- AN IN-VITRO STUDY”

“A COMPARATIVE ANALYSIS OF FRACTURE STRENGTH OF ROOTS INSTRUMENTED WITH SINGLE FILE SYSTEMS

- AN IN-VITRO STUDY”

Dissertation submitted to

THE TAMILNADU Dr. M.G.R. MEDICAL UNIVERSITY

In partial fulfillment for the Degree of MASTER OF DENTAL SURGERY

BRANCH IV

CONSERVATIVE DENTISTRY AND ENDODONTICS

APRIL 2016

This is to certify that DR.AARTHI.G Post Graduate Student (2013-2016) from the Department Of Conservative Dentistry and Endodontics, J.K.K.Nataraja Dental College, Komarapalayam, Namakkal District–638183,Tamilnadu has done the dissertation titled “A COMPARATIVE ANALYSIS OF FRACTURE STRENGTH OF ROOTS INSTRUMENTED WITH SINGLE FILE SYSTEMS : A IN VIRTO STUDY” under my direct guidance and supervision in the partial fulfillment of the regulations laid down by THE TAMIL NADU DR. M.G.R

MEDICAL UNIVERSITY, CHENNAI,FOR M.D.S BRANCH – IV

CONSERVATIVEDENTISTRY ANDENDODONTICS DEGREE

EXAMINATION.It has not been submitted(partial or full) for the award of any other degree or diploma.

Dr. J.V. Karunakaran. M.D.S, Professor & Head,

Department of Conservative Dentistry & Endodontics, J.K.K.Nataraja Dental College Komarapalayam,

NamakkalDist – 638183, Tamilnadu.

Dr. A. Siva Kumar. M.D.S, Principal,

J.K.K.NatarajaDentalCollege Komarapalayam,

NamakkalDist – 638183, Tamilnadu.

I take this opportunity to sincerely thank my post graduate teacher and my guide Dr.J.V.Karunakaran.M.D.S, Professor and Head, Department of Conservative Dentistry & Endodontics, J.K.K.Nattraja Dental College, for his academic and technical assistance, perseverance in motivating and supporting me throughout my study period.

My sincere thanks to Dr.A.Sivakumar.M.D.S, Principal, J.K.K. Nattraja Dental College, who had helped with his advice throughout my postgraduate course.

I would like to express my sincere gratitude to Dr.N.S.MohanKumar.M.D.S, Professor, Department of Conservative Dentistry & Endodontics J.K.K.Nattraja Dental College, for his valuable suggestions, support and encouragement throughout my post graduate curriculum.

I extend my sincere thanks to Dr.S.Senthil Kumar.M.D.S, Associate Professor, J.K.K. Nattraja Dental College & Hospital, for his continuous support, guidance and constant encouragement throughout my study period.

I thank Dr.Satyanarayanan.M.D.S, Reader, Dr.Jayaprakash.M.D.S, Dr.Satheesh Kumar.M.D.S, Senior Lecturers, Dr.Leo Sujith Samuel.B.D.S, Dr.Karthiga.B.D.S, Lecturer for their support and constant encouragement throughout the completion of this work.

I express my gratefulness to Mr.Ramachandran our College Librarian for his valuable assistance rendered during the course of the study.

I am extremely thankful to Dr.Raveendran, Mr.Amit Byron for guiding me in working with SAF FILES.

Department, PSG TECH, Coimbatore, for his guidance in working with fracture testing analysis.

My sincere thanks to Mr.M.Prasad Krishnan, Statistician for his guidance in Statistical Analysis.

I thank Mr.K.Murali Sundar, Chakra Printers-Komarapalayam, SPY Printers-Erode for data processing and binding works.

I express my gratefulness to my batchmates, colleagues for the help rendered during my thesis work.

I express my gratefulness to Mr. Chinnaraj, our lab technician and Ms.Valarmathy, Mrs.Saroja, our Department support staff for the help rendered during the course of the study.

Above all, it is my privilege to thank my husband Dr. R. Ranganathan and my parents Mr.M.Ganapathy, Mrs.P.Selvam and my mother-in-law Mrs.Sivagami for their sacrifice, support and constant encouragement.

CONTENTS

S.No INDEX PAGE.NO

1. INTRODUCTION 1

2. REVIEW OF LITERATURE 6

3. MATERIALS AND METHODS 23

4. RESULTS 34

5. DISCUSSION 40

6. SUMMARY 63

7. CONCLUSION 64

8. BIBLIOGRAPHY 65

The primary objective of the root canal obturation procedure during endodontic therapy is to reinforce the root canal space and increase fracture resistance of the remaining tooth structure. The teeth which have been treated endodontically have been reported to be more susceptible to fracture when compared to their vital counterparts. This necessitates sufficient care and protection of the remaining tooth structure by proper restoration. The most common cited cause for weakening of the tooth structure is excessive removal of tooth structure during endodontic therapy and subsequent dehydration of coronal and radicular dentin.

Bio-mechanical preparation of the root canal system is a key procedure in endodontic therapy. The anatomy of the root canal, the inherent variations, curvature of the roots especially in the mandibular and maxillary posterior teeth pose a challenge with regard to the preparation of the canal space, the irrigant delivery and debridement in the apical one third of the root. The root canal system is one where the coronal one third is highly accessible, middle one is third fairly accessible and the apical one third being the least accessible. This is more so in the case of curved canals where in order to access the apical third of the canals and to achieve sufficient debridement and cleansing, considerable amount of radicular dentin in the coronal and middle third is removed which would possibly weaken the structure of the root.

This makes the endodontically treated tooth more susceptible to fracture. (Sornkul et al in 1992)⁷⁹

A variety of possible reasons have been put forward as reasons for fracture of root which includes loss of tooth structure due to carious process or trauma, excessive removal of tooth structure during root canal preparation procedures, the dehydration of dentin after completion of endodontic therapy, obturation procedures

or post-space preparation, excessive stress during obturation and increased use of high concentration of irrigants with more exposure time. This in a clinical situation would mean a reduction in the long term survival rate of these endodontically treated teeth, which is undesirable. The major achievable goal of endodontic therapy should be reinforcement of the residual tooth structure in such a way that it prevents untoward events (Johnson M.E., et al in 2000)³⁸.

Earlier with hand instrumentation it was common practice to enlarge the canal to three sizes from the first initial file to bind at the apical third of the root.

This enlargement allowed efficient cleansing and allowed the irrigants and medicaments to reach the entire length of the canal system. The introduction of NiTi hand instruments in endodontics almost two decades ago, improved preparations as they were flexible. The most significant advantage was the predictable control of the preparation. The alloy was resistant to corrosion, had the property of super-elasticity and shape memory. With the advent of nickel titanium rotary instrumentation, things changed and negotiation of even severely curved canals became much easier to accomplish, was more complete and reduced the clinical working time.

