A finite element study on the mechanical behavior of reciprocating endodontic files

Abstract

Aim: To evaluate the mechanical behavior of reciprocating endodontic files, comparing nickeltitanium (NiTi) and stainless steel 316L (St.St. 316L) as manufacturing material for such instruments. Methods: A three-dimensional finite element model was designed for this study. The simplified instrument model geometry was created on commercial CAD/CAM software. Real strain stress curves of St.St. 316L and NiTi were used in the analysis. Non-linear static analysis was performed to simulate the instrument inside root canal at an angle of 45° in the apical portion, and subjected to torsion of 0.3 N.cm. Results: Non-linear NiTi material showed super elasticity and high functionality in such applications. Very high levels of stress appeared in the file at 3 mm from the tip close to yield point. Conclusions: St. St. 316L is not suitable for manufacturing reciprocating instruments. Modeling of the instrument with equivalent circular cross-sectional area did not affect results quality. Reciprocating instruments have short lifespan, thus manufacturers recommend using one file per tooth. Reciprocating instruments are recommended for less experienced dentist.

Finite Element Study on Continuous Rotating versus Reciprocating Nickel-Titanium Instruments

“…File cross sectional area is the dominant parameter affecting the instrument lifespan, as the cross sectional shape and angles affect directly the cutting efficiency of instrument. That matching proved the hypothesis and findings in previous studies (2,19), where NiTi instruments and wires showed similar behavior even with different cross section designs but equivalent cross section area. At 3 mm from file tip, GTX file cross sectional area is about 30% less than the WaveOne one.…”

“…The first advantage is reduced torsional stress, since during reciprocating movement counterclockwise, the instrument engages dentin at its tip, and disengages immediately with the clockwise movement (21). Second, extended fatigue life of the NiTi file when used in reciprocation compared to continuous rotation, which may be explained by smaller angular movement that induces less stress on the file in case of locking (2). Finally, hammering action of the reciprocating motion of the file's cutting edge increase the applied load on the root canal to double its value.…”

“…As the stiffness of traditional stainless steel endodontic instruments increases with instrument size, it may be responsible for curvature defects such as apical transportation, ledging or zipping (1). Nickel titanium (NiTi) is the favorite material for manufacturing continuous rotating and reciprocating instruments as it is more flexible than stainless steel instruments, due to two unique properties: shape memory and super-elasticity (2). NiTi alloys contain approximately 56% nickel and 44% titanium (3), and have three microstructural phases; austenite, martensite and R-phase, which determine the metal mechanical properties in use (3,4).…”

“…Both continuous rotation and reciprocating instruments have the same probability to fail in case of locking, thus manufacturers recommend using one file per tooth. In this way, reciprocating instruments have been recommended by some authors to less experienced dentists (2).…”

Shaping Ability of WaveOne and ProTaper NEXT Rotary Nickel–titanium File Systems in Simulated Curved Root Canals

“…Reciprocating NiTi file system presents as a new standard in root canal instrumentation with the possibility of reducing procedural abberations. 8 One of the popular single-file systems is the WaveOne ® (DENTSPLY Maillefer, Ballaigues, Switzerland) which is designed to be used with a dedicated reciprocating motion. These files are manufactured with M-wire technology which involves a special thermal processing of the metal that improves flexibility and resistance to cyclic fatigue.…”