Effects of nanostructured, diamondlike, carbon coating and nitrocarburizing on the frictional properties and biocompatibility of orthodontic stainless steel wires

Development and Evaluation of a New Orthodontic Ligature: Frictional Force Analysis

OBJECTIVE

 To evaluate and compare the friction of different ligature modes used in orthodontics, and to propose a new ligature model for conventional brackets ("H low-friction orthodontic ligature).

MATERIALS AND METHODS

 Samples were randomly divided into seven experimental groups: (1) resin H ligature (H3D), designed by the authors of this study and produced in a 3D printer, with conventional bracket; (2) metal H ligature (HFM), with conventional bracket; (3) passive self-ligating bracket (SLP); (4) "8" low-friction unconventional elastic (LT8), with conventional bracket; (5) loose conventional metal ligature (MLS), with conventional bracket; (6) conventional metal ligature fully tightened (MLT), with conventional bracket; (7) conventional elastic ligature (CEL), with conventional bracket-control. All samples were subjected to mechanical static friction testing using the EMIC DL 2000 universal testing machine.

STATISTICAL ANALYSIS

 To assess the normality requirement, the Shapiro-Wilk test was used, which showed a non-normal distribution for the means of the groups (p < 0.05). Therefore, statistical tests were performed to assess the existence of statistically significant differences between the groups through the Kruskal-Wallis, followed by Dunn's test, pairwise comparison, p < 0.05.

RESULTS

 The results obtained showed lower friction values for HFM (0.002 kgf), SLP (0.003 kgf), and LT8 (0.004 kgf)-these did not differ statistically from each other. These were followed by H3D (0.020 kgf), MLS (0.049 kgf), CEL (0.12 kgf), and, finally, MLT (0.21 kgf).

CONCLUSION

 The lowest friction value was found for the metal H ligature, similar to the self-ligating bracket and the "8" low-friction unconventional elastic. The resin H ligature presented intermediate friction values and the highest friction force was found for the MLT group.

Functional Surface Coatings on Orthodontic Appliances: Reviews of Friction Reduction, Antibacterial Properties, and Corrosion Resistance

Surface coating technology is an important way to improve the properties of orthodontic appliances, allowing for reduced friction, antibacterial properties, and enhanced corrosion resistance. It improves treatment efficiency, reduces side effects, and increases the safety and durability of orthodontic appliances. Existing functional coatings are prepared with suitable additional layers on the surface of the substrate to achieve the abovementioned modifications, and commonly used materials mainly include metal and metallic compound materials, carbon-based materials, polymers, and bioactive materials. In addition to single-use materials, metal-metal or metal-nonmetal materials can be combined. Methods of coating preparation include, but are not limited to, physical vapor deposition (PVD), chemical deposition, sol-gel dip coating, etc., with a variety of different conditions for preparing the coatings. In the reviewed studies, a wide variety of surface coatings were found to be effective. However, the present coating materials have not yet achieved a perfect combination of these three functions, and their safety and durability need further verification. This paper reviews and summarizes the effectiveness, advantages and disadvantages, and clinical perspectives of different coating materials for orthodontic appliances in terms of friction reduction, antibacterial properties, and enhanced corrosion resistance, and discusses more possibilities for follow-up studies as well as for clinical applications in detail.

Evaluation of surface-modified orthodontic wires by different concentration and dipping duration of titanium oxide (TiO2) nanoparticles

OBJECTIVE

To evaluate in-vitro surface characteristics and frictional properties of orthodontic stainless steel and beta-titanium archwires after surface modification with different concentrations and coating time of titanium oxide (TiO₂) nanoparticles by Sol-gel dip coating method.

MATERIALS AND METHODS

The experiment was carried out with 4 different concentrations (1:2, 1:4, 1:6, and 1:8) and three different dipping durations (24 hours, 48 hours, and 72 hours) over ten main test groups of SS and TMA archwires with uncoated wires acting as control in both dry and wet conditions. Phase analysis and surface characterization of TiO₂ was analyzed by X-ray Diffractometry, surface evaluation with the help of scanning electron microscopy (SEM), and frictional characteristics were evaluated.

