British Journal of Orthodontics
ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19
Superelastic nickel-titanium wires N. E. Waters MSc., PhD., C.Phys., F.Inst.P. To cite this article: N. E. Waters MSc., PhD., C.Phys., F.Inst.P. (1992) Superelastic nickel-titanium wires, British Journal of Orthodontics, 19:4, 319-322, DOI: 10.1179/bjo.19.4.319 To link to this article: http://dx.doi.org/10.1179/bjo.19.4.319
Published online: 21 Jun 2016.
Submit your article to this journal
View related articles
Citing articles: 14 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yjor19 Download by: [Tufts University]
Date: 22 November 2016, At: 08:32
British Journal of Ortlwdontics/Vol. 19/1992/319-322
Orthodontic Products Update Superelastic nickel-titanium wires N. E. WATERS, MSc., PHD., C.PHvs., F.INST.P. Department of Dental Materials Science, UMDS, Guy's Campus, London SE! 9RT
Introduction Sup~ralloy wires, like bouncing putty, have the ab1hty to fascinate us because they do not behave in the way in which we would expect. Until just over 5 ~ears ago, the concept of a wire which could be bent ~nto a grossly irregular shape and then could regain Its original form on release would have been thought impossible. So too would the idea of the Young's modulus of a wire changing by a factor of three or four over 20°C temperature range. However, both these features, as well as other strange forms of behaviour can be obtained with wires made from special alloys with a highly critical composition. Although there are a number of these alloys, those composed mainly of an intermetallic c.ompound of nearly equal parts of nickel and titanium are those most suitable for orthodontic use, because of their biocompatibility and their ability to form wires.
Superelastic behaviour and shape memory effects
The strange behaviour noted above can occur when a particular crystal structure known as martensite forms from the normal austenitic state. The marte?sitic crystal structure can be increasingly sheared Wtth only a gradually increasing force to approximately ten times the strain of normal alloys without exhibiting permanent deformation. The transformation from the austenitic to the martensitic state can occur either by lowering the temperature or, over a defined temperature range, by applying a stress; the martensite thus produced is known as stress induced martensite (SID). . Shape memory alloys (SMA) possess transformation temperatures above the normal working range, so that if deformed at a lower temperature where they are in the martensitic condition and then heated, a reverse martensitic transformation occurs and they revert to their original shape. Attempts were made by Andreasen and Hilleman 0971) to exploit the ability of nitinol archwires to return to their original preformed shape at a temperature close to body temperature, but pro030I·228XJ92Joosooo + ooso2.oo
cessing control to the required limits was not found possible at that time. Improvements in the control of the transformation temperatures have now reached the stage where at least one manufacturer has produced a wire to exploit the shape memory effect. With this brief simplistic picture of shape memory and superalloy effects it is possible to describe the types of wire now available commercially. Nitinol (NITINQL®, UNITEK/3M CORP U.S.A.) wires produced from an alloy of nickel and titanium introduced nearly 20 years ago have found use because of their low flexural rigidity and high elastic range. Nitinol wires behave 'normally' i.e. their properties are not affected by temperature within the range likely to occur in the oral cavity or by stress and it is said to possess a stabilized martensitic structure because its ability to behave in a superelastic manner is suppressed by the amount of cold working which has occurred during manufacture. Superalloy wires have been classified as those with transformation temperatures between room temperature and body temperature (martensitic active alloys) and those whose transformation temperature is below room temperature (austenitic active alloys). The austenitic type produce higher forces in general than the martensitic but both have a large elastic range and produce a nearly constant force over part of this range during unloading. Finally there are formed arch wires (e.g. Thermalloy) whose transformation temperature range (TTR) is close to body temperature and which are capable of being deformed by hand or pliers during insertion but which by virtue of the shape memory effect spring back to their original shape when activated by body heat. Mechanical behaviour
Previous reports of the behaviour in bending of superalloy wires have been concerned with demonstrating their extraordinary elastic deformability and hence their suitability for the initial aligning of grossly irregular teeth and their ability to produce '!'! 1992 British Society for the Study of Orthodontics
BJO Vol. /9 No. 4
320 N. E. Waters LOAD/eN
Increase In Temperature
200
Q
100
cC
0 ..I
0 o~~--~----~2~----3~----7 4----~5~ DEFLECTION/ mm
FIG. I Cyclic load-deflection plots in three point bending for a superalloy wire with gradually increasing maximium deflection. Span 13.3 mm.
