Fatigue and Mechanical Properties of Nickel-Titanium Endodontic Instruments

Abstract

Shape memory alloys are increasingly used in superelastic conditions under complex cyclic deformation situations. In these applications, it is very difficult to predict the service life based on the theoretical law. In the present work, fatigue properties of NiTi engine-driven rotary files have been characterized by using differential scanning calorimetry (DSC) and mechanical testing (bending). The DSC technique was used to measure precise transformation. The degree of deformation by bending was studied with combined DSC and mechanical property measurements. In these cold-worked files, the high dislocation density influences the reorientation processes and the crack growth. Some thermal treatments are involved in promoting some changes in the mechanical properties and transformation characteristics. Annealing around 400 degrees C shows good results; the recovery allows a compromise between an adequate density for the R-Phase germination and a low density to limit the brittleness of these instruments. In clinical usage, it is important to consider different canal shapes. It could be proposed that only few cycles of use is safe for very curved canals but to follow the manufacturer's advise for straight canals.

Current Challenges and Concepts of the Thermomechanical Treatment of Nickel-Titanium Instruments

“…DSC curves were very complex with irregular peaks. These results were also confirmed by other studies (28,32). Therefore, the manufacturer must perform an appropriate heat treatment, which will be accompanied by beneficial changes in mechanical properties and improved clinical performance.…”

“…At the beginning of 2000, a series of studies (27)(28)(29)(30) found that changes in the transformation behavior via heat treatment were effective in increasing the flexibility of NiTi endodontic instruments. Since then, heat-induced or heat-altering manipulations were used to influence or alter the properties of NiTi endodontic instruments, which were once cited as the main reasons for pursuing the use of NiTi instruments in endodontics.…”

Deflecting load of nickel titanium rotary instruments during cyclic fatigue

“…Consistent with our results, Li et al 34) suggested the fracture failure criterion to be a decrease in stiffness. On the contrary, Kuhn and Jordan 35) found that stiffness of PF instruments was increased after clinical use.…”

Comparação entre as limas Reciproc e WaveOne na formatação e centralização do canal: uma revisão integrativa

“…No entanto, outros estudos 25,27,42,44 demonstraram que as limas Reciproc promoveram menor remoção dentinária e mantiveram melhor a anatomia interna original do canal do que limas WaveOne.…”