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

Effect of Quaternary Ammonium-Based Antimicrobial Coating on the Mechanical Properties and Bacterial Adhesion to Gummetal Archwire

Objectives: This in vitro study investigated the mechanical and bacterial adhesion properties of Gummetal (GM) orthodontic archwire after application of quaternary ammonium compounds (QACs)-based antimicrobial coating. Methods: Sixty orthodontic archwires were divided into three groups: coated GM (C-GM) group, consisting of a 0.016 × 0.022-inch GM core wire coated with QACs, and two control groups-one with a 0.016 × 0.022-inch uncoated GM wire and the other with a 0.016 × 0.022-inch stainless steel (SS) wire. The elastic modulus, yield strength, and static friction forces were compared between the C-GM and control groups. Measurements were conducted using a Dillon Quantrol TC2i universal testing machine. Surface roughness was evaluated using confocal profilometry, and bacterial adhesion was quantified through crystal violet dye staining. Results: The mean elastic modulus for the C-GM, GM, and SS groups was 6.68 ± 0.1, 6.71 ± 0.2, and 19.7 ± 0.4 GPa, respectively, with significant differences observed between the C-GM vs. SS and GM vs. SS groups (p  < 0.001). The mean yield strength for the C-GM, GM, and SS groups was 7.5 ± 0.1, 7.6 ± 0.1, and 19.5 ± 0.2 N, with yield strength being significantly lower in the C-GM group compared to the GM (p=0.036) and SS (p  < 0.001) groups. For friction forces measured within metal brackets, the C-GM group exhibited a mean friction force of 1.0 ± 0.1 N, which was significantly lower than both the GM (1.1 ± 0.1 N, p=0.017) and SS (1.2 ± 0.1 N, p  < 0.001) groups. Confocal profilometry analysis indicated that the SS group had the lowest surface roughness, followed by GM and then C-GM. The mean bacterial count for the C-GM, GM, and SS groups was 0.605, 1.066, and 0.882 AU cm⁻1, respectively, with significant differences observed between each wire pair (adj. p  < 0.001). Conclusions: The application of antimicrobial QACs to GM wires effectively reduced friction while preserving their strength and rigidity. Furthermore, the QAC coating demonstrated a significant reduction in bacterial adherence.

Evaluation of the Tribological Behavior of Materials Used for the Production of Orthodontic Devices in 3D DLP Printing Technology, Due to Oral Cavity Environmental Factors

This study evaluated the effect of oral cavity environmental factors on the friction and wear of materials used in 3D-printed orthodontic devices. Commercial materials GR-10 (Pro3Dure) and NextDent SG (NextDent) were examined, with samples produced using ASIGA UV MAX and Phrozen Shuffle Lite 3D printers. Our tests included measurements of hardness, stiffness, elastic modulus, cyclic loading, scratch resistance, and tribological assessments in oscillatory motion. Surface analyses were conducted using scanning electron microscopy with an energy-dispersive spectroscopy analyzer. The results showed that NextDent SG exhibited higher hardness and modulus of elasticity, while GR-10 demonstrated better scratch resistance. Despite similar friction coefficients, significant variations in wear were observed under different environmental conditions, highlighting the importance of considering these factors in the performance of orthodontic materials.

Dynamics of the oral microbiome during orthodontic treatment and antimicrobial advances for orthodontic appliances

The oral microbiome plays an important role in human health, and an imbalance of the oral microbiome could lead to oral and systemic diseases. Orthodontic treatment is an effective method to correct malocclusion. However, it is associated with many adverse effects, including white spot lesions, caries, gingivitis, periodontitis, halitosis, and even some systematic diseases. Undoubtedly, increased difficulty in oral hygiene maintenance and oral microbial disturbances are the main factors in developing these adverse effects. The present article briefly illustrates the characteristics of different ecological niches (including saliva, soft tissue surfaces of the oral mucosa, and hard tissue surfaces of the teeth) inhabited by oral microorganisms. According to the investigations conducted since 2014, we comprehensively elucidate the alterations of the oral microbiome in saliva, dental plaque, and other ecological niches after the introduction of orthodontic appliances. Finally, we provide a detailed review of recent advances in the antimicrobial properties of different orthodontic appliances. This article will provide researchers with a profound understanding of the underlying mechanisms of the effects of orthodontic appliances on human health and provide direction for further research on the antimicrobial properties of orthodontic appliances.

