working in reciprocating motion

compared with those working in continuous rotation.36

Priya NT et al in 2014 compared the incidence of dentinal microcracks after

instrumentation with various types of NiTi files in rotary and reciprocating

motion. One hundred human extracted mandibular central incisors were taken

and divided into 10 groups (n=10); Group 1- No preparation (Positive Control

group), Group 2 – Hand instrumentation with NiTi K-files (Negative Control

group), Groups 3,4 - ProTaper files (Dentsply Maillefer) in rotary and

reciprocating motion respectively , Groups 5,6 - ProTaper Next files (Dentsply

Maillefer) in rotary and reciprocating motion respectively, Groups 7,8 –


Page 14

Oneshape files (Micro-Mega) in rotary and reciprocating motion respectively,

Groups 9,10 – Reciproc files (VDW) in rotary and reciprocating motion

respectively. Specimens were sectioned horizontally at 3, 6 and 9 mm from the

apex and dentinal micro cracks were observed under a stereomicroscope. No

cracks were observed in the controls, whereas all other instrumentation

protocols resulted in dentinal microcracks. Least cracks were seen in canals

instrumented with ProTaper Next files both in rotary and reciprocating motion.

Full sequence rotary systems showed less cracks than single file systems and

full sequence rotary systems showed less cracks in reciprocating motion than in

rotary motion.37

Capar ID, Arslan H, Akcay M and Uysal B in 2014 investigated the incidence

of cracks in root dentin after root canal preparation with ProTaper Next, Hyflex

and ProTaper universal rotary instruments. One-hundred mandibular premolars

were selected. Twenty-five teeth were left unprepared and served as negative

control; another 25 teeth were instrumented with the ProTaper Universal system

(Dentsply Maillefer) up to size F4 as positive control, and the remaining 50 teeth

were shaped with the following experimental groups with an apical size 40 file:

ProTaper Next X4 (Dentsply Maillefer) and HyFlex 40/0.4 (VDW), with 25

teeth in each experimental group. After root canal preparation, all of the roots

were sectioned horizontally at 2, 4, 6 and 8 mm from the apex, and the sections

were then observed under a stereomicroscope. No cracks were observed in the

negative control group. The ProTaper Next and Hyflex instruments caused

fewer cracks (28%) than the ProTaper Universal instrument (56%) and the

difference was statistically significant (p < 0.05). However, there were no


Page 15

significant differences in crack formation between the ProTaper Next and

Hyflex groups (p > 0.05). The authors concluded that all of the instrumentation

systems created cracks in root dentin. However, the ProTaper Next and Hyflex

instruments caused fewer dentinal cracks compared with the ProTaper Universal

instrument.38

Cicek E, Kocak MM, SaglamBC and Kocak S in 2014 evaluated the

formation of microcracks in root canals after instrumentation with different NiTi

rotary file systems. Sixty extracted mandibular molars were selected. The mesial

roots were resected and teeth were randomly divided into four groups (n=15).

Group 1 samples were prepared with K- Flexofiles (Dentsply-Maillefer), group

2 with ProTaper Universal (Dentsply Maillefer), group 3 with ProTaper Next

(Dentsply Maillefer) and group 4 with WaveOne reciprocating system

(Dentsply Maillefer). The roots were then sectioned horizontally at 3mm, 6mm

and 9mm from the apex and digital images were captured at 40 fold

magnification using scanning electron microscopy to detect microcracks. It was

observed that the prevalence of microcracks in group2, group 3 and group 4

were significantly higher when compared to group 1 (p < 0.001). Group 2, group

3 and group 4 demonstrated similar prevalence of mocrocracks without

significant difference (p > 0.05) in all sections. Also the highest percentage of

microcrack was recorded in 3mm section for all the groups.39

El Nasr HM and El Kader KGA in 2014 conducted an in vitro study to

determine the dentinal damage and fracture resistance of oval roots prepared

with single–file systems using different kinematics. Sixty-five maxillary


Page 16

premolars with oval root canals were allocated into a control group (n = 5) and

3 experimental groups of 20 roots each. Group WO was instrumented with the

WaveOne primary file (Dentsply Maillefer), group PT-Rec was prepared with

F2 ProTaper files (Dentsply Maillefer), used in a reciprocating motion, and

group PT-Rot was prepared with F2 ProTaper files used in a rotational motion.

For crack evaluation, half of the samples (n = 30) were embedded in acrylic

resin, and the blocks were sectioned at 3, 6, and 9 mm from the apex. The

sections were examined under a stereomicroscope and scored for crack

presence. The other half of the specimens (n = 30) were obturated using lateral

condensation of gutta-percha and AdSeal sealer (Meta Biomed Co, Ltd, Korea).

The specimens were then subjected to a load of 1 mm/min to determine the force

required to fracture the roots. It was observed that WaveOne instruments

induced the least amount of cracks and exhibited greatest resistance to fracture

compared with ProTaper F2 files whether used in rotary or reciprocating motion.

ProTaper F2 files exhibited more microcracks when used in rotary motion as

compared to reciprocating motion.40

De Deus G et al in 2014 evaluated the frequency of dentinal microcracks

observed after root canal preparation with two reciprocating and a conventional

full sequence rotary system using micro-computed tomographic analysis. Thirty

mesial roots of mandibular molars presenting a type II Vertucci canal

configuration were scanned at an isotropic resolution of 14.16 mm. The sample

was randomly assigned to 3 experimental groups (n = 10) according to the

system used for the root canal preparation: group A—Reciproc (VDW, Munich,

Germany), group B—WaveOne (Dentsply Maillefer, Baillagues, Switzerland),


Page 17

and group C—BioRaCe (FKG Dentaire, La-Chaux-de-Fonds, Switzerland).

