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Metallurgical properties of stainless steel orthodontic archwires: a comparative study.

Abstract:

Orthodontic archwires are designed to move teeth with light continuous forces. Mechanotherapy depends on both the elastic behavior of the material and the biochemical reaction of the teeth. Stainless steel A. J. Wilcock (Australian) wires have been the backbone of Begg treatment since its inception. During the last few years, two other manufacturers have introduced their brands of high tensile strength stainless steel wires, which they claim to be equivalent to or superior to the Australian wires. This study was undertaken to evaluate and compare the physical properties of high tensile A.J. Wilcock (Australian) wires with the newly introduced high tensile wires and critically assess their claim for superiority. The results obtained were statistically analyzed. It was found that in 0.020" size, Wilcock Special Plus wire had greater strength and stiffness than the Ortho Organizers wire. In the 0.018" size, Wilcock Premium and Special Plus wire had greater strength and range and lesser friction and relaxation, while T. P. Premier wires had almost the same strength, but greater friction and relaxation and lesser range. In the 0.016" size, Wilcock Premium and Special Plus wire had superior stiffness, range and lesser friction and relaxation. In the 0.014" size, Wilcock Premium and Special Plus wire had greater strength and range while the Ortho Organizers wires had greater stiffness. In the 0.012" and 0.010" sizes, the Wilcock Premium Plus and Supreme wires had superior strength and stiffness than the Ortho Organizers wires.

Keywords : Orthodontic archwires, 3 point bend test, SEM

Introduction:

Advances in metallurgy during the twentieth century have been considerable and the field of orthodontics is in a position to reap great benefits from it. Orthodontic archwires are designed to move teeth with light continuous forces. Mechanotherapy depends on both the elastic behavior of the material and the biochemical reaction of the teeth. During the early years of our specialty, appliances were constructed mainly of precious metals. Since its introduction in the early 1930s, stainless steel has proved to be a better material than alloys of precious metals for orthodontic appliances. The A. J. Wilcock (Australian) stainless steel wires have been the backbone of Begg treatment since its inception. During the last few years, two other manufacturers have introduced their brands of high tensile strength stainless steel wires, which they claim to be equivalent to or superior to the Australian wires.

The present comprehensive investigation was undertaken to evaluate and compare the following physical properties of high tensile A. J. Wilcock (Australian) wires with the newly introduced high tensile wires and critically assess their claim for superiority. The Ultimate Tensile strength, Tensile strength, Maximum load via three point bending, Working range, Kinetic friction, Stress relaxation, Surface topography, Elemental analysis, Microhardness and Micro structure were evaluated and analyzed.

Materials and Method:

The study was conducted at the Department of Orthodontics, S.D.M. College of Dental Sciences, Dharwad. The physical tests were conducted at the Indian Institute of Science, Bangalore and Geological and Metallurgical Laboratories, Bangalore.

The wire samples were divided into 3 groups: Group I from Ortho Organizers, Group II from A. J. Wilcock and Group III from T. P. Orthodontics. The samples included only round stainless steel wires.

As per the information obtained from the distributors,

"The Super Plus grade wires of Ortho Organizers have properties, which place them in between Special Plus and Premium grade of A.J. Wilcock wires".

"The Premier, Premier Plus and Bowflex grades of T. P. wires are comparable to Special, Special Plus and Premium grades of A. J. Wilcock wires."

Hence, they were compared with the respective grades. Before the start of the experiments, the diameters of all the samples were recorded using a Screw Gauge [least count = 0.01 millimeters (mm)] and tabulated.

The wires used in this study were grouped as shown in the table 1.

All the samples were coded separately in order to avoid any observer bias. Five wires of each sample were taken for each experiment.

Methodology:

Yield strength and Ultimate Tensile Strength

All wires were tested using a Universal testing machine (Instron Model No. 1341) with a load cell capacity of 500 kgs for tensile strain. The distance between the grips was maintained at a constant of 20mm and the cross-head moved at a uniform speed of 2mm/min.

