Nickel-titanium Wires Research Articles

Mechanical properties of several nickel-titanium alloy wires in three-point bending tests

The purpose of this study was to clarify the mechanical properties of 42 brands of nickel-titanium alloy orthodontic wires from 9 manufacturers by conducting three-point bending tests under uniform testing conditions. Manufacturers included A-Company, Hoya Medical, Lancer, Ormco, Rocky Mountain, Sankin, Tomy (GAC), TP, and 3M/Unitek. Cobalt-chrome, and titanium-molybdenum alloy wires were also tested as a reference for comparison of force levels. All reported data were recorded during the unloading process to simulate the force that a wire exerts on a tooth as it is moved into the dental arch from a position of malocclusion. The following results were obtained for the nickel-titanium wires tested. (1) Among the 0.016 inch round wires tested under a maximum deflection of 1.5 mm, the difference between the smallest (Copper nickel-titanium 35) and the largest (Aline) load values was 136 g. For the 0.016 × 0.022 inch rectangular wires tested, the difference between the smallest (Copper nickel-titanium 40) and the largest (Aline) load values was 337 g. (2) The change in load between 1.5 and 0.5 mm of deflection was examined to clarify the superelastic properties of the wires tested. For the 0.016 inch wires, 17 wire brands produced a load difference of less than 100 g, and two brands produced a difference of at least 100 g (Aline and Titanal = 100 g). For the 0.016 × 0.022 inch wires, 15 brands produced a load difference of less than 100 g, and eight brands produced a difference of over 100 g. The smallest and largest load differences were 3 g (Copper nickel-titanium 35) and 200 g (Aline). (3) The majority of the samples with a smaller load difference between deflections of 1.5 mm and 0.5 mm in the unloading process were found among super-elastic wires, while samples with a larger load difference were predominantly found among work-hardened wires. Compared with cobalt-chrome and TMA wires, nickel-titanium alloy wires exert significantly less force. However, the amount of force varies greatly from brand to brand. Consequently, when using nickel-titanium alloy wires, brands must be selected carefully by taking into consideration the severity of the malocclusion and the stage of orthodontic treatment in each case. It is the intent of this study to offer clinicians an unbiased guide for the selection of appropriate nickel-titanium alloy wires. (Am J Orthod Dentofacial Orthop 1999;115:390-5)

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.

Influence of angulation on the resistance to sliding in fixed appliances

The resistances to sliding were studied as a function of five angulations (0°, 3°, 7°, 11°, and 13°) using nine different couples made of stainless steel, single crystal sapphire, or polycrystalline alumina brackets against stainless steel, nickel titanium, or beta-titanium arch wires. After 22 mil brackets were mounted to fixtures and 21 × 25 mil arch wires were ligated with 10 mil stainless steel ligatures, the arch wires were slid through the brackets at 1 cm/minute in the dry state at 34°C. The resistance to sliding was measured by one computer while five normal forces (nominally 0.2, 0.4, 0.6, 0.8, and 1.0 kg) were serially maintained by another computer. A second couple was prepared for each material combination with five normal forces that were each 0.1 kg less. Statistical fits of linear regressions were such that p < .001 for most tests. When couples were in the passive configuration at low angulations, all stainless steel wire-bracket couples once again had the least resistance to sliding. When the angulation exceeded about 3°, however, the active configuration emerged and binding quickly dominated as the resistance to sliding increased over 100-fold. Under these conditions, the relative rankings among the materials transposed; couples of stainless steel had the most resistance to sliding, whereas, couples of the more compliant alloys, such as nickel titanium wire, had the least. Results suggested that the active configuration and subsequent binding emerged when no bracket clearance remained. This binding component increased in importance with angulation and was additive to the frictional component, that is, they followed the principle of superposition. (Am J Orthod Dentofacial Orthop 1999;115:39-51)

Evaluation of titanium brackets for orthodontic treatment: Part I. The passive configuration