Second and third scans were taken after the root canals were prepared with

instruments sizes 25 and 40, respectively. Then, pre- and postoperative cross-

section images of the roots (N = 65,340) were screened to identify the presence

of dentinal defects. Dentinal microcracks were observed in 8.72% (n = 5697),

11.01% (n = 7197), and 7.91% (n = 5169) of the cross-sections from groups A

(Reciproc), B (WaveOne), and C (BioRaCe), respectively. All dentinal defects

identified in the postoperative cross-sections were also observed in the

corresponding preoperative images. The authors concluded that no causal

relationship between dentinal microcrack formation and canal preparation

procedures with Reciproc, WaveOne, and BioRaCe systems was observed. 41

Aydin U, Aksoy F, Karatasliogu E and Yildirim C in 2014 evaluated the

incidence of crack formation while using Reciproc (VDW), WaveOne (Dentsply

Maillefer) and Twisted File Adaptive (Kerr Dental) with and without

ethylenediaminetetraacetic acid (EDTA). Seventy extracted mandibular

premolars were included in the study. The teeth were decoronated until roots of

16 mm were obtained. Samples were distributed into seven groups (n=10):

group 1, no canal preparation (control); group 2, Reciproc; group 3, Reciproc +

EDTA; group 4, WaveOne; group 5, WaveOne + EDTA; group 6, Twisted File

Adaptive; group 7, Twisted File Adaptive + EDTA. After instrumentation, roots

were horizontally sectioned 3, 6 and 9 mm from the apex and observed under

stereomicroscope. The authors concluded that no microcracks were observed in

the control group, whereas, all other NiTi instruments resulted in dentinal

defects. However, there was no significant difference in crack formation


Page 18

between the experimental groups. Also, EDTA gel did not reduce the incidence

of crack occurrence.42

Ustun Y, Aslan T, Sagsen B, Kesim B in 2015 investigated the effects of

different NiTi instruments on dentinal microcrack formation during root canal

preparation. 120 extracted human mandibular incisor teeth were divided into

five experimental groups and one control group (n = 20): Group 1: Hand

preparation with balanced force technique up to #25 K-file. Group 2:

Preparation with only ProTaper F2 (Dentsply Maillefer) instrument in a

reciprocating movement. Group 3: Preparation with Reciproc R25 (VDW)

instrument in a reciprocating movement. Group 4: Preparation with ProTaper

instruments up to F2 instrument in rotational movement. Group 5: Preparation

with ProTaper Next (Dentsply Maillefer) instruments up to X2 instrument in

rotational movement. No procedure was applied to the control group. The roots

were sectioned horizontally at 3, 6 and 9 mm from the apex and examined under

stereomicroscope for the absence or presence of dentinal microcracks. The

authors concluded that except the hand file and control group, all experimental

groups showed microcrack formation. However, there was no statistically

significant difference amongst the experimental groups regarding the incidence

of microcrack formation.43

Yigit DH, Aydemir S and Yilmaz A in 2015 evaluated the presence of dentinal

defects after root canal preparation with hand instruments and two different

reciprocating instruments. Sixty freshly extracted mandibular incisor teeth were

selected for the in vitro study. On the basis of root length, mesiodistal and


Page 19

buccolingual dimensions, the teeth were allocated into three experimental

groups and one control group (n =15). The teeth in the control group (Group A)

were left unprepared. In group B, teeth were prepared with stainless steel K-files

(Mani). In groups C and D, canals were prepared with WaveOne primary

(Dentsply Maillefer) and Reciproc R25 (VDW) instruments, respectively.

Horizontal sections were made 3, 6 and 9 mm from the apex. Samples were

stained with methylene blue and viewed through a stereomicroscope for the

detection of microcracks. It was concluded that no defects were observed in the

control group and hand file group. Other than these, all other experimental

groups induced dentinal microcracks, with no significant difference between

them. It was also observed that significantly more defects were demonstrated at

3 mm level in comparison to the control (p =0.032), whereas, at the other levels,

there was no significant difference between the groups.44

Karatas E et al in 2015 conducted an in vitro study to compare the incidence

of root cracks after root canal instrumentation with the Twisted File Adaptive

(Kerr Dental), WaveOne (Dentsply Maillefer), ProTaper Next ( Dentsply

Maillefer) and ProTaper Universal (Dentsply Maillefer) system. Seventy five

extracted mandibular central incisors with mature apices and straight root canals

were selected for the study. The teeth were randomly assigned to one control

group and four experimental groups (n=15). In control group, teeth were not

instrumented. Root canals in other groups were instrumented by using the

ProTaper Universal, ProTaper Next, WaveOne, and TF Adaptive systems. All

the roots were then horizontally sectioned 3, 6, and 9 mm from the apex with a

low-speed saw under water cooling. The slices were then viewed through a


Page 20

stereomicroscope at x 25 magnification. The samples were photographed with

a camera to determine the presence of dentinal cracks. It was concluded that

except for the control group, all experimental groups resulted in microcrack

formation, and the difference between the control group and the experimental

groups was statistically significant (p < 0.001). Also, the ProTaper Next and TF

Adaptive systems produced significantly less cracks than the ProTaper

Universal and WaveOne systems in the apical section (p < 0.05).45

Li SH et al in 2015 evaluated the occurrence of dentinal microcracks in severely

curved root canals with ProTaper Universal, WaveOne, and ProTaper Next file

systems. Sixty extracted human molars with 25° to 40° root curvatures were

divided into 3 groups of 20 canals each (n=20). ProTaper Universal (Dentsply

Maillefer) , WaveOne (Dentsply Maillefer), and ProTaper Next (Dentsply

Maillefer ) file systems were used for root canal procedures. Untreated root

canals of 60 molars served as negative controls. After preparation, all roots were

stained with 1% methylene blue for 24 hours. Roots were then sectioned at the

most curved plane and 2 mm below and above the most curved plane with a

low-speed saw under cold water. A stereomicroscope was used to inspect

dentinal microcracks at 60 x magnification. It was observed that the ProTaper

Next system induced less complete and incomplete dentinal microcracks

compared with the ProTaper Universal and WaveOne systems (p < 0.05), and

there were no significant differences between ProTaper Universal and WaveOne

systems (p > 0.05). Thus, the authors concluded that The ProTaper Next system

induced less dentinal microcracks during root canal procedures in severely


Page 21

curved root canals as compared with the ProTaper Universal and WaveOne

systems.46

El-Sayed MA, Al amoud MO and M’gharfaoui MR in 2015 compared the

incidence of dentinal defects after using EDTA gel during root canal

preparations by three different instrumentation techniques. One hundred and

forty maxillary central incisors were decoronated and roots were embedded in

resin blocks. Twenty samples were left unprepared (Control group), and the

remaining 120 samples were divided into three groups (n=40). Each group was

divided equally into two subgroups (n=20) according to the use of EDTA gel

during root canal instrumentation. Roots were prepared with stainless steel K-

files (Group 1), ProTaper Universal (Dentsply Maillefer) (Group 2) and

WaveOne (Dentsply Maillefer) (Group 3). Roots were then sectioned 3, 6, and

9 mm from the apex, and the cut surface was observed microscopically and the

presence of dentinal defects was checked. It was observed that unprepared roots

did not show any dentinal defects. Dentinal defects were seen in all experimental

groups and the difference between experimental groups and subgroups

regarding the incidence of dentinal defects was not statistically significant. The

authors concluded that canal preparation using hand or rotary files created

radicular dentinal defects. The use of EDTA gel during root canal preparation

did not reduce the incidence of dentinal defects.47

Shori DD et al in 2015 undertook an in vitro study to compare the dentinal

defects caused by ProTaper Universal, Hero Shaper and ProTaper Next files.

