The effect of surface treatment and clinical use on friction in NiTi orthodontic wires.

OBJECTIVES: Since the low friction of NiTi wires allows a rapid and efficient orthodontic tooth movement, the aim of this research was to investigate the friction and surface roughness of different commercially available superelastic NiTi wires before and after clinical use. The surface of all of the wires had been pre-treated by the manufacturer. MATERIALS: Forty superelastic wires (Titanol Low Force, Titanol Low Force River Finish Gold, Neo Sentalloy, Neo Sentalloy Ionguard) of diameter 0.016 x 0.022 in. were tested. The friction for each type of NiTi archwire ligated into a commercial stainless steel bracket was determined with a universal testing machine. Having ligated the wire into the bracket, it could then be moved forward and backwards along a fixed archwire whilst a torquing moment was applied. The surface roughness was investigated using a profilometric measuring device on defined areas of the wire. Statistical data analysis was conducted by means of the Wilcoxon test. RESULTS: The results showed that initially, the surface treated wires demonstrated significantly (p < 0.01) less friction than the non-treated wires. The surface roughness showed no significant difference between the treated and the non-treated surfaces of the wires. All 40 wires however showed a significant increase in friction and surface roughness during clinical use. SIGNIFICANCE: Whilst the Titanol Low Force River Finish Gold (Forestadent, Pforzheim, Germany) wires showed the least friction of all the samples and consequently should be more conservative on anchorage, the increase in friction of all the surface treated wires during orthodontic treatment almost cancels out this initial effect on friction. It is therefore recommended that surface treated NiTi orthodontic archwires should only be used once.     

Force relaxation in orthodontic arch wires

Wire selection for use in an orthodontic appliance is usually based upon clinical impressions. This is unsatisfactory. A far better basis for selection would be measured values of the forces exerted by the arch wire, both initially on insertion of the appliance and their variation with time as a result of tooth movement and of stress relaxation in the wire. An apparatus has been designed to measure force relaxation in orthodontic arch wires shaped into a representative arch form. Measurements of the force relaxation have been made in stainless steel, Elgiloy, and nitinol wires at 21 degrees C and 37 degrees C. All the wires were found to relax at 21 degrees C, but no relaxation was observed in nitinol at 37 degrees C. The rates of relaxation were found to vary widely; stainless steel wires produced by Wilcock in Australia relaxed significantly less than Elgiloy wires. A heat treatment performed on green Elgiloy eliminated the relaxation altogether and had a significant but lesser effect on blue Elgiloy.     

Controlled localized buckling responses of orthodontic arch wires.

The orthodontic arch wire is often activated locally, in transverse bending and/or longitudinal torsion, to engage an individual malaligned tooth. Arch wires with substantial flexibilities and elastic ranges in bending are available. Several clinical reports of distal displacements of molars with appliances activated by locally buckling the arch wire have appeared in the recent published literature. This article contains an explanation of buckling or "column" action and the postbuckling response of a wire, and a report of the results of a controlled, in-vitro study of a sample of 256 wire segments subjected to activation-deactivation, buckling-postbuckling-unbuckling cycles. Continuous force-displacement diagrams were obtained from mechanical tests run at oral temperature. Four orthodontics-relevant, mechanical characteristics were quantified from each diagram, and each specimen was subjected to posttest evaluation for inelastic behavior. Although the deformation of the buckled wire is, in fact, bending, the force-displacement diagrams obtained differed substantially from their familiar counterparts generated in transverse bending. Judging from the force magnitudes induced as the deactivation half-cycles commenced as well as the deactivation rates, not all of the 8 wires seem to be clinically suitable for activation initiated by buckling. Magnitudes of springback were substantial from activations as large as 6 mm, and only 2 of the 8 wires exhibited full deactivations less than 80% of their activating displacements. This relatively new mode of arch wire activation that enables delivery to the dentition of mesiodistal pushing forces has substantial potential for clinical application from several biomechanical standpoints.     

Super-elasticity and thermal behavior of Ni-Ti alloy orthodontic arch wires.

Bending properties and thermal behavior of twenty commercial Ni-Ti alloy orthodontic arch wires were investigated quantitatively to characterize their suitability for clinical use. There was substantial difference among the load-deflection curves obtained by a three-point bending test. Some wires exhibited super-elasticity; load decreased little with decreasing deflection. Others showed good spring-back properties only; load was nearly proportional to deflection. Thermal behavior due to phase transformation of the alloy was examined by differential scanning calorimetry (DSC). Some of the wires did not have the correct transformation temperatures to exhibit super-elasticity at body temperature. Moreover, thermal behavior was closely related to super-elasticity. There were clear thermal peaks in the DSC curves of the super-elastic wires. However, wires without super-elasticity had no peak in the DSC curves.     

