Nickel-titanium Wires Research Articles

Phase transitions in coated nickel titanium arch wires: A differential scanning calorimetric and X-ray diffraction analysis

Shape memory and super-elastic properties of orthodontic nickel titanium wires, which are crucial for its clinical performance are dependent on the austenitic–martensitic phase transitions in its metallic microstructure that happen as a result of temperature or stress. The objective of this study was to compare the austenitic–martensitic phase transitions in new, black oxide coated nickel titanium (0·016 inch, Black Diamond, NiTi) arch wires in the ‘as-received’ form, from the manufacturer and ‘retrieved form’ after two months of intraoral use. This was done to analyse whether the new oxide coated nickel titanium wires suffered any significant loss in shape memory and super elasticity properties at the end of two months of intra oral use, findings of which could give valuable inferences prior to its widespread application in clinical practice.Five arch wire samples in both groups were investigated for their austenitic–martensitic phase transitions in an in vitro set up, using differential scanning calorimetry (DSC), (−90° to 100°C at a rate of 10°C/min) and X-ray diffraction (XRD) analysis (10° to 90°), as a function of temperature. Martensitic–austenitic thermograms showed an intermediate rhombohedral phase in the heating cycle of both groups, but cooling cycles showed direct reversal from austenitic to martensitic phase. Lower austenitic start (\(A_{\rm \textbf{s}}\) = 10·78 ± 0·46°C) and finish (\( {A}_{\rm \textbf{f}}\) = 22·26 ± 0·24°C) temperatures of coated wires compared to the conventional wires showed (i) ability of the wire to remain in austenitic phase below oral temperature, that permits it to take up greater force during activation, (ii) increased springiness and (iii) consistent force delivery for an extended period of time. Statistical analysis with paired Student’s ‘t’ test did not show any significant difference in mean values of transition temperatures and enthalpies between the two groups which proved similar shape memory and super-elastic properties at the end of intra oral use. Black oxide coating of NiTi wires may, therefore, be effective in diversified oral conditions and may find acceptable for re-use after sterilization. Low enthalpy values (0·92–3·59 j/g) compared to conventional ones, implied complete phase transition at the atomic level that can improve performance of the material in activation and deactivation cycles of NiTi wires. X-ray diffraction analysis of the two groups demonstrated predominance of austenitic phases (A, 110, 220 and 211) with complete reversibility at the atomic level. Discrete crystallographic structure and absence of multiple phases showed complete martensitic–austenitic transition, which authenticated the differential scanning calorimetric findings. This can earn acceptance for the new product in contemporary orthodontic practice with adequate scope for indigenization.

Mechanical Properties of Controlled Memory and Superelastic Nickel-Titanium Wires Used in the Manufacture of Rotary Endodontic Instruments

IntroductionThe aim of this study was to investigate the structure and mechanical properties of newly developed controlled memory (CM) nickel-titanium wires used in the manufacture of rotary endodontic instruments. MethodsThe composition and the phase transformation behavior of both types of wires were examined by x-ray energy dispersive spectroscopy and differential scanning calorimetry, respectively. Conventional superelastic (SE) nickel-titanium wire was used as a control. The mechanical properties of the wires at selected temperatures (room temperature, 37°C, and 60°C) were evaluated with tensile, cyclic tensile, and cantilever bending tests by using an Instron 3365 universal testing machine. The data of austenitic transformation finishing temperature (Af) were analyzed statistically by using 1-way analysis of variance test at a significance level of P < .05. ResultsThe raw CM wires contained a nickel content of 50.7% ± 0.5% and possessed a relatively higher Af than SE wires (P < .05). The critical plateau stress and ultimate tensile strength of the CM wires were lower than they were for the SE wires, but the maximum strain before fracture of the CM wires (58.4% ± 7.5% to 84.7% ± 6.8%) was more than 3 times higher than it was for SE wires (16.7% ± 3.8% to 27.5% ± 5.4%). The maximum strain of the CM wires with a diameter of 1.22 mm tested at room temperature (23°C ± 2°C) was up to 84% ± 6.4%. CM wires were not SE at either room temperature or 37°C; however, they exhibited superelasticity when heated to 60°C. ConclusionsThe raw CM wires exhibited different phase transformation behavior and mechanical properties when compared with SE wires, attributing to the special heat treatment history of CM wires. This study suggested greater flexibility of endodontic instruments manufactured with CM wires than similar instruments made of conventional SE wires.