Sixty single-rooted premolars were selected. All the specimen were decoronated


Page 22

and divided into four groups, each group having 15 specimens (n=15). Group I

specimens were prepared by Hand K-files (Mani), Group II with ProTaper

Universal (PT;Dentsply Maillefer), Group III with Hero Shaper ( HS;Micro-

Mega, Besancon, France), and Group IV with ProTaper Next (PTN ;Dentsply

Maillefer). Roots of each specimen were sectioned at 3, 6, and 9mm from the

apex and were then viewed under a stereomicroscope to evaluate for the

presence or absence of dentinal defects. It was observed that roots prepared with

hand files (HFs) showed lowest percentage of dentinal defects (6.7%); whereas,

roots prepared with PT, HS, and PTN showed dentinal defects in 40 %, 66.7% ,

and 26.7%, of the samples respectively. There was significant difference

between the HS group and the PTN group (P < 0.05). The authors concluded

that dentinal defects were observed irrespective of the type of instrumentation.

However, hand instrumentation induced minimal defects as compared to rotary

instrumentation.48

Garg S, Mahajan P, Thaman D, Monga P in 2015 compared dentinal damage

caused by different NiTi rotary instruments during root canal preparation. One

hundred and fifty freshly extracted mandibular premolars were randomly

divided into five experimental groups of 30 teeth each (n=30) and

biomechanical preparation was done: Group 1 with unprepared teeth; Group 2

were prepared with stainless steel K-files (Dentsply Maillefer); Group 3 with

ProTaper rotary instruments (Dentsply Maillefer); Group 4 with K3 rotary

(Sybron Endo); Group 5 with Easy RaCe rotary instruments (FKG Dentaire).

Then, roots were cut horizontally at 3, 6, and 9 mm from apex and were viewed

under stereomicroscope for detection of microcracks. Significant difference was


Page 23

seen between groups. No defects were found in unprepared roots and those

prepared with hand files. ProTaper, K3 rotary, and Easy RaCe preparations

resulted in dentinal defects in 23.3%, 10%, and 16.7% of teeth, respectively.

More defects were shown in coronal and middle sections, and no defect was

seen in apical third. The authors concluded that use of rotary instruments could

result in an increased chance for dentinal defects as compared to hand

instrumentation.49

Karatas E, Gunduz HA, Arslan H in 2015 assessed the effect of root canal

preparation using ProTaper Gold, Profile Vortex, F360, Reciproc and ProTaper

Universal instruments on dentinal crack formation. Ninety mandibular central

incisor teeth with mature apices and straight canals were selected and stored in

distilled water. Fifteen teeth were left unprepared (control group) and the

remaining 75 teeth were assigned to the five root canal shaping groups (n = 15):

ProTaper Gold (Dentsply Maillefer), ProFile Vortex (Dentsply, Tulsa Dental),

F360 (Komet Dental) , Reciproc (VDW) and ProTaper Universal (Dentsply

Maillefer). All the roots were sectioned perpendicular to the long axis at 3, 6

and 9 mm from the apex with a low-speed saw under water cooling. The slices

were then viewed through a stereomicroscope at 25× magnification. The

presence of dentinal cracks was determined by photographing all samples using

a digital camera. It was concluded that all the experimental groups, except F360,

produced significantly more cracks than the control group (P < 0.05). No

significant difference was observed amongst the groups at the 6 and 9 mm levels

(P > 0.05). The ProTaper Universal group produced significantly more cracks


Page 24

than the control, ProTaper Gold, ProFile Vortex, F360 and Reciproc groups at

the apical section (3 mm) (P < 0.05). 50

Materials and Method

Page 25

The present in-vitro study was carried out in the Department of Conservative

Dentistry and Endodontics, Krishnadevaraya College of Dental Sciences and

Hospital, Bangalore.

MATERIALS AND EQUIPMENTS USED :

Safe sided diamond disc (Mani, Japan)

Straight hand piece (NSK, Japan)

K-Flexofiles (Dentsply Maillefer, Switzerland)

NiTi hand K files (Dentsply Maillefer, Switzerland)

ProTaper hand files (Dentsply Maillefer, Switzerland)

Mtwo rotary files (VDW, Munich, Germany)

ProTaper rotary files (Dentsply Maillefer, Switzerland)

Reciproc files (VDW, Munich, Germany)

WaveOne files (Dentsply Maillefer, Switzerland)

Endo Block (Dentsply Maillefer, Switzerland)

Endodontic motor (X-smartTM plus, Dentsply Tulsa Dental,Tulsa,OK)

2.5% sodium hypochlorite irrigating solution (Azure Laboratories Pvt. Ltd.,

Kochi)

Distilled water

Normal Saline (Parenteral Surgicals Ltd.)

Isomet precision saw (Buehler Ltd, Lake Bluff, IL)

Stereomicroscope (Olympus 5010 ,Tokyo, Japan )

Digital camera ( Nikon E 4500, Tokyo, Japan )


Page 26

METHOD OF DATA COLLECTION:

Sample Collection:

Eighty four freshly extracted human mandibular premolars were collected from

the Department of Oral & Maxillofacial Surgery, Krishnadevaraya College of

Dental Sciences & Hospital, Bangalore. All the teeth were vital at the time of

surgical removal and were extracted for periodontal reasons (clinical grade III

mobility). Immediately after extraction, the teeth were rinsed under running

water and stored in specimen bottles filled with purified filtered water. This

storage medium causes the smallest changes in dentin over time and was

previously recommended for investigations of human dentin.51

Sample Size:

Eighty four single rooted human mandibular premolars of similar sizes were

randomly selected from the sample collected as mentioned above which met the

inclusion and exclusion criteria.

Selection of Teeth:

All the teeth were radiographed in both buccolingual and mesiodistal directions

using radiographs to detect for the presence of single canal and each tooth was

studied.

Inclusion Criteria:

Freshly extracted, intact single rooted human mandibular premolars with a

single root canal and closed apex.


Page 27

Exclusion Criteria:

Teeth with cervical abrasion, dental caries, occlusal wear, immature apices,

previous restorations or endodontic manipulation, calcifications, fracture or

crack, internal or external resorption, dilacerations and anatomical variations in

root canal morphology were excluded.

