| Abstract|| |
Aim: To evaluate the changes in surface topography and roughness of stainless steel (SS), nickel-titanium and beta-titanium (β-Ti) archwires after clinical use and sterilization.
Settings and Design: Thirty wires each of SS, nitinol, and β-Ti (3M Unitek) were tested in as received, as received and autoclaved, and clinically retrieved then autoclaved conditions.
Materials and Methods: A sterilization protocol of 134°C for 18 min was performed using an autoclave. Surface topography of specimens from each subgroup was examined using an environmental scanning electron microscope (ESEM model Quanta 200, The Netherlands) at ×100, ×1000, and ×2500 magnifications. Surface roughness was measured using arithmetic mean roughness (Ra) values obtained from optical profilometric scanning (Taylor Hobson, Leicester, UK).
Statistical Analysis: Data were analyzed by one-way analysis of variance and Tukey's post-hoc procedures.
Results: Scanning electron microscope images revealed an increase in surface irregularities in SS and nitinol wires after clinical use. There was a significant increase in Ra values of SS orthodontic wires after intra-oral exposure (P = 0.0002).
Conclusion: Surface roughness of SS wires increased significantly after clinical use. Autoclave sterilization did not affect considerably on surface characteristics of any archwire.
Keywords: Orthodontic archwires, surface roughness, surface topography
|How to cite this article:|
Isac J, Chandrashekar B S, Mahendra S, Mahesh C M, Shetty BM, Arun A V. Effects of clinical use and sterilization on surface topography and surface roughness of three commonly used types of orthodontic archwires. Indian J Dent Res 2015;26:378-83
|How to cite this URL:|
Isac J, Chandrashekar B S, Mahendra S, Mahesh C M, Shetty BM, Arun A V. Effects of clinical use and sterilization on surface topography and surface roughness of three commonly used types of orthodontic archwires. Indian J Dent Res [serial online] 2015 [cited 2019 Jul 19];26:378-83. Available from: http://www.ijdr.in/text.asp?2015/26/4/378/167628
Orthodontic wires, which generate biomechanical forces communicated through brackets for tooth movement, are central to the practice of the profession. Orthodontic wires made from different alloys offer alternative sequences of wire usage during all phases of treatment. The surface topography of an orthodontic wire is an essential functional property known to influence the mechanical characteristics, esthetic result, corrosion behavior, and biocompatibility of device. The resulting surface structure depends on alloy used, complex manufacturing process and the surface finish treatment.,,
Stainless steel (SS) archwire is one of the most widely used materials in orthodontics. However, nickel-titanium (NiTi) archwire and beta-titanium (β-Ti) are becoming increasingly popular. NiTi wire has super-elastic (SE) and shape memory property, whereas β-Ti produced gentler forces per unit of deactivation and had substantially more range and higher springback.
Orthodontic alloys in mouth are in contact with a variety of substances that impose potent effects on their reactive status and surface integrity, such as saliva that may contain acids arising from degradation and decomposition of food, environmental factors and oral flora and its byproducts. Recycling involves repeated exposure of the wire for several weeks or months to mechanical stresses and elements of the oral environment, as well as sterilization. The combined effects of repeated clinical use and sterilization may subject the wire to corrosion and cold working, with a resultant alteration in its properties. Surface roughness may modify frictional coefficient. In orthodontics, it interferes with correct sliding of the bracket along the wire., Therefore, a critical step in the evaluation of archwire performance is an analysis of surface roughness of different orthodontic archwires available in the market.
The purpose of this investigation was to evaluate the changes in surface topography and roughness of SS, NiTi, and β-Ti archwires after clinical use and sterilization.
| Materials and Methods|| |
Thirty wires of each type: SS, nitinol SE, and beta III titanium (3M Unitek, St. Paul, USA) were used: 0.017″ × 0.025″ (0.43 mm × 0.64 mm) OrthoForm III- Ovoid rectangular wires were selected in each group.
Group A comprises 10 wires each of SS (A1), nitinol SE (A2), and beta III titanium (A3) in their as-received condition from manufacturer to serve as the control group.