The effect of the thermal treatment on the stress–corrosion of nickel–titanium wires

The effect of the thermal treatment on the stress–corrosion of nickel–titanium wires

800 The Gore Septal Occluder: Initial Experience

800 The Gore Septal Occluder: Initial Experience

The effect of temperature on the mechanical behavior of nickel-titanium orthodontic initial archwires

To investigate and compare the characteristics of commonly used types of traditional and heat-activated initial archwires at different temperatures by plotting their load/deflection graphs and quantifying three parameters describing the discharge plateau phase. Forty-eight archwires of cross-sectional diameters ranging from 0.010 inches to 0.016 inches were obtained from seven different manufacturers. A modified three-point wire-bending test was performed on three analogous samples of each type of archwire at 55°C and 5°C, simulating an inserted archwire that is subjected to cold or hot drinks during a meal. For each resulting load/deflection curve the plateau section was isolated and the mean value of each parameter for each type of wire was obtained. Permanent strain was exhibited by all wires tested at 55°C. Statistically significant differences were found between almost all wires for the three considered parameters when tested at 55°C and 5°C. Loads were greater at 55°C than at 5°C. Differences were also found between traditional and heat-activated archwires, the latter of which generated longer plateaus at 55°C, shorter plateaus at 5°C, and lighter mean forces at both temperatures. The increase in average force seen with increasing diameter tended to be rather stable at both temperatures. All nickel-titanium wires tested showed a significant change related to temperature in terms of behavior and force for both traditional and heat-activated wires. Stress under high temperatures can induce permanent strain, whereas the residual strain detected at low temperatures can be recovered from as temperature increases.

Grinding the sharp tip in thin NiTi and stainless steel wires

This paper investigates the grinding process to generate the sharp tip of thin nickel titanium (NiTi) and stainless steel (SS) wires, which are commonly used in medical device applications. The large deflection of thin wires and variation of forces during grinding a 15° bevel angle tip are studied experimentally using the cubic boron nitride (CBN) and silicon carbide (SiC) wheels, respectively. During grinding, as the wire length gradually decreases and the stiffness increases, the wire deflection generally reaches a peak value and then gradually decreases. The results show that CBN grinding has a lower (about 1/3−1/2) grinding force and smaller (about 1/4−1/3) wire deflection than that of the SiC. Compared to SS wire, the NiTi exhibits a larger grinding force and wire deflection, lower surface roughness, and the breakage of wire at the collet chucking location using the SiC wheel due to the high stress induced phase transformation and brittle fracture. The grinding forces and wire tip deflection have large effects on the contact length and grinding time. A model based on the measured grinding forces as the input is developed to estimate the wire deflection and grinding time. This model is validated with experimental measurements and the effects of burr formation and NiTi phase transformation on grinding time are discussed.

Nickel-titanium alloys: a systematic review

OBJECTIVE: A systematic review on nickel-titanium wires was performed. The strategy was focused on Entrez-PubMed-OLDMEDLINE, Scopus and BioMed Central from 1963 to 2008. METHODS: Papers in English and French describing the behavior of these wires and laboratorial methods to identify crystalline transformation were considered. A total of 29 papers were selected. RESULTS: Nickel-titanium wires show exceptional features in terms of elasticity and shape memory effects. However, clinical applications request a deeper knowledge of these properties in order to allow the professional to use them in a rational manner. In addition, the necessary information regarding each alloy often does not correspond to the information given by the manufacturer. Many alloys called "superelastic" do not present this effect; they just behave as less stiff alloys, with a larger springback if compared to the stainless steel wires. CONCLUSIONS: Laboratory tests are the only means to observe the real behavior of these materials, including temperature transition range (TTR) and applied tensions. However, it is also possible to determine in which TTR these alloys change the crystalline structure.