Molecular Docking and Experimental Analysis of Essential Oil-Based Preparations on Biofilm Formation on Orthodontic Archwires

Good oral hygiene is crucial during treatment with fixed appliances, emphasising the need for additional or alternative oral health methods during orthodontic treatment. This study investigates the effect of essential oil (EO)-based preparations on biofilm adhesion to orthodontic archwires. Five identical-sized orthodontic archwires of different materials were tested using therapeutic and preventive applications of essential oils. This study also used molecular docking to explore how essential oil compounds interact with key proteins of common oral pathogens like Staphylococcus aureus and Streptococcus mutans. We found that the constituent materials heavily influence the antimicrobial effects of essential oils on different orthodontic archwires. Stainless steel-based orthodontic archwires demonstrated the highest efficacy in antimicrobial protection against S. mutans strains (maximum BIP = 28.82% on the epoxy-coated SS). Conversely, inhibition effects in preventive applications against S. aureus were observed exclusively with titanium-molybdenum alloy orthodontic archwires across all tested emulsions (maximum BIP = 29.44%). CuNiTi alloys showed ineffectiveness in preventive treatments, as none of the EO mixtures inhibited biofilm development on this material. After biofilm contamination with S. mutans and S. aureuss strains, the ternary emulsion was most effective for four out of five orthodontic archwires. Computational analysis revealed strong binding interactions between essential oil compounds and key proteins of S. aureus and S. mutans, highlighting specific amino acid residues that are critical for these interactions. Based on the results, stainless steel with epoxy coating or TMA archwires, combined with BEO/CEO/OEO ternary mixture, are recommended for optimal antibacterial protection against biofilm formation on orthodontic archwires.

Comprehensive evaluation of the antibacterial and antibiofilm activities of NiTi orthodontic wires coated with silver nanoparticles and nanocomposites: an in vitro study

BACKGROUND

Fixed orthodontic appliances act as a niche for microbial growth and colonization. Coating orthodontic wires with antimicrobial silver nanoparticles (AgNPs) and nanocomposite was adopted in this study to augment the biological activity of these wires by increasing their antibacterial and antibiofilm properties and inhibiting bacterial infections that cause white spot lesions and lead to periodontal disease.

METHODS

Three concentrations of biologically synthesized AgNPs were used for coating NiTi wires. The shape, size, and charge of the AgNPs were determined. Six groups of 0.016 × 0.022-inch NiTi orthodontic wires, each with six wires, were used; and coated with AgNPs and nanocomposites. The antimicrobial and antibiofilm activities of these coated wires were tested against normal flora and multidrug-resistant bacteria (Gram-positive and Gram-negative bacterial isolates). The surface topography, roughness, elemental percentile, and ion release were characterized.

RESULTS

AgNPs and nanocomposite coated NiTi wires showed significant antimicrobial and antibiofilm activities. The chitosan-silver nanocomposite (CS-Ag) coated wires had the greatest bacterial growth inhibition against both Gram-positive and Gram-negative bacteria. The surface roughness of the coated wires was significantly reduced, impacting the surface topography and with recorded low Ni and Ag ion release rates.

CONCLUSIONS

NiTi orthodontic wires coated with AgNPs, and nanocomposites have shown increased antimicrobial and antibiofilm activities, with decreased surface roughness, friction resistance and limited- metal ion release.

Evaluation of surface roughness, cytotoxicity, and antibacterial effects of silver nanoparticle coating on copper nickel titanium orthodontic arch wires - in vitro study

BACKGROUND

Surface roughness of arch wires directly impacts their corrosion behavior, friction resistance, and plaque accumulation, which may hinder tooth movement and lead to dental caries.

OBJECTIVES

The study aims to synthesize vanillin-mediated silver nanoparticles (AgNPs), characterize them, assess surface roughness and cytotoxicity of arch wires after silver nanoparticle coating, and test their antibacterial properties.

MATERIALS AND METHODS

Nine copper-nickel-titanium arch wires (CuNiTi) were cut into equal pieces. Three were sent for surface roughness assessment, three for cytotoxicity, and three for antibacterial testing. Dip coating of wires was done using the sol-gel thin film method. The surface roughness (Ra) before and after coating was evaluated using scanning electron microscopy and atomic force microscopy. Cytotoxicity testing was done with a (3- (4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay using gingival fibroblasts. Statistical analysis was done using SPSS software. Antibacterial activity against S. mutans was tested using the Agar-well diffusion method.

RESULTS

The CuNiTi wires were coated successfully, and the coating appeared homogeneous. The mean Ra after coating (297.3+/- 30.4 nm) was significantly less than that before coating (339.7+/-49.2 nm). AgNPs showed minimal cytotoxicity against human gingival fibroblasts at different concentrations. Optical microscopy showed over 90% viability between 12.5 and 100 µg/ml. At 100 µg/ml, only 80% of cells remained viable. AgNP coating is biocompatible at concentrations up to 75 µg/ml. There was a significant intergroup difference in the zone of inhibition (antibacterial activity) noted with higher values in noncoated wires. (P value <0.007).

CONCLUSION

AgNPs coated on CuNiTi arch wires showed reduced surface roughness and minimal cytotoxic effects on human gingival cells and good antibacterial activity against S. mutans compared to noncoated arch wires.

