Metal release from heat-treated orthodontic archwires

Stainless steel and cobalt-chromium orthodontic archwires were subjected to an immersion corrosion test. Wires in the as-received state and wires subjected to a 1-min heat treatment at different temperatures were tested. Iron from the stainless steel and cobalt from the cobalt-chromium product were analyzed in artificial saliva after 1 week of immersion. Both products were analyzed for nickel. The results showed that the cobalt-chromium wire in the as-received state released more metals than the stainless steel. The metal release from the stainless steel wire increased rapidly when subjected to 400°C or higher. For the colbalt-chromium product the increase started at about 500°C. At temperatures above 500°C the release of metals was 15 to 60 times higher than the lowest values. The present results should be considered in procedures involving application of heat to orthodontic wires. □ Cobalt-chromium alloy; corrosion; stainless steel     

Corrosion behavior and surface structure of orthodontic Ni-Ti alloy wires.

The corrosion behaviors of a commercial Ni-Ti alloy orthodontic wire and a polished plate with same composition in 0.9% NaCl and 1% lactic acid solutions were examined using an electrochemical technique, an analysis of released ions, and a surface analysis by X-ray photoelectron spectroscopy (XPS). The effect of polishing the wire on the corrosion was also examined. The XPS analysis demonstrated the presence of a thick oxide film mainly composed of TiO2 with trace amounts of Ni hydroxide, which had formed on the wire surface during the heat treatment and subsequent pickling processes. This oxide layer contributed to the higher resistance of the as-received wire to both general and localized corrosion in 0.9% NaCl solution, compared with that of the polished plate and the polished wire. The thick oxide layer, however, was not stable and did not protect the orthodontic wire from corrosion in 0.1% lactic acid solution.     

Metal release from heat-treated orthodontic archwires

Stainless steel and cobalt-chromium orthodontic archwires were subjected to an immersion corrosion test. Wires in the as-received state and wires subjected to a 1-min heat treatment at different temperatures were tested. Iron from the stainless steel and cobalt from the cobalt-chromium product were analyzed in artificial saliva after 1 week of immersion. Both products were analyzed for nickel. The results showed that the cobalt-chromium wire in the as-received state released more metals than the stainless steel. The metal release from the stainless steel wire increased rapidly when subjected to 400 degrees C or higher. For the cobalt-chromium product the increase started at about 500 degrees C. At temperatures above 500 degrees C the release of metals was 15 to 60 times higher than the lowest values. The present results should be considered in procedures involving application of heat to orthodontic wires.     

4种镍钛正畸弓丝钛离子析出量的体外实验研究

目的:通过测试在人工唾液中4种品牌镍钛正畸弓丝钛离子的析出量,以了解其耐腐蚀性。方法:选择临床常用的4种品牌的镍钛正畸弓丝,分别为3M、SL、TP、SMT,调配人工唾液,并将人工唾液的pH值分别调节为4.0及6.75,减取的正畸弓丝两端较直的部分(每段2 cm)放入EP树脂管中,加入已调节好pH值的人工唾液1 mL,保存置37 ℃电子恒温箱,在1、7、28 d时分别取出弓丝样本后测试试管中钛离子的析出量,进行统计学分析。结果:第1天时4种品牌镍钛正畸弓丝钛离子的析出量最大,7、28 d时钛离子的析出量平均后,均要少于弓丝浸泡第1天时的析出量,不同品牌间钛离子的析出量的差别不具有统计学意义。结论:4种品牌的镍钛正畸弓丝具有良好的抗腐蚀性,但是酸性环境可以加速镍钛正畸弓丝中钛离子的析出量影响镍钛正畸弓丝的抗腐蚀性。     

Stress corrosion cracking of NiTi in artificial saliva.