正畸方丝转矩力的分析

目的研究正畸方丝的转矩力。方法运用自行研制的转矩测量仪测量0.46 mm×0.63 mm、0.48 mm×0.63 mm不锈钢方丝和相同截面尺寸的镍钛方丝在单个0.56 mm槽沟的中切牙托槽内的转矩力矩与转矩角度;根据转矩力矩与转矩角度,使用SPSS 11.0软件制作散点图,拟合出4种弓丝的负荷形变曲线,并据此建立直线回归方程;根据方程得出弓丝的抗扭刚度及转矩力矩为20 N·mm时的转矩角度。结果以上4种弓丝抗扭刚度分别为4.909、6.417、1.325、1.363 N·mm/°,达到20 N·mm转矩力矩时的转矩角度分别为19.14°、15.33°、36.83°、35.07°。结论相同截面尺寸不锈钢方丝的抗扭刚度明显大于镍钛方丝;两种截面尺寸镍钛方丝的抗扭刚度相差很小,而不锈钢方丝则相差较大。     

On the use of nomograms to determine the elastic property ratios of orthodontic arch wires

With an 0.012 inch stainless steel arch wire as the base line, a series of calculating charts which express the strength, stiffness, and range ratios of orthodontic arch wires is introduced. In each case, both the bending and the torsional stress states are computed over a broad range of wire sizes. Three distinct situations are addressed: the over-all spectrum of elastic property ratios among stainless steel, nickel-titanium, and beta titanium wires; the intra- and interproperty relationships of these wire compositions; and the role which elastic property ratios play in the selection of the right arch wire. Via these nomograms, clinicians will have another means available by which the plethora of wire compositions and cross sections may be assessed.     

Elastic energy/stiffness ratios for selected orthodontic wires

This investigation determined the ratio of the energy available for orthodontic tooth movement to the stiffness and flexibility of a given wire. Twenty-five specimens each of five brands of orthodontic wire were tested in tension in the as-received condition. Force versus elongation diagrams were obtained and then converted into stress-strain data. Mean values were determined for the yield strength and yield strain for each brand of wire. The modulus of elasticity (E), modulus of resilience (R), and elastic compliance (C) were then calculated. Two ratios were established by using the three mechanical properties: (1) the modulus of resilience/modulus of elasticity (R/E) ratio and (2) the modulus of resilience/elastic compliance (R/C) ratio. The results confirmed that the use of these two ratios in combination permitted one to differentiate among the various types of orthodontic wires, with respect to stored energy and its relationship to the stiffness or flexibility of the wire. (AM J ORTHOD DENTOFAC ORTHOP 1994;106:588-96.)     

Mechanical properties and clinical applications of orthodontic wires

This review article describes the mechanical properties and clinical applications of stainless steel, cobalt-chromium, nickel-titanium, beta-titanium, and multistranded wires. The consolidation of this literature will provide the clinician with the basic working knowledge on orthodontic wire characteristics and usage. Mechanical properties of these wires are generally assessed by tensile, bending, and torsional tests. Although wire characteristics determined by these tests do not necessarily reflect the behavior of the wires under clinical conditions, they provide a basis for comparison of these wires. The characteristics desirable in an orthodontic wire are a large springback, low stiffness, good formability, high stored energy, biocompatibility and environmental stability, low surface friction, and the capability to be welded or soldered to auxiliaries. Stainless steel wires have remained popular since their introduction to orthodontics because of their formability, biocompatibility and environmental stability, stiffness, resilience, and low cost. Cobalt-chromium (Co-Cr) wires can be manipulated in a softened state and then subjected to heat treatment. Heat treatment of Co-Cr wires results in a wire with properties similar to those of stainless steel. Nitinol wires have a good springback and low stiffness. This alloy, however, has poor formability and joinability. Beta-titanium wires provide a combination of adequate springback, average stiffness, good formability, and can be welded to auxiliaries. Multistranded wires have a high springback and low stiffness when compared with solid stainless steel wires. Optimal use of these orthodontic wires can be made by carefully selecting the appropriate wire type and size to meet the demands of a particular clinical situation.     

口腔正畸托槽与弓丝之间最大静摩擦力与静摩擦系数的实验研究

目的 设计一种体外装置,研究正畸托槽与弓丝之间的最大静摩擦和静摩擦系数.方法 实验选择了一种方丝托槽与两种直径0.4 mm的正畸钢丝,设计实验装置在干燥和有唾液条件下测量托槽与弓丝之间在不同正压力下的最大静摩擦力和静摩擦系数.结果 研究发现,在干燥条件下,国产弓丝与托槽之间产生的最大静摩擦力和静摩擦系数显著大于3 M弓丝,在有唾液时两者无显著区别.结论 不同条件下,弓丝与托槽之间产生的静摩擦力与静摩擦系数不同.     

A comparative study of frictional forces between orthodontic brackets and arch wires

An in vitro study of simulated canine retraction was undertaken to evaluate the difference in frictional resistance between stainless steel arch wires and steel and ceramic brackets with elastomeric, steel, and self-ligation. Each bracket slot was 0.018 x 0.025 inch. The arch wires used were 0.014-inch, 0.016-inch, 0.018-inch, 0.016 x 0.016-inch, and 0.016 x 0.22-inch stainless steel. A testing apparatus was designed to attempt to simulate the clinical situation in which teeth tip slightly while they slide along the arch wire. Under these testing conditions, the self-ligating steel bracket did not demonstrate less friction than the elastic or steel-ligated stainless steel brackets. For most wire sizes, elastomer-ligated ceramic brackets demonstrated the greatest friction when compared with other bracket/ligation technique combinations. The clinical significance of this study becomes apparent when stainless steel brackets are used on the posterior teeth and ceramic brackets are used on the anterior teeth. If sliding mechanics are used, the anterior teeth may be more resistant to movement than the posterior teeth because of the greater friction of the ceramic brackets. This could result in more posterior anchorage loss than would be expected if only one type of bracket were used.     