unloading curves with a 'plateau region'. These general characteristics can be seen in Figure I taken from the work of Tanner (1990) which shows superimposed cyclic load-defection results obtained in 3 point bending for an 016 in superalloy wire over a span of 13.3 mm, firstly for a central deflection of I mm, and then for the maximum deflection increasing by approximately millimeter increments up to a deflection of 5 mm. It will be observed that even for a 5 mm deflection the wire behaves perfectly elastically. Also notable is the marked reproducibility of the loading curves. However, the unloading curves, which is the part of the curve in which the orthodontist has the most interest, has a central region which only exhibits a small change in load with recovery over a reasonable range (i.e. a plateau region) if the deflection is greater than 2 mm. However, even if the ability of these wires to produce a near constant force is limited in this way, it is clear that their ability to produce relatively low loads over a large deflection range without distortion is a considerable asset. One interesting clinical point may also be deduced from these curves. It has been reported (Burstone, 1985) that the release and retying of an archwire after a specific amount of deactivation, increased the force on unloading. As release of the wire and then retying will entail transferring to the unloading curve for a smaller deflection the force will increase but the rate of change of load with recovery clearly will be greater than it was before release of the wire.
DEFLECTION FIG. 2 Diagrammatic representation of the effect of temperature on the cyclic load-deflection behaviour of a superalloy wire within the temperature transition region.
through a critical range three phenomena occur. firstly, the initial slope of the load-deflection plot increases suddenly by a factor of between 2 and 4. Secondly, both the loading and unloading 'plateau' regions are raised. Thirdly, if the temperature is lowered below a critical temperature for a given alloy, full recovery is not obtained on unloading, although the wire does recover if the temperature is raised (dashed line in Fig. 2). The temperature at which 'permanent' strain was first observed was found to be closely associated with the temperature at which there was a singificant increase in the initial load-deflection gradient, i.e. at the lower end of the transition region. If the mean 'plateau' load for both the loading and unloading curves is plotted against temperture approximately linear relationships were obtained by Tanner (1990) over the normal temperature range of the oral cavity as shown diagramatically in Figure 3, the actual slopes of the lines and their interception with the axes varying from one wire product to another.
The effect of temperature on the bending characteristics Other recent work by Tonner(l990) has shown that the load-deflection behavior of most of these wires is markedly affected by temperature. The general effect is shown diagramatically in Figure 2 where it may be observed that as the temperature rises
0 o~--~10~~~20~--3~0~~4~0~~5~0---=6o
TEMPERATURE
I
°C
FIG. 3 Diagram to show the type of dependence found by Tanner ( 1990) for the effect of temperature on the loading and unloading 'plateau' values of nickel-titanium superalloy wires.