OBJECTIVES: This paper aimed to study the mechanism of the cracking of orthodontic NiTi wire. METHODS: Two orthodontic NiTi wires were subjected: (1) optical and scanning electron microscopy (SEM) to observe the fracture surface; (2) energy dispersive X-ray spectroscopy to determine the composition of the surface product; (3) anodic polarization to remove the surface product. Samples of NiTi alloy were subjected to the constant loading test to study the stress corrosion cracking (SCC) behavior of NiTi shape memory alloy in artificial saliva. RESULTS: The results showed that there were three typical areas at the fracture surface of NiTi orthodontic wire. Area '1' was a tool-made notch. Crack initiated from the root of this notch and propagated to form Area '2', which was perpendicular to the wire axis and covered by surface film. This film consisted of Na, K, Cl, P, S and O except Ni and Ti. The cracking process of NiTi alloy under the constant loading test depended on the pH of saliva and applied stress. The crack length was about 262microm, the longest at 300MPa and pH 3.0. SIGNIFICANCE: A tool-made notch in orthodontic NiTi wires can cause SCC. At high stress and low pH, this NiTi alloy was most sensitive to cracking.     

The electrochemical behavior and surface analysis of Ti50Ni47.2Co2.8 alloy for orthodontic use

OBJECTIVES: The aim of this study was to investigate the electrochemical behavior of Ti50Ni47.2Co2.8 alloy in deaerated artificial saliva solutions with binary NiTi alloy as reference and to characterize the composition and structure of the passive film after polarization tests. METHODS: The corrosion behavior of NiTiCo alloy was systematically studied by open circuit potential, potentiodynamic and potentiostatic techniques. The surface characterization after anodic polarization tests were demonstrated by XPS. The electrolytes were maintained at 37 degrees C by immersing the test cell in water bath. 500 mV vs. SCE was applied on the samples for potentiostatic tests. The metal ions concentration was measured by ICP/OES. RESULTS: Potentiodynamic and potentiostatic tests results showed that the corrosion behavior of NiTiCo was similar to that of NiTi alloy. With the increase of pH value of the electrolytes, both corrosion potential (Ecorr) and pitting corrosion potential (Eb) decreased. XPS results revealed that the outmost passive film consisted mainly of TiO2 which were identical with that of NiTi alloy. The Ni ion release amount of NiTiCo was very close to that of NiTi alloy as examined by ICP/OES. Neither Ti nor Co ion was detected due to the detection limitation. SIGNIFICANCE: The corresponding relationship between corrosion behavior and pH value of the artificial saliva should be taken into consideration during the application of orthodontic wires. The addition of Co had little effect on the corrosion behavior of NiTi as well as the formation of the passive film.     

Corrosion of stainless steel, nickel-titanium, coated nickel-titanium, and titanium orthodontic wires

Orthodontic wires containing nickel have been implicated in allergic reactions. The potential for orthodontic wires to cause allergic reactions is related to the pattern and mode of corrosion with subsequent release of metal ions, such as nickel, into the oral cavity. The purpose of this study was to determine if there is a significant difference in the corrosive potential of stainless steel, nickel titanium, nitride-coated nickel titanium, epoxy-coated nickel titanium, and titanium orthodontic wires. At least two specimens of each wire were subjected to potentiostatic anodic dissolution in 0.9% NaCl solution with neutral pH at room temperature. Using a Wenking MP 95 potentiostat and an electrochemical corrosion cell, the breakdown potential of each wire was determined. Photographs were taken of the wire speci mens using a scanning electron microscope, and surface changes were qualitatively evaluated. The breakdown potentials of stainless steel, two nickel titanium wires, nitride-coated nickel titanium, epoxy-coated nickel titanium, and titanium were 400 mV, 300 mV, 750 mV, 300 mV, 1800 mV, and >2000 mV, respectively. SEM photographs revealed that some nickel titanium and stainless steel wires were susceptible to pitting and localized corrosion. The results indicate that corrosion occurred readily in stainless steel. Variability in breakdown potential of nickel titanium alloy wires differed across vendors' wires. The nitride coating did not affect the corrosion of the alloy, but epoxy coating decreased corrosion. Titanium wires and epoxy-coated nickel titanium wires exhibited the least corrosive potential. For patients allergic to nickel, the use of titanium or epoxy-coated wires during orthodontic treatment is recommended.     

