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Article

Study of Al–SiO2 Aesthetic Composite Coating on Orthodontic Metal Archwire

by
Haopeng Wu
1,
Jie Yang
1,
Yuwen Yan
1,
Bowen Zheng
1,
Ahmed Lotf Algahefi
1,
Song Ma
2 and
Yi Liu
1,*
1
Liaoning Provincial Key Laboratory of Oral Diseases, School and Hospital of Stomatology, China Medical University, Shenyang 110002, China
2
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
*
Author to whom correspondence should be addressed.
Coatings 2022, 12(6), 746; https://doi.org/10.3390/coatings12060746
Submission received: 26 April 2022 / Revised: 24 May 2022 / Accepted: 26 May 2022 / Published: 29 May 2022
(This article belongs to the Special Issue 10th Anniversary of Coatings: Invited Papers in Corrosion, Wear and Erosion Section)
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Abstract

:
Nickel–titanium orthodontic wires (NTWs) play an essential role in orthodontic treatment. However, their corrosion and aesthetic properties limit their applications. To improve the aesthetic effects of nickel–titanium orthodontic archwires, we prepared aluminium–silicon dioxide (Al–SiO2) as a biocompatible layer coated onto the NTWs. The Al–SiO2 coating was first fabricated using physical vapor deposition magnetron sputtering, and its physicochemical and biocompatibility properties were investigated. Al–SiO2 layers were well coated on the NTWs. The corrosion currents in the nickel–titanium (NiTi) control, Al–SiO2-coated NiTi experimental, stainless steel (SS) control and Al–SiO2-coated SS experimental groups were 23.72 μA cm−2, 1.21 μA cm−2, 0.22 μA cm−2 and 0.06 μA cm−2, respectively. Al–SiO2-coated NTWs with reduced corrosion current density indicated that the preparation of Al–SiO2 coating on the surface of NiTi and SS could reduce the tendency of electrochemical corrosion. The friction coefficients of orthodontic wires in the NiTi control, NiTi experimental, SS control, and SS experimental groups were 0.68, 0.46, 0.58 and 0.45, respectively. A low friction coefficient was observed in the Al–SiO2-coated NTWs, and the reduced friction coefficient improved the efficiency of orthodontics. Furthermore, the excellent biocompatibility of the NTWs and SS coated with Al–SiO2 indicates that Al–SiO2 as a novel aesthetic layer could improve the physicochemical properties of NTW and SS without causing cytotoxicity, which has considerable potential for modification of NTW and SS surfaces.