Group B includes 10 wires each of SS (B1), nitinol SE (B2), and beta III titanium (B3) which were autoclaved in their as-received condition from manufacturer.
In Group C includes 10 wires each of SS (C1), nitinol SE (C2), and beta III titanium (C3) which were used in orthodontic patients treated with pre-adjusted edgewise mechanotherapy for 1–2 months. After clinical use, all wires were disinfected with an 70% absolute alcohol (seven parts alcohol and three parts distilled water) for 10 min, and allowed to air-dry before being placed into separate storage envelopes (Sterilization Flat Reel Pouch, Libral Traders, New Delhi) with a blue color indicator which turns brown after sterilization.
Wires were discarded if bends were placed by a clinician or if the surface was corroded.
The sterilization technique
The autoclave sterilization was chosen because it is a technique frequently used in orthodontic practice and is recommended by manufacturers. A sterilization protocol of 134°C at 2.1 kg/cm 2 for 18 min (12 min sterilization + 6 min drying period) was performed using an autoclave (Unique Clave C-79, Confident Dental Equipments Ltd., Pete Channappa Industrial Estate, Kamakshipalya, Bangalore).
Assessment of surface characteristics
Scanning electron microscope (SEM) was used to view one representative specimen of anterior segment of archwire selected from each group to qualitatively characterize the topography of the wire surface. One cm long specimen of each alloy wire was mounted on studs and was placed in the vacuum chamber of environmental SEM (ESEM model Quanta 200, FEI Company, The Netherlands) and observed. The wider surface was scanned and viewed on the monitor at different magnifications (×100, ×1000, and ×2500) and representative micrographs were obtained.
A Taylor Hobson three-dimensional (3D) optical profilometer (Talysurf CCI, Leicester, UK) was used with a Taly map software (Talysurf, UK) to measure roughness of wire specimens of each groups. Optical profilometers are inherently 3D, they measure height (the z-axis) over an area of x and y lateral dimensions. The study was focused on arithmetic mean roughness (Ra) of specimens in microns. Coherence correlation interferometry technique was used with a ×50 magnification and area of measurement was 325 µ × 325 µ. Three profilometric scans of the wider surface of each specimen were taken at three different positions on the anterior segment of archwire surface, and the mean and the standard deviation were calculated. The measurement time was 5–40 s.
The Excel and SPSS software (IBM) packages were used for data entry and analysis. Results obtained were analyzed using one-way analysis of variance and Tukey's multiple post-hoc test.
| Results|| |
In the present study, surface topography of archwires in all three groups was evaluated by SEM at ×100, ×1000, and ×2500 magnifications. At ×100 magnification, SS wire has the smoothest surface and β-Ti wire exhibited an irregular roughest surface. At ×1000 and ×2500 magnifications, SS as-received wires showed a surface with striations parallel to long axis as shown in [Figure 1]a. Pitting pattern was also noticed. SEM images of in vivo SS archwires revealed an increase in a number of surface regularities and parallel striations as shown in [Figure 1]c.
|Figure 1: Scanning electron microscope images of stainless steel wires at ×1000 magnification: (a) Subgroup A1 (as received stainless steel wire image), (b) subgroup B1 (autoclaved stainless steel wire image), (c) subgroup C1 (clinically retrieved stainless steel wire image)|
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Nitinol wires demonstrated a highly irregular surface with striations in the longitudinal axis and areas of pores or white inclusion spots as shown in [Figure 2]. Nitinol wires showed more indentations and pitting corrosion after recycling as shown in [Figure 2]c.
|Figure 2: Scanning electron microscope images of nitinol wires at ×1000 magnification: (a) Subgroup A2 (as received nitinol wire image), (b) subgroup B2 (autoclaved nitinol wire image), (c) subgroup C2 (clinically retrieved nitinol wire image)|
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TMA wires exhibited a rough surface with a large number of uniformly distributed pores as shown in [Figure 3]. There was no much variation seen in autoclaved specimen images and in vivo specimen micrographs.