These rotary instruments when used to prepare the canal exert considerable stresses in certain areas resulting in formation of micro-cracks or craze lines which later predisposes the tooth to vertical root fracture. These areas of most stress are mostly located in the mid root canal wall area. It has been observed that lateral forces result in high stress concentrations in radicular dentin in the coronal one-third of the root, and make the teeth susceptible to fracture at the cemento-enamel junction. There is a direct proportional correlation between the root thickness and the ability of the tooth to resist lateral forces. The amount of remaining dentin has

been directly correlated to the ability of the tooth to withstand fracture (Lertchirakarn V., et al in 2002)⁴⁹.

Studies have pointed out a potential relationship between the design of the nickel titanium rotary instruments and the incidence of vertical root fractures (Kim H.C et al in 2010)⁴². The mechanical behaviour and the geometry of the rotary instruments decide the kind of complications encountered during usage, as also the operator training and skill.

Different presentations of the incidence of fractures in roots of endodontically treated teeth have been observed. They can be broadly classified as horizontal and vertical root fractures. Numerous clinical studies have shown that 11%- 13% of extracted teeth with endodontic treatment are associated with vertical root fractures (Fuss Z., et al in 1999)²⁴. Endodontic procedures induce craze lines and cracks on the canal walls which become areas of high stress concentration.

These cracks may spread slowly over a period of time to the surface eventually resulting in a vertical root fracture (Yoldas O., et al in 2012)⁸¹. Vertical root fracture is one of the most serious complications of root canal procedures with an unfavourable prognosis that can occur before, during, or after root canal obturation and most often leads to the removal of the affected tooth (Meister F et al in 1980)⁵⁰.

This has lead to various researches looking to reinforce the structure of the crown and the root. The commonly used root canal filling material is gutta-percha in combination with sealer, but the low elastic modulus of gutta-percha presents little or no capacity to reinforce roots after completion of therapy (Ribero F.C., et al in 2008)⁵⁴.

Thus there is a need to develop different materials and methodologies to overcome the shortcomings of current endodontic filling materials to reinforce root structure. Intra-orifice barrier is an efficient alternative method to decrease coronal leakage in endodontically treated teeth (Yavari H R., et al in 2012)⁸⁹. This procedure includes placing additional material into the canal orifices immediately after removal of the coronal portion of gutta-percha and sealer and also improves the fracture resistance of the root (Roghanizad N., et al in 1996)⁶⁴. Materials like resin modified GIC, flowable composite, and bonded amalgam can ideally be used as intra-orifice barriers.

Swartz D B., et al in 1983⁸⁰ stated that failure rate of endodontically treated teeth was almost double in cases without the process of adequate post endodontic restoration. Newer generation of materials tend to improve the bond between radicular dentin and the sealer and the sealer-core interface which helps to increase the fracture resistance and reduces ingress pathways. To reinforce the roots, the modulus of elasticity of the root filling material should approximate that of the dentin (Williams C., et al in 2006) ⁸⁸. This presents the concept of a monoblock, which aims at creating mechanically sound homologous units with radicular dentin.

This is easier said than done as the complexity of the canal system, difficulties in access and cleansing present difficulties in predictably achieving the target monoblock unit. Priming the radicular dentinal surface and creating a bond between the sealer and dentin, sealer and core material would effectively achieve this. A number of sealer and core materials have been formulated with the aim of achieving this. The modulus of elasticity of the post, the filling material and the sealer has to

match that of radicular dentin so that the load stresses are evenly distributed and borne by the components of the monoblock (Tay F.R., et al in 2007)⁸².

Traditionally the rotary NiTi file systems were designed to be used in a sequence and consisted of multiple rotary tools. Recently the advances in metallurgy have seen introduction of newer file systems with a single rotary file which are efficient and effective. Also rotary files for use in reciprocating motion have been designed. A new concept of endodontic file adjusting to the size of the canal and which works with vibration and continuous irrigation, the self adjusting file system has been developed (Metzger Z, et al in 2010)⁵¹. These single file systems have been based on practicality, simplicity, reduce clinical working time and have been reported to reduce the amount of stresses on the canal walls. They have also been recommended and designed for a single use which tackles the issue of sterilization and cross contamination.

This study aims to compare the fracture strength of the mesial roots of the mandibular first molars when prepared with five different single file rotary preparation systems.

Tay F R, and Pashley D H., et al in 2007⁸² in their analysis of the concept of creation of a monoblock in root canals review how this term can be effectively applied to materials that have been used in the past and present for rehabilitation of the root canal space. The role and the ability of the bondable materials available to achieve a monoblock unit in the root canal presently and comparison with the classical concept of a monoblock which was first employed in restorative dentistry and then subsequently in endodontics have been reviewed.

A comparative study of fracture resistance of endodontically treated teeth filled with Resilon and gutta percha in an in-vitro setting was done by Shetty R R., et al in 2009⁷⁶ and they found that Resilon was superior and the results were statistically significant. The weakest teeth in terms of fracture resistance were those that belonged to the gutta percha without sealer. The authors also note that in this clinically relevant comparison between Resilon and gutta percha, the monoblock concept is important not only to resist microbial leakage through the material, but also holds the root as a single unit thereby increasing fracture resistance.

The role of the effect of the sealers on the fracture resistance of endodontically treated teeth with and without smear layer removal was evaluated by Jhamb S., et al in 2009³⁷ in an in-vitro setting. They compared a glass ionomer based sealer and acroseal. The authors concluded that the roots were significantly weakened after instrumentation. Though the glass ionomer based sealer exhibited better results there was no significant difference between both the sealers tested regardless of the presence or absence of the smear layer. They also observed that the sealer could possibly play a role in improving the fracture resistance of the teeth.

The current developments in rotary root canal instrument technology and clinical use was reviewed by Peters O.A., et al in 2010⁵⁷. The review summarised clinical and laboratory findings for several current instruments with some guidelines and usage parameters. The development of the nickel titanium alloy developed first for the U.S. navy which has got a shape memory and super elasticity. They compare it with steel instruments which can withstand a maximum of 3% elastic deformation while Nickel titanium instruments can withstand a 7% elastic deformation without permanent damage or plastic deformation. Steel can also withstand up to 20 bending cycles whereas nickel titanium can be bent up to 1000 times and the difference is due to the atomic structure of the two alloys. They discuss in detail the rotary instrument design, usage and fracture prevention of nickel titanium instruments, and usage parameters and strategies. They observe that clinical studies on the rotary instruments are sparse and that the results of the current studies indicate that their use leads to a reduced incidence of gross preparation errors and possibly improved clinical outcomes.