RESULTS

Among all the concentrations 1:6 ratio with 48 hours of dipping duration showed better surface characteristics. A statistically significant difference in frictional coefficient was observed in both SS and TMA wires than their respective controls (p = 0.001). Intragroup comparison among SS and TMA groups showed that groups with 1:6 ratio and 48 hours dipping duration had least frictional coefficient in both dry and wet conditions (p = 0.001). Intergroup comparison between SS and TMA showed that SS group had significantly reduced friction than TMA (p = 0.001) except in few groups.

CONCLUSION

TiO₂ nanoparticle with a concentration ratio of 1:6 and 48 hours dipping duration is recommended for surface modification of orthodontic archwires.

Application of nanoparticles in Dentistry

Nanoparticles(NPs) are of particle sizes lesser than 100nm and are insoluble the field which deal with the handling of these particles is coined as "Nanotechnology" as their particle size is smaller, they can penetrate easily therefore they are applied in various medical fields, drug delivery and in dentistry as they have antimicrobial property, reduces friction, anti-inflammatory and antioxidant property. Many studies have been done to evaluate its application and its cytotoxicity by varying its concentration and various studies have been done to evaluate its physical property. Therefore, it is of interest to describe concepts of nanoparticles, mode of action, tissue reaction and its application in orthodontics.

Effect of Graphene Sheets Embedded Carbon Films on the Fretting Wear Behaviors of Orthodontic Archwire-Bracket Contacts

Carbon films were fabricated on the orthodontic stainless steel archwires by using a custom-designed electron cyclotron resonance (ECR) plasma sputtering deposition system under electron irradiation with the variation of substrate bias voltages from +5 V to +50 V. Graphene sheets embedded carbon (GSEC) films were fabricated at a higher substrate bias voltage. The fretting friction and wear behaviors of the carbon film-coated archwires running against stainless steel brackets were evaluated by a home-built reciprocating sliding tribometer in artificial saliva environment. Stable and low friction coefficients of less than 0.10 were obtained with the increase of the GSEC film thickness and the introduction of the parallel micro-groove texture on the bracket slot surfaces. Particularly, the GSEC film did not wear out on the archwire after sliding against three-row micro-groove textured bracket for 10,000 times fretting tests; not only low friction coefficient (0.05) but also low wear rate (0.11 × 10^-6 mm³/Nm) of the GSEC film were achieved. The synergistic effects of the GSEC films deposited on the archwires and the micro-groove textures fabricated on the brackets contribute to the exceptional friction and wear behaviors of the archwire-bracket sliding contacts, suggesting great potential for the clinical orthodontic treatment applications.

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

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.

Incorporation of Plant Extracted Hydroxyapatite and Chitosan Nanoparticles on the Surface of Orthodontic Micro-Implants: An In-Vitro Antibacterial Study

In our study, the structural and morphological applications of hydroxyapatite and chitosan nanoparticles and coated micro-implants were assessed for their ability to combat oral pathogenic bacteria. The hydroxyapatite, as well as chitosan nanoparticles, were synthesized from the Salvadora persica plant. The crystal morphology, phase composition, particle size, and surface functional groups of the nano-samples were analyzed via classical examinations and energy dispersive X-ray analysis. The prepared nanoparticles have been examined for antibacterial activity against four common oral bacterial strains. The antimicrobial effect was also assessed by the Live/Dead BacLight technique in combination with confocal scanning laser microscopy. Titanium micro-implants were coated with regular hydroxyapatite (HAP) and chitosan nanoparticles, and the surface was characterized by scanning electron microscopy. The analysis asserted elemental composition of the prepared nanoparticles and their textural features, metal crystallization, and functional bonds. The antibacterial activity of the nanoparticles was evaluated against oral pathogenic microorganisms by the disc diffusion method, minimum bacterial concentration (MBC), and minimum inhibitory concentration (MIC). Chitosan nanoparticles showed (MICs) of 8 μg mL⁻¹ for (Streptococcus salivarius, Streptococcus mutans and Enterococcus faecalis), and 16 μg mL⁻¹ for Streptococcus sanguinis. HAP nanoparticles showed (MICs) of 16 μg/mL for E. faecalis, and S. sanguis, 8 μg/mL for S. salivarius and finally 4 μg/mL for S. mutans. HAP nanoparticles showed enhanced antibacterial activity and more obvious damage in the bacterial cell membrane than that of synthesized chitosan nanoparticles. The prepared nanoparticles could successfully coat titanium microplates to enhance their efficiency.