The deflections obtained for the respective loads were plotted on an x-y plotter. The data obtained was converted into stress-strain curves, and the yield load values and ultimate tensile load values were calculated from the slopes of the graphs. The formulae used to calculate the yield strength and the ultimate tensile strength were:

Y.S. = [Yield load in Newtons/Cross- sectional area in [mm.sup.2]] and U T S = [Breaking load in Newtons/Cross-sectional area in [mm.sup.2]]

Maximum Load via 3-Point Bending

All wires were subjected to the bending test on a Universal testing machine, and a load required to produce 2mm deflection was recorded.

The setup included a specially constructed fixture comprising of two poles placed 14 mm apart on a stage attached to the lower jaw of the machine. The single pole was attached to the upper jaw, which moved at a speed of 1mm/min and deflected the wire to a distance of 2 mm. The wire sample was placed between the 2 poles and a load range of 1 kg full scale was used.

Working Range

Wires with 0.014", 0.016" and 0.018" diameters were evaluated for springback property. Upper acrylic teeth with screws fitted into them to represent their roots were placed in a predetermined archform. One-third of the root was covered with a mixture of modeling wax and sticky wax in the ratio 1:1 and the remaining portion was embedded in the self-cure acrylic, which formed the base of the typodont. Begg brackets were bonded on each tooth and buccal tubes were bonded on the molars using an adhesive (Super Glue). The protocol followed was as outlined by Jyothindra Kumar (1989) (1) and modified by Mandhani and Jalili (2). Starting from the left, alternate teeth were displaced palatally in increments of 1 mm from 2-4 mm and 1.5 mm from 4-7 mm, resulting in five points of displacement. As displacing a 0.018" wire by 7 mm caused deformation of the wire during engagement and snapping of the wire at times, the protocol was slightly modified for this size wire. Starting from the left, alternate teeth were displaced palatally in increments of 1 mm from 1-5 mm resulting in 5 points of displacement. The interbracket spaces were measured as the shortest distance from one bracket slot to the other. The midline of each wire and the points of engagement in the slot in the span between the undisplaced teeth were marked. The shortest distance between the marked points and the bracket slots was measured.

The wire was then pinned using Begg stage I pins in all the undisplaced teeth and ligated using 0.010" stainless steel ligature wire in the displaced teeth. The setup was left undisturbed for one hour and then the ligature3s were cut. Archwire recovery was measured as the shortest distance from the bracket slot to the marked point on the wire using a vernier caliper (least count = 0.01 mm). The wire was then removed and photographed to observe its recovery pattern.

Kinetic Friction

Wires with 0.016" diameter were evaluated using 0.018" x 0.025" slot standard edgewise brackets and wires with 0.018" diameter were evaluated using 0.22" x 0.028" slot standard edgewise brackets. All wires were tested on the Universal testing machine under dry conditions.

The setup was based on the method proposed by Tidy in 1989 (3). It consisted of a simulated fixed appliance with the archwire in a vertical position. Four standard edgewise brackets were bonded onto a rigid Perspex sheet at intervals of 8mm with a 16mm space for the moveable bracket at the center. This 16mm space represented the space taken up by the canine plus the space of an extracted premolar. The archwire was secured with 0.010" stainless steel wire ligatures. The ligature on the moveable bracket was at first fully tightened, then slackened to permit free sliding.

The moveable bracket was fitted with a 10mm power arm made of 0.017" x 0.025" stainless steel rectangular wire, from which weights (50 gms. and 100 gms.) could be hung to represent the single equivalent force acting at the center of resistance of an average size tooth root.

The length of the power arm was chosen to represent the distance from the slot to the center of resistance of a typical canine tooth. The base plate was mounted on the lower jaw of the universal testing machine and the movable bracket was suspended from the load cell. A cross-head speed of 5mm/min was maintained. At the start of each test, a trial run was performed with no load on the wire. Then 50 gms and 100 gms weights were suspended successively from the power arm, and the load required to move the brackets was recorded. The coefficient of friction was calculated using the following formula (3).