The static and kinetic frictional coefficients of commercially pure titanium brackets were evaluated in the passive configuration in the dry and wet states against stainless steel, nickel-titanium, and beta-titanium archwires. For comparison, stainless steel brackets were evaluated under identical conditions. Titanium brackets were grayer in color and rougher in texture than the stainless steel brackets. Bracket slots were up to 0.002 inch greater than the nominally stated values. Remarkably, the static and kinetic frictional coefficients of the couples formed by titanium and stainless steel brackets were comparable. When evaluated against stainless steel and nickel-titanium archwires in the dry state at 34°C, the static coefficient averaged .12 and .20, respectively, independent of bracket alloy. When evaluated against stainless steel and nickel-titanium wires in the wet state at 34°C using human saliva, the static coefficient averaged .15 and .20, respectively, independent of bracket alloy. Only the beta-titanium archwires increased by about 15%, when tested in either the dry or the wet state against titanium versus stainless steel brackets. Noteworthy, too, was the decrease of both coefficients in the beta-titanium wire couples from their previously reported values. Analyses of electron spectroscopy for chemical analysis spectra and depth profiles show that these new brackets are titanium only in the bulk. Indeed the immediate surfaces are composed of, at least, 80 atomic percent (at.%) carbon and oxygen; whereas, the titanium that is present (>11 at .%) is mostly in the form of titanium dioxide. The presence of this quite thin passivating layer, which resides on top of an oxygen-hardened titanium substrate, reduces the galling and fretting that would normally be expected in such materials. Pending the outcome of future angulation tests, these frictional measurements show that titanium brackets are not only comparable to stainless steel brackets but also are more biocompatible with nickel having been eliminated from their constitution.(Am J Orthod Dentofacial Orthop 1998;114:558-72)

Short-term temperature changes influence the force exerted by superelastic nickel-titanium archwires activated in orthodontic bending

Background : Alterations in mouth temperature may lead to changes in the force exerted by an activated superelastic wire. It has been assumed that variations in archwire stiffness associated with short-term cooling or heating are transient. This investigation studied the effect of short-term cooling or heating on the bending force exerted by nickel-titanium archwire. Material and methods : Six rectangular superelastic wires and one conventional nickel-titanium wire were tested in bending at 37 o C. The test specimens were deflected 0.5 mm, and the bending force was measured continually. The activated specimens were subjected to cold (10 o C) or hot (80 o C) water under constant deflection, simulating an inserted archwire that is subjected to cold or hot drinks or food during a meal. Results : The conventional nickel-titanium wire was marginally affected by brief cooling or heating. In contrast, some of the superelastic wires were strongly affected by short-time application of cold or hot water. Whereas the effect of brief heating disappeared quickly, some wires continued to exert sub-baseline bending forces (up to 32% less) after short-time application of cold water and showed little or no tendencies toward increase even after 30 minutes of postexposure restitution (up to 43% less). Conclusions : Short-term exposures to hot liquid increased the bending force exerted for a given deflection transiently. The effect of short-term exposures to cold liquid was not always transient; the bending force remained sub-baseline for a number of the thermosensitive wires tested for a prolonged time.(Am J Orthod Dentofacial Orthop 1998;114:503-9)

Transluminal endovascular branched graft placement for a pseudoaneurysm: Reconstruction of the descending thoracic aorta including the celiac axis