Effects of chemical composition on the corrosion of dental alloys

The aim of this study was to determine the effect of the oral environment on the corrosion of dental alloys with different compositions, using electrochemical methods. The corrosion rates were obtained from the current-potential curves and electrochemical impedance spectroscopy (EIS). The effect of artificial saliva on the corrosion of dental alloys was dependent on alloy composition. Dissolution of the ions occurred in all tested dental alloys and the results were strongly dependent on the general alloy composition. Regarding the alloys containing nickel, the Ni-Cr and Ni-Cr-Ti alloys released 0.62 mg/L of Ni on average, while the Co-Cr dental alloy released ions between 0.01 and 0.03 mg/L of Co and Cr, respectively.The open-circuit potential stabilized at a higher level with lower deviation (standard deviation: Ni-Cr-6Ti = 32 mV/SCE and Co-Cr = 54 mV/SCE). The potenciodynamic curves of the dental alloys showed that the Ni-based dental alloy with >70 wt% of Ni had a similar curve and the Co-Cr dental alloy showed a low current density and hence a high resistance to corrosion compared with the Ni-based dental alloys. Some changes in microstructure were observed and this fact influenced the corrosion behavior for the alloys. The lower corrosion resistance also led to greater release of nickel ions to the medium. The quantity of Co ions released from the Co-Cr-Mo alloy was relatively small in the solutions. In addition, the quantity of Cr ions released into the artificial saliva from the Co-Cr alloy was lower than Cr release from the Ni-based dental alloys.     

Long-term corrosion studies in vitro of gold, cobalt-chromium, and nickel-chromium alloys in contact

Specimens of various types of dental casting alloys were stored in phosphate-buffered 0.9% NaCl solution for 35 weeks. Every 7 weeks the solutions were changed and analyzed with regard to elements released from the alloys. The release of Cu from type III gold alloy increased in contact with gold alloys for metallo-ceramic use in a 1:2 area relation. However, when the area relation was reversed, no difference in the amounts of elements released was observed. Crevice corrosion was initiated with one of the Co-Cr alloys in contact with type III gold alloy. The crevice corrosion increased the amounts of Co and Cr released into the solutions. The release of Ni and Cr from the Ni-Cr alloys was prominent. These alloys were very susceptible to crevice corrosion. With one of the Ni-Cr alloys the release of elements increased in contact with type III gold alloy.     

Ion release from orthodontic appliances.

OBJECTIVE: The microbiological and enzymatic characteristics of the oral cavity would seem to provide a suitable environment for the corrosion of metals. We assayed the release of metal ions from one orthodontic appliance which included two 304 and 316 steel molar bands, ten 316 steel brackets, one nickel-titanium archwire and a brazing alloy to connect the elements of molar bands and brackets. METHODS: The orthodontic appliance was dipped in both inorganic (pH 3.5-6.5) and organic acid solutions (w/v 1% each of tartaric, citric and ascorbic acid at pH 2.2 or 1.5% each of lactic and acetic acid at pH 2.5). The release of nickel (Ni), chromium (Cr), copper (Cu), silver (Ag) and palladium (Pd) was determined using an atomic absorption spectrophotometer Varian AA 10. RESULTS: The release of Ni, Cr and Cu was markedly less at pH 6.5 than at pH 3.5 at all time points in acid solution. Daily release/single appliance after the first day decreased. Contrary to expectations, appliances immersed in organic acid solutions at pH 2.2 or 2.5 after 28 days generally released an amount of ions similar to that observed in inorganic acid solution at pH 3.5, with the exception of Cu. Release of silver and palladium, two metals present in the brazing alloy, proved to be very low (approximately 0.2 microgram after 28 days). CONCLUSIONS: The daily release of Ni, Cu and Cr by an orthodontic appliance in acid pH, particularly favourable to corrosion, was well below that ingested with a normal daily diet. It is therefore concluded that the quantities of metal ions released in our experimental conditions should not be cause for concern in utilising the appliance.     