Influence of autoclave sterilization on the surface parameters and mechanical properties of six orthodontic wires

Orthodontic wires are frequently packaged in individual sealed bags in order to avoid cross-contamination. The instructions on the wrapper generally advise autoclave sterilization of the package and its contents if additional protection is desired. However, sterilization can modify the surface parameters and the mechanical properties of many types of material.The aim of this research was to determine the influence of one of the most widely used sterilization processes, autoclaving (18 minutes at 134 degrees C, as recommended by the French Ministry of Health), on the surface parameters and mechanical properties of six wires currently used in orthodontics (one stainless steel alloy: Tru-Chrome RMO; two nickel-titanium shape memory alloys: Neo Sentalloy and Neo Sentalloy with Ionguard GAC; and three titanium-molybdenum alloys: TMA(R) and Low Friction TMA Ormco and Resolve GAC).The alloys were analysed on receipt and after sterilization, using surface structure observation techniques, including optical, scanning electron and atomic force microscopy and profilometry. The mechanical properties were assessed by three-point bending tests.The results showed that autoclave sterilization had no adverse effects on the surface parameters or on the selected mechanical properties. This supports the possibility for practitioners to systematically sterilize wires before placing them in the oral environment.     

Effects of sterilization on the mechanical properties and the surface topography of nickel-titanium arch wires

The effects of sterilization on the mechanical properties and the surface topography were determined on 0.017 x 0.025-inch Nitinol and Titanal arch wires. Three approved heat sterilization methods were used: dry heat, formaldehyde-alcohol vapor, and steam autoclave. Elastic moduli were obtained on 1-inch segments in 3-point bending. Laser scans of flatwise wire surfaces were conducted to detect surface alterations--whether they were caused by tarnish, corrosion, or pitting. Tensile properties were determined on 7-inch lengths: the 0.1% yield strength, the ultimate tensile strength, and the percent elongation at break. Within the confines of the present sterilization experiments, no detrimental changes were observed for either the selected mechanical properties or the surface topography. When the mean values of the two products were compared, Nitinol was less compliant but stronger than Titanal. Laser spectroscopy showed that Titanal possessed at least three times more specular reflectivity than Nitinol.     

直流电热处理改变镍钛合金唇弓宽度的研究

目的评价直流电热处理方法对镍钛合金丝唇弓宽度的影响。方法选取8种镍钛方丝（0.016×0.022″）,采用加热仪分别对弓丝进行1s、1.5s、2s、2.5s的直流电热处理,加热后分别测量弓丝末端宽度变化,然后用SPSS10.0统计软件进行单因素方差分析。结果所有镍钛合金丝在加热1s后,唇弓宽度无显著变化,加热1.5s以后,唇弓宽度发生显著性改变,加热2s后,唇弓宽度变化最显著。结论镍钛合金丝的形状可以通过直流电热处理重新定型,临床可通过该方法调节镍钛合金丝的形态并弯制各种曲,但在热处理过程中,应注意电流大小的选择及加热时间的控制。     

Load-deflection characteristics of nickel-titanium alloy wires after clinical recycling and dry heat sterilization.

The desirable mechanical properties of nickel-titanium alloy wires and their relatively high cost has prompted many clinicians to recycle these wires. Clinical recycling exposes the wires to several weeks or months of mechanical stresses and elements of the oral environment, as well as sterilization between uses. In a previous study it was noted that clinical recycling combined with cold sterilization alters the load-deflection characteristics and surface topography of nickel-titanium wires. Whether similar changes in mechanical properties occur in wires subjected to repeated clinical use and dry heat sterilization is not yet clear. The purpose of this investigation was to determine the effects of in vivo recycling interposed by dry heat sterilization (together referred to as clinical recycling, CR) on the load-deflection characteristics of nickel-titanium alloy wires. To differentiate the effects of dry heat sterilization (DHS) from those of CR on the behavior of these wires, a series of wires were also subjected to DHS only. Two types of nickel-titanium wires, namely Nitinol and NiTi were subjected to a three-point bending test in an as-received condition (T0), after one cycle (T1), and two cycles (T2) of DHS or CR. Ten wires comprised each subsample. Statistical analyses were done by one-factor repeated measures analysis of variance and Scheffe F test. Both DHS alone, as well as CR, produced significant changes in the loading and unloading characteristics of Nitinol and NiTi wires. However, the changes in the load-deflection characteristics of these wires after DHS only were relatively small, and the clinical significance of these changes is open to question.(ABSTRACT TRUNCATED AT 250 WORDS)