We I have previously reported a successful transluminal endovascular placement of a branched graft that had a sidearm extending into the left subclavian artery for repair of type B aortic dissection. The sidearm was properly positioned by catching and pulling back the free end of a detachable wire attached to its end by means of a gooseneck snare wire, which was percutaneously inserted through the left brachial artery. However, it is impossible to place sidearm grafts into the celiac axis and renal arteries in a similar manner. In this article, we describe a new method of inserting a sidearm into the celiac axis and report successful transluminal endovascular repair of a pseudoaneurysm with the use of the branched graft. A 73-year-old man with severe chronic renal failure requiring hemodialysis had previously undergone surgical repair of an aneurysm of the descending thoracic aorta. However, a pseudoaneurysm of the descending thoracic aorta resulting from dehiscence of the suture line at the proximal and distal anastomoses after composite graft surgery had continued to dilate, reaching 80 mm in diameter. Although surgical treatment was attempted, the effort was given up because of marked adhesions caused by a previous thoracotomy. He was admitted to our hospital for endovascular treatment of the pseudoaneurysm. The structure of the Inoue endovascular graft was previously described in detail. 2 The graft was constructed from a Dacron polyester fabric cylinder and the surface was supported by multiple rings of extra-flexible nickel titanium wire. The patient gave informed consent in conformance with the protocols approved by the institutional review board of Takeda Hospital. Endovascular grafting with the straight graft was performed on June 28, 1995. Although the proximal communication was completely obliterated after the procedure, the distal communication persisted because the distal orifice of the pseudoaneurysm was in close proximity to the celiac axis. Although transluminal embolization was

Distal end cutters--efficiency, safety and design.

This investigation aimed to evaluate the efficiency of a range of different distal end cutters in cutting and holding the ends of orthodontic arch wires. Fourteen different types of distal end cutter were used to cut a range of orthodontic arch wires under standard conditions. The arch wires comprised nickel-titanium and stainless steel wires of different dimensions, as well as twist flex and coaxial wires. The number of times each wire was successfully cut and held by each cutter was recorded. Significant differences in performance between the cutters were noted, particularly in holding the cut distal ends. Small diameter nickel-titanium wires were significantly less well held than heavier grade or stainless steel wires. Twist flex and coaxial wires were less easily cut cleanly than nickel-titanium and plain stainless steel wires.

The Effects of Cross-infection Control Procedures on the Tensile and Flextural Properties of Superelastic Nickel-titanium Wires

The development of superelastic nickel-titanium archwires has simplified the alignment phase of orthodontic treatment by permitting the use of highly flexible, resilient archwires and avoiding the need for complex loops. The majority of these archwires appear undistorted when removed from the mouth after use. This feature, coupled with the disadvantage of relatively high cost has led to sterilization and recycling of these wires by some clinicians. This study was designed to examine the effects of currently used infection control procedures on the mechanical properties of superelastic nickel-titanium alloy (SENTA) archwires. One-hundred-and-forty lengths of a SENTA wire were subjected to various sterilization and disinfection procedures. These included cold disinfection in 2 per cent glutaraldehyde solution for 3- and 24-hour cycles, and steam autoclaving. Single and double cycles were used. The properties investigated were the 0.1 per cent yield strength, the ultimate tensile strength, and the flexural rigidity. No statistically significant differences were found between the groups or against an untreated control.

Multiflex versus superelastic: A randomized clinical trial of the tooth alignment ability of initial arch wires

Two arch wires commonly used for initial tooth alignment were compared with regard to their clinical effectiveness. The two arch wires tested were 0.0155-inch diameter multiple-stranded stainless steel wire (Dentaflex, Dentaurium, Optident, Yorkshire, England) and 0.014-inch diameter nickel-titanium alloy wire (NiTi, ORMCO Co., Monrovia, Calif.). Consecutive patients attending an orthodontic clinic for routine placement of a fixed appliance were randomly assigned one of these two initial arch wires. Good quality alginate impressions of the appropriate dental arch were taken before arch wire placement and also at the subsequent appointment, which was, on average, 6 weeks later. Seventy-four arches were used in this study. The degree of tooth alignment achieved for each wire type was compared with a Reflex Microscope (Reflex Measurement Ltd., Butleigh, England) to make detailed measurements on the resultant casts. The degree of initial alignment achieved with the two wires was similar over this 6-week period. However, some differences were found for the lower labial segment where the interbracket span is usually reduced and where the superelastic nickel-titanium wire was found to give improved alignment. No threshold of crowding was found where one arch wire performed better than the other. (A M J O RTHOD D ENTOFAC O RTHOP 1995;108:464-71.)

Surface structure and roughness of Nickel-Titanium wires.

