A COMPARATIVE EVALUATION OF DENTIN WALL THICKNESS USING CONE BEAM COMPUTED TOMOGRAPHY AFTER BIO-MECHANICAL PREPARATION BY THREE DIFFERENT ROTARY FILE

Dr.B Rajkumar 1 , Dr.Anika Bhasin 2 , Dr.Devang Kankane 2 , Dr.Lalit Boruah 3 , Dr.Vishesh Gupta 3 , * Dr.Akanksha Bhatt 3 . 1. Professor & Head of Department, Department of Conservative Dentistry &Endodontics, BabuBanarasi Das College of Dental Sciences, BBD University, Lucknow, india. 2. Post Graduate Student, Department of Conservative Dentistry &Endodontics, BabuBanarasi Das College of Dental Sciences, BBD University, Lucknow, india. 3. Associate Professor, Department of Conservative Dentistry &Endodontics, BabuBanarasi Das College of Dental Sciences, BBD University, Lucknow, india.


Introduction:-
The objectives of biomechanical preparation are to remove the necrotic pulp tissue and micro-organisms from the root canal system followed by three-dimensional obturation. 1 This bio-mechanical preparation causes inadvertent loss of some amount of coronal and radicular dentin. Preservation of remaining root canal thickness during root canal treatment is essential for strength and enhancing the longevity of an endodontically treated tooth. Studies show a direct relationship between loss of tooth structure and possibility of fracture of tooth after root canal therapy.
The design features,mechanical properties and technology used to manufacture different endodontic rotary files are different which may effect its cleaning efficiency, quantity of dentin removal and finishing of canal. 2 Various studies evaluated the root canal wall thickness after instrumentation with rotary systems at different levels of the root canal 3,4,5,6 . The present study was designed to evaluate and compare the remaining dentin thickness after preparation with three different file systems i.eHyflexCM,V-Taper and Hero Shaper.

Clinical report:-
Threehealthy orthodontic patients were selected, slated for extraction of all first premolars and weresubjected to CBCT scan prior to instrumentation.Images were captured using i-cat CB 500 machine with total scan time of 23 seconds.
After recording data,access cavities were prepared using highspeedairotorhandpiece (NSK,PANA AIR, Japan) with endo-access bur (Dentsplymallifer ,Switzerland) in rubber dam isolation.The working length was measured using iPexIIapex locator(NSK,Japan) and verified digital radiography . Bio-mechanical preparation was performed in all the four first premolars of each patient using three different file systems i.e. Hyflex in the first patient,V-Taper in secondand Hero-Shaper in third.For all the groups standard irrigation protocol was followed using 5.25% sodium hypochlorite(Pyrex),0.9% saline(nirlife),17% EDTA solution(Merck) and 2% chlorhexidine(V-concept)and preparation was done till 4% #25 in all the patients.
After the preparation of canals the patient was again subjected to CBCT scans in the manner similar to Pre-scan.
The actual dentin thickness was evaluated prior and the remaining dentin thickness after instrumentation from pre and post scans respectively.

Discussion:-
The amount of dentin removed by Hyflex,V-Taper and HeroShaper were evaluated and compared using CBCT. CBCT based root canal length measurements are accurate and reliable when compared with a gold standard. 7 CBCT was used in this study since it can show morphological features from a three dimensional prespective,it displays axial,saggital and coronal sections. 8 The Hyflex CM system was launched in 2011 by ColteneWhaledent, Switzerland. It constitutes of 6 files which has been manufactured by a unique process that controls the material's memory 9 , makes it extremely flexible and provides higher resistance to cyclic fatigue. These files are available with a fixed taper of 0.8, 0.6 and 0.4. Except its orifice opener i.e 0.8 taper all files have positive rake angle.The cutting profile of each file facilitates penetration in canal and presents a root canal shape corresponding with original anatomy. 10 Other than this accelerated flutes design (variable pitch), no radial lands and a safe ended cutting tip is common feature in all files.It has higher resistance to cyclic fatigue and flexibility than conventional super elastic NiTi files. 10 11 V-TaperSS White are NiTi endodontic files with Variable taper design which creates conservative coronal shape and preserves dentin.This system is a three file system file no.17,20 and 25 which encompasses a more anatomic design that creates a shape closely mirroring the natural shape of root.
Hero shaper files (France) is in use since 2001. It is a six file system with a variable helical angle and adapted pitch. It has a positive rake angle and a blade shows a triple helix cutting edge with no radial land. 12 Their helical angle increases from tip to shank that is claimed to reduce threading.
In this study, dentin thickness was measured before and after instrumentation. These values suggested that the mechanical limits of the instruments used to enlarge the root canal to approximate predetermined values would significantly weaken the dentinal walls. It has been indicated that 0.3 mm of canal wall should exist after canal preparation as the minimum remaining dentin thickness (RDT). This is important for providing enough resistance against lateral forces during canal filling and occlusal forces.
The result showed significant difference between Hyflex and V-Taper( p value-.002) and Hyflex and Heroshaper(p value-.029) while there were no significant differences between Heroshaper and V-Taper(p value-.223) The results of the study showed maximum cutting efficiency of Hyflex and minimum of V-Taper. Hence the amount of remaining dentin thickness which is a critical parameter for success of post-endodontic restoration is maximum in preparations done with V-taper and minimum with Hyflex.The aggressive cutting of Hyflex may be dueto highest torque and speed used during preparation than its other counterparts while standardizing the time duration for each preparation. Moreover among all these three file systems Hyflex were used with an orifice opener which allowed the consecutive files to make more contact with dentin due to coronal enlargement. Also Hyflex files have a property of controlled memory as a result of which they respond to excessive resistance with straightening of the spirals.