|Figure 3: Scanning electron microscope images of beta-titanium wires at ×1000 magnification: (a) Subgroup A3 (as received beta-titanium wire image), (b) subgroup B3 (autoclaved beta-titanium wire image), (c) subgroup C3 (clinically retrieved beta-titanium wire image)|
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The present study evaluated Ra of all sample archwires in Group A, B, and C using 3D optical profilometer as shown in [Figure 4] and inter-group comparisons were analyzed using Tukey's post-hoc procedures.
|Figure 4: Profilometry images of archwires: (a) Subgroup A1 specimen image, (b) subgroup B1 specimen image, (c) subgroup C1 specimen image, (d) subgroup A2 specimen image, (e) subgroup B2 specimen image, (f) subgroup C2 specimen image, (g) subgroup A3 specimen image, (h) subgroup B3 specimen image, (i) subgroup C3 specimen image|
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Ra for SS wires in sub Group B1 showed higher values when compared with subgroup A1 which was not significant (P = 0.9391). Subgroup C1 wires showed higher Ra values when compared with subgroup A1 and was statistically significant (P = 0.0002) as illustrated in [Table 1].
|Table 1: Comparison of three stainless steel archwire groups (A1, B1, C1) with respect to arithmetic roughness (microns) by one-way ANOVA|
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Nitinol wires in subgroup C2 showed lower Ra values when compared with subgroup A2 and subgroup B2 and were statistically significant as depicted in [Table 2].
|Table 2: Comparison of three Nitinol archwire groups (A2, B2, C2) with respect to arithmetic roughness (microns) by one-way ANOVA|
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β-Ti wires in subgroup B3 showed higher Ra values when compared with subgroup A3 which was not significant (P = 0.7805). Subgroup C3 also showed higher Ra values when compared with subgroup A3 which was also not significant (P = 0.1337) as illustrated in [Table 3].
|Table 3: Comparison of three beta titanium archwire groups (A3, B3, C3) with respect to arithmetic roughness (microns) by one-way ANOVA|
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| Discussion|| |
Orthodontic archwires should be able to move teeth with a light continuous force. The availability of different alloys for orthodontic archwires has been one of the main breakthroughs in orthodontic materials research, leading to key improvements in the field of mechanotherapy.
The surface structure of an orthodontic archwire is an essential functional property known to influence the esthetic result, the corrosion behavior and the biocompatibility of devices. Furthermore, plaque accumulation is also affected by surface roughness variation and this in turn has a key role in corrosion behavior and esthetics. The surface properties such as roughness, hardness, and topography of orthodontic archwires may affect the sliding mechanics by influencing the coefficient of friction between the archwire and bracket. However, the relationship comprising roughness and frictional forces existing between wire and brackets is more complex and not yet totally clear.
In the present study, surface topography of archwires in all three groups was evaluated by SEM at ×100, ×1000, and ×2500 magnifications. Each archwire specimen appeared to have its characteristic surface structure. At ×100 magnification, SS wire has the smoothest surface, and beta III titanium wire exhibited an irregular roughest surface. There was no obvious difference in surface topography of used and as received samples. Striations parallel to long axis of archwire was noticed in all samples that may be resulted from archwire drawing process. At ×1000 and ×2500 magnifications, SS as received wires showed surface with striations parallel to long axis. These may be related to mechanical impact during manufacturing. Pitting pattern was also noticed, which may be resulted from chemical interactions during manufacturing. Scratches not parallel to long axis were observed on some samples. As received and autoclaved SEM images also showed similar patterns.
SEM images of in vivo SS archwires revealed an increase in number of surface irregularities generated by handling during orthodontic treatment.In vivo specimens showed an increase in parallel striations that may be attributed to handling of wires using orthodontic pliers. Handling with orthodontic pliers causes plastic deformation on surfaces and borders of archwires. SEM images also revealed corroded areas at irregularities caused not only by orthodontic treatment and manufacturing process but also at the bracket-archwire contact areas.
In contrast to SS wires, β-Ti wires exhibited a rough surface with a large number of uniformly distributed pores as reported extensively in literature.,, These rough surfaces are attributed to adherence or cold welding by titanium to the dies or rollers during processing. There was no much variation seen in autoclaved specimen images and in vivo specimen micrographs.