The mechanical properties of the self adjusting files system was evaluated by Hof R., et al in 2010³⁴ and they observed that this file system was mechanically sound and was able to endure the canal preparation procedure with very little loss of efficiency under the recommended operating conditions. They noted that the irrigant flow was within the confines of the canal and did not cross the apical constriction.

The reduction in efficiency was found to be about 40% after continuous operation for 30 minutes. They also found that the self adjusting file was elastically compressible from a dimension of 1.5mm to the size of a #20 k-file and that

compressing the self adjusting file creates a circumferential force which coupled with in and out vibration and rough surface removes dentin from the canal walls.

Metzger Z., et al in 2010⁵¹ evaluated the smear and debris removal ability of the self adjusting file systems. The irrigants used were 3% sodium hypochlorite and 17% Ethylene Diamino Tetra Acetic acid (EDTA) alternatively as continuous irrigation. They observed that cleanliness of the canal is very important and significant amount of debris is found in canals with a flat cross-section prepared with hand or rotary instrumentation. They observed that using only sodium hypochlorite as continuous irrigation alone produced a smear layer. When combined alternatively with 17% EDTA the smear layer was totally eliminated in all parts of the canal system. The irrigation time for sodium hypochlorite was 2 minutes and that of EDTA were 2.5 minutes. The result of this study was also better than those which were previously published for the coronal and the middle portions of the canal.

There was a pronounced difference in the apical third of the root where the previously published protocols failed to adequately clean the canal and the self adjusting file protocol resulted in smear free surfaces in most samples and debris free in all samples.

A new concept in endodontic files, the self adjusting files was discussed by Metzger Z., et al in 2010⁵⁰ and they compared it with the rotary nickel titanium file systems. This was a single file system which was designed as a hollow thin cylindrical nickel titanium lattice that adapts to the cross section of the root canal.

This file is used after preparation of the canal to # 20 k-file. It was operated with a in and out motion with vibration and continuous irrigant flow which is also activated by vibration. The self adjusting file is operated with a transline vibration resulting in

circumferential pressure which allows the files abrasive surface to remove a thin uniform hard tissue layer from the entire root canal surface resulting in a canal with similar cross-section but with larger dimensions. The straightening of the root canals was also reduced due to lack of a rigid metal core and high pliability. This concept allowed the file to retain the original shape of the root canal both in cross-section as well as longitudinally. The author claims that the file has got a high amount of mechanical endurance and failure when it occurs happens as small tears in the metal lattice network. They proposed this as a method of overcoming the many shortcomings of the rotary nickel titanium file systems.

The fracture resistance of endodontically treated teeth was investigated by Michael M C., et al in 2010⁵² and they concluded that the endodontically treated teeth were generally weaker than their counter parts. However the strengths were almost equal when posts were used for restoring the endodontically treated teeth.

The fracture patterns noted were oblique, horizontal and vertical in the order of incidence. The area of fracture was most commonly near the cemento-enamel of the incisor teeth used in the study.

Topcuoglu H S., et al in 2011⁸³ assessed the fracture resistance of the roots filled with three different obturation techniques and concluded under the limitations of this study the resistance of the root to fracture is decreased with instrumentation and the root canal space and that the obturation of the root canal space in all the techniques in this study did not reinforce the structure of the root.

The fracture strength of mesiobuccal roots was evaluated in a in-vitro setting by Jahromi M.Z., et al in 2011³⁵. They compared hand and rotary instrumentation

techniques. They note that vertical root fracture is a challenging complication subsequent to root canal therapy. They observed that the manual instrumentation did not lower the fracture resistance of teeth more than the rotary instrumentation technique used. The authors used rotary NiTi Hero 642 and suggest that other rotary instrument techniques should also be further evaluated for resistance to fracture.

They observe that the prognosis of the fractured teeth is very poor and are often extracted or hemisected. The dentin of the root canal prepared teeth is also very brittle and hence more susceptible to fracture. They concluded that the manual preparation of the canals did not weaken the tooth structure more than the rotary preparation. They also suggest the teeth at risk of vertical root fracture might benefit from preparation with an appropriate rotary system.

Bhat S.S., et al in 2012⁹ in an in-vitro setting investigated the fracture resistance of teeth using different root canal sealers. They observed that within the limitations of this study the resin sealers were effective when compared to the zinc oxide based sealers. In this study a vertical force was applied parallel to the long axis of the teeth. They noted that the resin sealers have more adhesion less volumetric shrinkage, and better penetration which contributed to their better performance.

Milani A S., et al in 2012⁵³ in a in-vitro study design, assessed the effect of root canal preparation in development of dentinal cracks. They compared the Protaper rotary instruments and hand instruments. The authors concluded that under the conditions of this study the hand instruments produced more pronounced structural defects in dentin. They also observed that the Protaper instruments when used as per the manufacturer recommendations caused fewer cracks. The authors

used a step back technique for hand instruments and noted that the technique of hand instrumentation may have an effect on crack formation and that it needs further investigation.

In a in-vitro study of comparison of fracture resistance of roots of

endodontically treated teeth using different root canal filling materials, Ravi N., et al in 2012⁵⁹ found that the highest fracture resistance of almost more than 75%

was found in the resilon obturated roots when compared with other filling materials (gutta percha) independent of the filling technique used. The authors suggest long term clinical studies which are evidence based to assess whether resilon reduces the vertical root fractures clinically.

Vallabhaneni S., et al in 2012⁸⁶ in their review of single file rotary endodontic systems observe that the recently introduced files such as self adjusting file, twisted file, wave one, protaper next and reciproc etc., claim to be able to completely prepare and clean the root canals with only use of a single instrument after the preparation of a glide path. This reduces clinical time, reduces instrument fatigue, cost effective and reduces cross contamination. The advent of nickel titanium rotary files removes the smear and debris effectively even from curved root canals. They suggest further clinical studies of these single file systems and discuss in detail the individual method and technique of use of these systems.

The fracture resistance of the root canals obturated with gutta percha versus resilon with two different techniques was assessed by Ashraf H., et al in 2013⁵ in an in vitro setting and came to a conclusion that the root canal obturation using resilon

had the potential and may improve the fracture resistance of the teeth. The manual and Race rotary preparation methods have also similar effects.