P = [2Fh[mu]]/W Therefore [mu] = [PW]/[2Fh]

Where: P = Frictional resistance (difference between load cell reading and load on the power arm).

F = Equivalent force acting at distance 'h'.

h = 10mm.

W = Width of the slot.

[mu] = Coefficient of friction.

Stress Relaxation:

Wires with 0.016" and 0.018" diameters were evaluated. Artificial saliva, (Modified Meyer's artificial saliva--Tai et al (4) 1992) having the following composition was used.

Sodium chloride (NaCl) = 8 gms.

Potassium Chloride (KCl) = 8 gms.

Di sodium hydrogen phosphate = 13.8 gms.

1-hydrate ([Na.sub.2]H, P[O.sub.4] x [H.sub.2]O) Sodium sulphide ([Na.sub.2]S. 9[H.sub.2]O) = 0.1 gms.

Urea = 20 gms.

Calcium chloride (Ca[Cl.sub.2] - [H.sub.2]O) = 15.9 gms.

Distilled water = 20 litres.

pH = 7

All the ingredients were weighed using Precisa electronic balance and dissolved in 20 litres of distilled water to obtain the inorganic artificial saliva.

To evaluate stress relaxation, the wires were given a predetermined archform. An anchor bend of 45[degrees] was placed on each wire. Begg molar tubes were placed on cement sheets and secured in place using Super glue adhesive. The wires were then placed in the tubes. Simulating the clinical usage, the wire was brought down to the level of the molar tubes and kept engaged at 3 points.

The sheets with the wires were kept immersed in artificial saliva for 8 days after which they were removed and the reduction in the anchor bend was recorded.

Elemental Analysis:

Wires from all the 3 groups were evaluated at the Geological and Metallurgical Laboratories, Bangalore. Elements analyzed were Carbon, Silicon, Manganese, Sulphur, Phosphorous, Chromium, Nickel and Molybdenum.

SEM Evaluation of Surface Topography:

Wires with 0.016" diameter from both the groups were scanned. The wires were scanned using a Scanning Electron Microscope at magnifications of 35X, 200X, 500X and 1000X. Photographs were taken and analyzed.

Microstructural Analysis

Wires from both the groups were evaluated at the Geological and Metallurgical Laboratories, Bangalore. Longitudinal sections of wire were mounted on acrylic resin. The samples were first ground and then etched with aqua regia to reveal the different phases.

Microhardness

Wires from both the groups were evaluated for hardness at the Geological and Metallurgical Laboratories, Bangalore. Vickers microhardness was measured using Matsuzawa microhardness tester using a diamond pyramid indentor. The diagonal of the indentation was measured to determine the hardness.

Results:

Values obtained from all tests with the exception of Elemental analysis, surface topography, microstructural analysis and micro hardness were statistically analyzed.

All data are expressed as Mean [+ or -] SD.

Categorical data was studied using ANOVA test for sizes in which there were more than 2 samples and the Student unpaired t-test at significance levels of 0.05, 0.01 and 0.001. The results are shown in graphical form.

Discussions:

Interpretation of the Results:

Yield strength and ultimate tensile strength

General observations:

It was observed that, in general, the yield strength and ultimate tensile strength of all the wires went hand in hand meaning, if the yield strength of one wire was more than the other, the ultimate tensile strength of the former was also more than the latter. However, this did not apply to the 0.016" wires, as can be seen from the following table in which different wires are shown in descending order with respect to the two properties.
 Yield strength Ultimate tensile strength

1. A.J.Wilcock (Pm) A.J.Wilcock (Pm)
2. A.J.Wilcock (Sp+) T.P.(BF)
3. T.P. (BF) A.J.Wilcock (Sp+)
4. OO (Su+) T.P.(Pr+)
5. T.P. (Pr+) OO (Su+)


It was seen that with an increase in the diameter of the wire, the Yield strength and Ultimate Tensile Strength decreased except in the case of 0.012" and 0.010" sizes.