BJO Not·emher /992
TABLE
I
Superelastic nickel-titanium wires
Unloading 'plateau'forces (eN) at 35°C
Sentalloy 016
H M L Sentalloy 014 H M L Orthocare Niti 016 Titanol Remititam-lite Elastinol Ormco Niti Titanium memory wire Memory wire Supernitane
GAC
Orthocare Forestadent Dentaurum Masel Ormco American Orthodontics Orthomax Hawley Rusell
77 58 20 71 54 40 88 126 118 92 102 88 75 130
Intrabatch variation and the variation between different proprietary wires Examination of a range ofsuperalloy wire products has shown that the wire diameter is no longer a guide to wire behaviour as it is with more conventional wires. Indeed, with the wires that have been examined so far processing control seems to have its Problems for most of the wires were undersized i.e. smaller than their nominal diameters, were more ellipsoidal in cross-section and exhibited greater intra-batch variation in size than conventional Wires. Again, the variation in the initial loaddeflection slope in bending for wires taken from the same batch was found to be nearly 8%, and this variation could not be accounted for by the variation in wire diameter. Furthermore Tonner (1990) found that Sentalloy® 014L (SENTALLOY, F.A.C. International Ltd, N.Y., U.S.A.) produced higher unloading plateau forces at 35 and 50°C than Sentalloy® 016L (SENTALLOY, F.A.C. International Ltd, N.Y., U.S.A.), although for a given wire diameter the high (H), medium (M) and light (L) gradings reflected the forces produced by the wire. Unloading 'plateau' forces for a number of nickel-titanium wires at 35°C are given in the accompanying table where it may be observed that an approximate 6 fold difference in these values exists between different brands. As already noted altering the temperature can affect these readings, for example the 'plateau' value for Sentalloy 016L was found to change from 20 eN at 35oc to 62 eN at 50°C,
321
has shown that three American Dental Association (ADA) approved heat sterilization methods (dry heat, 80°C for 60 min; formaldehyde-alcohol vapour, 138-173 kpa at l32°C for 30 min; steam autoclave, 104-138 kpa at 121 oc for 20 min) produced no detrimental changes for either Nitinol or Titinal arch wires. For the same two wires Buckthal and Kusy (1988) found that no definite changes were brought about by three cold disinfectants approved by the ADA (2% acidic glutaraldehyde, chlorine dioxide and codophor) when used at the concentrations and for the immersion times recommended. It therefore seems unlikely that standard sterilization procedures will affect superalloy nickel-titanium wires. Tanner ( 1990) found that there was a slight fall in the values of the initial slope and in the 'plateau' load on deactivation when tested in the temperature range 5-50°C of many superalloy wires when subject to five loading cycles with a maximum deflection of 3 mm on a 13.3 mm span. A minor deterioration in the properties in NiTi® (NJTJ® ORMCO Corp, Glendora, C.A. U.S.A.) has also been found by Kapila et al ( 1991) in wires subject to up to two cycles of clinical exposure of 8 weeks per cycle. Harris et a/ (1988) using only 016 in NitinoJ® examined the effect of acidity (pH 3-7) and the amount of deflection (0-4 mm on a I0 mm span) and found a 15% decrease in the yield stress over a 4 month period which was independent of the acidity or deflection imposed. The available evidence therefore suggests that a slow deterioration in wire characteristics may occur which will limit the extent to which wires may be reused. Perhaps more serious from the clinical point of view is that a recent report by Mohlin et a/ (1991) of a combined clinical and laboratory study has shown that the incidence of fracture in clinical use was: multistranded stainless steel (12·5'Yo) Nitinol® (16%) and Chinese NiTi® (28·3%). SEM of the fractured surfaces indicated that the high incidence of fracture with NiTi® was due to the large number of surface defects observed and to frequent nonmetallic inclusions. However, it must be remembered that manufacturers are continually improving processing controls and techniques.