Ganesh A., et al in 2013²⁵ assessed the fracture resistance of endodontically treated teeth and re-treated teeth in an in-vitro setting and observed that the retreated teeth showed a significant resistance to fracture and this positively correlated to the additional loss of dentin during the retreatment procedures. They confirmed this with the aid of spiral computed tomography. They note that the spiral CT provides a means of non-invasive assessment of the samples without destruction and a precise reconstruction of the root canal system. The present study followed a protocol of increasing the apical size following retreatment to one size larger than the initial treatment group which accounted for the loss of dentin in the apical thirds in this study which might have contributed to the lower fracture resistance of the re- treatment group.

Rippe M.P., et al in 2013⁶² evaluated the effect of the root canal filling methods on resistance to root fracture. They also used finite element analysis to assess the expansion of the root canal sealer in two different filling techniques. The authors observed that vertical root fractures have been the cause of fracture of many root canal treated teeth and are most likely caused by the propagation of small critical and less pronounced defects rather than the force exerted during the filling procedure or the canal preparation. These fractures occur in the area of increased occlusal stresses during mastication that originate in small defects and propagate through small and constant impulses which result in root fracture. They also discussed the role of the sealer expansion as one of the cause of stress concentration in the root canal which would weaken the root. They found that the filling technique

influenced the fracture strength but did not influence the fracture type. The finite element analysis revealed that greater the sealer thickness the greater the concentration of the stresses in the root canal. The more amount of gutta-percha increased the fracture resistance. The filling technique influenced the fracture strength of the teeth but did not influence the type of fracture. This study was done in an in-vitro setting and the load was directly applied on the core.

Shaheen N A., et al in 2013⁷¹ assessed the role of different preparation obturation combinations on the resistance to fracture of endodontically treated teeth and recommended that alternative strategies to reinforce the endodontically treated roots need to be considered as the currently available preparation and obturation materials lack the necessary properties physically to result in a strengthening effect.

In this study the forces of fracture were applied at an angle of 45 degrees as in the anterior teeth the forces are not vertical but at an angle.

Wadhwani K K, et al in 2013⁸⁷ evaluated the effect of sealers on the fracture resistance of root canal treated teeth in an in-vitro setting and concluded that all the materials used in this study reinforce the root structure. Resilon, Epiphany sealer, Gutta percha and AH plus sealer, gutta percha and endomethasone sealer were evaluated in this study and appeared promising. The authors suggest the collection of evidence based data to be able to support the use of these materials in day to day situations.

Arslan H., et al in 2014⁴ assessed the effect of irrigation of citric acid on the fracture resistance of roots which were endodontically treated. They observed that within the limitations of this study the use of citric acid concentrations at different

time period did not significantly change the fracture resistance of endodontically treated roots and that this property of citric acid would be very beneficial in use of it as an irrigant in endodontic therapy.

In a comparative study of the dentin removal during the root canal preparation by the self-adjusting file systems and Protaper systems using a micro-CT analysis was done by Bakir D.K., et al in 2014⁷ and concluded that the self adjusting system removed more dentin and was more effective when compared with the protaper file systems. They also noted that the self adjusting file systems with their compressibility, vibration, and continuous irrigation removed dentin gradually and uniformly resulting in a surface which appeared as if sand blasted and delicately rough with 3 micron peak to bottom dimensions. The pressure is also greatest when the file is inserted into the canal and gradually decreases as the canal increases in width and a single file is used throughout the procedure.

Capar I.D, et al in 2014¹³ in their evaluation of the fracture strength of roots instrumented with self adjusting file and the protaper rotary systems concluded that instrumentation with both the systems did not change the fracture strength of the standardized roots with respect to their cross-sectional diameter and weight within the limitation and standardization conditions of this study. This study was an in-vitro study on mandibular premolars with straight canals. They observed that standardization of the samples is an important step and a lot of variables could affect the results of the study. The filling of the canals with an adhesive sealer did not significantly strengthen the roots compared with instrumented but not filled canals.

Saeed M., et al in 2014⁶⁶ analysed the influence of hand stainless steel and nickel titanium rotary instruments on the resistance to fracture of endodontically treated roots. The authors have chosen a lower premolar for the study as it has been reported with a high incidence of vertical root fracture and the amount of forces during occlusal loading during chewing was three times as high as other teeth. They observed that there was a significant difference between hand and rotary instrumented teeth with the fracture resistance being more in teeth instrumented with k-files. They noted that the amount of removal of dentin affects the fracture resistance and that the rotary instrument significantly affects the fracture resistance as they remove more dentin due to varying tapers. They suggest rotary instruments should be used with caution without excessive removal of intra-radicular dentin.

Between the two rotary instruments tested there was no significant difference in fracture resistance. The authors also found that gutta percha can effectively transmit forces on to root structure and the type of filling material and technique can influence resistance to fracture.

Ertas H., et al in 2014²³ evaluated the effects of the physical and morphological properties of roots on the fracture resistance. The authors observed that for study of fracture resistance of roots standardization is very important and the roots if not distributed among the groups equally the variables could possibly affect the results. This leads to large standard deviations within the groups rendering the results meaningless prompting the researchers to use more number of samples. This study principally aimed to determine how the physical properties of weight volume and density and morphological properties of mesio-distal dimensions affect the fracture resistance and the important criteria for standardization in fracture

resistance studies. They concluded that the volume or weight of the root as the most important determining factor in root fracture and that the roots should be equally distributed according to their volumes or weights rather than the morphological dimensions which cannot closely simulate the entire strength of the root.

The fracture resistance of endodontically treated teeth obturated with resilon and gutta-percha was evaluated by Halkai K., et al in 2014²⁸. This study compared resilon and epiphany sealer with conventional gutta-percha using different sealers.

The authors observed that resilon was superior to other materials and was statistically significant. This implied that the monoblock concept was important not only to avoid microleakage but also to improve the resistance to fracture of the roots.

Gutta percha, gutta flow with gutta-percha and resilon-epiphany as obturation materials were evaluated for their effect on the fracture strength of obturated teeth in an in-vitro setting by Kala M., et al in 2014³⁹ and the authors as per the conditions used in this study came to a conclusion that AH plus with gutta- percha was superior. The authors note that thermo cycling and periodontal ligament simulation were not done in this study and the forces used fundamentally differed from the masticatory forces in a clinical situation.

Khan K., et al in 2014⁴⁰ in a in-vitro setting evaluated the vertical fracture resistance of teeth obturated with three different materials i.e., AH plus, Endorez and Metaseal. They used the matched taper single cone technique and the lateral condensation technique for obturation. The authors concluded that when used with the matched taper single cone technique Metaseal and AH plus have the potential to reinforce endodontically treated teeth. various studies have pointed out that the

single cone technique as a contributing to increase in fracture resistance when compared to other obturation techniques. They also observed that the lower fracture resistance observed in the lateral condensation technique could be possibly due to the increase in the interfaces and gives an additive effect to the polymerization stresses present along the interfaces.

