Effect of cryogenic treatment on nickel‐titanium endodontic instruments

Abstract

Aim-To investigate the effects of cryogenic treatment on nickel-titanium endodontic instruments. The null hypothesis was that cryogenic treatment would result in no changes in composition, microhardness or cutting efficiency of nickel-titanium instruments.Methodology-Microhardness was measured on 30 nickel-titanium K-files (ISO size 25) using a Vicker's indenter. Elemental composition was measured on two instruments using X-ray spectroscopy. A nickel-titanium bulk specimen was analysed for crystalline phase composition using X-ray diffraction. Half of the specimens to be used for each analysis were subjected to a cryogenic treatment in liquid nitrogen (−196 °C) for either 3 s (microhardness specimens) or 10 min (other specimens). Cutting efficiency was assessed by recording operator choice using 80 nickel-titanium rotary instruments (ProFile ® 20, .06) half of which had been cryogenically treated and had been distributed amongst 14 clinicians. After conditioning by preparing four corresponding canals, each pair of instruments were evaluated for cutting efficiency by a clinician during preparation of one canal system in vitro. A Student's t-test was used to analyse the microhardness data, and a binomial test was used to analyse the observer choice data. Composition data were analysed qualitatively.Results-Cryogenically treated specimens had a significantly higher microhardness than the controls (P < 0.001; β > 0.999). Observers showed a preference for cryogenically treated instruments (61%), but this was not significant (P = 0.21). Both treated and control specimens were composed of 56% Ni, 44% Ti, 0% N (by weight) with a majority in the austenite phase.Conclusions-Cryogenic treatment resulted in increased microhardness, but this increase was not detected clinically. There was no measurable change in elemental or crystalline phase composition.

Effects of Cryo-Treatment on Corrosion Behavior and Mechanical Properties of Laser-Welded Commercial Pure Titanium

“…17,18) Cryo-treatment immerses the samples in a cold medium (such as liquid nitrogen) according to a certain processing curve until achieving a certain temperature. The material's performance will be improved by inducing microstructural changes and stress redistribution.…”

Evolution of Nickel–titanium Alloys in Endodontics

“…61 Finally, surface hardening can be achieved through cryogenic treatment. 62 The samples tested showed increased microhardness but no detectable change in crystalline phase composition or elemental composition. This was also confirmed by another study that concluded that deep dry cryogenic treatment "increases the cutting efficiency significantly but not the wear resistance."…”

Effect of Cryogenic Treatment on Fracture Resistance of Nickel Titanium Rotary Instruments a Systematic Review

“…Anderson et al in 2007 showed that electropolished instruments performed significantly better than non-electropolished instruments in both the cyclic fatigue testing and static torsional loading, which is likely to be caused by a reduction in surface irregularities that serve as points of stress concentration and crack initiation in nickel titanium. 21 Kim et al 2005 22 studied the effect of cryogenic treatment on nickel-titanium endodontic instruments.30 size 25 nickeltitanium K-files (NTO2525; Dentsply-Tulsa Dental) were embedded in epoxy resin (811-563-103 and 811-563-104; Leco, St Joseph, MI, USA) mixed according to the manufacturer's instructions. 15 control instruments and 15 cryogenically treated instruments were used.…”