1. Introduction

Brackets and archwires are two major parts of fixed appliances. In detail, brackets can align teeth under continuous forces exacted by the archwires. Although several aesthetic appliances have been utilized in orthodontic treatment, stainless steel (SS) brackets and nickel-titanium wires (NTWs) are still the most commonly used in clinical treatment [1].
Metal materials are vulnerable to corrosion when exposed to air or water [2], let alone the oral cavity, which is an extremely complex environment and easily affected by saliva, bacterial flora, food, temperature fluctuations and mechanical forces. Corrosion can increase the surface roughness of the metal surface, resulting in increased friction forces between the archwire and the bracket and subsequently hindering teeth movement. Additionally, the increased friction can accelerate the corrosion process under continuously increasing stress [3,4].
There are many kinds of commercially available aesthetic coatings. For example, rhodium coating, epoxy coating, polytetrafluoride coating, platinum and silver coating, and polymer coating [5,6,7,8] have inherent limitations and are therefore not widely used in clinical practice. Alsanea et al. [5] investigated the color stability of rhodium, epoxy resin, and polytetrafluoroethylene nickel titanium aesthetic coatings. They found that the archwires of polytetrafluoron coating, epoxy resin coating and rhodium aesthetic coating all changed after being immersed in a dyeing solution for 4 weeks, among which the polytetrafluoron coating changed most markedly. Pezzato et al. [9] evaluated the tribocorrosion behavior of plasma electrolytic oxide-coated AZ91 samples. Magnesium alloys are characterized by low wear resistance and poor corrosion resistance. After plasma electrolytic oxidation, the tribo-corrosion performance was markedly improved, indicating that the addition of the coating to the alloy surface can obviously improve the material properties. Rachele et al. [10] examined that wear and corrosion-caused metal ion release shortens the lifespan of a prosthesis. Cryogenic machining weakens the corrosion and fretting corrosion performance of the additive Ti6Al4V. Polyether ether ketone is a high-temperature thermoplastic polymer composed of aromatic main chain molecules connecting ketone and ether functional groups and has been used in the development of orthodontic archwire coating. Although it is cosmetically appealing, more studies are needed to determine its physical properties [6]. Researchers and clinicians have found that the current clinical aesthetic archwire coating is prone to damage under the masticatory force and oral salivary enzymes, along with color changes over time. Moreover, the archwire coating cracks and detaches during the force application, thus exposing the inner metal, increasing the surface roughness and further affecting the correction process [7,8]. Hence, development of archwires with stable coating properties and a certain level of corrosion or friction resistance is gaining interest in orthodontic treatment.
Aluminum (Al), the most abundant metal element on the planet, is widely used in biomedical materials. Silicon dioxide (SiO2) is a common modification layer given its superior physicochemical stability and biocompatibility. Importantly, the oxide layer may obstruct ion movement and release, improving metal mechanical properties and stability [11].
Magnetron sputtering can produce a uniform, smooth coating on the substrate surface. SiO2 is applied in many fields due to its rich properties, low cost, good chemical stability, and strong physical properties such as biocompatibility, high mechanical strength, wear resistance, corrosion resistance, hydrophobicity and high optical transparency [12,13,14]. The oxide layer can inhibit the outward movement of ions, thus becoming a barrier to ion release and playing a protective role against material decomposition [15,16,17]. SiO2 is widely used in metal protective coatings on metals and in biomedical and biotechnological applications while showing great potential in enzymes and metal catalysis, drugs, genes, protein transport, biological imaging, pollution repair, chromatography, and vector or carrier platforms for sensors and structural templates [14,18]. There are various methods for film preparation, such as micro-arc oxidation, physical vapor deposition magnetron sputtering (PVDMS), plasma spray, chemical vapor deposition, solvent-gel coating, ion beam-assisted deposition, and pulsed laser deposition [15,19,20,21,22,23,24,25]. Among them, magnetron sputtering is widely used to prepare SiO2 thin films, and the silica thin films produced through this process are transparent. Magnetron sputtering has many advantages: (i) strong binding force of coating and substrate; (ii) good metal surface uniformity; (iii) high deposition rate; (iv) high purity film; (v) easy to automate and high reproducibility; (vi) easy to sputter many metals and alloys; (vii) controllable film thickness; and (viii) low cost [5,17,26].
Considering the advantages of Al and SiO2, we prepared a novel modified layer based on the Al-SiO2 composite and explored its potential application in fixed appliances. In detail, the Al-SiO2 coating layer was first fabricated by PVDMS. Its physicochemical properties were evaluated utilizing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electrochemical corrosion and friction analysis [15,16,27,28]. Mouse fibroblasts were used to investigate the biocompatibility of Al-SiO2-coated samples.
Herein, we demonstrated the newly developed Al–SiO2 coated NiTi and SS archwires using PVDMS. The morphology of the Al–SiO2 coating was systematically characterized and its corrosion resistance was electrochemically assessed. Meanwhile, the wear and scratch tests were performed to confirm the friction coefficient and bonding strength. The biocompatibility properties were also investigated. This work aimed to confirm that the Al–SiO2 aesthetic composite coating was prepared based on the aesthetic appearance of Al coating and the corrosion resistance, low friction and wear resistance of silica to realize the combination of aesthetics with function.