The ANOVA test revealed that between wires of different manufacturers as well as between the samples of every wire there is a difference which ranges from highly significant to very highly significant.

The t-test revealed that A.J. Wilcock Premium and Special Plus wires in 0.020", 0.018", 0.016" and 0.014" sizes, Premium Plus (0.012") and Supreme (0.010") grades have much greater yield strength and ultimate tensile strength compared to the wires from Ortho Organizers in all the respective sizes and grades, the level of significance varying from significant to very highly significant.

A comparison between Wilcock Premium wires with T. P. Bowflex wires using the t-test revealed that in 0.018" size, Wilcock Premium grade has superior strength, the difference being very highly significant. However, in the 0.016" size, Wilcock Premium wire is similar to T.P. Bowflex wire since the statistical comparison is non-significant.

On the other hand, in the 0.018" size, the A. J. Wilcock Special grade wire has much lesser yield strength and ultimate tensile strength than the T.P. Premier wire, which is statistically very highly significant. Also, Wilcock Premium and Special Plus wires in the same size have comparable strength to that of T.P. Premier grade (difference being nonsignificant for yield strength and lowly significant for ultimate tensile strength of Special Plus wires). Hence, T.P. Premier wires could be substituted for Wilcock Premium and Special Plus wires in 0.018" size.

A similar comparison in 0.016" size wires revealed that the Wilcock Special Plus wires have greater strength than T.P. Premier Plus wires (difference being highly significant in yield strength and non significant in ultimate tensile strength).

A comparison between Ortho Organizers and T. P. wires showed that in 0.018" size, the Ortho Organizers wires have greater strength than T.P. Bowflex wires, the level of significance being very highly significant, while in the same size it has lesser strength than T.P. Premier grade, the level of significance being very highly significant for yield strength and highly significant for ultimate tensile strength.

In the 0.016" size, the Ortho Organizers wires have lesser yield strength than the T. P. Bowflex (difference being highly significant) and almost the same yield strength as T.P. Premier Plus (difference being non-significant) wires, but lesser ultimate tensile strength than T.P. Premier Plus and Bowflex grade (difference highly significant) wires [Fig 1].

[FIGURE 1 OMITTED]

Thus, in general, A.J. Wilcock wires are superior to Ortho Organizers and slightly superior to the T.P. wires (except in 0.018" as mentioned above) so far as yield strength and ultimate tensile strength are concerned.

However, the surprising finding with respect to 0.020" size was that the Wilcock Special Plus wire has greater yield as well as ultimate tensile strength than the Premium grade. It is difficult to explain this finding. The only possibility is that the Premium grade wire spool came from a batch that had some manufacturing problem.

Maximum loading via 3-point bend test

The ANOVA test revealed no statistical difference between wires of different manufacturers as well as between the samples of every wire in 0.020" and 0.016" sizes and highly significant to very highly significant difference in the 0.018" and 0.014" sizes respectively.

The t-test showed that the Ortho Organizers wires in 0.018" and 0.010" sizes have almost the same stiffness as the Wilcock Premium, Special Plus and Supreme (0.010") grade wires (difference being nonsignificant). Further, 0.020" Ortho Organizers wire has similar stiffness to that of 0.020" Wilcock Premium wire but much lesser stiffness than the Wilcock Special Plus (difference is significant) wire. In the case of 0.016" and 0.012" (Premium Plus) sizes, Ortho Organizers wires have much lesser stiffness than the corresponding Wilcock wires (difference varying between significant to highly significant). Similarly in the 0.014" size wires, Ortho Organizers wires have similar stiffness to that of Wilcock Special Plus wires but much greater stiffness than the Wilcock Premium wires (difference being very highly significant) [Fig 2].

[FIGURE 2 OMITTED]

A comparison between the Wilcock and T.P. wires revealed that in 0.018" size Wilcock Premium wires have lesser stiffness that the T.P. Bowflex wires, the difference being significant. While in the same size the Wilcock Special wires have almost the same stiffness as the T.P. Bowflex and Premier wires (difference nonsignificant), it had greater stiffness (difference being significant to highly significant) than the Premium and Special Plus grades [Fig 2].