Nickel-Titanium wires not only show the well known shape memory effect, but also pseudoelastic behaviour. This means, as the material is bent in a wide range of tension, the stress in the material stays constant. This special behaviour allows the improvement of orthodontic devices. The investigation of wires for this application reveals great differences in the surface roughness of the wires from various suppliers. The roughness causes a loss of spring energy for the orthodontic wire by frictional effects. The investigation of the mechanical behaviour of these materials leeds to differences compared with the ideal behaviour expected for the stress/strain curve. Obviously these differences are caused by surface effects of the wires. To evaluate these questions intensive roughness measurements with profilometry, laser spectroscopy and scanning force microscopy have been performed. Further more defined bending and tensile experiments have been carried out and corresponding roughness and structure analysis with the scanning force microscope has been taken into account. By etching the wires significant surface effects could be found.

The Effects of Archwire Forces on Incisor Intrusion

The forces exerted by archwires were measured in association with both Begg and Straight-Wire attachments. Seven stainless steel and three nickel-titanium wires were tested at vertical deflections equivalent to 20, 30, and 40 degrees, these being incorporated via anchor bends or reverse curve of Spee as appropriate to each system. All seven brands of stainless steel arches demonstrated similar performance. An increase in archwire diameter from 0.016 to 0.018 inch increased intrusive forces by 64 per cent for stainless steel and 58 per cent for nickel-titanium. Increasing anchor bend or reverse curve of Spee produced considerable force increases across the range of specimens. Begg archforms produced more force than Straight-Wire archforms of similar deflection when attached to molars only. Attachment of archwires to second premolars in addition to molars reduced the intrusive forces produced by Begg arches, but increased the forces of Straight-Wire arches.

Development of a NiTi Anterior Cruciate Ligament Prosthesis

For the devolpment of a Shape Memory Alloy (SMA) ligament prosthesis model, it is necessary to overcome the problem of the fatigue life under mechanical loading of nickel titanium wires. The degradation of the superelastic parameters as a function of the cyclic strain was evaluated and the number of cycles to failure under controlled strain was established. On the basis of these results, an orientation in the design of the SMA ligament prosthesis can be proposed

Surface structure and roughness of Nickel-Titanium wires

Surface structure and roughness of Nickel-Titanium wires

A comparison study of thermodynamic nickel-titanium arch wires and Chinese NiTi

A comparison study of thermodynamic nickel-titanium arch wires and Chinese NiTi

The characteristics of super-elastic Ni-Ti wires in three-point bending. Part II: intra-batch variation

Intra-batch variation in the load-deflection characteristics of 13 superalloy nickel-titanium wires has been examined at nominal mouth temperature (35 degrees C). The results indicate that although most of the superalloy nickel-titanium wires were undersized, the variation in diameter within a batch was of the same order as that reported for 18/8 stainless steel wire. The largest coefficients of variation for the intra-batch variation for the initial slope and the unloading plateau values were found to be approximately 7.5 and 10 per cent, respectively. A high degree of correlation was found between the mean slopes of the initial load-deflection curve in three-point bending at 35 degrees C and the mean wire diameter raised to the fourth power for the 13 superalloys wires, from which a value for Young's modulus (E) of 55.4 GPa was deduced on the basis that at this temperature the wires will have an austenitic structure and virtually identical compositions.

A study of forces originating from orthodontic appliances for splinting of teeth.

Management of dental trauma in children sometimes requires the use of a dental splint. This can be constructed with composite materials, kevlar, fiberglass, wire and composite or orthodontic wires and brackets. However, there have been no studies of the control of dental movement when orthodontic materials are used for a dental splint. The purpose of this study was to determine the forces exerted by an orthodontic appliance used as a dental splint. To measure such forces, a transducer with a detection of 0.01 N (+/- 5%) was inserted into a maxillary dental arch model. The results showed that the orthodontic wire was rarely passive and the forces developed ranged from 0 to 27 x 10(-2) N. The force developed was independent of the length of the dental splint (p < 0.05) and wire size (p < 0.05). The mean force developed by nickel-titanium wires (14.27 x 10(-2) N) was significantly greater (p < 0.05) than the mean force developed by stainless steel and cobalt-chromium wires. Moreover, the mean force developed by rectangular wires (12.07 x 10(-2) N) was significantly greater (p < 0.05) than the mean force developed by square and round wires. The results suggested that stainless steel or cobalt-chromium, square or round wires should be used for construction of a dental splint.