Re-use of Superalloy wires
Summary
Inevitabiy because of the expense of these wires in comparison with conventional wires it is of interest to know whether they can be reused. Work carried out by Mayhew and Kusy (1988)
Superelastic nickel-titanium archwires, unlike conventional wires, are capable of withstanding very large deflections and on returning to their original shape on deactivation will produce more moderate
322 N. E. Waters
forces. The region over which there is a 'plateau' depends on the deflection and is greater the larger the deflection. With most wires both the initial wire stiffness in bending and the 'plateau' deactivation loads are very dependent on temperature. Wire size is no longer a guide to wire behaviour and force values for a given temperature and for wires of the same nominal diameter from different manufacturers can vary by a factor of six. References Andreasen, G. F. and Hilleman, T. B. (1971) 55 Cobalt Substituted Nitinol wire for orthodontics, Journal of American Dental Association, 82, 1373-1375. Buckthal, J. E. and Kusy, R. P. (1988) Effects of cold disinfectants on the mechanical properties and the surface topography of nickel-titanium arch wires, American Journal of Orthodontics and Dentofacial Orthopedics, 94, 117-122. Burstone, C. J. (1985) Chinese NiTi wire-a new orthodontic alloy, American Journal of Orthodontics and Dentofacial Orthopedics, 87, 445-452. Harris, E. F., Newman, S. M. and Nicholson, J. A. (1988) Nitinol arch wire in a simulated oral environment: changes in mechanical properties,
BJO Vol. /9 No. 4
American Journal of Orthodontics and Dentofacial Orthopedics, 93, 508-513. Kapila, S., Reichhold, G. W., Anderson, R. S. and Watanake, L. G. (1991) Effects of clinical recycling on mechanical properties of nickeltitanium alloy wires, American Journal of Orthodontics and Dentofacial Orthopedics, 100, 428-435. Mayhew, M. J. and Kusy, R. P. (1988) Effect of sterilization on the mechanical properties and surface topography of nickel-titanium arch wires, American Journal of Orthodontics and Dentofacial Orthopedics, 93, 323-236. Miura, F., Magi, M., Ohura, Y. and Hamanaka, H. (1986) The superelastic property of the Japanese NiTi alloy wire for use in Orthodontics, American Journal of Orthodontics and Dentofacial Orthopedics, 90, 1-10. Mohlin, B., Milller, J. H., Odman, J. and Thirlander, B. (1991) Examination of Chinese NiTi wire by a combined clinical and laboratory approach. European Journal of Orthodontics, 13, 386-391. Tonner, R. I. M. (1990) An investigation into the effect of temperature variation on the physical properties, in particular, stiffness of superelastic NiTi wires in Bending, M.Sc. (Orthodontics) University of London.
ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19
Superelastic nickel-titanium wires N. E. Waters MSc., PhD., C.Phys., F.Inst.P. To cite this article: N. E. Waters MSc., PhD., C.Phys., F.Inst.P. (1992) Superelastic nickel-titanium wires, British Journal of Orthodontics, 19:4, 319-322, DOI: 10.1179/bjo.19.4.319 To link to this article: http://dx.doi.org/10.1179/bjo.19.4.319
Published online: 21 Jun 2016.
Submit your article to this journal
View related articles
Citing articles: 14 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yjor19 Download by: [Tufts University]
Date: 22 November 2016, At: 08:32
British Journal of Ortlwdontics/Vol. 19/1992/319-322
Orthodontic Products Update Superelastic nickel-titanium wires N. E. WATERS, MSc., PHD., C.PHvs., F.INST.P. Department of Dental Materials Science, UMDS, Guy's Campus, London SE! 9RT
Introduction Sup~ralloy wires, like bouncing putty, have the ab1hty to fascinate us because they do not behave in the way in which we would expect. Until just over 5 ~ears ago, the concept of a wire which could be bent ~nto a grossly irregular shape and then could regain Its original form on release would have been thought impossible. So too would the idea of the Young's modulus of a wire changing by a factor of three or four over 20°C temperature range. However, both these features, as well as other strange forms of behaviour can be obtained with wires made from special alloys with a highly critical composition. Although there are a number of these alloys, those composed mainly of an intermetallic c.ompound of nearly equal parts of nickel and titanium are those most suitable for orthodontic use, because of their biocompatibility and their ability to form wires.