Evaluation of surface roughness of orthodontic wires by means of atomic force microscopy

To compare the surface roughness of different orthodontic archwires. Four nickel-titanium wires (Sentalloy(®), Sentalloy(®) High Aesthetic, Titanium Memory ThermaTi Lite(®), and Titanium Memory Esthetic(®)), three β-titanium wires (TMA(®), Colored TMA(®), and Beta Titanium(®)), and one stainless-steel wire (Stainless Steel(®)) were considered for this study. Three samples for each wire were analyzed by atomic force microscopy (AFM). Three-dimensional images were processed using Gwiddion software, and the roughness average (Ra), the root mean square (Rms), and the maximum height (Mh) values of the scanned surface profile were recorded. Statistical analysis was performed by one-way analysis of variance (ANOVA) followed by Tukey's post hoc test (P < .05). The Ra, Rms, and Mh values were expressed as the mean ± standard deviation. Among as-received archwires, the Stainless Steel (Ra = 36.6 ± 5.8; Rms = 48 ± 7.7; Mh = 328.1 ± 64) archwire was less rough than the others (ANOVA, P < .05). The Sentalloy High Aesthetic was the roughest (Ra = 133.5 ± 10.8; Rms = 165.8 ± 9.8; Mh = 949.6 ± 192.1) of the archwires. The surface quality of the wires investigated differed significantly. Ion implantation effectively reduced the roughness of TMA. Moreover, Teflon(®)-coated Titanium Memory Esthetic was less rough than was ion-implanted Sentalloy High Aesthetic.

Transformation Behaviour, Bending Properties and Surface Quality of 22 Commercial Nickel-Titanium Wires: A Batch-to-Batch Evaluation

Aims: The aims of this study were to investigate batch-to-batch differences in mechanical and thermal properties of 22 commercial nickel-titanium wires and evaluate the surface quality. Secondly the percentages of superelasticity at mouth temperature were measured. Study Design: In vitro laboratory study.

The effect of splint material and thickness on tooth mobility after extraction and replantation using a human cadaveric model

Although current guidelines for the treatment of traumatic injuries recommend the use of 'flexible' splints, the precise definition of what is considered flexible versus rigid has not been rigorously defined, leaving the clinician with a wide range of options for this critical factor. The purpose of this study was to quantify and compare the effect of eight different splints on tooth mobility after extraction and replantation using a human cadaveric model. Following strict selection criteria including complete root maturation, lack of periodontal disease, normal bone levels, and crown integrity, a maxillary central incisor was atraumatically extracted and splinted with eight different splints. The experimental splints included a 20-pound test (9.072-kilogram test) [corrected] monofilament nylon-composite splint and six wire-composite splints made of wires of 0.012' (0.3 mm), 0.016' (0.4 mm), or 0.020' (0.5 mm) diameter stainless steel (SS) or nickel titanium (NT). A direct composite splint represented the most rigid type of splint. These eight splints were applied five times each, and tooth mobility was measured before and after each splint was applied. The average splint effect, defined as the difference between the presplint and the postsplint measurements quantified using the Periotest, was calculated for each splint and compared. No significant differences were found between the nylon-composite and the wire-composite splints. There was significantly less tooth mobility with the direct composite splint compared to all other splints. In conclusion, the results of this study suggest that nylon and SS or NT wires up to 0.016' diameter are significantly more flexible than direct composite splints and thus may be better suited for the splinting and management of traumatized teeth.

Effect of coating on properties of esthetic orthodontic nickel-titanium wires

To determine the effect of coating on the properties of two esthetic orthodontic nickel-titanium wires. Woowa (polymer coating; Dany Harvest) and BioForce High Aesthetic Archwire (metal coating; Dentsply GAC) with cross-section dimensions of 0.016 × 0.022 inches were selected. Noncoated posterior regions of the anterior-coated Woowa and uncoated Sentalloy were used for comparison. Nominal coating compositions were determined by x-ray fluorescence (JSX-3200, JOEL). Cross-sectioned and external surfaces were observed with a scanning electron microscope (SEM; SSX-550, Shimadzu) and an atomic force microscope (SPM-9500J2, Shimadzu). A three-point bending test (12-mm span) was carried out using a universal testing machine (EZ Test, Shimadzu). Hardness and elastic modulus of external and cross-sectioned surfaces were obtained by nanoindentation (ENT-1100a, Elionix; n = 10). Coatings on Woowa and BioForce High Aesthetic Archwire contained 41% silver and 14% gold, respectively. The coating thickness on Woowa was approximately 10 µm, and the coating thickness on BioForce High Aesthetic Archwire was much smaller. The surfaces of both coated wires were rougher than the noncoated wires. Woowa showed a higher mean unloading force than the noncoated Woowa, although BioForce High Aesthetic Archwire showed a lower mean unloading force than Sentalloy. While cross-sectional surfaces of all wires had similar hardness and elastic modulus, values for the external surface of Woowa were smaller than for the other wires. The coating processes for Woowa and BioForce High Aesthetic Archwire influence bending behavior and surface morphology.