The effects of different rotary systems and a resin based canal filling procedure on the fracture resistance of endodontically treated teeth was investigated by Kustarci A., et al in 2014⁴⁶. In this study there was a significant difference between the instrumented and filled groups. They concluded that the rotary instrumentation significantly reduced the fracture resistance of teeth and use of resilon or epiphany partially negated the weakening. They observed the need for sample standardization as the natural teeth vary considerably anatomically.

Rippe M.P., et al in 2014⁶¹ analysed the effect of root canal preparation, type of endodontic post and mechanical cycling on the root fracture strength. They observe that as per the design of this study in an in vitro setting the root canal preparation seems to have no influence on the root fracture strength. The mechanical cycling did not influence the fracture resistance or the type of failure. The cast post and core preparations exhibited the highest fracture resistance values in comparison to fibre posts. They concluded that the type of endodontic instrument only influenced the root fracture strength when restoring with a fibre post and mechanical cycling.

Sadikci T., et al in 2014⁶⁸ in a comparative evaluation of fracture resistance of root canal filled teeth using five different root canal filling systems and observe

that root canal filling procedures decrease the fracture resistance of the teeth. The present study evaluated whether there is any difference when epiphany sealer was used with gutta-percha and resilon. Gutta percha/epiphany SE showed a higher fracture resistance when compared with resilon/epiphany SE.

In a comparative analysis of centering ability of different single file systems using Cone Beam Computed Tomography, Agarwal R S., et al in 2015³ came to the conclusion that the single file canal systems demonstrated average canal transportation and centering ability comparable to a full sequence protaper system in curved canals. This improved the safety during canal preparation procedures with these new single file systems. The authors noted that these single file systems were quicker and therefore sufficient irrigant volume should be used during the instrumentation process and activation of these irrigants should be definitely considered.

The resistance to fracture of dental root obturated with different materials was assessed by Celikten B., et al in 2015¹⁷ in an in-vitro situation. The authors observed that under the conditions of this study the glass ionomer based obturation system had a similar resistance to fracture as that of sound teeth. They observed that one of the important steps of the endodontic therapy is adequate obturation after bio- mechanical preparation and that the filing material has the potential to strengthen and increase the fracture resistance of the tooth structure, the root canal obturated with active GP sealer and cone produced a true tertiary monoblock and was superior.

Celik D., et al in 2015¹⁶ investigated the fracture resistance of roots after instrumentation with two rotary nickel titanium instruments protaper universal and

profile GT. The authors concluded that the protaper universal rotary instruments lowered the fracture resistance of the treated roots. The authors noted that the tooth type significantly affects the risk of tooth fracture during or after root canal instrumentation. They also noted that the remaining dentin thickness affected the root fracture strength.

The effects of three nickel titanium rotary systems on the formation of root fracture were evaluated by Jalali S., et al in 2015³⁶ in an in vitro setting. The NiTi rotary instruments are used more today for canal preparation as it offers less clinical time scheduling, increased cleanliness of the canal walls and fewer procedural accidents like apical canal transportation and ledges. The rotary instruments have been shown to form craze lines and microcracks in dentin which predispose the root to fracture. The authors observed that of the three NiTi instruments Reciproc, Mtwo and protaper instruments used Reciproc had the least amount of dentinal crack formation during canal preparation and the results are statistically significant. The authors noted that the design of the instruments plays a role in the formation of cracks in the dentinal structure of the root.

The resistance to fracture of roots obturated with novel hydrophilic obturation systems was researched by Hegde V., et al in 2015³¹. They compared this with the hydrophobic systems and have come to the conclusion that the hydrophilic obturation systems reinforce the root and thereby increase the fracture resistance of the root structure. Resilon/epiphany, gutta-percha AHplus, C point system and Endo sequence BC sealer were the materials tested. There was no significant difference between the resilon obturated group and the conventional

gutta-percha AH plus group. Compared to the C-point system and bioceramic sealer the fracture resistance of the gutta-percha AH-plus system was significantly lower.

Kurthukoti A J., et al in 2015⁴⁵ evaluated the fracture resistance of endodontically treated teeth in an in-vitro setting with three different aesthetic post systems and concluded that the biologic dentin post system demonstrated the highest fracture resistance and was repairable. The authors observed that the results of this in-vitro study should be used with caution as the limitation of this study was the use of unidirectional force for effecting fracture. The masticatory forces are multi- directional in a clinical situation. They suggest the development of tooth banks for ready availability of these dentin biologic posts.

The fracture resistance of roots instrumented with three different single file systems in curved root canals of the mesial root of maxillary molars was studied by Nur B.G. et al in 2015⁵⁴. They hypothesized that the instrument design, kinematics and mechanical behavior of the single file rotary systems affect the extent of dentinal defects which subsequently translates into vertical root fracture susceptibility. They compared three file systems namely Waveone, Reciproc and One shape which are single file NiTi systems. They concluded that the one shape rotary file system enhances the fracture strength of the roots as compared with the control group within the limitations of this study. The Waveone and Reciproc rotary file systems were found to be similar to the control group. All the three single file systems had different designs and kinematics.

Singh V., et al in 2015⁶⁷ assessed the fracture resistance of endodontically treated teeth restored with resin fibre post and stainless steel posts as an in-vitro

study. They concluded that the fibre posts exhibited better fracture resistance under static loading under the conditions of this study. Not using crowns which would reflect the clinical situation was a limitation of this study.

The in-vitro fracture resistance of endodontically treated teeth obturated with two different filling materials resilon and gutta-percha with different sealers was evaluated by Shetty RR., et al in 2015⁷⁶ and observed that adhesive sealer materials enhanced the fracture resistance of endodontically treated teeth, They found that teeth filled with resilon increased the fracture resistance of the roots when compared with conventional gutta-percha filling techniques. The authors also noted that the material resilon though found to be better in terms of fracture resistance they are biodegradable under the attack of certain enzymes which may exist as a component of saliva and other bacterial by products and also prone to alkaline hydrolysis.