PREPARATION OF THE SPECIMENS:

All the teeth were cleaned of tissue fragments and any visible debris using

ultrasonic scaler (EMS, Switzerland) and were stored in purified filtered water

until use. To standardize canal instrumentation, teeth were decoronated by using

diamond disc, establishing a standardized root length of 15mm. All roots were

inspected with a stereomicroscope (Olympus 5010, Japan) under 12x

magnification to detect any pre-existing craze lines or cracks. Teeth with such

findings were excluded and replaced by similar teeth in the study. During the

study, specimens were wrapped in 4×4 gauze and kept moist. Canals were

negotiated with size #10 K files and after removal of gross pulpal tissue,

working length was established by advancing file into canal until just visible at

the apical foramen and then subtracting 1 mm from it.

Eighty four samples collected were divided into seven groups with twelve teeth

in each group (n=12). All groups, except the Reciproc group, were first enlarged

to a size 20 K- Flexofile following which they were subjected to one type of

instrumentation as mentioned below except the control group, which was not

subjected to further instrumentation. Hand NiTi files were used for root canal


Page 28

preparation in Group 2 and 3, rotary files in Group 4 and 5 and reciprocating

files in group 6 and 7.

GROUP 1 - Control (unprepared teeth).

GROUP 2 - NiTi K files (Dentsply Maillefer)

GROUP 3- Protaper (Dentsply Maillefer)

GROUP 4- Mtwo (VDW)

GROUP 5- Protaper (Dentsply Maillefer)

GROUP 6- Reciproc (VDW)

GROUP 7- Wave One (Dentsply Maillefer)

Rotary and reciprocating instruments were set into rotation with a 6:1 reduction

hand piece powered by a torque- limited endo motor (X-smartTM plus, Dentsply

Tulsa Dental).For each file, the individual torque limit and rotational speed

recommended by the manufacturer were used. Reciprocating files were used in

a reciprocating working motion generated by the motor. Canals were prepared

according to the following protocol.

Group 1 (Control): No preparation.

Group 2 (NiTi hand K file): Canals were enlarged to #40 size using the

balanced force technique.

Group 3 (ProTaper hand file): Canals were instrumented manually in a crown

down fashion. The ProTaper shaping SX was used in coronal enlargement, and

shaping S1, S2, finishing F1, F2, F3, F4 files were sequentially used to the

Hand files

Rotary files

Reciprocating

files


Page 29

working length. F4, which was the last file to be used in the apical area

corresponds to K file #40 and with a taper of .06.

Group 4 (Mtwo rotary file): These files were used to the full length of the

canals by using a gentle in-and-out motion. The instrumentation sequence was

10/.04, 15/.05, 20/.06, 25/.06, 30/.05, 35/.04 and 40/.04.

Group 5 (ProTaper rotary file): Canals were prepared in a crown down

fashion with the aid of endodontic motor at 250 rpm. The ProTaper shaping SX

was used in coronal enlargement, and then S1, S2, F1, F2, F3, F4 files were

sequentially used to the working length. F4, which was the last file to be used

in the apical area corresponds to K file #40 and with a taper of .06.

Group 6 (Reciproc file): A R40 Reciproc file with size #40 at the tip and taper

of .06 over the first 3 mm was used in a reciprocating, slow in-and-out pecking

motion, no more than three to four times with minimum apical pressure at 300

rpm .

Group 7(Wave One file): A large reciprocating Wave One file with size #40

and taper of .08 was used in a reciprocating, slow in-and-out pecking motion,

no more than three to four times with minimum apical pressure at 350 rpm.

Each instrument was used to prepare no more than four canals. In each group,

canals were irrigated with 2.5% sodium hypochlorite between each instrument

or after three pecks while using the reciprocating files, using a syringe with 27


Page 30

G needle. A total of 12 ml of 2.5% sodium hypochlorite was used in each canal.

After preparation, the specimens were rinsed with 5 ml normal saline.

SECTIONING AND MICROSCOPIC EXAMINATION

All roots were sectioned perpendicular to the long axis at 3, 6, and 9 mm from

the apex using a slow speed water-cooled saw (Isomet; Buehler Ltd, Lake Bluff,

IL). Sections were then viewed under stereomicroscope (Olympus 5010) under

30x magnification. The appearance of dentinal defects was registered by the

pictures that were taken digitally using a digital camera (Nikon E 4500, Japan)

attached to the stereomicroscope. In order to avoid confusing definitions of

root fractures, three distinguished categories were made: “no defect,”

“fracture,” and “other defects”.13

Roots were classified as “defected” if at least one of the three sections

showed either a craze line, partial crack, or a fracture.

No

defect

Root dentin devoid of any lines or cracks where

both the external surface of the root and the

internal root canal wall will not show any evident

defects.

Fracture A line extending from the root canal space all the

way to the outer surface of the root.

Other

defects

All other lines observed that will not extend from

the root canal to the outer root surface (e.g. - a

craze line; a line extending from the outer surface

into the dentin but will not reach the canal lumen,

or a partial crack; a line extending from the canal

walls into the dentin without reaching the outer

surface).


Page 31

FIGURE 1: Eighty four single rooted human mandibular premolars.


Page 32

FIGURE 2: Decoronation using safe sided diamond disc.

FIGURE 3: Standardizing root length to 15mm.


Page 33

FIGURE 4: Decoronated specimens.

FIGURE 5: Armamentarium.

GROUP I

GROUP II

GROUP III

GROUP IV

GROUP VI

GROUP V

GROUP VII


Page 34

FIGURE 6: Experimental hand Ni-Ti files used in the study.

FIGURE 7: Experimental rotary Ni-Ti files used in the study.

FIGURE 8: Experimental reciprocating Ni-Ti files used in the study.


Page 35

FIGURE 9: Canal instrumentation.

FIGURE 10: Isomet low speed saw.


Page 36

FIGURE 11: Securing the instrumented specimen in holder

.

FIGURE 12: Sectioning using Isomet.


Page 37

FIGURE 13: Sections from 3mm, 6mm and 9mm from the root apex.

FIGURE 14: Specimens stored in distilled water.

3 mm 6 mm 9 mm

GROUP I

GROUP II

GROUP III

GROUP VI

GROUP V

GROUP IV

GROUP VII


Page 38

FIGURE 15: Stereomicroscope.