Effect of loading force on the dissolution behavior and surface properties of nickel-titanium orthodontic archwires in artificial saliva

For orthodontic applications, equiatomic nickel-titanium (NiTi) wires are used to level and align the teeth under bending conditions in the oral environment for long periods. The aim of study was to investigate the influence of bending stress on the nickel release of commercial NiTi orthodontic wires in vitro, simulating the intraoral environment as realistically as possible. Two types of as-received orthodontic NiTi wires, free of performed internal stress, were immersed in artificial saliva. Half of the NiTi wires were exposed to continuous bending stress throughout the 14-day experimental period. The stressed NiTi wires exhibited substantial increases in the nickel release compared with the unstressed specimens during all experimental periods. The highest dissolution rate during the 0 to 1 day incubation period was observed for all stressed specimens. However, a slight increase of nickel released as a function of time was observed in the 3 groups of stressed specimens after 3 days of immersion. For the stressed specimens, it was hypothesized that the bending stress would induce buckling or cracking of the protective oxide film of the NiTi wires. In this study, the mechanism of nickel release was the underlying metal surface reacting with the surrounding environment. The results indicated that bending stress influences the nickel release of NiTi wires. The factor of loading condition with respect to corrosion behavior and passive film should be considered in view of the widespread use of NiTi wires for dental devices.

Aesthetic nickel titanium wires--how much do they deliver?

The purpose of this study was to evaluate and compare the force levels of aesthetic Ni-Ti wires to regular Ni-Ti wires of the same dimension and evaluate their mechanical properties. Aesthetic and regular maxillary superelastic Ni-Ti wires (0.016 × 0.022) from four different manufacturers (G&H Wire Company, TP Orthodontics, GAC International, and Ortho Organizers) were selected and grouped I-IV. The loading and unloading values were compared using a three-point bending test. The unloading end values were also recorded to evaluate the recovery of archwires after each deflection. The unloading values were recorded at 0.5, 1.5, and 2.5 mm after loading deflections of 1, 2, and 3 mm, respectively. Cross-sectional scanning electron microscopy was used to assess the coating thickness of aesthetic wires. The results, statistically analysed, showed a significant decrease in force values for the aesthetic wires in groups I, III, and IV (P < 0.001) as compared to regular Ni-Ti wires of the same dimension from the same manufacturer. There was no significant difference in force values for group II wires. A statistically significant decrease in force values of epoxy-coated wires was observed in groups I, III, and IV only. This is of obvious clinical significance during wire selection. The group II coated wires, however, exhibited forces comparable to their regular Ni-ti wires with a difference that was statistically insignificant. The end values of aesthetic wires showed almost complete recovery for groups I, II, and III after 2 and 3 mm deflections.