On the other hand, in the 0.016" size, Wilcock Premium wires have the same stiffness as the T.P. Bowflex (difference being nonsignificant) while the Wilcock Special Plus wires, though showed no significant difference statistically, considering the mean and standard deviation, have greater stiffness than the T.P. Premier Plus wires.

The Ortho Organizers wires when compared to the T.P. Wires, showed that in both 0.018" and 0.016" sizes, the wires from Ortho Organizers have lesser stiffness than the T.P. Premier (0.018") and Bowflex (0.016" and 0.018") wires, the level of significance ranging from lowly significant to highly significant, with the exception of the 0.016" size where the Ortho Organizers wires have similar stiffness as that of T.P. Premier Plus wires (difference being nonsignificant).

Increased loads were required to deflect the wire by 2mm as the diameter of the wire increased. A few unusual findings worth mentioning are:

The Premium grade of A.J. Wilcock (Australian wire) of 0.014" diameter required only 5.8 Newtons to deflect it by 2mm, while the Special Plus grade wire in the same size required almost twice the load (11.0 N) to deflect it. The reason probably was a defective spool / length of the spool of wire.

The Special Plus grade of A.J. Wilcock (Australian wire) of 0.018" required a relatively higher load than the Premium grade and a relatively lower load than the Special grade (0.018") for deflecting the wire up to 2mm possibly due to the same reason as mentioned above.

Working Range

Overall, the Wilcock wires seem to have greater working range, which matches the inference drawn from the discussion of yield strength [Figs 3-5].

[FIGURES 3-5 OMITTED]

It was observed that at 1mm and 2mm displacements and occasionally at 3mm displacements, all wires (except T.P. Premier grade) showed more than 100% recovery. This phenomenon was also noted by Skaria. The explanation he gave was that it could be attributed to progressive increase in the displacement of the teeth in the typodont. Since the larger displacements were mainly in the anterior segment, it would create an outward thrust of the archwire in the buccal segment when the archwire is tightly ligated to the slots. If the larger tooth displacement had been located posteriorly, then this effect would have manifested in the posterior segment.

Kinetic Friction / Frictional Resistance

In our study, the values for the coefficient of friction were individually evaluated for 50 gms and 100 gms as they showed significant change in the values of coefficient of friction when a mean of the two was calculated. To minimize these erroneous readings, individual values were evaluated.

The ANOVA test revealed that in both 0.018" and 0.016" sizes, very highly significant difference was observed both between wires from different manufacturers and within the groups [Figs 6-7]. An interesting feature observed was that the wires which had a smooth surface topography, had a greater value of friction than the wires with a rougher surface, for example: the wires from Ortho Organizers and T.P. Orthodontics had a much smoother surface than those of A.J. Wilcock Australian wires but their frictional resistance values in most instances were high. Proffit has made a similar observation based on a study reported by Kusy and Whitley "There is little or no co-relation for orthodontic wires between the coefficient of friction and surface roughness". The explanation that he gave is "Friction is independent of the apparent area of contact. This is because all surfaces no matter how smooth, have irregularities that are large on a molecular scale, and real contact occurs only at a limited number of small spots at the peaks of the surface irregularities. These spots, called "Asperities", carry the entire load between the two surfaces. Even under light loads, local pressure at the asperities may cause appreciable plastic deformation of those small areas. Because of this, the true contact area is to a considerable extent determined by the applied load and is directly proportional to it" (5).

[FIGURES 6-7 OMITTED]

Stress Relaxation

One of the treatment procedures where minimum stress relaxation plays an important role is bite opening. Hence the test was carried out to assess how the bite opening bends maintain over long time spans in conditions similar to oral environment. In an attempt to simulate the oral conditions we evaluated the stress relaxation of the wires in an artificial saliva medium. The archwire was brought down to the level of the molar tubes and held in place using eyelets made from rectangular stainless steel wire.