Investigation of the effects of orthodontic brackets coated by silver hydroxyapatite, copper oxide, and titanium oxide nanoparticles on wire-bracket friction

Objectives:

Coating orthodontic brackets with metal nanoparticles seem to affect surface roughness and friction. We aim to compare the effects of coating brackets with copper oxide (CuO), titanium dioxide (TiO2), and silver hydroxyapatite (S-HAP) on friction between brackets and various sizes and materials of orthodontic wires.

Material and Methods:

In this experimental study, we selected four groups of stainless steel (SS) brackets with eight orthodontic wires (SS and nickel-titanium [Niti]) in different sizes. Three groups were coated with CuO, TiO2, and S-HAP nanoparticles using dip coating. Then, we attached a 100 g weight to the wires and hung it from the universal testing machine. The wire passed through the brackets at a speed of 0.5 mm/min for 25 s. Finally, the friction between wires and brackets was compared using a two-way analysis of variance.

Results:

The results showed that friction of brackets coated with TiO2 was significantly lower than S-HAP (P = 0.021) and did not differ significantly between CuO and the control (P = 1). Furthermore, friction between CuO brackets was not significantly different from other groups (P > 0.05). Niti round wires had significantly lower friction with all brackets compared to 0.16 × 0.22 square inch Niti wire (p< 0.05), which, in turn, showed significantly lower friction compared to 0.16 × 0.22 square inch stainless steel (SS) wire (P = 0.008).

Conclusion:

Coating brackets with TiO2 and CuO nanoparticles can reduce the friction Moreover, Niti round wires show the least friction compared to rectangular or SS wires with all types of brackets.

Structural, Mechanical, and Decorative Properties of Sputtered TiN and Ti (N, C) Films for Orthodontic Applications; an In Vitro Study

In this paper, we explore and modify the structural, mechanical, and decorative properties of films composed by TiN and Ti (N, C) with a wide range of N₂ gas flow during the deposition in order to be used on orthodontic systems. The films were grown using reactive DC magnetron sputtering from a pure Ti target and customized with C pellets onto Si and stainless steel 316L substrates. The structural properties were studied using X-ray diffraction and scanning electron microscopy, while the mechanical ones were obtained through hardness, elastic modulus, and friction coefficient. Moreover, the wear rate has been measured under an artificial saliva medium to simulate the oral cavity. The color of the films deposited onto stainless steel 316 L substrate was characterized through CIELab color code. Our findings show that the addition of N₂ and C in the Ti matrix improves the mechanical properties of the films. With the increase in the amount of N₂ and C, the hardness reaches a value of 739 HV, higher than the one reported in the literature (600 HV), a low value of the coefficient of elasticity (8.0 GPa), and also a low friction coefficient (0.30). Moreover, with the addition of N₂ and C in the Ti films, the color of the films changes from metallic aspect until “with” gold, which means that our coatings exhibit versatile mechanical and color characteristics to be used in orthodontic wires applications.

Evaluating the Mechanical Properties of Zinc-Coated Stainless Steel Orthodontic Wires Using Physical Vapor Deposition

The aim of this study was to evaluate the mechanical properties of stainless steel (SS) orthodontic wires coated with zinc (Zn), using a Physical Vapored Deposition (PVD) machine. A total of 100 straight SS orthodontic wires were cut into pieces of 5 centimeters in length and were divided into two groups. Half of the wires were coated with Zn using a PVD machine, and the others remained uncoated. Tensile strength (n = 15), three-point bending (n = 15), and frictional resistance at 0° (n = 10) and 10° (n = 10) were measured to compare the mechanical properties of the Zn-coated and uncoated orthodontic wires using the universal testing machine. The surface of the coated wires was observed by SEM and AFM. An independent t-test, multivariate ANOVA, and measurement ANOVA were used for data analysis. SEM and AFM showed a homogenous Zn layer of 0.28 ± 0.006 µm on the SS wires. The tensile strength and three-point bending strength significantly increased after Zn coating of wires with the PVD method (P < 0.05). The friction resistance significantly reduced at both angulations following the coating procedure. The angle between the wire and bracket had no significant effect on the frictional resistance (P > 0.05). Coating with Zn improved the tensile and load-bending strength of SS orthodontic wires and reduced their frictional resistance which might be advantageous in terms of reducing the risk of root resorption during the orthodontic treatment.