2. Materials and Methods

2.1. Preparation and Characterization of Al–SiO2-Coated Samples

Commercial orthodontic SS archwires and NiTi archwires (NTA) were selected as substrates (Shanghai Emundi, 0.016 × 0.022 inch, Shanghai, China). Nearly equiatomic NTA consists of Ni (55 wt.%) and Ti. It is a special shape memory alloy that can automatically restore its own plastic deformation to its original shape at a specific temperature [29]. Moreover, 2 × 2 × 0.2 cm3 SS archwire and NTA samples were prepared for further research. Before delivery, the cross-sections were ground using 600-, 1000-, 1500- and 2000-grit silicon carbide (SiC) paper to remove the oxide layer. As it was mechanically polished, only 2.5 μm diamond grinding paste is used for further polishing. They were ultrasonically cleaned with acetone and alcohol for 15–20 min and blow-dried with argon.
An unbalanced magnetron sputtering coating system was employed. Figure 1 presents the schematic diagram of PVDMS process. The distance between the target materials and the specimen was 7 cm. Argon gas could be passed into the vacuum chamber when the pressure value in the vacuum was lower than 3 × 10−3 Pa. This sequentially initiated the process of pre-sputtering of the target with the following parameters: pressure, 0.5 Pa; pre-sputtering time, 15 min; time required for Al deposition, 10 min; SiO2 deposition time, 150 min; pulse voltage, 350 V; duty cycle, 15%; substrate voltage, 340 V; and deposition temperature, 250 °C.
SEM characterized specimens’ microstructure and surface morphology after gold spraying under vacuum pressure for 90 s. Additionally, the elemental composition of the coated layer was analyzed using EDS.

2.2. Cytotoxicity Tests

The cells used in this study were mouse fibroblasts NIH3T3. The experiment was divided into two groups: In the blank control group, uncoated SS archwires and Al–SiO2 aesthetic SS archwires were used; in the blank control group, uncoated NiTi archwires and Al–SiO2 aesthetic NiTi archwires were used. Mouse fibroblasts NIH3T3 were cultured at a density of 2 × 104 per sample for 1, 3, 5, and 7 days. Cell viability was evaluated using the Cell Counting Kit-8 (CCK-8, Beyotime, Shanghai, China). The samples were washed twice with phosphate-buffered saline at each time point. Fresh culture medium (200 μL) was mixed with 20 μL of CCK-8 reagent and the mixture was added to each sample. Then, the culture was incubated at 37 °C for 2 h. Subsequently, 100 μL of the medium was transferred to a 96-well plate and absorbance was measured at 450 nm.

2.3. Electrochemical Corrosion Experiments

The electrochemical work station CHI760D (Reference 600, Gamry company, Warminster, PA, USA) was used to investigate the electrochemical performance of the coated layer. A conventional three-electrode setup was used for electrochemical measurement, with Pt as a counter electrode, standard Ag/AgCl as the control, and the anodized specimen as the working electrode. To simulate the human oral environment, artificial saliva was prepared and included the following components: 0.4 g/L NaCl, 0.4 g/L KCl, 0.906 g/L CaCl2∙H2O, 0.69 g/L NaH2PO4∙2H2O, 0.005 g/L Na2S∙9H2O, and 1 g/L urea. Electrochemical tests were performed on the specimens in artificial saliva [30]. NiTi control, Al–SiO2-coated NiTi experimental, SS control and Al–SiO2-coated SS experimental groups were used. Uncoated surface was sealed with nail polish at room temperature. Dynamic polarization curves were recorded when open circuit potential was stable. Scanning speed was 0.33 mV·s−1, and scanning range was from −0.1 V to 1.5 V. Ecorr and its current density, icorr were defined from collected Tafel quantitative data.

2.4. Wear Test

A rotary friction and wear machine (Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences) was used to investigate the friction and wear performance of the coated layers. The test conditions are presented in Table 1. The counterpart for the friction test was an Al2O3 ball with a diameter of 4 mm. The test was performed at room temperature in the NiTi control, Al–SiO2-coated NiTi experimental, SS control and Al–SiO2-coated SS experimental groups. The friction and wear of the coating were generally divided into three phases, namely the running-in phase, stable phase, and failure phase. Then, the average value of the friction coefficient in the stable phase was recorded as the friction coefficient of the coating.