Galvanic corrosion between orthodontic wires and brackets in fluoride mouthwashes

The aim of this investigation was to determine the influence of fluoride in certain mouthwashes on the risk of corrosion through galvanic coupling of orthodontic wires and brackets. Two titanium alloy wires, nickel-titanium (NiTi) and copper-nickel-titanium (CuNiTi), and the three most commonly used brackets, titanium (Ti), iron-chromium-nickel (FeCrNi) and cobalt-chromium (CoCr), were tested in a reference solution of Fusayama-Meyer artificial saliva and in two commercially available fluoride (250 ppm) mouthwashes, Elmex and Meridol. Corrosion resistance was assessed by inductively coupled plasma-atomic emission spectrometry (ICP-MS), analysis of released metal ions, and a scanning electron microscope (SEM) study of the metal surfaces after immersion of different wire-bracket pairs in the test solutions. The study was completed by an electrochemical analysis. Meridol mouthwash, which contains stannous fluoride, was the solution in which the NiTi wires coupled with the different brackets showed the highest corrosion risk, while in Elmex mouthwash, which contains sodium fluoride, the CuNiTi wires presented the highest corrosion risk. Such corrosion has two consequences: deterioration in mechanical performance of the wire-bracket system, which would negatively affect the final aesthetic result, and the risk of local allergic reactions caused by released Ni ions. The results suggest that mouthwashes should be prescribed according to the orthodontic materials used. A new type of mouthwash for use during orthodontic therapy could be an interesting development in this field.     

Structure and mechanical properties of as-received and heat-treated stainless steel orthodontic wires

A combination of x-ray diffraction analysis with mechanical testing in tension and bending has been used to investigate the metallurgical structures and mechanical properties for as-received and heat-treated stainless steel orthodontic wires. Two different proprietary wire types were selected, having a wide range in cross-sectional dimensions: 0.016-, 0.030-, and 0.050- or 0.051-inch diameters, and 0.017 X 0.025-inch rectangular specimens. Heat treatments were performed for 10 minutes in air at temperatures of 700 degrees, 900 degrees, and 1100 degrees F. The x-ray diffraction patterns showed that the as-received 0.016-inch diameter and 0.017 X 0.025-inch wires of both proprietary types consisted of a two-phase structure containing a martensitic phase along with the austenitic phase. This duplex structure was converted entirely to austenite with heat treatment for one wire type, but persisted after heat treatment for the other wire type. The largest diameter, 0.050- or 0.051-inch, wires of both types were single-phase austenitic structure for both the as-received and heat-treated conditions. Evidence of substantial preferred crystallographic orientation or texturing in these orthodontic wires was also found by x-ray diffraction. As in our previous studies, the modulus of elasticity in bending was significantly less than the value obtained in tension for only the smaller cross-sectional wires. The 0.05 radian flexural yield strength correlated more closely with the 0.2% offset yield strength in tension than with the yield strength for 0.05% and 0.1% permanent offsets.     

Nickel content of as-received and retrieved NiTi and stainless steel archwires: assessing the nickel release hypothesis

This study assesses the nickel content of as-received and retrieved stainless steel and NiTi archwires alloys. New and used brand-matched, composition-matched, and cross section-matched archwires were subjected to scanning electron microscopy and energy-dispersive electron probe microanalysis. Elemental analysis was performed on three randomly selected areas, and the nickel content, expressed as ratios of Ni/Ti (in NiTi wires) or Ni/Fe (in stainless steel), was statistically analyzed with a t-test (alpha = .05). No changes were detected with respect to Ni content ratios between as-received and retrieved NiTi or stainless steel wires, suggesting an absence of nickel release. Wear and delamination phenomena on the wire surface and the formation of galvanic couple between the stainless steel wires and bracket brazing materials intraorally may modify the corrosion susceptibility of the wire alloys in clinical conditions.     

An investigation into the effects of polishing on surface hardness and corrosion of orthodontic archwires.