The ANOVA test revealed that in 0.018" size wires, both between wires and within the samples no significant difference was observed, while in the 0.016" size a significant difference between wires and within wires was observed.

The t-test for all the 0.018" size wires and most of 0.016" wires revealed no statistical difference between the samples. However, considering the mean and standard deviation, the Ortho Organizers wires showed greater relaxation than the Wilcock Premium wires in 0.018" size and almost the same relaxation in 0.016" size wires. The Wilcock Special Plus grade wires in 0.018" size have almost the same relaxation as the Ortho Organizers wires, but in 0.016" the Ortho Organizers wires have slightly lesser relaxation (difference being lowly significant) [Figs 8-9].

[FIGURES 8-9 OMITTED]

In comparison with the T.P. wires, the Wilcock Premium wires in both 0.018" and 0.016" sizes showed lesser relaxation than the T.P. Bowflex wires (difference lowly significant in 0.016" size). Also the Wilcock Special (0.018") wires have lesser relaxation than the T.P. Premier grade wires, while the Wilcock Special Plus wires have almost the same relaxation as the T.P. Premier Plus (0.016") wires.

A comparison between the wires from Ortho Organizers and T.P. wires revealed that in 0.018" size, the Ortho Organizers wires have the same relaxation as the T.P. Premier and Bowflex wires, while in the 0.016" size, the Ortho Organizers wires have slightly lesser relaxation than the T.P. Bowflex and Premier Plus (difference lowly significant) wires.

SEM evaluation of the surface topography

The scanned images at 35X, 200X, 500X and 1000X for wires with diameters 0.016" and 0.014" were studied. In general, the A.J. Wilcock wires showed a rougher surface topography than the wires from the other two groups, which showed a much smoother surface. The surface of the wires appears to have a striated appearance, which could be due to the drawing process during the manufacture of the wires. Also, numerous impurities were found plugged on the surface of all the wires.

Elemental Analysis

Wires from all the three groups belonged to the 18-8 stainless steel. The significant increase in the percentage of chromium content in the wires from Ortho Organizers could be the cause for the extra shine of these wires.

Microstructure Analysis

The reports showed that the microstructure of the three wires consisted of highly deformed grains of austenite with strain-induced martensite. It was in the formed condition.

Microhardness

Surface hardness is the "resistance to indentation". Among the properties that influence the hardness of a material are its strength, proportional limit, ductility, malleability and resistance to abrasion and cutting. The Vickers hardness test is one of the microhardness tests, capable of measuring very thin objects and giving hardness values of small regions (6).

Thus, the results showed that the wires from A.J. Wilcock and T.P. Orthodontics had similar hardness values and a higher hardness value than the wires from Ortho Organizers.

Manufacturer's claims / recommendations v/s experimental findings

M/S Ortho Organizers claim is validated with respect to stress relaxation and working range properties in the 0.016" size wires only. In the 0.014" size the Ortho Organizers wire is superior to the Wilcock (Premium) wire with respect to stiffness.

However, with respect to all the other properties, the Ortho Organizers wires in all sizes were inferior to A.J.Wilcock (Special Plus) wires.

Ortho Organizers wires have much less Y.S and U.T.S. in 0.012" Premium Plus grade and just about 50% of the strength values in 0.010" Supreme grade. The claim of M/s T.P. Orthodontics is validated only with respect to stiffness and stress relaxation in 0.018" size wires.

Inconsistent behaviors of different grades of wires

Wilcock Premium 0.020" wire had lesser Y.S, U.T.S. and stiffness than Special Plus wire.

Wilcock 0.018" Special wire had greater stiffness than Special Plus or even Premium.

Wilcock 0.014" Premium wire had much lesser stiffness than Special Plus.

T.P.Premier 0.018" wire had greater yield and ultimate tensile strength and almost the same stress relaxation as the Bowflex wire.