Comparison of self- and conventional-ligating brackets in the alignment stage

This prospective study investigated the difference in clinical efficiency between Damon™ 3 self-ligating brackets (SLB) compared with Mini Diamond conventional ligating brackets (CLBs) during tooth alignment in straightwire fixed appliance therapy. Twenty-nine patients (10 males and 19 females), aged between 14 and 30 years, were randomly divided into two groups: 14 patients received the SLB and 15 received the CLB. Upper arch impressions were taken for pre-treatment records (T(0)). A transpalatal arch was soldered to both maxillary first molar bands prior to extraction of the maxillary first premolars, followed by straightwire fixed appliances (0.022 × 0.028 inch). A 0.014 inch nickel titanium (NiTi) wire was used as the levelling and aligning archwire. Four monthly reviews were undertaken and impressions of the upper arch were taken at each appointment (T(1), T(2), T(3), and T(4)). Displacements of the teeth were determined using Little's irregularity index (LII). Data were analysed using the Mann-Whitney U-test. In the aligning stage, the CLB group showed significantly faster alignment of the teeth compared with the SLB group at the T(1)-T(2) interval (P < 0.05). However, there were no differences at T(2)-T(3), and T(3)-T(4) for either group (P > 0.05). The CLB group showed 98 per cent crowding alleviation compared with 67 per cent for the SLB after 4 months of alignment and levelling. Mini Diamond brackets aligned the teeth faster than Damon™ 3 but only during the first month. There was no difference in efficacy between the two groups in the later 3 weeks. Alleviation of crowding was faster with CLB than with SLB.

Polyphenylene polymers as esthetic orthodontic archwires

There is continuing interest in an esthetic, effective labial archwire. In this study, we evaluated the potential of new, high-strength polyphenylene polymers to fill this need. Polyphenylene (Primospire, Solvay Advanced Polymers, Alpharetta, Ga) polymer was extruded into wires with clinically relevant round and rectangular cross sections. Tensile, flexure, spring-back, stress-relaxation, and formability characteristics were assessed. Arch forms and secondary shapes were formed. Smooth wires with consistent cross-sectional dimensions, high spring-back, and good ductility were produced. Forces delivered were generally similar to typical beta-titanium and nickel-titanium wires of somewhat smaller cross sections. The polyphenylene wire did experience stress relaxation for up to 75 hours. The force magnitudes place polyphenylene wires in the category of an alignment or leveling wire. High formability allowed shape bending similar to that associated with stainless steel wires. Polyphenylene polymers could serve as esthetic orthodontic archwires; further study is warranted.

Transformation behavior of nickel-titanium orthodontic wires under tensile load

This study investigated transformations of nickel-titanium wires using differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) under tensile load (100 gf or 500 gf). Two nickel-titanium wires, 35°C Copper Ni-Ti and Nitinol SE, were selected. DSC analyses were performed between -90° and 100°C. Specimens prepared for TMA were approximately 150 µm thick and 12 mm long. TMA analyses were performed between -120° and 100°C. With TMA, all transformation temperatures for a tensile load of 500 gf, obtained from both the heating and cooling curves, were higher than those for a tensile load of 100 gf. While mean A(s) and A(f) temperatures for Copper Ni-Ti obtained by TMA were much higher than those obtained by DSC analysis, mean M(s) and M(f) temperatures obtained by TMA were much lower than those obtained by DSC analysis. The transformation behavior of nickel-titanium wires with change in temperature was affected by application of tensile load.

Seismic response attenuation of structures using shape memory alloy dampers

Smart materials such as shape memory alloys (SMAs) are recently being used in earthquake engineering applications to control the response of structures. In this paper, a shape-memory alloy damper device made up of austenite wires (e.g. Nickel Titanium wires) is used as a passive energy absorber. NiTi wires are very attractive for passive vibration control as they have a pseudo-elastic property and can sustain large amounts (upto 10% strain) of inelastic deformation. Moreover, in contrast to regular metallic materials they can recover that deformation. The damper device is designed, fabricated and tested. Validity study is made using a thermo-mechanical model of SMA taking into account the residual martensite accumulation irreversibly due to cyclic forward/reverse martensitic transformation. Further an analytical study of a supporting steel structure of dump tanks with and without SMA dampers subjected to design wave earthquake loading is carried out. Performance of the structure with SMA dampers is compared with that of the same structure with yielding dampers. Copyright © 2010 John Wiley & Sons, Ltd.

Nickel-Titanium (NiTi) Arch Wires: The Clinical Significance of Super Elasticity

The introduction of nickel-titanium (NiTi) wires has revolutionized the field of orthodontics by delivering light continuous forces over a wider range of displacements than the traditional stainless-steel wires. Over the years improvements in NiTi wire manufacturing and composition have been introduced; however, the claimed wire capabilities are not always easy to verify in the clinical setting. We aim at presenting an overview of the use and applications of NiTi alloys in orthodontics. The implications of the metallurgical and mechanical properties and intraoral aging of the wires in their clinical application is discussed. Finally, time variants of orthodontic therapy duration with the use of NiTi and alternative arch wires are presented, and the clinical implication of superelasticity is analyzed.