The purpose of this study was to investigate the effect of surface roughness on the relative corrosion rates of wires of four alloys-stainless steel, nickel titanium, cobalt chromium, and beta titanium. Batches of wire were divided into two groups. Wires in one group were industrially polished to provide a uniform surface finish; wires in the other group were left for comparison "as received." Wire diameter, hardness, and relative corrosion rates were compared within groups before and after polishing. Comparisons were also made across the four groups of alloys. The samples of as-received wires showed variations in surface finish, with beta titanium having the roughest appearance and cobalt chromium the smoothest. Nickel titanium and stainless steel surfaces were similar. Polishing provided a more uniform finish, but significantly reduced the diameter of the wires. Microhardness testing of wire surfaces of each alloy indicated that no significant work-hardening occurred as a result of polishing. The relative corrosion rates (expressed in terms of corrosion current density) in a 0.9% sodium chloride solution were estimated using the electrochemical technique of polarization resistance. Nickel titanium wires exhibited the greatest corrosion current density in the as-received state. Polishing significantly reduced the corrosion rate of nickel titanium, such that comparison between the four alloys in the polished state revealed no significant difference in their relative corrosion rate/corrosion current density.     

Beta-钛与镍钛、不锈钢正畸弓丝合金成分、表面形貌以及力学性能的对比研究

目的:比较Beta-钛丝与正畸临床常用的超弹性镍钛丝及不锈钢丝的合金成分、表面形貌以及力学性能,为临床应用提供参考。方法:选取Beta-钛丝、超弹性镍钛丝及不锈钢丝,弓丝尺寸均为0.43 mm×0.64 mm。选用EDAX X-射线能谱分析仪联合SUPRATM55热场发射扫描电子显微镜分析弓丝的合金成分,观察其表面形貌。使用Nano Indenter XP纳米压痕测试机测定弓丝弹性模量及硬度,使用Instron 5848微力材料试验机,三点弯曲测定弓丝的负荷-形变曲线。结果:Beta-钛丝合金成分中含有Ti、Zr、Mo、Sn 4种元素,不锈钢丝含有Fe、Mn、Cr、Si,超弹性镍钛丝含有Ni、Ti 2种元素。不锈钢丝表面比Beta-钛丝及镍钛丝光滑。Beta-钛丝的弹性模量及硬度明显小于不锈钢丝,略大于超弹性镍钛丝。当形变3 mm的负荷完全去除时,Beta-钛丝及不锈钢丝均有残余形变,超弹性镍钛丝形变完全恢复。结论:Beta-钛丝、超弹性镍钛丝及不锈钢丝依据其性能适用于正畸治疗的不同阶段。     

Tissue reactions to implanted orthodontic wires in rabbits

Tissue response to a Fe-Cr-Ni and a Co-Cr-Ni orthodontic wire, in the as-received state and with silver soldered joints, was investigated. Specimens with polytetrafluoroethylene (PTFE) as a reference material were implanted in the subcutaneous tissue of rabbits. Six rabbits were sensitized to nickel, four animals were sham-sensitized, and two were left untreated. The results showed that the as-received wires gave no tissue response relative to the PTFE control. In soldered specimens that were moderate to extreme reactions adjacent to the soldered joint and around the wire portion as well. The soldered Co-Cr-Ni wire elicited the most severe reactions, most pronounced in the nickel-sensitized animals. The agar overlay cell culture test of some retrieved implants showed pronounced cytotoxicity of the soldered specimens. Leachable toxic components of the silver solder seemed to be of major importance in the observed cell culture and tissue response to the soldered specimens.     

Variation in corrosion resistance of nickel-titanium wires from different manufacturers

Nickel-titanium (NiTi) wires produced by various manufacturers may have different corrosion resistance in acidic oral environments. The purpose of this study was to investigate the variation during in vitro corrosion resistance of commercial NiTi dental orthodontic wires from different manufacturers using the fast electrochemical technique. The linear polarization test was used to evaluate the corrosion resistance, in terms of polarization resistance (Rp), of as-received commercial NiTi wires in acidic artificial saliva at 37 degrees C. One-way analysis of variance was used to analyze Rp with the wire manufacturer as the variable factor. Atomic force microscopy was used to analyze the three-dimensional surface topography and roughness (Ra). Electron spectroscopy for chemical analysis was used to identify the chemical structure of the passive film on the NiTi wires. The results showed that NiTi wires from different manufacturers had a statistically significant difference in Rp (P < .001). Different surface topography was present among the tested NiTi wires, whereas the same surface chemical structure was observed for the tested NiTi wires. The surface roughness of the commercial NiTi wires with similar surface chemical structure does not correspond with the difference in corrosion resistance.     

