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Influence of heat treatment on torsional resistance and surface roughness of nickel‐titanium instruments
Author(s) -
Silva E. J. N. L.,
Giraldes J. F. N.,
de Lima C. O.,
Vieira V. T. L.,
Elias C. N.,
Antunes H. S.
Publication year - 2019
Publication title -
international endodontic journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.988
H-Index - 119
eISSN - 1365-2591
pISSN - 0143-2885
DOI - 10.1111/iej.13164
Subject(s) - nickel titanium , materials science , surface roughness , profilometer , scanning electron microscope , surface finish , composite material , titanium alloy , universal testing machine , alloy , metallurgy , shape memory alloy , ultimate tensile strength
Aim To evaluate the influence of controlled memory ( CM ) thermal treatment on the torsional resistance and surface roughness of nickel‐titanium instruments with identical geometric and dimensional characteristics. The influence of environmental temperature on torsional resistance was also evaluated. Methodology A sample of 25 conventional NiTi alloy and 25 CM thermal‐treated NiTi instruments, with an identical geometric design and a nominal size of 0.25 mm at D 0 and a nominal taper of .06 mm mm −1 were selected. The torsional strength and the angle of rotation of the instruments were tested following ISO 3630‐1 at two temperatures: 21 and 35 °C. The fracture surfaces of all tested instruments were verified with a scanning electron microscope. The surface roughness of the blades of conventional NiTi alloy and CM wire files was evaluated by using a New View 7100 Profilometer. Statistical analysis was performed using Student's t ‐test and paired t ‐test to analyse the torsional resistance and surface roughness at a significance level of P < 0.05. Results The torsional strength of thermally‐treated instruments was significantly lower than nontreated instruments ( P < 0.05). However, thermally‐treated instruments had significantly greater angular rotation to fracture than nontreated instruments ( P < 0.05). Temperature did not influence the torsional strength ( P > 0.05) and the angular rotation ( P > 0.05) of the instruments. Regarding the roughness measurements, groove depth was lower at the surface of thermally‐treated instruments when compared to nontreated instruments ( P < 0.05). Conclusion Thermal treatment influenced the torsional resistance and surface roughness of NiTi instruments with identical geometric and dimensional characteristics. Temperature did not affect torsional behaviour.