Superelastic behaviour and shape memory effects
The strange behaviour noted above can occur when a particular crystal structure known as martensite forms from the normal austenitic state. The marte?sitic crystal structure can be increasingly sheared Wtth only a gradually increasing force to approximately ten times the strain of normal alloys without exhibiting permanent deformation. The transformation from the austenitic to the martensitic state can occur either by lowering the temperature or, over a defined temperature range, by applying a stress; the martensite thus produced is known as stress induced martensite (SID). . Shape memory alloys (SMA) possess transformation temperatures above the normal working range, so that if deformed at a lower temperature where they are in the martensitic condition and then heated, a reverse martensitic transformation occurs and they revert to their original shape. Attempts were made by Andreasen and Hilleman 0971) to exploit the ability of nitinol archwires to return to their original preformed shape at a temperature close to body temperature, but pro030I·228XJ92Joosooo + ooso2.oo
cessing control to the required limits was not found possible at that time. Improvements in the control of the transformation temperatures have now reached the stage where at least one manufacturer has produced a wire to exploit the shape memory effect. With this brief simplistic picture of shape memory and superalloy effects it is possible to describe the types of wire now available commercially. Nitinol (NITINQL®, UNITEK/3M CORP U.S.A.) wires produced from an alloy of nickel and titanium introduced nearly 20 years ago have found use because of their low flexural rigidity and high elastic range. Nitinol wires behave 'normally' i.e. their properties are not affected by temperature within the range likely to occur in the oral cavity or by stress and it is said to possess a stabilized martensitic structure because its ability to behave in a superelastic manner is suppressed by the amount of cold working which has occurred during manufacture. Superalloy wires have been classified as those with transformation temperatures between room temperature and body temperature (martensitic active alloys) and those whose transformation temperature is below room temperature (austenitic active alloys). The austenitic type produce higher forces in general than the martensitic but both have a large elastic range and produce a nearly constant force over part of this range during unloading. Finally there are formed arch wires (e.g. Thermalloy) whose transformation temperature range (TTR) is close to body temperature and which are capable of being deformed by hand or pliers during insertion but which by virtue of the shape memory effect spring back to their original shape when activated by body heat. Mechanical behaviour
Previous reports of the behaviour in bending of superalloy wires have been concerned with demonstrating their extraordinary elastic deformability and hence their suitability for the initial aligning of grossly irregular teeth and their ability to produce '!'! 1992 British Society for the Study of Orthodontics
BJO Vol. /9 No. 4
320 N. E. Waters LOAD/eN
Increase In Temperature
200
Q
100
cC
0 ..I
0 o~~--~----~2~----3~----7 4----~5~ DEFLECTION/ mm
FIG. I Cyclic load-deflection plots in three point bending for a superalloy wire with gradually increasing maximium deflection. Span 13.3 mm.
unloading curves with a 'plateau region'. These general characteristics can be seen in Figure I taken from the work of Tanner (1990) which shows superimposed cyclic load-defection results obtained in 3 point bending for an 016 in superalloy wire over a span of 13.3 mm, firstly for a central deflection of I mm, and then for the maximum deflection increasing by approximately millimeter increments up to a deflection of 5 mm. It will be observed that even for a 5 mm deflection the wire behaves perfectly elastically. Also notable is the marked reproducibility of the loading curves. However, the unloading curves, which is the part of the curve in which the orthodontist has the most interest, has a central region which only exhibits a small change in load with recovery over a reasonable range (i.e. a plateau region) if the deflection is greater than 2 mm. However, even if the ability of these wires to produce a near constant force is limited in this way, it is clear that their ability to produce relatively low loads over a large deflection range without distortion is a considerable asset. One interesting clinical point may also be deduced from these curves. It has been reported (Burstone, 1985) that the release and retying of an archwire after a specific amount of deactivation, increased the force on unloading. As release of the wire and then retying will entail transferring to the unloading curve for a smaller deflection the force will increase but the rate of change of load with recovery clearly will be greater than it was before release of the wire.