Shortcomings of the study:

Inavailability of testing machine with grips suitable for wires with diameters ranging from 0.020" to 0.010".

Machine sensitivity could not be accounted for, as the machines were not designed for evaluation of such fine wires.

Errors occurring due to power fluctuations and manual noting of the readings etc were unavoidable.

The information obtained from this study cannot be extrapolated directly to clinical situations, as the study was an in--vitro study.

Certain grades of wires (for example, 0.018", 0.016" Premium Plus) and other Pulse straightened wires were not included in the study as the samples obtained from the other manufacturers did not include wires comparable to the Premium Plus grade nor was it clear if the T.P. wires were Pulse Straightened.

Summary and Conclusions:

It was found that in 0.020" size, Wilcock Special Plus wire had greater strength and stiffness than the Ortho Organizers wire. In the 0.018" size, Wilcock Premium and Special Plus wire had greater strength and range and lesser friction and relaxation, while T. P. Premier wires had almost the same strength, but greater friction and relaxation and lesser range. In the 0.016" size, Wilcock Premium and Special Plus wire had superior stiffness, range and lesser friction and relaxation. In the 0.014" size, Wilcock Premium and Special Plus wire had greater strength and range while the Ortho Organizers wires had greater stiffness. In the 0.012" and 0.010" sizes, the Wilcock Premium Plus and Supreme wires had superior strength and stiffness than the Ortho Organizers wires.

References:

(1.) K. J. Kumar, Working range characteristics of Newer Arch Wire Materials Used in Stage I of Begg Technique. A Study. J. Ind. Orthod. Soc, Vol. 20(4), 251 (1989).BIBLIOGRAPHY

(2.) S. Mandhani, V.P. Jalili, Springback properties of some orthodontic wires. A comparative study, JPFA, Vol. 12, 7 (1998).

(3.) D.C. Tidy, Frictional forces in fixed appliances, Am. J. Orthod. Dentofac. Orthop, Vol. 96, 249 (1989).

(4.) Y. Tai, R. D. Long, R. J. Goodkind, W. H. Douglas, Leaching of nickel, chromium and beryllium ions from base metal alloys in an artificial oral environment, J. Prosthet. Dent, Vol. 68, 692 (1992).

(5.) W. R. Proffit: Contemporary Orthodontics, Ed.2, Mosby-Year Book Inc., St. Louis, USA: (1993).

(6.) R. W. Philips: Skinner's Science of Dental Materials, Ed.9, W.B. Saunders Company: (1992).

K. Anuradha Acharya * and V.P. Jayade **

* Assistant Professor Department of Orthodontics Manipal College of Dental Sciences Manipal-576 104, Karnataka

** Chairman Department of Orthodontics & Dentofacial Orthopaedics S.D.M. College of Dental Sciences & Hospital Sattur, Dharwad.
Table 1: Division of the samples into three groups along with
their respective measured diameters (in mm)

Sl. Wire size Ortho Organizers A.J. Wilcock
No. (in (Australian
 inches) wires)

1. 0.020" Super Plus 0.51 Premium 0.50
 Special Plus 0.50
2. 0.018" Super Plus 0.46 Premium 0.45
 Special Plus 0.45
 Special 0.45
3. 0.016" Super Plus 0.41 Premium 0.41
 Special Plus 0.41
4. 0.014" Super Plus 0.46 Premium 0.35
 Special Plus 0.35
5. 0.012" Premium Plus 0.31 Premium Plus 0.31
6. 0.010" Supreme 0.26 Supreme 0.26

Sl. Wire size T.P. Orthodontics
No. (in
 inches)

1. 0.020"
2. 0.018" Premier 0.45
 Bowflex 0.45
3. 0.016" Premier Plus 0.41
 Bowflex 0.41
4. 0.014"
5. 0.012"
6. 0.010"
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Author:Acharya, K. Anuradha; Jayade, V.P.
Publication:Trends in Biomaterials and Artificial Organs
Geographic Code:9INDI
Date:Jan 1, 2005
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