Chang SW. Restor Dent Endod. 2012 Nov;37(4):188-193. http://dx.doi.org/10.5395/rde.2012.37.4.188

The aim of this study was to investigate the effect of thermomechanical treatment on mechanical and metallurgical properties of nickel-titanium (NiTi) rotary instruments. Eight kinds of NiTi rotary instruments with sizes of ISO #25 were selected: ProFile, K3, and One Shape for the conventional alloy; ProTaper NEXT, Reciproc, and WaveOne for the M-wire alloy; HyFlex CM for the controlled memory- (CM-) wire; and TF for the R-phase alloy. Torsional fracture and cyclic fatigue fracture tests were performed. Products underwent a differential scanning calorimetry (DSC) analysis. The CM-wire and R-phase groups had the lowest elastic modulus, followed by the M-wire group. The maximum torque of the M-wire instrument was comparable to that of a conventional instrument, while those of the CM-wire and R-phase instruments were lower. The angular displacement at failure (ADF) for the CM-wire and R-phase instruments was higher than that of conventional instruments, and ADF of the M-wire instruments was lower. The cyclic fatigue resistance of the thermomechanically treated NiTi instruments was higher. DSC plots revealed that NiTi instruments made with the conventional alloy were primarily composed of austenite at room temperature; stable martensite and R-phase were found in thermomechanically treated instruments.

Several single-file systems manufactured using different heat treatment and operated by different kinematics have been released. This study compared the bending resistance and cyclic fatigue resistance of three NiTi files, and examined their phase-transformation behavior. WaveOne Gold Primary (WOG), Reciproc Blue R25 (RPB), and HyFlex EDM OneFile (HDM) were tested (N = 40/instrument). A vertical load was applied to a point 3 mm from the tip, and the stress was measured until a displacement of 3 mm. Tests were conducted at either room temperature (RT: 22 °C) or body temperature (BT: 37 °C) (n = 10). Cyclic fatigue resistance tests were performed in an artificial canal, which had a curvature angle of 40° and a 5-mm radius. Tests were conducted at either RT or BT (n = 10). Instruments were operated according to the manufacturers' instructions. Test results were analyzed using the Kruskal–Wallis and the Mann–Whitney tests. Additional three instruments of each brand were subjected to differential scanning calorimetry (DSC). At RT the bending resistance of three files were not significantly different. However, at BT the bending resistance of RPB was highest, followed by WOG, and HDM (P < 0.05). At RT, RPB demonstrated the longest fracture time, followed by HDM, and WOG (P < 0.05). At BT, HDM had the longest fracture time, followed by RPB, and WOG (P < 0.05). The WOG, RPB consisted of austenite in a considerable proportion, whereas HDM was mainly martensite state at BT. HDM presented superior flexibility and cyclic fatigue resistance at BT.

Current classification of the genus Tamiops is mainly based on pelage color pattern that is prone to seasonal variation or convergent adaptation to environmental selection. The arrangement of four species, Tamiops mcclellandii, Tamiops rodolphii, Tamiops swinhoei and Tamiops maritimus, is regarded as tentative due to difficulty in delineating species, especially the latter two species. We constructed multi‐locus phylogenies of all four Tamiops species on the basis of paternal (Y‐chromosomal SRY and SMCY7), maternal (mitochondrial cytochrome b gene) and biparental (autosomal IRBP, RAG1 and PRKCI) sequences. Maximum likelihood and Bayesian tree‐constructing methods resulted in phylogenies with similar topologies. All genetic markers supported diversification of three main lineages: (1) T. mcclellandii; (2) T. rodolphii; (3) T. swinhoei–maritimus complex. On the basis of 24 T. maritimus from five localities and 10 T. swinhoei from four localities, T. swinhoei and T. maritimus were not reciprocally monophyletic. The six populations of the T. swinhoei–maritimus complex were monophyletic in all loci, except for autosomal loci in one T. maritimus population from Tam Dao, Vietnam. Autosomal phylogenies were more similar to Y‐chromosomal than to mitochondrial phylogenies. Incongruence between nuclear and mitochondrial phylogenies indicates that either T. maritimus from Taiwan or T. maritimus from Phu Yen, Vietnam probably descended from ancient hybridization. Diversification of the three main Tamiops lineages was estimated to occur 8.8–6.7 million years ago (mya) and may have been affected by rapid uplift of the Himalayan Mountains in the western part of their range. Multiple divergences from 5.8 to 1.7 mya likely led to the formation of modern Tamiops species. All six populations of T. swinhoei–maritimus complex could be regarded as distinct species. Divergence among T. rodolphii populations in mitochondrial DNA was also at the interspecies level. Our analyses highlight the underestimation of species diversity in the genus Tamiops.