2.5. Scratch Test

The bonding strength of the coating layers was tested using an MFT-4000 scratch tester (Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, China). Test parameters were depicted as follows: radius, 0.2 ± 0.01 mm; scratch length, 5 mm; loading speed, 30 N·min−1; end load: 70 N. Scratch test was performed in the NiTi control, Al–SiO2-coated NiTi experimental, SS control and Al–SiO2-coated SS experimental groups.

2.6. Statistical Analysis

Statistical analysis was performed using SPSS 21.0 software (IBM Corporation, Armonk, NY, USA). All data are represented as mean ± standard deviation. One-way analysis of variance (ANOVA) was used to evaluate the statistical significance among the four groups. A paired t-test was used to evaluate the differences between the two groups. A p-value of <0.05 was considered statistically significant. All experiments were performed in triplicate to ensure reproducibility.

3. Results

3.1. Coating Morphology Analysis

The cross-section and surface morphologies of the coating layers are shown in Figure 2. As shown in Figure 2a, the thickness of the coated layers was 1.8 μm. SEM findings regarding surface morphologies of Al–SiO2-coated SS and Al–SiO2-coated NiTi are shown in Figure 2b,c. All samples displayed uniform and dense layers securely attached to the substrate without any interfacial defects. Figure 2d shows the Al–SiO2 coating, and its surface revealed a clear, smooth spherical structure. Al–SiO2 coated on the SS and NiTi archwires is shown in Figure 2e,f, respectively. The color of the prepared aesthetic archwire was similar to that of the teeth, and the aesthetic effect was achieved.

3.2. EDS Analysis

Figure 3 shows the EDS findings of the particle distribution of the coatings. Uniform distribution of Al, O and Si elements was observed across the whole layer in the samples, which demonstrated that the Al–SiO2 layers were well coated on the samples.

3.3. Cytotoxicity

The cytotoxic level of the archwires was measured using a CCK-8 kit at 1, 3, 5, and 7 days (Figure 4). Statistical results showed that there was no significant difference in cytotoxic levels among the blank control, uncoated NiTi, and Al–SiO2-coated NiTi groups. The three groups’ optical density (OD) values increased with the increase in culture time, indicating that the cells grew well and preserved proliferation ability. Similarly, there was no significant difference in OD values among the other blank control, uncoated SS and Al–SiO2-coated SS groups at 1, 3, 5, and 7 days and OD values in each of the three groups also increased with culture time. According to the cytotoxicity assessment, the OD values of the coated layer archwire in the experimental group were lower than those in the control group. The above results indicated no cytotoxicity of the coated archwire in the experimental group.

3.4. Electrochemical Corrosion Experiment

The results of the electrochemical experiments are shown in Figure 5. The corrosion currents in the NiTi control, NiTi experimental, SS control, and SS experimental groups were 23.72 μA cm−2, 1.21 μA cm−2, 0.22 μA cm−2 and 0.06 μA cm−2, respectively. The icorr values decreased considerably from 23.72 μA cm−2 to 1.21 μA cm−2 while coating with Al–SiO2 on the NiTi sample. Meanwhile, the icorr value for Al–SiO2 coated SS sample as 0.06 μA cm−2 was lower than the SS sample of 0.22 μA cm−2. The polarization current shows that the preparation of the Al–SiO2 coating on the surface of NiTi and SS could reduce the tendency of electrochemical corrosion. Therefore, Tafel extrapolation results demonstrate that the Al–SiO2 coating improved the corrosion resistance of the archwires. A summary of the electrochemical test quantitative data is shown in Table 2.