Tavanafar S., et al in 2015⁸¹ on their research on the effect of different instrumentation techniques on the vertical fracture resistance of endodontically treated teeth, observe that vertical root fractures are catastrophic events which eventually results in removal of the tooth. They observe that root preparation is one of the predisposing factors for this condition. They compared the effect of three different instrumentation techniques on susceptibility to root fracture. They used a single file system, reciprocating, NiTi rotary and a NiTi hand file system. They found that all the instrumentation techniques weakened the structure of the roots making them fracture with lesser loads when compared with that of unprepared roots. The single file reciprocating technique was found to be comparable to NiTi rotary and hand instrumentation techniques. The most common fracture observed

was buccolingual and then proximal and compound type was the last in this study which was in consonance with other studies on root fractures.

The effects of different nickel titanium instruments on dentinal microcrack formations during root canal preparations was investigated by Ustun Y., et al in 2015⁸⁴ and concluded that within the limitations of this study, with the exception of the hand and the control groups all other experimental groups showed microcrack formation. They evaluated Reciproc, Protaper next and protaper. There was no statistically significant difference between the experimental groups. Microcracks have been shown to be caused by rotary instruments. The present study also evaluated the rotary files used in a reciprocating motion. One of the limitations of this study was that the pre-existing defects were unable to be analysed with the current methodology.

ARMAMENTARIUM

Collection of teeth

1. Disposable gloves (Dispodent, Chennai)

2. 2% Thymol solution (Alpha Chemicals, Maharashtra, India ) 3. Normal saline solution (Nirlife Health Care, Nirma Products, India) 4. Vented labelled glass bottles

5. Tissue forceps

Selection & Preparation of samples

1. Stainless steel trays 2. Glass beakers large

3. EMS ultrasonic scaler unit

4. Illuminated Magnifying Lens ( large size ) 5. Electronic weighing machine

6. Vernier Calipers Digital ( Baker) 7. Diamond disc ( double sided )

8. Indelible marker pen bold and fine ( Camlin ) 9. DG-16 Endodontic probe ( Hu-Friedy )

10. Operating microscope (AM-3000 Series, China) 11. Stainless steel tweezers

12. Labelled glass bottles

13. RadioVisuoGraphy unit (Carestream, KODAK RVG 5200)

Root canal preparation

1. Size 8, 10, 15 K file of 21mm length (Dentsply, Maillefer, Ballaigues, Switzerland)

2. Endo block (Dentsply Maillefer, Ballaigues, Switzerland)

3. Endomotor (X-smart with 1:16 reduction hand piece- Dentsply Maillefer, Ballaigues, Switzerland)

4. X-smart plus (Dentsply Maillefer, Ballaigues, Switzerland) 5. Endostation SAF unit.

6. SELF-ADJUSTING FILE-1.5mm-21mm L; ReDent Nova, Raanana, Israel) 7. NEONITI rotary endodontic files-Two files C1( tip 0.25 mm-taper at tip

12%,length 15 mm), A1-(tip 0.25mm, taper -8%, 21mm L)(NEOLIX, France) 8. ONESHAPE rotary endodontic files (25.06) (Micro Mega, Besançon, France) 9. RECIPROC rotary endodontic files-, R25 (25.08) (VDW, GmBH, Munich,

Germany)

10. WAVE ONE Endodontic rotary files. (25.08) (Dentsply Tulsa) 11. 28 gauge side-vent needle (Prime dent)

12. 5ml syringe with leur-lock needle (Dispovan, Hindustan Syringes and Medical Devices Ltd, Faridabad, India)

13. 5ml, 10ml Unolock Syringe (Hindustan Syringes and Medical Devices Ltd, Faridabad, India)

14. Endoprep RC (Anabond Stedman Pharma Research, India)

Irrigating solutions

1. Normal saline (Nirlife Health Care, Nirma Products, India)

2. 5% Sodium Hypochlorite solution (Nice chemicals Pvt Ltd, India) 3. 17% EDTA solution (pulpdent corporation, USA)

4. Sterile Distilled water (Ives drugs, Pvt Ltd, India) Obturation of samples

1. Gutta percha points and paper points 2%,4% ,6% (Dentsply Maillefer, Ballaigues, Switzerland)

2. Lentulospiral size 25 (Mani Inc., Tochigi, Japan) 3. Hand spreaders 21mm size:15-40

4. AH plus resin sealer (Dentsply Maillefer, Ballaigues, Switzerland ) 5. Mixing pad and agate spatula

6. Spirit lamp

7. GP condenser ( Dispodent, India)

8. Luxacore Z Dual (DMG, Germany)- core build up kit 9. Cotton holder

10. Stainless steel tray

Preparation for Fracture testing

1. Sterile self sealing pouches (AK Product; West Bengal; India)

2. Sample base former block unit – custom made (4 cm X 3 cm X 2 cm) 3. Acrylic resin polymer and monomer (DPI, India)

4. Emery paper 5. Storage containers

6. 3mm diameter Stainless Steel Tip mounted on acrylic block for fracture testing

7. Stainless steel millimetre scale 8. Wax knife and carver set

9. White soft paraffin (Medisan, Trichy, India) Fracture testing

1. Universal testing machine(Zwick Roell Z010,Germany) 2. Storage media

3. Digital SLR camera (NIKON 3300) Fracture strength analysis and tabulation

1. HP and Sony VIAO computing systems 2. Zip lock covers

3. Storage boxes for individual groups 4. Magnifying loupe with illumination

5. Observation sheets

6. Software for fracture recording and analysis (Zwick Roell)

Fracture type analysis and tabulation

1. Magnifying loupe - Illuminated 2. Observation sheets.

Statistical Analysis

1. SPSS Version 16.0 software for statistical analysis

MATERIALS AND METHODS

1. Collection of teeth:

One hundred and sixty extracted human permanent mandibular first molars were collected and stored in isotonic saline solution for a maximum of 72 hours.

Sufficient protocols for infection control as per OSHA and CDC guideline regulations in collection, storing, sterilization and handling were followed.

2. Selection of samples:

Teeth devoid of gross destruction, restorations and endodontic treatments were separated. They were then observed for cracks under magnification and such teeth were excluded. Teeth with mature and intact root apices were selected for the purpose of the study. The selected teeth were then stored in normal saline solution at 4°C until use. A total of ninety teeth were selected for the purpose of the study.

3. Standardization of samples

Access cavity preparation was done on the collected teeth and the pulp chamber debrided and cleaned with ultrasonic scaler tip under irrigation with normal saline. A 6# K file was inserted to the working length in the mesio-buccal canal and a digital radiograph done in a bucco-lingual direction. Teeth with canal calcifications were discarded. The teeth were then analysed for the canal curvature using the Schneiders technique and the root canal curvature computed.

The teeth with the curvature in the mesial root of more than 25 degrees and less than 35 degrees were selected for purpose of the study. The mesial roots were separated at the level of furcation. The roots were individually coded and stored for further analysis. The roots which confirmed to the inclusion criteria were kept moist with normal saline throughout the experimental procedure to avoid dehydration.