Results

Page 39

The present in-vitro study aimed to compare the incidence of dentinal microcracks caused by

hand, rotary and reciprocating instrumentation during root canal preparation. Eighty four

human mandibular premolar teeth were instrumented using different file systems according to

the groups divided, following which they were sectioned and viewed under stereomicroscope

for the detection of dentinal defects.

Three distinguished categories for dentinal defects were made: “no defect,” “fracture,” and

“other defects”.

No

defect

Root dentin devoid of any lines

or cracks where both the

external surface of the root and

the internal root canal wall will

not show any evident defects.

Fracture A line extending from the root

canal space all the way to the

outer surface of the root.

Other

defects

All other lines observed that

will not extend from the root

canal to the outer root surface

(e.g. - a craze line; a line

extending from the outer

surface into the dentin but will

not reach the canal lumen, or a

partial crack; a line extending

from the canal walls into the

dentin without reaching the

outer surface).

Results

Page 40

FIGURE 16: No defect

FIGURE 17: Craze lines

FIGURE 18: Fracture

Results

Page 41

Roots were classified as “defected” if at least one of the three sections showed either a craze

line, partial crack, or a fracture. The data obtained from the study was subjected to statistical

analysis. Results are expressed as the number and percentage of defected roots in each

group.

Table 1: Comparison of complete cracks/fracture in seven groups studied

Groups

3 mm

(n=12)

6 mm

(n=12)

9 mm

(n=12)

Total

(n=36)

No % No % No % No %

GROUP 1(CONTROL) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 2 (Ni-Ti K

FILES) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 3 (HAND PRO

TAPER FILES) 1 8.33 0 0.00 0 0.00 1 2.8

GROUP 4 (M TWO

FILES) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 5 (ROTARY

PROTAPER FILES) 1 8.33 1 8.33 0 0.00 2 5.6

GROUP 6 (RECIPROC

FILES) 2 16.67 2 16.67 1 8.33 5 11.1

GROUP 7 (WAVE ONE

FILES) 1 8.33 2 16.67 0 0.00 3 8.3

P value 0.893 0.404 1.000 0.055+

Results

Page 42

Graph 1: Percentage of complete cracks/fracture in seven groups studied

Table 1 and Graph 1: Incidence of complete cracks caused by different groups was compared

at three different levels, i.e. 3mm, 6mm and 9mm from the apex. Control (Group 1) and Ni-Ti

K-file (Group 2) groups were not associated with complete crack/fracture at any of the three

levels studied.

At 3mm level, Reciproc group (Group 6) was associated with maximum incidence of complete

cracks, i.e. in 2 out of 12 samples (16.67%). There was no statistical difference among different

instrumentation groups as tested by Chi-square test (P=0.893).

At 6mm level, Reciproc group (Group 6) and WaveOne group (Group 7) were associated with

maximum incidence of complete cracks, i.e. both caused fracture in 2 out of 12 samples

0

5

10

15

20

Pe

rce

nta

ge

3 mm

6 mm

9 mm

Results

Page 43

(16.67%), respectively. There was no statistical difference among different instrumentation

groups as tested by Chi-square test (P=0.404).

At 9 mm level, Reciproc group (Group 6) was associated with maximum incidence of complete



Overall, Reciproc group (Group 6) was associated with maximum incidence of complete



Table 2: Comparison of other defects (incomplete cracks/craze lines) in seven groups

studied

Groups

3 mm

(n=12)

6 mm

(n=12)

9 mm

(n=12)

Total

(n=36)

No % No % No % No %

GROUP 1(CONTROL) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 2 (Ni-Ti K

FILES) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 3 (HAND PRO

TAPER FILES) 3 25.00 4 33.33 1 8.33 8 22.2

GROUP 4 (M TWO

FILES) 3 25.00 3 25.00 3 25.00 9 25.0

GROUP 5 (ROTARY

PROTAPER FILES) 4 33.33 5 41.67 2 16.67 11 30.6

GROUP 6 (RECIPROC

FILES) 8 66.67 6 50.00 1 8.33 15 41.7

GROUP 7 (WAVE ONE

FILES) 7 58.33 4 33.33 2 16.67 13 36.1

P value 0.037* 0.090+ 0.697 <0.001**

Results

Page 44

Graph 2: Percentage of other defects (incomplete cracks/craze lines) in seven groups

studied

Table 2 and Graph 2: Incidence of other defects (incomplete cracks and craze lines) caused

by different groups was compared. Control (Group 1) and Ni-Ti K-file (Group 2) groups were

not associated with incomplete cracks or craze lines at any of the three levels studied, i.e. 3mm,

6mm and 9mm.

At 3mm level, Reciproc group (Group 6) was associated with maximum incidence of

incomplete cracks or craze lines, i.e. in 8 out of 12 samples (66.67%). There was a statistically

significant difference among different instrumentation groups as tested by Chi-square test

(P=0.037).

0

20

40

60

80

Pe

rce

nta

ge

3 mm

6 mm

9 mm

Results

Page 45

At 6mm level, Reciproc group (Group 6) was associated with maximum incidence of

incomplete cracks or craze lines, i.e. in 5 out of 12 samples (50.00%). There was no statistical

difference among different instrumentation groups as tested by Chi-square test (P=0.090).

At 9mm level, Mtwo group (Group 4) was associated with maximum incidence of incomplete

cracks or craze lines, i.e. in 3 out of 12 samples (25.00%). There was no statistical difference

among different instrumentation groups as tested by Chi-square test (P=0.697).

Overall, Reciproc group (Group 6) was associated with maximum incidence of incomplete

cracks or craze lines, i.e. in 15 out of 36 samples (41.70%). There was a statistically significant

difference among different instrumentation groups as tested by Chi-square test (P=0.001).

Statistical Method: Descriptive and inferential statistical analysis was carried out in the

present study. Results on categorical measurements are presented in Number (%). Significance

is assessed at 5 % level of significance.

Chi-square test was used to find the significance of study parameters on categorical scale

between two or more groups.

Significant figures:

+ Suggestive significance (P value: 0.05<P<0.10)

* Moderately significant (P value:0.01<P 0.05)

** Strongly significant (P value: P0.01)

Results

Page 46

Statistical software: The Statistical software namely SAS 9.2, SPSS 15.0, Stata 10.1, MedCalc

9.0.1,Systat 12.0 and R environment ver.2.11.1 were used for the analysis of the data and

Microsoft word and Excel were used to generate graphs and tables.