3.5. Friction and Wear Properties

The friction coefficient curve of the coated layers is shown in Figure 6. The recorded friction process was divided into two phases. In phase I, the friction coefficient changed over time, which was in the unstable running-in phase. In phase II, the friction coefficient tended to be stable. The mean value of the friction coefficient in the stable phase was recorded as the friction coefficient of the coating. NiTi control and experimental groups showed a steady-state friction coefficient after an initial 12 min of sliding, which indicated a transmission from phase I to phase II. The SS control and experimental groups showed a steady-state friction coefficient after an initial 9 min of sliding. The friction coefficients of the NiTi control and experimental groups, SS control and experimental groups were 0.68, 0.46, 0.58 and 0.45, respectively.

3.6. Bonding Strength

The critical load (Lc) is at the peak of the curve, as shown in Figure 7. The position of the inflection point coincided with the location of the first acoustic signal, which corresponded to the Lc. The Al–SiO2-coated NiTi archwire’s and SS archwire’s mean Lc values were 15.07 N and 8.3 N, respectively. High-vacuum plasma ion titanium sputtering was carried out on the NiTi archwires with a titanium disc (>99.9%) as the sputtering target material, according to the experiment by Anuradha et al. [31]. The coatings were found to be relatively stable in a linear scratch test when the Lc was >8 N. Therefore, 8 N was used as a control group to evaluate the binding force of the Al–SiO2 coating. The Al–SiO2 coatings were found to be relatively stable in the linear scratch test and could meet clinical requirements.

4. Discussion

For the development of esthetic dental appliances, orthodontic archwires must meet certain requirements before being used clinically; these include high strength, low friction, corrosion resistance, friction resistance, and biocompatibility [32]. Various coatings were developed to modify the surface of orthodontic archwires to improve their physicochemical and biological properties. In this study, Al–SiO2-coated layers were used to create esthetic orthodontic archwires with good biocompatibility and physical properties.
The CCK-8 (cell counting kit-8) was tested at various time intervals (1, 3, 5, and 7 days) as shown in Figure 3 and Figure 4. There was no significant difference in cytotoxicity between the Al–SiO2 samples and the control group. Therefore, Al–SiO2-coated layers could be considered safe and useful for clinical application.
Various substances in the mouth can cause electrochemical corrosion reactions on the surface of the archwires [33]. Since different metallic elements are present in the mouth, it may lead to electro-galvanic cell formation, which can contribute to corrosion. Microorganisms such as sulfate-reducing bacteria may also be present in the metabolic flora of the oral cavity, which can cause biological corrosion. Therefore, the presence of microorganisms can change the state of the biomaterial surface and accelerate the biological corrosion process [34]. The formation of biofilms leads to changes in oral cavity parameters including pH, electrolytic concentration and oxygen levels. Furthermore, there are three types of corrosive cells in the oral environment: cells with varying degrees of oxygenation, cells containing different concentrations of metal ions and active–passive cells [34,35,36]. Currently, the corrosion resistance of aesthetic archwires in clinical practice needs further improvement. The rhodium coating is aesthetically pleasing but has low corrosion resistance, which may be due to galvanic coupling between the noble coating and the base alloy [37]. Previous literature has investigated polymer coatings such as epoxy resins, which reduce the corrosion resistance of archwires compared to uncoated NiTi and SS archwires [38]. Therefore, it is urgent to produce orthodontic archwires with a high level of corrosion resistance. The current findings demonstrated that Al–SiO2 coatings could reduce the corrosion rates of NiTi and SS archwires in artificial saliva through polarization curves, which were achieved from corrosion tests. The microstructures and compositions of the Al–SiO2 coatings with a smooth surface are uniform and could well protect the surface of the archwires.
