Bending and torsional behavior of three rotary NiTi files and stress distribution during instrumentation of curved root canals (Finite Element Study)

Abstract

Nickel-titanium (NiTi) rotary instruments were introduced to improve root canal preparation.The fracture modes of rotary NiTi files could be classified into two types, flexural) fatigue and torsional failure.Thus both torsional stiffness and bending flexibility are essential characteristics for file performance and safety concerns.Knowledge of the distribution of stresses in an instrument can help reduce the chance of fracture during clinical use.Finite element analysis (FEA) offers an efficient way for evaluation of mechanical behavior of endodontic files such as stress distribution, which are difficult to obtain by experimental tests.This study was conducted to evaluate Bending and torsional behavior of WaveOne, Twisted File, and ProTaper rotary NiTi files and stress distribution in curved root canalsduring root canal preparation usingFinite element analysis. Each file will be scanned with computed tomography (C.T) machine and imaged with Stereomicroscope.The files FE models were built using Matlab and SoildWorks software.The mechanical behavior of the three files were analyzednumericallyby applying bending; torsion and instrumentation motions simulated loading conditions to the FE models of the files using a FE analysis package (soildworks software). Each FE model of the files was simulated in continuous rotation and reciprocation motions. This motion was applied for each file model in (30, and 45) degrees angles of curvature. Six extracted mandibular molars with mesiobuccal root canals had 30˚ angle of curvature and radius range (5-7) mm were used.Thesamples were two groups,Continuous rotation group and Reciprocation motion group.Each group was further subdivided into three subgroups according to the type of instrument usedWaveOne,Twisted File and ProTaper Universal.The prepared teeth were scanned with CT and finite element models were constructed. Stressdistribution analysis on the walls of curved root canals was evaluated numerically byFEAusing SolidWorks software package. The results showed thatunder bending conditionsTwisted file had the highest maximum stress value followed by WaveOne primary file and Protaper F2 file had the lowest maximum value.Under torsion test Twisted file had the highest maximum stress value followed by Protaper F2 fileand WaveOne primary file had the lowest maximum stress value. During simulation of continuous rotation motion in 30 °and 45° curved canalsTwisted file had the highest maximum stress value followed by WaveOne primary file and Protaper F2 file had the lowest maximum value.During simulation of reciprocation motion in30 °and 45° curved canalsTwisted file had the highest maximum stress value followed by Protaper F2 fileand WaveOne primary file had the lowest maximum stress value. Stress analysis of teeth models prepared with continuous rotation motion showed that tooth model prepared with Twisted file had the highest maximum stress value followed by tooth model prepared with WaveOne primary file while tooth model prepared with Protaper files had the lowest value of maximum stresses. Stress analysis of teeth models prepared with reciprocation motion showed that tooth model prepared with Twisted file had the highest maximum stress value followed by tooth model prepared with Protaper file while tooth model prepared withWaveOne primary file had the lowest value of maximum stresses.