DEFLECTION FIG. 2 Diagrammatic representation of the effect of temperature on the cyclic load-deflection behaviour of a superalloy wire within the temperature transition region.
through a critical range three phenomena occur. firstly, the initial slope of the load-deflection plot increases suddenly by a factor of between 2 and 4. Secondly, both the loading and unloading 'plateau' regions are raised. Thirdly, if the temperature is lowered below a critical temperature for a given alloy, full recovery is not obtained on unloading, although the wire does recover if the temperature is raised (dashed line in Fig. 2). The temperature at which 'permanent' strain was first observed was found to be closely associated with the temperature at which there was a singificant increase in the initial load-deflection gradient, i.e. at the lower end of the transition region. If the mean 'plateau' load for both the loading and unloading curves is plotted against temperture approximately linear relationships were obtained by Tanner (1990) over the normal temperature range of the oral cavity as shown diagramatically in Figure 3, the actual slopes of the lines and their interception with the axes varying from one wire product to another.
The effect of temperature on the bending characteristics Other recent work by Tonner(l990) has shown that the load-deflection behavior of most of these wires is markedly affected by temperature. The general effect is shown diagramatically in Figure 2 where it may be observed that as the temperature rises
0 o~--~10~~~20~--3~0~~4~0~~5~0---=6o
TEMPERATURE
I
°C
FIG. 3 Diagram to show the type of dependence found by Tanner ( 1990) for the effect of temperature on the loading and unloading 'plateau' values of nickel-titanium superalloy wires.
BJO Not·emher /992
TABLE
I
Superelastic nickel-titanium wires
Unloading 'plateau'forces (eN) at 35°C
Sentalloy 016
H M L Sentalloy 014 H M L Orthocare Niti 016 Titanol Remititam-lite Elastinol Ormco Niti Titanium memory wire Memory wire Supernitane
GAC
Orthocare Forestadent Dentaurum Masel Ormco American Orthodontics Orthomax Hawley Rusell
77 58 20 71 54 40 88 126 118 92 102 88 75 130
Intrabatch variation and the variation between different proprietary wires Examination of a range ofsuperalloy wire products has shown that the wire diameter is no longer a guide to wire behaviour as it is with more conventional wires. Indeed, with the wires that have been examined so far processing control seems to have its Problems for most of the wires were undersized i.e. smaller than their nominal diameters, were more ellipsoidal in cross-section and exhibited greater intra-batch variation in size than conventional Wires. Again, the variation in the initial loaddeflection slope in bending for wires taken from the same batch was found to be nearly 8%, and this variation could not be accounted for by the variation in wire diameter. Furthermore Tonner (1990) found that Sentalloy® 014L (SENTALLOY, F.A.C. International Ltd, N.Y., U.S.A.) produced higher unloading plateau forces at 35 and 50°C than Sentalloy® 016L (SENTALLOY, F.A.C. International Ltd, N.Y., U.S.A.), although for a given wire diameter the high (H), medium (M) and light (L) gradings reflected the forces produced by the wire. Unloading 'plateau' forces for a number of nickel-titanium wires at 35°C are given in the accompanying table where it may be observed that an approximate 6 fold difference in these values exists between different brands. As already noted altering the temperature can affect these readings, for example the 'plateau' value for Sentalloy 016L was found to change from 20 eN at 35oc to 62 eN at 50°C,
321