To the best of our knowledge, the presence of friction may have affected the efficiency of tooth movement during fixed orthodontic treatment. Kusy et al. [39] demonstrated that friction could reduce 12%–60% of the orthodontic force during orthodontic treatment, influencing clinical treatment. Previous research has verified that certain aesthetic-coated archwires can increase the roughness [40]. Moreover, some studies have investigated the microscopic observations of uncoated archwires and rhodium-coated aesthetic archwires. The results show that rhodium archwires increase the roughness of NiTi archwires [31,40]. Another study found that the surface roughness of rhodium-coated archwires was similar to that of uncoated archwires [31]. However, compared to uncoated archwires, Teflon- and epoxy-coated archwires showed a significant difference in surface roughness. The surface roughness of the epoxy coating was reported to be higher than that of the Teflon coating [5]. The latter can meet aesthetic requirements; however, the coating’s surface roughness is unacceptable. The friction coefficients of Al–SiO2-coated SS and NiTi archwires were lower than those of uncoated groups, according to the wear test results in this study. Therefore, Al–SiO2-coated layers produced by magnetron sputtering improve the friction resistance of orthodontic archwires.
The thickness of the coating is an essential factor that is closely related to the expression of torque. The thickness of the coating achieved by the PVD is thinner than that achieved by electroplating and electroless plating [41]. Anuradha et al. [42] reported a uniform, dense titanium coating layer observed by magnetron sputtering, with a thickness ranging from 3–5 μm. Woowa aesthetic archwire has a compound, double-layered coating structure with a silver and platinum coating on the inside and a special polymer coating on the outside with a thickness of 10 μm [42]. Alavi and Hosseini [43] found that the thickness of the epoxy resin coating on G and H1 wire was approximately 0.05 mm. These archwires were used in clinical applications. The thickness of the Al–SiO2 coating in this experiment is about 1.8 μm, which is obviously less than the thickness of the current clinical aesthetic coatings. Therefore, the Al–SiO2 coating has little impact on the size of the archwire, and the Al–SiO2 coating prepared by magnetron sputtering can be used on the surface of orthodontic archwires.
Al–SiO2-coated archwires have various advantages, including aesthetics, corrosion resistance, bonding strength, and biological safety compared with uncoated archwires. The Al–SiO2 coating can meet the mechanical properties necessary for orthodontics and match the aesthetics that metal archwires cannot achieve. The newly formed Al–SiO2-coated layers exhibited a color difference that was nearly identical to that of commercially used coated wires in the clinic. However, the color of the Al–SiO2-coated layer must be further optimized and validated through fading experiments to better approximate the natural color of the teeth. Because this study was conducted under ideal laboratory conditions, the presence of saliva, plaque, and corrosion in the oral cavity may affect the archwire’s performance [44]. Further research is needed to simulate orthodontic tooth movement concerning the clinical scenario for specific evaluation under different situations, focusing on optimizing the Al–SiO2-coated archwire. Further improvements in the technological parameters and manufacturing technology are needed to increase the bonding force of the coating.

