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- Characterization and evaluation of the mechanical behaviour of endodontic-grade NiTi wiresPublication . Pereira, Samuel; Carvalho, André; Reis, Luís; Freitas, Manuel; Montalvão, DiogoThe orthodontic files have been used in dentistry since the middle ages and, as so, the shape, material and operation mode have changed since those days. In the late days, we have seen an increasing use of Nickel-Titanium (NiTi) alloys, to the detriment of more conventional alloys. At body temperature, these NiTi alloys present a superelastic behaviour, which allow the file to follow the teeth root in an easier way comparing to conventional alloys and have been reported to be more effective in the removal of the tooth pulp tissue, and in the protection of the tooth structure. Not withs tanding, these NiTi instruments, as all the others being subjected to bending loading, they fracture without any visual signal of degradation. Thereby, there is a need of studying these alloys, as they present a high hysteresis cycle and a high non-linearity in the Elastic Domain. Currently, there is not an international standard for these alloys, so various authors have attempted to design systems that can test NiTi endodontic files under fatigue loads, usually based on empirical setups. Following a systematic approach, this work presents the results of rotary fatigue tests for two Alfa Aesar® Nitinol wires with different diameters (0,58mm and 0,25mm).
- Determination of the rotary fatigue life of NiTi alloy wiresPublication . Carvalho, André; Montalvao, Diogo; Freitas, Manuel; Reis, Luís; Fonte, M.Nickel-Titanium (NiTi) alloys with superelastic properties have been increasingly introduced as a substitute to more conventional alloys, such as stainless steel, in a variety of applications. In Dentistry, NiTi alloys are used in tools such as Endodontic rotary files, allowing the file to follow teeth root canals more easily than their stainless steel counterparts. Nevertheless, during surgery, the file is subjected to cyclic bending loading, since it is rotating while being deformed inside the curved canals and is prone to fracture due to fatigue, without showing any visible signals of degradation. Following a systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (Memry and Euroflex). The formulation is presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure. Experimental tests as well as numerical Finite Element Analysis (FEA) simulations are presented to better understand the fatigue fracture mechanisms present in NiTi alloys, showing that there is good agreement between the predicted strains (difficult to measure in such small wires) and the cycles to failure.
- Rotary fatigue life of NiTi alloy wires and FEA modelling of fatigue damagePublication . Montalvão, Diogo; Carvalho, André; Freitas, Manuel; Reis, LuísNickel-Titanium (NiTi) alloys with superelastic properties have been increasingly introduced as a substitute to more conventional alloys. For example, NiTi alloys used in Dentistry, such as in Endodontic rotary files, possess superelastic properties that allow for the file to follow teeth root canals more easily than their stainless-steel counterparts. Nevertheless, during surgery, the file is subjected to cyclic bending loading, since it is spinning while being deformed inside the curved canal. Therefore, these instruments are prone to fracture due to fatigue, without showing any visible signals of degradation. This problem brought new challenges on how new instruments should be tested, as NiTi alloys are highly non-linear. However, most existing test setups ignore the fracture mechanics involved in the fatigue phenomenon. In this work, the results of rotary fatigue tests for NiTi wires from different manufacturers is presented. The formulation is described, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure. Experimental tests as well as numerical Finite Element Analysis (FEA) simulations are presented to better understand the fatigue fracture mechanisms present in NiTi alloys, showing that there is good agreement between the predicted strains (difficult to measure in such small wires) and the cycles to failure. One characteristic is that these alloys exhibit a large hysteresis in the elastic domain if loaded up to the mixture of austenitic and martensitic phases (also known as B19’ martensite) and then unloaded. Rotating bending fatigue tests of NiTi wires show that, when loaded up to the B19’ martensite, the number of cycles to failure decrease with the applied strain.
- Rotary fatigue testing machine to determine the fatigue life of NiTi alloy Wwres and endondontic filesPublication . Carvalho, André; Freitas, Manuel; Reis, Luís; Montalvao, Diogo; Fonte, M.Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough transformations in recent years when stainless steel was replaced by Nickel-Titanium (NiTi). NiTi alloys used in Endodontics possess superelastic properties at body temperature (37C) that bring many advantages on the overall performance of the root-canal treatment. They can follow curved root canals more easily than stainless steel instruments and have been reported to be more effective in the removal of the inflamed pulp tissue and protection of the tooth structure. However, these instruments eventually fracture under cyclic bending loading due to fatigue, without any visible signals of degradation to the practitioner. This problem brought new challenges on how new instruments should be tested, as NiTi alloys are highly non-linear and present a large hysteresis cycle in the Elastic domain. Current existing standards are only available for Stainless Steel testing. Thus, many authors have attempted to design systems that can test NiTi endodontic files under fatigue loads. However, no approach has been universally adopted by the community yet, as in most cases they are based on empirical set ups. Following a more systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (MemryTM and EuroflexTM). The tests were done on a versatile fully automatic rotary bending testing machine. The formulation is also presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure.
- Rotary fatigue testing to determine the fatigue life of NiTi alloy wires: an experimental and numerical analisysPublication . Carvalho, André; Freitas, Manuel; Reis, Luís; Montalvao, Diogo; Fonte, M.Endodontic rotary file instruments used to treat root canals in dentistry suffered breakthrough transformations in recent years when stainless steel was replaced by Nickel-Titanium (NiTi). NiTi alloys used in Endodontics possess superelastic properties at body temperature (37C) that bring many advantages on the overall performance of the root-canal treatment. They can follow curved root canals more easily than stainless steel instruments and have been reported to be more effective in the removal of the inflamed pulp tissue and protection of the tooth structure. However, these instruments eventually fracture under cyclic bending loading due to fatigue, without any visible signals of degradation to the practitioner. This problem brought new challenges on how new instruments should be tested, as NiTi alloys are highly non-linear and present a large hysteresis cycle in the Elastic domain. Current existing standards are only available for Stainless Steel testing. Thus, many authors have attempted to design systems that can test NiTi endodontic files under fatigue loads. However, no approach has been universally adopted by the community yet, as in most cases they are based on empirical set ups. Following a more systematic approach, this work presents the results of rotary fatigue tests for several NiTi wires from different manufacturers (Memry™ and Euroflex™). The formulation is presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure, as well numerical FEM simulation to verify the analytical model predictions.