The mesio-distal and bucco-lingual diameters of the sectioned teeth were then tabulated with the help of digital Vernier callipers. The samples were then weighed using a precision weighing machine and the results tabulated. The samples were evenly distributed based on their weights across the six experimental and control groups (n=15). The selected roots were then rinsed with distilled water and stored in normal saline at 4^°C in separate glass bottles.

4. Preparation of the Sample

The working length was determined by passively placing a size 6K file (Dentsply Maillefer, Ballaigues, Switzerland) into the canal until the tip was visualized at the apical foramen using a magnifying loupe and was adjusted to the apical foramen. Then the actual canal length was measured and working length was calculated by subtracting 0.5mm from this measurement and recorded for each sample. The canal systems of the experimental groups were prepared with the single file system assigned to the respective group as per the manufacturer recommendations.

5. Root Canal Preparation Technique

The instrumentation was initiated with K files (Dentsply, Maillefer, Ballaigues, Switzerland) up to size 10 followed by the respective single file rotary system as per the manufacturer recommendations for each group. NEOLIX, ONESHAPE, WAVEONE GOLD, RECIPROC and SELF-ADJUSTING FILES were the single file systems used in this study. The irrigant was delivered using a 28 - gauge side vent needle (Prime dent) at the working length. 1ml of the irrigant was used for canal irrigation after using each instrument and before proceeding to the next. For the Self-adjusting file system the protocols recommended by the manufacturer were followed. A total of 5ml of the irrigant 5% sodium hypochlorite was used during the instrumentation process for the other groups. The roots used in this study were mesial roots of the human permanent mandibular first molar teeth and both the canals in the mesial root were instrumented and prepared following the guidelines recommended for the respective single file system.

6. Final Rinse of Samples

Subsequent to the canal preparation the samples were irrigated with a final rinse of 5ml of the irrigant solution. The delivery of the initial and final rinses was done as per the manufacturer recommendations for use in the respective experimental groups. For irrigants used as final rinse, a total of 5ml of 17% EDTA was delivered using a 28- gauge side vent needle (Prime dent). The exposure time of the final rinse solution was three minutes. After the completion of three minutes a post-final rinse irrigation of 10ml of distilled water was done to flush out the remaining final rinse irrigant from within the canal system.

7. Obturation of the samples

The canals were then dried and then coated with a sealer using a lentulospiral.

The sealer used in all the groups was AH plus. Obturation was done subsequently with gutta-percha cones with a cold lateral condensation technique; excess gutta-percha removed and allowed to set for 72 hours under conditions of humidity. The quality of root canal fillings were confirmed with radio-visuography. The access cavities were prepared, bonded and sealed with Luxacore a core buildup material. The samples were then stored at 37°C at 100% relative humidity for 72 hours. Each group was processed and stored separately for further analysis.

8. Preparation for fracture testing

The samples belonging to each group were removed from the bases and mounted on resin blocks (40mm high and 30 mm diameter) with the help of a custom made base block former. The apical root ends embedded vertically along the long axis of the block in such a way that only 4 millimetre of the tooth was inside the resin. The resin was allowed to set and the sample blocks coded. The samples were kept covered by moist cotton and wet towel to prevent dehydration till they were ready for fracture testing.

9. Fracture testing procedure:

The samples were tested with the help of a universal testing machine. A custom made metal indenter of size 3 millimetres was mounted on the upper arm jig and the tooth specimen block was mounted on the lower arm jig. A cross head speed of 1mm/min was set and the load applied on the surface of the tooth vertically parallel to the long axis of the tooth from above. The force required to fracture the tooth

10. Tabulation of result:

The result of the fracture testing was tabulated after recording the maximum load at which fracture occurred. The fracture strength results and the type of fracture were analysed. The type of fractures which have taken place in each sample were observed under magnification, grouped and recorded. The results were assessed by two different operators and the results compared and tabulated.

11. Statistical analysis:

The samples were distributed across the groups based on their weights and homogeneity. They were subjected to a statistical test to assess the normality of these continuous variables. The results of the fracture test were statistically analysed using one way ANOVA test of variance with Tukey post hoc test for multiple comparisons.

TABLE 1: SINGLE FILE SYSTEM PREPARATION GROUPING

GROUPS (n=15) SINGLE FILE SYSTEM

I SELF ADJUSTING FILE SYSTEM

II NEOLIX FILE ROTARY SYSTEM

III ONE SHAPE ROTARY SYSTEM

IV WAVE ONE GOLD RECIPROCATING SYSTEM

V RECIPROC RECIPROCATING SYSTEM

VI CONTROL

TABLE 2: TYPE OF FRACTURE

Total Samples

(n=90)

Percentage Of Incidence

Buccolingual Mesiodistal Communited Transverse Others

90 54.44 30 13.33 2.22 Nil

CHART I: PERCENTAGE INCIDENCE OF

TYPE OF FRACTURE

TABLE 3: TYPE OF FRACTURE - DISTRIBUTION

GROUPS (n=15)

PERCENTAGE OF INCIDENCE OF FRACTURE

Buccolingual Mesiodistal Communited Transverse Others

I 53.33 33.33 13.33 0 0

II 60 33.33 6.66 0 0

III 53.33 33.33 13.33 0 0

IV 53.33 26.66 13.33 6.66 0

V 53.33 26.66 0 0 0

VI 53.33 26.66 13.33 6.66 0

OVERALL 54.44 30 13.33 2.22 0

CHART II: TYPE OF FRACTURE - DISTRIBUTION

TABLE 4: SAMPLE DISTRIBUTION DATA FOR GROUPS

GROUPS (n= 15)

Buccolingual width (A)

Mesiodistal width (B)

(A*B) (A+B) Weight (g)

I 9.045 ± 0.34 4.529 ± 1.5 38.02 ± 4.44 13.22 ± 0.57 0.514 ± 0.07

II 8.917 ± 0.45 4.048 ± 1.07 38.37 ± 4.07 13.21 ± 0.61 0.555 ± 0.07

III 9.045 ± 0.34 4.175 ± 0.39 38.02 ± 4.48 13.22 ± 0.57 0.514 ± 0.07

IV 9.114 ± 0.47 3.984 ± 0.83 34.58 ± 4.74 12.89 ± 0.75 0.500 ± 0.07

V 9.061 ± 0.74 4.314 ±0.40 39.12 ± 5.11 13.37 ± 0.89 0.574 ±0.09

VI 8.94 ± 0.68 4.062 ± 0.33 36.35 ± 4.39 13.00 ± 0.80 0.544 ± 0.07

TABLE 5: MAXIMUM LOAD VALUES OF ROOT FRACTURE

GROUPS (n= 15)