Functional Coatings for Orthodontic Archwires-A Review

In this literature review, the current state-of-art of coatings for orthodontic archwires’ increasing antimicrobial and relevant mechanical properties, such as surface topography, friction or corrosion resistance, has been presented. There is a growing request for orthodontic appliances, therefore, most researchers focus on innovative functional coatings to cover orthodontic archwires and brackets. Orthodontic appliances are exposed to the unfavorable oral cavity environment, consisting of saliva flow, food, temperature and appliance force. As a consequence, friction or biocorrosion processes may occur. This can affect the functionality of the orthodontic elements, causing changes in their microstructure, surface topography and mechanical properties. Furthermore, the material which the orthodontic archwire is made from is of particular importance in terms of the possible corrosion resistance. This is especially important for patients who are hypersensitive to metals, for example, nickel, which causes allergic reactions. In the literature, there are some studies, carried out in vitro and in vivo, mostly examining the antibacterial, antiadherent, mechanical and roughness properties of functional coatings. They are clinically acceptable but still some properties have to be studied and be developed for better results. In this paper the influence of additives such as nanoparticles of silver and nitrogen-doped TiO₂ applied on orthodontic brackets by different methods on the antimicrobial properties was analyzed. Future improvement of coating techniques as well as modification of the archwire composition can reduce the release of nickel ions and eliminate friction and bacterial adhesion problems, thus accelerating treatment time.

Evaluation of titanium dioxide coating on surface roughness of nickel-titanium archwires and its influence on Streptococcus mutans adhesion and enamel mineralization: A prospective clinical study

INTRODUCTION

This research aimed to evaluate the effect of titanium dioxide (TiO₂) coating on surface roughness (R_a) of nickel-titanium (NiTi) archwires and its influence on Streptococcus mutans (S mutans) adhesion and enamel mineralization at the end of 1 month in orthodontic patients and to evaluate the integrity of the TiO₂ coating.

METHODS

Twelve patients undergoing orthodontic treatment with preadjusted edgewise appliance formed the sample for this prospective clinical study. Uncoated NiTi archwires and TiO₂ nanoparticle coated NiTi archwires in as-received condition and after 1 month of intraoral use were subjected to R_a analysis using surface profilometry, and surface topography using scanning electron microscopy. S mutans adhesion was evaluated on the retrieved archwires using real-time polymerase chain reaction (PCR). Enamel mineral content in the arches related to the uncoated and coated archwires was evaluated using DIAGNOdent.

RESULTS

After 1 month of intraoral use, both coated and uncoated archwires exhibited a rougher surface with coated archwires demonstrating greater quantum of increase (control, P = 0.002; experimental, P = 0.002). S mutans adhesion was more in uncoated archwires (P = 0.0005). The TiO₂ nanoparticle coating on the NiTi archwires showed delamination, deterioration and was lost by 60% at the end of 1 month. Laser fluorescence values did not show any significant difference (control, P = 0.182; experimental, P = 0.105).

CONCLUSIONS

TiO₂ nanoparticle coating on NiTi archwires causes an initial reduction in roughness; however, at the end of 1 month, the benefit was lost. S mutans adhesion was lesser on the coated wires, which could be attributed to reduced initial R_a and antibacterial property of TiO₂. Orthodontic archwire appears to have a limited role in enamel demineralization.

Thermo-Mechanical Properties of Glass Fiber Reinforced Shape Memory Polyurethane for Orthodontic Application

OBJECTIVES

Glass fiber reinforced shape memory polyurethane (GFRSMPU) has great potential to be an alternative kind of material for orthodontic archwires for overcoming the disadvantages of metal wires in terms of esthetic and allergy and deficiency of pure shape memory polyurethane (SMPU) wires in mechanical properties. The objective of this study was to investigate the thermo-mechanical properties and shape recovery functions of GFRSMPU and evaluate the feasibility of using this composite for orthodontic archwires.

MATERIAL AND METHODS

GFRSMPU were made from short cut glass fibers and SMPU by mixing extrusion. Scanning electron microscope (SEM) and differential scanning calorimetry (DSC) were performed to investigate the distribution of glass fibers in the mixture and glass transition temperature (T_g). Then the thermo-mechanical properties, including tensile modulus, flexural modulus and stress relaxation effects, were measured. Furthermore, shape recovery functions of GFRSMPU characterized by the shape recovery ratio and force were investigated through shape recovery tests, typodont models and finite element analysis (FEA).