Discussion

Page 47

Endodontic therapy involves treating vital and necrotic dental pulps so that

patients can retain their natural teeth in function and esthetics. Although,

successful therapy depends on many factors, one of the most important steps in

any root canal treatment is canal preparation. This is essential because

preparation determines the efficacy of all subsequent procedures and includes

mechanical debridement, creation of space for medicament delivery, and

optimized canal geometries for adequate obturation.2

Traditionally, the shaping of root canals was achieved by the use of stainless

steel hand files. However, various undesirable apical preparation outcomes,

such as perforations9, canal transportation, ledge and zip formation52 were

encountered during biomechanical preparation using these files.

Significant changes in the endodontic instrumentation have occurred over the

last two decades. Paramount among these being the introduction of nickel-

titanium (Ni-Ti) instrumentation. Since the introduction of rotary Ni-Ti

instruments in 1988,53 there has been a growing shift from manual to rotary

engine-driven preparation.

Due to the property of super elasticity, Ni-Ti rotary files have become a

mainstay in clinical endodontics as they have the ability to shape root canals

with fewer procedural complications. Nickel-titanium (Ni-Ti) instruments offer

many advantages over conventional files. They are flexible,53 have increased

cutting efficiency54 and are time saving.55 Furthermore, Ni-Ti instruments

Discussion

Page 48

maintain the original canal shape during preparation and have a reduced

tendency to transport the apical foramen.55-57

Despite the obvious clinical advantages of rotary Ni-Ti instruments over

traditional hand instrumentation, the influence of the design of the cutting blades

is still controversial2,58 and could generate increased friction and stresses within

the root canal.59 Rotary instrumentation results in significantly more rotations of

the instrument inside the canal,14 which may cause more friction between the

files and the canal walls. Additionally, it has been suggested that the total

volume of dentin removed from the root canals is significantly greater with Ni-

Ti rotary systems in comparison with hand files,31`which implicates that rotary

files with large taper may cause significantly more dentinal damage in the form

of complete or incomplete cracks.19

It has been observed clinically that vertical root fracture (VRF) occurs

commonly in endodontically treated teeth,59-61 and as a result, endodontic

procedures have been blamed as a frequent cause of VRF. Numerous

experimental studies have challenged this conclusion. Dentin of endodontically

treated teeth does not exhibit mechanical properties that are significantly

different from those of vital teeth; that is, dentin does not appear to become more

brittle.62,63 It has been shown that access cavity preparation has non-significant

effects on tooth stiffness.64 The load generated during lateral condensation is

generally far lower than the load required to fracture the roots.65,66 Thus,

obturation should not be regarded as a major cause of VRF except in very weak

roots. Canal preparation involves dentin removal and may compromise the

Discussion

Page 49

fracture strength of the roots; it is, therefore, another area that has been studied

as a potential cause of VRF.5

Fracture susceptibility of an endodontically treated tooth depends primarily on

the final canal shape, the extent of canal enlargement and the elimination of

irregularities, which are the stress concentration sites.7 Thus, various

instrumentation techniques and systems, with different cutting blades and tip

designs and tapers, lead to different types and degrees of dentinal damage to the

root canal wall.10-12

ProTaper Universal hand and rotary instruments (Dentsply Maillefer,

Ballaigues, Switzerland) are amongst the most widely used Ni-Ti instruments

globally. The ProTaper Universal instruments were designed by Dr.Cliff

Ruddle, Dr.John West and Dr.Pierre Machtou and originally comprised of just

six instruments: three shaping files and three finishing files. This set is now

complemented with two larger finishing files. It has a convex, triangular cross

section and no radial lands; this creates a stable core and sufficient flexibility

for the smaller files. The cross section of finishing files F3, F4 and F5 is slightly

relieved for increased flexibility. A unique design element is varying tapers

along the instruments’ long axes. The three shaping files have tapers that

increase coronally, and the reverse pattern is seen in the five finishing files.

Shaping files #1 and #2 have tip diameters of 0.185mm and 0.2mm,

respectively, 14 mm long cutting blades, and partially active tips. The diameter

Discussion

Page 50

of these files at D14 are 1.2 and 1.1 mm, respectively. The finishing files, F1-F5

have tip diameters of 0.2, 0.25, 0.3, 0.4 and 0.5mm, respectively, between D0

and D3, and the apical tapers are 0.07, 0.08, 0.09, 0.06, and 0.05, respectively.

The finishing files have rounded noncutting tips67 and are used in crown down

manner.

Recently, a new instrument design has been introduced which no longer

requires a crown down instrumentation sequence. The new Mtwo instruments

(VDW, Munich, Germany) have a S-shaped cross sectional design and a

noncutting safety tip. Thus, these instruments are characterised by a positive

rake angle with two cutting edges, which are claimed to cut dentine effectively.

Moreover, Mtwo instruments have an increasing pitch length from the tip to the

shaft. This design is alleged to have two functions: (i) to eliminate threading and

binding in continuous rotation, and (ii) to reduce the transportation of debris

towards the apex. The basic series of Mtwo instruments comprises eight

instruments with tapers ranging between 4% and 7% and sizes from 10 to 40.

According to the manufacturer the instruments should be used in a single length

technique. That means, all files of the instrumentation sequence should be used

to the full length of the root canal.68

In 2008, a novel canal preparation technique with only the F2 ProTaper

instrument used in clockwise and counter clockwise movement was described.20

The concept of using a single NiTi instrument to prepare the entire root canal is

interesting because the learning curve is considerably reduced as a result of

technique simplification. Moreover, the use of a single NiTi instrument is more

Discussion

Page 51

cost-effective than the conventional multifile NiTi rotary systems. Added

benefits include reduced cross contamination and reduced instrument fatigue.