Surface changes induced by fluoride prophylactic agents on titanium-based orthodontic wires

This study investigated the effect of fluoride prophylactic agents on the surfaces of titanium-based orthodontic wires. Four types of titanium-based orthodontic wires (2 nickel-titanium alloy wires [nickel-titanium and copper-nickel-titanium] and 2 beta-titanium alloy wires [titanium-molybdenum and titanium-niobium], all from Ormco, Glendora, Calif) with similar sizes were prepared and immersed in 5 fluoride prophylactic agents (2 acidulated phosphate fluoride agents [Nupro APF (Dentsply International, York, Pa) and Florentine III (Confi-Dental, Louisville, Colo)], 1 neutral agent [Neupro Neutral (Dentsply International)] and 2 stannous fluoride agents [Florentine II (Confi-Dental) and Perio-Med (Omni International, Warrenton, Va)]) for 5 minutes, 1 hour, and 24 hours. After immersion, average surface roughness and color changes were evaluated. The surface changes were observed with a scanning electron microscope. The average surface roughness data were statistically analyzed by analysis of variance and Tukey post hoc test at a significance level of alpha = 0.05. There were no significant differences in average surface roughness value among fluoride solutions or orthodontic wires, except for the titanium-molybdenum wire, which showed significantly (P <.05) higher average surface roughness values after immersion in Nupro APF for 24 hours. The results suggested that a few applications of acidulated phosphate fluoride agents might change the surface color of the beta-titanium alloy wires, particularly the titanium-molybdenum wire, which contains a large amount (about 80%) of titanium.     

The super-elastic property of the Japanese NiTi alloy wire for use in orthodontics

A new Japanese nickel-titanium (NiTi) alloy wire was developed by the Furukawa Electric Co., Ltd. of Japan. This wire was subjected to uniaxial tensile testing and a specially designed three-point bending test to determine the wire stiffness, and to evaluate spring-back, shape memory, and super-elasticity. The Japanese NiTi wire exhibited an unusual property termed "super-elasticity," which no other orthodontic wire has shown. This phenomenon was researched thoroughly. The wire delivered a constant force over an extended portion of the deactivation range. Among all the wires compared, Japanese NiTi alloy wire was the least likely to undergo permanent deformation during activation. The new alloy exhibited a specific stress-strain curve unlike those of the other tested materials. Stress remained nearly constant despite the strain change within a specific range. This unique feature is the manifestation of so-called super-elasticity. Heat treatment enabled the load magnitude at which super-elasticity is reflected to be influenced and controlled by both temperature and time. A unique and useful process was also developed so that an arch wire delivering various magnitudes of force for a given activation could be fabricated from the wire of the same diameter. The clinical application of wires of this new alloy should be more likely to generate a physiologic tooth movement because of the relatively constant force delivered for a long period of time during the deactivation of the wire. Japanese NiTi alloy should be considered an important material addition to clinical orthodontic metallurgy.     

Effects of recasting on the amount of corrosion products released from two Ni-Cr base metal alloys

The corrosion products released from two recast Ni-Cr base metal alloys Wirolloy and Wiron 99 were investigated. Cast samples were placed in Meyer's modified Fusayama solution for 2 months and in 0.1M Lactic acid 0.1M NaCl solution for 7 days. The release of Ni, Cr and Mo ions from both alloys was measured by using a flame model Atomic Absorption Spectrophotometer. A Scanning Electron Microscope was used to evaluate the surface morphology of the samples before and after corrosion tests. Release of Ni and Cr from Wirolloy samples immersed in 0.1M Lactic acid 0.1M NaCl solution were much higher than those of Wiron 99. The number of recastings was found to have negligible effect on surface texture and on the amount of corrosion products released.