Experimental Analysis of Torque Characteristics of Orthodontic Wires

A major requirement for orthodontic wires is superior elasticity. The question arises whether today's nickel titanium wires display a distinctively superelastic plateau also under torsional loading, and whether typical torsion angles are sufficient to produce adequate torquing moments with superelastic wires. The objective of this study was to compare various nickel titanium and steel wires in a pure torsion experiment. To experimentally examine the torque characteristic of orthodontic wires, we used nickel titanium wires manufactured by Dentaurum (Tensic®) and ODS (Euro Arch NiTi) measuring 0.40 × 0.40 mm2, 0.40 × 0.56 mm2, 0.43 × 0.64 mm2, 0.46 × 0.64 mm2, 0.48 × 0.64 mm2, 0.51 × 0.51 mm2, and steel wires made by Dentaurum (remanium®), 3M Unitek (HI-T™ II Stainless Steel) measuring 0.40 × 0.40 mm2, 0.40 × 0.56 mm2, 0.43 × 0.56 mm2, 0.43 × 0.64 mm2, 0.46 × 0.64 mm2, 0.48 × 0.64 mm2, 0.51 × 0.51 mm2. Torque was measured at an ambient temperature of 37 ° C for the nickel titanium wires. The distance between the bearing points was 10 mm for all measurements. The steel wires' torquing moments were determined at a torsion angle of 20 °, the torquing moments of the nickel titanium wires were investigated on the plateau, and we compared the results of the means and the standard deviations of all wires. Starting and end points of the loading and unloading plateau were determined for all nickel titanium wires. The torquing moment/torsion angle diagrams of the nickel titanium wires by different manufacturers displayed the curves typical of superelastic wires. The torquing moments of the wires with a smaller cross-section yielded values below 5 Nmm and thus appear obviously too small (e.g. Dentaurum Tensic®, 0.40 × 0.40 mm2: 1.3 Nmm). The mean values of the loading plateau's starting point yielded values of about 20 °. As the torsional play in the bracket slot of the wires with a smaller cross-section is typically about 10 °, we doubt whether these wires reach the superelastic plateau. Moreover, we observed production-associated variations in the material properties of various nickel titanium wires. It is thus difficult for the practitioner to draw a correlation between a wire's crosssection and the actual torquing moment delivered.

Role of Mechanical Stress-induced Glutamate Signaling-associated Molecules in Cytodifferentiation of Periodontal Ligament Cells

In this study, we analyzed the effects of tensile mechanical stress on the gene expression profile of in vitro-maintained human periodontal ligament (PDL) cells. A DNA chip analysis identified 17 up-regulated genes in human PDL cells under the mechanical stress, including HOMER1 (homer homolog 1) and GRIN3A (glutamate receptor ionotropic N-methyl-d-aspartate 3A), which are related to glutamate signaling. RT-PCR and real-time PCR analyses revealed that human PDL cells constitutively expressed glutamate signaling-associated genes and that mechanical stress increased the expression of these mRNAs, leading to release of glutamate from human PDL cells and intracellular glutamate signal transduction. Interestingly, exogenous glutamate increased the mRNAs of cytodifferentiation and mineralization-related genes as well as the ALP (alkaline phosphatase) activities during the cytodifferentiation of the PDL cells. On the other hand, the glutamate signaling inhibitors riluzole and (+)-MK801 maleate suppressed the alkaline phosphatase activities and mineralized nodule formation during the cytodifferentiation and mineralization. Riluzole inhibited the mechanical stress-induced glutamate signaling-associated gene expressions in human PDL cells. Moreover, in situ hybridization analyses showed up-regulation of glutamate signaling-associated gene expressions at tension sites in the PDL under orthodontic tooth movement in a mouse model. The present data demonstrate that the glutamate signaling induced by mechanical stress positively regulates the cytodifferentiation and mineralization of PDL cells.