The recently introduced nickel-titanium (Ni-Ti) files Reciproc (VDW, Munich,

Germany) and WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) are

claimed to be able to completely prepare and clean root canals with only one

instrument. These files are made of a special Ni-Ti alloy called M-Wire that is

created by an innovative thermal-treatment process. The benefits of this M-Wire

Ni-Ti are increased flexibility of the instruments and improved resistance to

cyclic fatigue.1These files are used in a reciprocal motion that requires special

automated devices. Reciproc files are available in different sizes 25, taper 08;

40, taper 06; 50, taper 05 and WaveOne are available in the sizes 21, taper 06;

25, taper 08; and 40, taper 08. The reciprocating movement relieves stress on

the instrument and, therefore, reduces the risk of cyclic fatigue caused by tension

and compression.25,26 The reciprocation working motion consists of a counter

clockwise (cutting direction) and a clockwise motion (release of the instrument),

while the angle of the counter clockwise cutting direction is greater than the

angle of the reverse direction. Due to the fact that the counter clockwise angle

is greater than the clockwise one, it is claimed that the instrument continuously

progresses towards the apex of the root canal. The angles of reciprocation are

specific to the design of the particular instruments and are programmed in an

electronic motor. The angles of reciprocating are smaller than the elastic limit

of the files in a single reciprocating movement, but not when multiple

anticlockwise/clockwise movements are made and the tip of the file binds in the

canal. In general, reciprocating root canal preparation is an evolution of the

Discussion

Page 52

balanced force technique that allows shaping of even severely curved canals

with hand instruments to larger apical diameter.69

During instrumentation, the contact between the instrument and dentine creates

many momentary stress concentrations in the dentine that might exceed the

tensile strength of the collagen matrix of dentine.30Several in vitro studies have

reported consistently that engine-driven instruments caused dentinal

defects.34,35,70 Besides the kinematics of the root canal instruments,71 the design

features of instruments such as tip design and cross-sectional geometry,31 taper2

and flexibility21 have been shown to exert an impact on the incidence of dentinal

defects.

In the present study, during selection of the specimens, only teeth with poor

periodontal support (clinical grade III mobility) were collected, as they can be

extracted with minimal trauma.72 Teeth showing signs of occlusal wear were

excluded as they are expected to have structural changes in dentine. All the teeth

were inspected with a stereomicroscope under 12x magnification to detect any

pre-existing craze lines or cracks. However, absolute ruling out the presence of

dentinal defects before the start of the experiment is impossible because some

defects could be internal and would therefore not be visible on the external root

surface.12 An alternative non-invasive and more accurate recent method would

be to use the micro-computed tomography (µ CT) technology;41 however, it

needs precise and strict standardization of all acquisition parameters to be able

to select the same pre- and postoperative slices for comparison.

Discussion

Page 53

ProTaper files were chosen as they are amongst the most commonly used Ni-Ti

instruments globally.73 The Reciproc and WaveOne files were compared with

Mtwo and ProTaper files because both systems are the direct full sequence

counterparts of the single file reciprocating system, respectively, and till date,

Reciproc and WaveOne are the only commercially available instruments

designed specifically to be used in reciprocating motion.27

The storage of specimens during all stages of the experimental procedures may

affect the results, particularly with regard to the mechanical properties of the

root dentine.34 In the present study, purified filtered water was chosen as storage

medium for the specimens. This medium was previously recommended for

investigations of human dentine because it causes the least amount of changes

in dentine over time.51

High concentrations of sodium hypochlorite (NaOCl) can significantly decrease

the elastic modulus, and flexural strength of dentine when used as an endodontic

irrigant.74 Sim et al. (2001) reported decreased microhardness of radicular

dentine after exposure to NaOCl in concentrations 5.25%, but not when NaOCl

was used in lower concentrations. In the present study, 2.5% NaOCl was used

to minimize alterations of the mechanical properties of dentine during the

experimental procedures especially as the specimens of the control group were

not irrigated.

In the present study, roots were not covered by elastomeric materials to mimic

periodontal ligament (PDL), which is in accordance with the study design

Discussion

Page 54

followed by Onnink et al.72 , Ribeiro et al.75 and Yigit et al.44 However, some

studies are reported in literature where PDL simulation was done using

elastomeric materials.5,37,65 Saw and Messer stated that these attempts are

insufficient to mimic the anatomical and biological aspects of tooth structure

and could contribute to the introduction of artificial changes in force distribution

themselves.76 Soros et al. stated that elastomeric materials are incapable of

withstanding compaction forces in the way that the natural periodontal ligament

does and that they may collapse under pressure.77

The sectioning method used in the present study allowed the evaluation of the

effect of root canal preparation procedures on root dentine by direct inspection

of the roots and is similar to the methodology described in recent studies

(Beurklein et al. 201334, Capar et al. 201438, 201578, Topcuoglu et al. 201479).

However, this method has some limitations. Besides the inability to detect pre-

existing defects, it is possible that some defects extended to different levels of

the root and are counted as separate defects.72

The specimens of the control group had no defects. This implies that neither the

extraction protocol nor the sectioning method induced dentinal damage. Thus,

it may be concluded that the defects observed were caused by the preparation

procedures. This finding is in agreement with the previous studies (Burklein et

al. 201334, Capar et al. 201438, 201578, Kansal et al.201436, Nasr & Kader 201440,

Topcuoglu et al. 201479). However, Arslan et al.80 and De-Deus et al.41 reported

that the incidence of dentinal defects in unprepared mesial canals of mandibular

molars to be about 16% and 27%, respectively. These contradicting results can

Discussion

Page 55

be explained on the basis that the reasons for extraction were not defined in both

studies, as traumatic extraction may lead to dentinal defects, besides that

implementation of the micro-CT technology in the later study, allowed the

examination of thousands of slices.

No defects were seen in the specimens of Ni-Ti hand K-file group. Similar

results were reported by Bier et al19 , Yoldas et al.31 , Ashwinkumar et al.35 and

Cicek et al.39 This could be related to avoidance of continuous rotational motion

and removal of less dentin as a consequence of less taper of the hand

instruments.

ProTaper hand files resulted in lesser dentinal defects as compared to rotary

instrumentation, although the difference was not significant. The primary reason

for this is the motion kinematics of the files. ProTaper hand files employ

balanced force technique unlike the rotary files that use continuous rotation.

Overall, the rotary ProTaper was associated with dentinal cracks in 30.6% of the

samples. Similar results were reported by Yoldas et al.31 and Hin et al.12 who

reported an overall incidence of cracks in 30% and 35% of the samples,

respectively, prepared by rotary ProTaper.

Rotary ProTaper and Mtwo groups resulted in significantly more dentinal

defects as compared to control and hand Ni-Ti K-file groups. Mtwo files

resulted in an overall defect in 25% of the samples. Similar study conducted

earlier by Hin et al.12 also reported defects in 25% of the specimens prepared

with Mtwo files. Although, there was no significant difference in the incidence

Discussion

Page 56

of dentinal cracks caused by Mtwo and rotary ProTaper , Mtwo resulted in lesser

defects at all the levels compared to ProTaper. Similar results were reported by

Burklein et al.34 and Hin et al.12 It is mainly because of greater flexibility of

Mtwo files as compared to ProTaper. Arbab-Chirani et al.81 had reported that

Mtwo is three times as flexible as ProTaper. Besides this, taper of preparation

can be a contributing factor. The taper of Mtwo instrument used was 4%,

whereas that of ProTaper was 6%.