has shown that three American Dental Association (ADA) approved heat sterilization methods (dry heat, 80°C for 60 min; formaldehyde-alcohol vapour, 138-173 kpa at l32°C for 30 min; steam autoclave, 104-138 kpa at 121 oc for 20 min) produced no detrimental changes for either Nitinol or Titinal arch wires. For the same two wires Buckthal and Kusy (1988) found that no definite changes were brought about by three cold disinfectants approved by the ADA (2% acidic glutaraldehyde, chlorine dioxide and codophor) when used at the concentrations and for the immersion times recommended. It therefore seems unlikely that standard sterilization procedures will affect superalloy nickel-titanium wires. Tanner ( 1990) found that there was a slight fall in the values of the initial slope and in the 'plateau' load on deactivation when tested in the temperature range 5-50°C of many superalloy wires when subject to five loading cycles with a maximum deflection of 3 mm on a 13.3 mm span. A minor deterioration in the properties in NiTi® (NJTJ® ORMCO Corp, Glendora, C.A. U.S.A.) has also been found by Kapila et al ( 1991) in wires subject to up to two cycles of clinical exposure of 8 weeks per cycle. Harris et a/ (1988) using only 016 in NitinoJ® examined the effect of acidity (pH 3-7) and the amount of deflection (0-4 mm on a I0 mm span) and found a 15% decrease in the yield stress over a 4 month period which was independent of the acidity or deflection imposed. The available evidence therefore suggests that a slow deterioration in wire characteristics may occur which will limit the extent to which wires may be reused. Perhaps more serious from the clinical point of view is that a recent report by Mohlin et a/ (1991) of a combined clinical and laboratory study has shown that the incidence of fracture in clinical use was: multistranded stainless steel (12·5'Yo) Nitinol® (16%) and Chinese NiTi® (28·3%). SEM of the fractured surfaces indicated that the high incidence of fracture with NiTi® was due to the large number of surface defects observed and to frequent nonmetallic inclusions. However, it must be remembered that manufacturers are continually improving processing controls and techniques.
Re-use of Superalloy wires
Summary
Inevitabiy because of the expense of these wires in comparison with conventional wires it is of interest to know whether they can be reused. Work carried out by Mayhew and Kusy (1988)
Superelastic nickel-titanium archwires, unlike conventional wires, are capable of withstanding very large deflections and on returning to their original shape on deactivation will produce more moderate
322 N. E. Waters
forces. The region over which there is a 'plateau' depends on the deflection and is greater the larger the deflection. With most wires both the initial wire stiffness in bending and the 'plateau' deactivation loads are very dependent on temperature. Wire size is no longer a guide to wire behaviour and force values for a given temperature and for wires of the same nominal diameter from different manufacturers can vary by a factor of six. References Andreasen, G. F. and Hilleman, T. B. (1971) 55 Cobalt Substituted Nitinol wire for orthodontics, Journal of American Dental Association, 82, 1373-1375. Buckthal, J. E. and Kusy, R. P. (1988) Effects of cold disinfectants on the mechanical properties and the surface topography of nickel-titanium arch wires, American Journal of Orthodontics and Dentofacial Orthopedics, 94, 117-122. Burstone, C. J. (1985) Chinese NiTi wire-a new orthodontic alloy, American Journal of Orthodontics and Dentofacial Orthopedics, 87, 445-452. Harris, E. F., Newman, S. M. and Nicholson, J. A. (1988) Nitinol arch wire in a simulated oral environment: changes in mechanical properties,
BJO Vol. /9 No. 4
American Journal of Orthodontics and Dentofacial Orthopedics, 93, 508-513. Kapila, S., Reichhold, G. W., Anderson, R. S. and Watanake, L. G. (1991) Effects of clinical recycling on mechanical properties of nickeltitanium alloy wires, American Journal of Orthodontics and Dentofacial Orthopedics, 100, 428-435. Mayhew, M. J. and Kusy, R. P. (1988) Effect of sterilization on the mechanical properties and surface topography of nickel-titanium arch wires, American Journal of Orthodontics and Dentofacial Orthopedics, 93, 323-236. Miura, F., Magi, M., Ohura, Y. and Hamanaka, H. (1986) The superelastic property of the Japanese NiTi alloy wire for use in Orthodontics, American Journal of Orthodontics and Dentofacial Orthopedics, 90, 1-10. Mohlin, B., Milller, J. H., Odman, J. and Thirlander, B. (1991) Examination of Chinese NiTi wire by a combined clinical and laboratory approach. European Journal of Orthodontics, 13, 386-391. Tonner, R. I. M. (1990) An investigation into the effect of temperature variation on the physical properties, in particular, stiffness of superelastic NiTi wires in Bending, M.Sc. (Orthodontics) University of London.