Reflections on my involvement in orthodontic research

Some years ago, Professor Takihashi, who was then the greatest living professor of orthodontics in Japan, called on us in Ann Arbor just before his retirement. I asked Dr. Takihashi who would replace him? and he replied, "There's a young man who will do better than I because he will be able to take Japanese orthodontics to the world and bring the world's orthodontics to Japan." That young man was Fujio Miura. Fujio Miura has, in the years since Takihashi spoke to me, written one of the most amazing records in the history of our specialty. His research is as far ranging as anyone's. For example, in biology he has written well on the ethnology of Japanese craniofacial morphology and that of the aborigines in Japan. He has written on developmental biology and on the tissue reaction of tooth movements. In metallurgy he has contrived alloys that have revolutionized our appliances, for he was a pioneer in the use of nickel-titanium wires. Fujio Miura invented direct bonding. Professor Miura has fulfilled Professor Takihashi's predictions well for he has become the most famous orthodontic professor in Japan's history. It is interesting to see that his students occupy most of the chairs of orthodontics in Japan and many elsewhere. Miura is an accomplished artist who has exhibited his work. This personable scholar probably attends more meetings of the American Association of Orthodontists Society than most American members, and he is equally at home in the European society, and many other orthodontic groups in the world.

The effects of sterilization on the tensile strength of orthodontic wires.

The purpose of this study was to evaluate the effect of sterilization on the tensile strength of 0.016" beta-titanium, nickel titanium and stainless steel wires. Three common methods of sterilization--autoclaving, dry heat and ethylene oxide--were evaluated in three test trials involving zero, one and five sterilization cycles. For each of the test trials, five pieces each of 0.016" TMA, 0.016" Sentalloy and 0.016" Tru-chrome stainless steel wires were sterilized using a standard autoclave. Five other pieces of each of the same wires were sterilized in a dryclave, while an additional five pieces of each of the three wire types were sterilized using ethylene oxide. The ultimate tensile strengths of the wires were then determined using an Instron Universal Testing Machine. The data were compared for statistical differences using analysis of variance. The results showed that dry heat sterilization significantly increased the tensile strength of TMA wires after one cycle, but not after five cycles. Autoclaving and ethylene oxide sterilization did not significantly alter the tensile strength of TMA wires. Dry heat and autoclave sterilization also significantly increased the tensile strength of Sentalloy wires, but the mean strength after five sterilization cycles was not significantly different than after one cycle. Ethylene oxide sterilization of Sentalloy wires did not significantly alter the tensile strengths of that wire. There were no significant differences in the tensile strengths of the stainless steel wires following zero, one or five cycles for any of the sterilization methods.

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)

Frictional coefficients of ion-implanted alumina against ion-implanted beta-titanium in the low load, low velocity, single pass regime

The frictional coefficients were measured for four wire alloys against the flats of polycrystalline alumina cylinders using a low load, low velocity, single pass device. Ion-implantations of titanium into polycrystalline alumina flats and nitrogen into beta-titatnium wires reduced the static and kinetic coefficients from 0.50 and 0.44 before implantation to 0.20 and 0.25 after implantation, respectively. These results are similar in magnitude to frictional coefficients for unimplanted, control couples of stainless steel, cobalt-chromium, and nickel titanium wires against polycrystalline alumina flats. For orthodontic applications, we conclude that more efficient and reproducible appliances can be engineered for tooth movement if ion-implantation is used to reduce the abrasion of beta-titanium by polycrystalline alumina.