Minimum Value

Maximum

Value Mean

Confidence interval at 95%

Standard Deviation

Median Lower

bound Upper bound

I 327 1790 953.80 705.09 1202.51 449.11 888

II 395 1930 1062.80 815.87 1309.73 445.89 1100

III 577 2250 1237.20 935.12 1539.28 545.49 1090

IV 514 1870 1058.60 837.66 1279.54 398.97 1010

V 450 1770 1156.93 892.24 1421.63 477.97 1130

VI 502 1880 1142.80 918.15 1367.45 405.67 1050

CHART III: MAXIMUM LOAD VALUES OF ROOT FRACTURE

TABLE 6: COMPARISON OF ALL GROUPS (ANOVA)

Sum of Squares df Mean Square F Sig. (p-value)

Between Groups 725171.822 5 145034.364

.696 .628

Within Groups 1.750 E7 84 208381.502

Total 1.823 E7 89

ANALYSIS AND INTERPRETATION:

• Analysis of Variance (ANOVA) test is used to compare the significance of difference between more than two groups at 5% level of significance.

• Note 1: If “p” value is more than 0.05, then we can conclude that there is no significant difference between the two groups considered with regard to mean.

• Note 2: If “p” value is less than 0.05, then we can conclude that there is a significant difference between the two groups considered with regard to mean.

• Since the p-value (0.628) is more than 0.05, it can be concluded that there is no significant difference between the 6 groups considered for comparison.

TABLE 7: GROUPS PHYSICAL DATA CORRELATION

ANALYSIS AND INTERPRETATION:

• If correlation co-efficient “r” is negative, it can be concluded that there is negative correlation between two variables considered.

• If correlation co-efficient “r” is positive, it can be concluded that there is positive correlation between two variables considered.

Physical Properties of Roots r – value p – value

Buccolingual Width (A) 0.362 0.480

Mesiodistal Width (B) 0.189 0.719

A * B -0.155 0.770

A + B 0.199 0.705

Weight 0.481 0.334

TABLE 8: NORMALITY TESTING FOR SAMPLES

Physical Properties of Roots p – value

Buccolingual Width (A) 0.739

Mesiodistal Width (B) 0.659

A * B 0.857

A + B 0.718

Weight 0.820

ANALYSIS AND INTERPRETATION:

• If when p>0.05, it can be concluded that the distribution is normal at 5% level of significance.

The primary objective of the root canal obturation procedure during endodontic therapy is to achieve a three dimensional obturation of the root canal system and sufficiently reinforce the root canal space so as to increase the fracture resistance of remaining tooth structure. During endodontic therapy the entire root canal system has to be accessed sufficiently, cleared of all the necrotic tissues, remnants, debris, microbes and subsequently appropriately restored. This process of cleansing of the root canal space is called the bio-mechanical preparation.

The root canal system presents a complex structure and consists of accessory canals, fins, Cul de sacs, and transverse anastamoses. They become colonized by the microorganisms which have been demonstrated in the dentinal tubules half way through radicular dentin of infected teeth. Therefore, while treating the infected root canal space the process of shaping and cleansing i.e., the biomechanical preparation of the canal is viewed as a key and vital step during endodontic therapy. An inadequate cleansing process would eventually lead to a failure of therapy and result in poor outcome of the treatment process. (Klevant FJ et al in 1983)⁴³

The inherent variations of anatomy of the root canal, the curvature of the roots especially in the mandibular and maxillary posterior teeth pose a challenge with regard to cleansing, preparation of the canal space, the irrigant delivery and replacement. The root canal system can be divided into three zones namely-coronal one third that is highly accessible, middle one that is fairly accessible and the apical one third being the least accessible. In case of curved roots in order to access the apical third of the canals and to achieve sufficient debridement and cleansing, considerable amount of radicular dentin in the coronal and middle third is removed

which would possibly affect the structural integrity of the of the root. This makes the endodontically treated tooth more susceptible to fracture. (Sornkul et al in 1992)⁷⁹

The teeth which have been treated endodontically have been reported to be more susceptible to fracture when compared to their vital counterparts. This necessitates sufficient care and protection of the remaining tooth structure by proper restoration. The most common cited cause for weakening of the tooth structure is excessive removal of tooth structure during endodontic therapy and subsequent dehydration of coronal and radicular dentin. A variety of possible reasons have been put forward as reasons for fracture of root which includes loss of tooth structure due to carious process or trauma, excessive removal of tooth structure during root canal preparation procedures, dehydration of dentin after completion of endodontic therapy, obturation procedures or post-space preparation, excessive stresses during obturation and increased use of high concentration irrigants with more exposure time. This in a clinical situation would mean a reduction in the long term survival rate of these endodontically treated teeth, which is undesirable. The major achievable goal of endodontic therapy should be reinforcement of the residual tooth structure in such a way that it prevents untoward events. (Johnson M.E., et al in 2000)³⁸

Earlier, the preparation of the canal was done with the help of stainless steel hand files which were more rigid and resulted in excessive removal of tooth structure and were not flexible enough to negotiate curved canals. With hand instrumentation it was common practice to enlarge the canal to three sizes from the first initial file to bind at the apical third of the root. This enlargement allowed

efficient cleansing and allowed the irrigants and medicaments to reach the entire length of the canal system.

The introduction of NiTi hand instruments in Endodontics almost two decades ago improved preparations as they were flexible. The most significant advantage was the predictable control of the preparation. The alloy was resistant to corrosion, had the property of Super-elasticity and shape memory.

The introduction of the rotary NiTi files was in the mid 1990s and the first generation of rotary files had inert cutting radial lands and fixed tapers over the length of the blades. They also needed a significant number of files to complete a thorough preparation of the canal system. The second generation of files were introduced in 2001. The protaper files had manifold increasing or decreasing proportion tapers on a single file. The next generation of files saw innovative technologies of metallurgy namely R-phase heat treatment by sybron which involves a non-grinding techinque of fabrication and surface conditioning. Dentsply Tulsa dentals introduced original metallurgical technology which involves the use of a new proprietary thermal procedure called the M-wire. This further led to the reduction in the number of rotaries required to execute the preparation, and then a concept of a single file system was developed which was attractive because of the reduced preparation time. The rotary single file system also saw another innovation by a French manufacturer with the introduction of a new industrial process of electrical discharge machining. Next concept was the innovative migration from a continuous rotary motion to a reciprocating motion involving different clockwise and counterclockwise angles.