RESULTS

SEM images indicated that an excellent dispersity of glass fibers was obtained after double-extrusion. DSC experiments showed T_g was not enormously affected with the existence of glass fibers, but the mechanical properties of GFRSMPU were greatly improved. Shape recovery tests showed reduction of shape recovery ratio of the GFRSMPU material with the addition of glass fibers, but dentition aligning time was reduced by 50% in the simulation performed on identical typodont models with GFRSMPU archwires filled with 30 wt.% glass fibers. The FEA results illustrated that the reacting forces of GFRSMPU archwires with 30 wt.% glass fiber was increased by 96.36% compared with pure SMPU archwires.

CONCLUSIONS

The mechanical properties of GFRSMPU can be considerably improved by adding glass fibers, and the shape memory function would be well preserved too. Enhanced SMPU owns a good application prospect in orthodontics for dentation aligning on the preliminary stage, as well as other medical fields.

Assessment of the hardness of different orthodontic wires and brackets produced by metal injection molding and conventional methods

Background:

This study was conducted to assess the hardness of orthodontic brackets produced by metal injection molding (MIM) and conventional methods and different orthodontic wires (stainless steel, nickel-titanium [Ni-Ti], and beta-titanium alloys) for better clinical results.

Materials and Methods:

A total of 15 specimens from each brand of orthodontic brackets and wires were examined. The brackets (Elite Opti-Mim which is produced by MIM process and Ultratrimm which is produced by conventional brazing method) and the wires (stainless steel, Ni-Ti, and beta-titanium) were embedded in epoxy resin, followed by grinding, polishing, and coating. Then, X-ray energy dispersive spectroscopy (EDS) microanalysis was applied to assess their elemental composition. The same specimen surfaces were repolished and used for Vickers microhardness assessment. Hardness was statistically analyzed with Kruskal–Wallis test, followed by Mann–Whitney test at the 0.05 level of significance.

Results:

The X-ray EDS analysis revealed different ferrous or co-based alloys in each bracket. The maximum mean hardness values of the wires were achieved for stainless steel (SS) (529.85 Vickers hardness [VHN]) versus the minimum values for beta-titanium (334.65 VHN). Among the brackets, Elite Opti-Mim exhibited significantly higher VHN values (262.66 VHN) compared to Ultratrimm (206.59 VHN). VHN values of wire alloys were significantly higher than those of the brackets.

Conclusion:

MIM orthodontic brackets exhibited hardness values much lower than those of SS orthodontic archwires and were more compatible with NiTi and beta-titanium archwires. A wide range of microhardness values has been reported for conventional orthodontic brackets and it should be considered that the manufacturing method might be only one of the factors affecting the mechanical properties of orthodontic brackets including hardness.

Mechanical properties of orthodontic wires on ceramic brackets associated with low friction ligatures

Abstract Introduction Few studies investigated the mechanical properties of orthodontic wires on ceramic brackets associated the ligatures. Objective This study aimed to compare the load-deflection of orthodontic wires with round section of 0.016” made of stainless steel (SS), nickel-titanium (NiTi) and glass fiber-reinforced polymer composite (GFRPC). Material and method Sixty specimens obtained from 10 sectioned pre-contoured arches (TP Orthodontics), were divided into 3 groups of 20 according to each type of material (1 esthetic-type wire and 2 not esthetic) and length of 50 mm. The methodology consisted of a 3-point bending test using esthetic ceramic brackets (INVU, TP Orthodontics, Edgewise, 0.022”x 0.025”) as points of support. The tensile tests were performed on a mechanical test machine, at a speed of 10 mm/min, deflection of 1 mm, 2 mm and 3 mm. Friedman’s Non Parametric Multiple comparisons test was used (P<0.05). Result The nickel-titanium wire presented smaller load/ deflection compared with stainless steel. GFRPC wires had lower strength values among all groups evaluated (P<.05). The steel wire showed permanent deformation after 3 mm deflection, NiTi wire demonstrated memory effect and the esthetic type had fractures with loss of strength. Conclusion It can be concluded that steel wires have high strength values, requiring the incorporation of loops and folds to reduce the load / deflection. NiTi and GFRPC wires produced low levels of force, however the esthetic wire was shown to fracture and break.