A Facile Surface Modification Scheme for Medical-Grade Titanium and Polypropylene Using a Novel Mussel-Inspired Biomimetic Polymer with Cationic Quaternary Ammonium Functionalities for Antibacterial Application

Medical device-associated infection remains a critical problem in the healthcare setting. Different clinical- or device-related methods have been attempted to reduce the infection rate. Among these approaches, creating a surface with bactericidal cationic functionality has been proposed. To do so, a sophisticated multi-step chemical procedure would be needed. Instead, a simple immersion approach was utilized in this investigation to render the titanium and polypropylene surface with the quaternary ammonium functionality by using a mussel-inspired novel lab-synthesized biomimetic catechol-terminated polymer, PQA-C8. The chemical oxidants, CuSO4/H2O2, as well as dopamine, were added into the novel PQA-C8 polymer immersion solution for one-step surface modification. Additionally, a two-step immersion scheme, in which the polypropylene substrate was first immersed in the dopamine solution and then in the PQA-C8 solution, was also attempted. Surface analysis results indicated the surface characteristics of the modified substrates were affected by the immersion solution formulation as well as the procedure utilized. The antibacterial assay has shown the titanium substrates modified by the one-step dopamine + PQA-C8 mixtures with the oxidants added and the polypropylene modified by the two-step scheme exhibited bacterial reduction percentages greater than 90% against both Gram-positive S. aureus and Gram-negative E. coli and these antibacterial substrates were non-cytotoxic.

Graphene-Based Coatings for Surface Modification and Their Applications in Fixed Orthodontics: A Scoping Review

BACKGROUND

Surface coating technology can assist fixed appliances by reducing friction, improving antibacterial characteristics, and increasing corrosion resistance. The application of functional coatings composed of graphene onto the surfaces of orthodontic brackets and archwires has been shown to enhance their mechanical qualities. The objective of the current study was to carry out a scoping analysis of published recent evidence on the utilization of graphene as a covering material in metallic orthodontic accessories, such as brackets and archwires; Methods: A scoping review was undertaken following the PRISMA-ScR guidelines. PubMed, Embase, the Cochrane Library, Dentistry and Oral Science Source, and Google Scholar were searched between 2003 and 2023; Results: In total, 38 potential references were detected, from which 10 were selected for this review. These articles addressed the benefits of the application of graphene-oxide functional coatings onto the surface of archwires and brackets during fixed orthodontic treatment. Orthodontic graphene-oxide-based coatings provide improved surface characteristics (e.g., reduced friction and anticorrosive effects), antibacterial capabilities, and biocompatibility. These characteristics can increase the effectiveness of orthodontic therapy, improve patient comfort, and lower the likelihood of problems; Conclusion: Orthodontists should be aware of and comprehend the prerequisites for using graphene-oxide-coated archwires and brackets to fulfill needs throughout their clinical practice.

Static friction, surface roughness, and antibacterial activity of orthodontic brackets coated with silver and silver chitosan nanoparticles

BACKGROUND

To determine the effect of silver and silver chitosan nanocoatings on monocrystalline ceramic, polycrystalline ceramic, and metallic brackets regarding friction, roughness, and antibacterial effect against Streptococcus mutans.

METHODS

A total of 99 upper right premolar brackets with a 0.022 × 0.025 -inch slot were divided into three groups, each 33 according to coating material; the non-coated group, silver nanoparticles (AgNPs), and silver chitosan nanoparticles (Ag-CsNPs) groups. Each group was equally subdivided into the following three subgroups regarding bracket materials: monocrystalline ceramic, polycrystalline ceramic, and metallic brackets. A universal testing machine determined static friction on a custom-made acrylic jig. Then a profilometer machine was used to collect roughness data, and finally, the anti-cariogenic effect was measured with the disc diffusion technique's "minimum zone of inhibition" against Streptococcus mutans. Two-way ANOVA was used to compare data between groups and subgroups, followed by the Bonferroni test for multiple pair-wise comparisons.

RESULTS

The nanocoating effect on ceramic brackets' static friction was non-significant. The AgNPs and Ag-CsNPs coated metallic group revealed a significant increase in static friction-a significant effect of the nanocoating in the surface roughness of monocrystalline and polycrystalline ceramic brackets. A significant favorable effect of AgNPs and Ag-CsNPs against Streptococcus mutans was observed.

CONCLUSIONS

AgNPs and Ag-CsNPs coats are unsuitable for decreasing friction in metallic brackets or improving roughness in polycrystalline ceramic brackets. Nano coating can improve roughness in monocrystalline ceramic brackets. Coating brackets with AgNPs and Ag-CsNPs has a tremendous antibacterial effect on Streptococcus mutans, a substantial factor in the incidence of dental caries.

Bio-inspired nanocomposite coatings on orthodontic archwires with corrosion resistant and antibacterial properties

The corrosion resistance and antibacterial properties of fixed orthodontic devices are insufficient in the complex oral cavity, which delays tooth movement and causes enamel demineralization. To overcome the challenges, this research constructs a series of polydopamine-graphene oxide (PDA-GO) nanocoatings on representative NiTi archwires via self-assembly. The morphology, chemical structure, and multifunctional properties of coatings showed tunability dependent on the PDA/GO ratio. Optimized PDA-GO coatings with uniform and dense characteristics prolonged the diffusion path for the corrosive medium and reduced Ni dissolution in NiTi alloys. Meanwhile, the applied coatings endowed NiTi alloys with antibacterial activity against Streptococcus mutans due to the surface structures and inherent properties of PDA-GO. In vitro cytotoxicity tests further verified their good biocompatibility. This bio-inspired nanocomposite coating provides a practical reference for modification of dental metal surfaces to better behave in the intraoral environment.