5. Conclusions

This work shows that the stable Al–SiO2 coatings with strong binding force were successfully fabricated on NiTi and SS archwires by PVDMS. Compared with uncoated ones, Al–SiO2 coatings provide better surface smoothness and markedly increase the corrosion resistance of NiTi and SS archwires, which will greatly enhance the efficiency of orthodontic treatment. The Al–SiO2 coating has no apparent cytotoxicity, indicating the possession of good biocompatibility, while the physicochemical properties of Al–SiO2 coating markedly improve the aesthetics of the archwires. This Al–SiO2 coating has excellent potential in orthodontic clinical treatment, which will provide a new idea for the research and development of multifunctional dental biomaterials.

Author Contributions

Conceptualization: H.W.; Data curation: J.Y. and B.Z.; Formal analysis: Y.Y. and H.W.; Investigation: J.Y. and S.M.; Supervision: Y.L.; Writing—original draft: H.W.; Writing—review and editing: S.M., Y.L. and A.L.A. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the Shenyang Young and middle-aged Scientific and technological Innovation Talents Support Program (RC210001), the Liaoning Province Key Research and Development Guidance Plan Project (Grant No. 2020JH2/10300038), and the Shenyang Science and Technology Project (20-205-4-099).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors would like to express their thanks to teachers and students in the Experimental Centre of School and Hospital of Stomatology, China Medical University, for their continuous help and support.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The schematic diagram of the physical vapor deposition magnetron sputtering process.
Figure 1. The schematic diagram of the physical vapor deposition magnetron sputtering process.
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Figure 2. SEM observation of Al–SiO2 coating and the macroscopic observation of archwire. Thickness of Al–SiO2 coating layer (a); cross-section of the Al–SiO2-coated SS (b); cross-section of the Al–SiO2-coated NiTi (c); SEM findings regarding surface morphology of Al–SiO2-coated layer (d); the macroscopic observation of NiTi archwire (e); the macroscopic observation of SS archwire (f).
Figure 2. SEM observation of Al–SiO2 coating and the macroscopic observation of archwire. Thickness of Al–SiO2 coating layer (a); cross-section of the Al–SiO2-coated SS (b); cross-section of the Al–SiO2-coated NiTi (c); SEM findings regarding surface morphology of Al–SiO2-coated layer (d); the macroscopic observation of NiTi archwire (e); the macroscopic observation of SS archwire (f).
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Figure 3. EDS mapping images of Al–SiO2 coating.
Figure 3. EDS mapping images of Al–SiO2 coating.
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Figure 4. Cytotoxicity test for the coated archwires. Optical density values at different time points in the NiTi group (a). Optical density values of mouse fibroblasts at different time points in the SS group (b).
Figure 4. Cytotoxicity test for the coated archwires. Optical density values at different time points in the NiTi group (a). Optical density values of mouse fibroblasts at different time points in the SS group (b).
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Figure 5. Electrochemical results for the coated archwires. Dynamic polarization curve of the NiTi group (a). Dynamic polarization curve of the SS group (b).
Figure 5. Electrochemical results for the coated archwires. Dynamic polarization curve of the NiTi group (a). Dynamic polarization curve of the SS group (b).
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Figure 6. Friction coefficient curve of the coated layers. NiTi group (a); SS group (b).
Figure 6. Friction coefficient curve of the coated layers. NiTi group (a); SS group (b).
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Figure 7. The scratch test of the coated archwires. The coating of NiTi specimen (a). The coating of SS specimen (b).
Figure 7. The scratch test of the coated archwires. The coating of NiTi specimen (a). The coating of SS specimen (b).
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Table
Table 1. Process parameters for the wear test.
Table 1. Process parameters for the wear test.
Friction PairsLoad (N)Turning Radius (mm)Speed (r/min)Test Time (min)
Alumina ball (Ø = 4 mm)1320030
Table
Table 2. Corrosion parameters from the polarization curves.
Table 2. Corrosion parameters from the polarization curves.
SampleEcorr/V vs. SCEicorr/μA cm−2
Uncoated NiTi−0.18 ± 0.0223.72 ± 4.99
Al–SiO2-coated NiTi−0.60 ± 0.081.21 ± 0.48
Uncoated SS−0.20 ± 0.030.22 ± 0.09
Al–SiO2-coated SS−0.61 ± 0.100.06 ± 0.01
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Wu, H.; Yang, J.; Yan, Y.; Zheng, B.; Algahefi, A.L.; Ma, S.; Liu, Y. Study of Al–SiO2 Aesthetic Composite Coating on Orthodontic Metal Archwire. Coatings 2022, 12, 746. https://doi.org/10.3390/coatings12060746

AMA Style

Wu H, Yang J, Yan Y, Zheng B, Algahefi AL, Ma S, Liu Y. Study of Al–SiO2 Aesthetic Composite Coating on Orthodontic Metal Archwire. Coatings. 2022; 12(6):746. https://doi.org/10.3390/coatings12060746

Chicago/Turabian Style

Wu, Haopeng, Jie Yang, Yuwen Yan, Bowen Zheng, Ahmed Lotf Algahefi, Song Ma, and Yi Liu. 2022. "Study of Al–SiO2 Aesthetic Composite Coating on Orthodontic Metal Archwire" Coatings 12, no. 6: 746. https://doi.org/10.3390/coatings12060746

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