Nitinol wires demonstrated a highly irregular surface with striations in the longitudinal axis. It depicted the stripes and markings inflicted on the wire during manufacture. This high roughness is mainly ascribed to the grain re-crystallizations that occur when NiTi wires are pulled through diamond moulds during its fabrication. SEM images also showed areas of pores or white inclusion spots that are characteristically described for NiTi wires., Nitinol wires showed more indentations and pitting corrosion after recycling. Initiation of this process may take place before intra-oral placement as surfaces of as received specimens exhibited crevices and pores. Surface irregularities observed in NiTi archwires are sites susceptible to the selective dissolution of Ni, may arise from manufacturing process  and the patterns differs with various manufacturers. Wire regions engaged to bracket slot showed surfaces demonstrating excessive wear and characteristic patterns of delamination. This may be attributed to compressive forces accompanying wire activation through ligation and possible frictional damage produced inside the slot.
A point of consideration is that the high magnification of SEM limited the investigation and interpretation of the surface topography of a smaller area of the wires. The SEM images provide poorly reproducible subjective interpretations, which render comparisons with other interpretations difficult. Therefore, we additionally employed the 3D optical profilometry technique for quantitative measurement of surface roughness.
The surface roughness of orthodontic archwires is an essential factor in determining the effectiveness of archwire guided tooth movement. The surface quality of archwires also affects the area of surface contact and influences its corrosion behavior and biocompatibility. The surface roughness also has a role in color stability and performance of appliance using sliding mechanics.,
The surface roughness of orthodontic archwires may be measured using several methods including laser spectroscopy, contact-surface profilometry,,,, and atomic force microscopy.,,, Bourauel et al. compared the surface roughness of different wires by using these three techniques and stated that the results of these three methods generally correspond well. In the present study, Ra was measured using a 3D optical profilometry technique. SS exhibited a smooth surface with mean Ra of 0.01 µ, nitinol SE with mean Ra of 0.14 µ and beta III titanium with a mean Ra of 0.17 µ. Ra values increased in clinically retrieved archwires in all categories except in nitinol SE were a statistically significant decrease in Ra was found.
Profilometry values revealed no significant difference in the average roughness of any wires before or after sterilization. The present study evaluated a very low Ra values for SS as-received wires with a mean of 0.01 µ. After intra-oral exposure of 4 weeks, there was a significant increase in Ra. Similarly, Marques et al. reported a significant increase in debris and roughness after 8 weeks of intra-oral exposure. Marques et al. and Normando et al. found an increase in frictional force in wires after clinical use and they reported a significant positive correlation between Ra and friction. The frictional force between brackets and wires is considered a harmful factor that influences the normal movement of teeth during sliding mechanics. Among the selected alloys, TMA generally exhibits the maximum frictional force, probably as a result of abrasive and adhesive wear produced with the slot of the bracket.
Retrieved nitinol wires exhibited a significant reduction in the surface roughness when compared to as-received wires in the present study. Widu et al. observed a smoothening of the surface of NiTi archwires tested under corrosive environment and they hypothesized that this could be a consequence of flattening of peaks and troughs on the surface that results from manufacturing process. The present study result was different in opinion to various studies which exhibited considerable increase in surface roughness., The difference in archwire manufacturer and measurement methods might have influenced the outcome in those studies.
| Conclusion|| |
- SS wires showed a smooth surface in SEM images, and β-Ti showed the roughest surface
- Surface roughness values were least for SS wires and highest for β-Ti
- There was a significant increase in surface roughness of SS wires after clinical use whereas nitinol wires exhibited a decrease in roughness values after clinical use
- There was no significant difference in roughness in any archwire group after sterilization.
The increase in surface roughness can cause an increase in friction between wire and bracket during sliding mechanics. Surface defects and irregularities can also make orthodontic wires more prone for corrosion. The clinician should consider changes in these properties before recycling any of these archwires.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Department of Orthodontics and Dentofacial Orthopedics, Krishnadevaraya College of Dental Sciences, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]