Reciproc group was associated with maximum dentinal damage. Similar results

were reported by Burklein et al.34 , Yigit et al.44 and Saber et al.82 who reported

an overall defect in 34%, 29% and 25% of the specimens, respectively, after

preparation with Reciproc group. However, Liu et al.33 reported only 5%

incidence of cracks after instrumentation with Reciproc. The contradicting

results might be because of pre flaring of the specimens with Gates Glidden

drills in Liu’s study, whereas in the present study, Reciproc files were used

according to the manufacturers’ instruction, without any preflaring and creation

of a glide path.

There was no significant difference between WaveOne and Reciproc in terms

of incidence of dentinal cracks. Overall, WaveOne files resulted in dentinal

defects in 36% of the specimens. Similar results were reported by Burklein et

al.34and Yigit et al.44 who reported an incidence of dentinal cracks in 30% and

27% of the samples, respectively. However, Kansal et al36 reported an incidence

of dentinal defects in only 15% of the samples. This contradicting result can be

explained on the basis of type of file used in both the studies. In the present

Discussion

Page 57

study large WaveOne (Tip size: ISO 40) was used, whereas primary WaveOne

(Tip size: ISO 25) was used by Kansal et al.

The methodology employed in the present study, i.e. root sectioning and direct

observation by optical microscopy, doesn’t permit for the evaluation of pre-

existing defects. However, future studies using µCT will make the detection of

pre-existing cracks much easier.

Extrapolation of the results from work that is purely in-vitro in nature must

always be made cautiously. The ultimate clinical decision-making should

always consider the patient related variables to maximize the long-term

prognosis of endodontically treated teeth.

Conclusion

Page 58

Under the conditions of the present study & within its limitations, the following

conclusions can be drawn:

All groups, except the Ni-Ti K-file group, induced dentinal defects in the

samples.

Full sequence rotary systems caused less defects than the single file

systems, with Reciproc group causing significantly more defects as

compared to the other groups.

Maximum samples showed defects at 3mm level from the apex.

Summary

Page 59

This in-vitro study was undertaken in the Department of Conservative Dentistry

& Endodontics, Krishnadevaraya College of Dental Sciences & Hospital,

Bangalore. The aim of the study was to compare and evaluate the incidence of

dentinal microcracks caused by hand, rotary and reciprocating instrumentation

during root canal preparation.

Eighty four freshly extracted human mandibular premolars of similar sizes were

randomly selected which met the inclusion and exclusion criteria. To

standardize canal instrumentation, teeth were decoronated by using diamond

disc, establishing a standardized root length of 15mm. Samples selected were

divided into seven groups with twelve teeth in each group. All groups, except

the Reciproc group, were first enlarged to a size 20 K- Flexofile following which

they were subjected to one type of instrumentation depending upon the group.

Group 1 served as control in which no further instrumentation was done. In

group 2, Ni-Ti hand K-files were used to enlarge the canals to size #40. In group

3, hand ProTaper files were used to instrument the canals to F4, corresponding

to size #40, 6% taper. In group 4, full sequence rotary Mtwo files were used to

enlarge the canals to size #40, 4% taper. In group 5, full sequence ProTaper

rotary files were used to instrument the canals to F4, corresponding to size #40,

6% taper. In group 6, single reciprocating file, Reciproc R40, corresponding to

size #40, 6% taper was used to instrument the canals and in group 7, canals were

enlarged by Single reciprocating large WaveOne file, corresponding to size #40,

8% taper. In each group, canals were irrigated with 2.5% sodium hypochlorite

between each instrument or after three pecks while using the reciprocating files,

Summary

Page 60

using a syringe with 27 G needle. After preparation, the specimens were rinsed

with normal saline.

All the roots were then sectioned perpendicular to the long axis at 3, 6, and 9

mm from the apex and viewed under stereomicroscope for the detection of

dentinal cracks. Data obtained was subjected to statistical analysis. Chi-square

test was performed to find the significance of study parameters between the

groups studied.

From the results obtained it was inferred that except for the Ni-Ti K-file group,

all other samples showed the presence of dentinal defects irrespective of the

instrumentation used. Overall, single file reciprocating systems, i.e. Reciproc

and WaveOne resulted in significantly more dentinal defects as compared to the

other groups. Although dentinal defects were detected at all the three levels,

maximum samples showed defects at 3mm from the apex.

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Page 61

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Annexure

Page 71

Table 1: Comparison of complete cracks/fracture in seven groups studied

Groups

3 mm

(n=12)

6 mm

(n=12)

9 mm

(n=12)

Total

(n=36)

No % No % No % No %

GROUP 1(CONTROL) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 2 (Ni-Ti K

FILES) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 3 (HAND PRO

TAPER FILES) 1 8.33 0 0.00 0 0.00 1 2.8

GROUP 4 (M TWO

FILES) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 5 (ROTARY

PROTAPER FILES) 1 8.33 1 8.33 0 0.00 2 5.6

GROUP 6 (RECIPROC

FILES) 2 16.67 2 16.67 1 8.33 5 11.1

GROUP 7 (WAVE ONE

FILES) 1 8.33 2 16.67 0 0.00 3 8.3

P value 0.893 0.404 1.000 0.055+

Annexure

Page 72

Table 2: Comparison of other defects (incomplete cracks/craze lines) in seven groups

studied

Groups

3 mm

(n=12)

6 mm

(n=12)

9 mm

(n=12)

Total

(n=36)

No % No % No % No %

GROUP 1(CONTROL) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 2 (Ni-Ti K

FILES) 0 0.00 0 0.00 0 0.00 0 0.0

GROUP 3 (HAND PRO

TAPER FILES) 3 25.00 4 33.33 1 8.33 8 22.2

GROUP 4 (M TWO

FILES) 3 25.00 3 25.00 3 25.00 9 25.0

GROUP 5 (ROTARY

PROTAPER FILES) 4 33.33 5 41.67 2 16.67 11 30.6

GROUP 6 (RECIPROC

FILES) 8 66.67 6 50.00 1 8.33 15 41.7

GROUP 7 (WAVE ONE

FILES) 7 58.33 4 33.33 2 16.67 13 36.1

P value 0.037* 0.090+ 0.697 <0.001**

INTRODUCTION

OBJECTIVES

REVIEW OF LITERATURE

MATERIALS & METHOD

RESULTS

DISCUSSION

CONCLUSION

SUMMARY

BIBLIOGRAPHY

ANNEXURE

stereomicroscopic evaluation of dentinal …

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