Use of Antimicrobial Silver Coatings on Fixed Orthodontic Appliances, Including Archwires, Brackets, and Microimplants: A Systematic Review

Introduction

Orthodontic treatments are integral to achieving optimal oral health and aesthetic outcomes for individuals with malocclusion. Fixed orthodontic appliances are devices used by orthodontists to straighten and align teeth, correct bite problems, and improve overall dental aesthetics. Unlike removable appliances like aligners, fixed appliances are bonded to the teeth and cannot be easily removed by the patient. They consist of various components, including archwires, brackets, and microimplants, each playing a crucial role in the orthodontic treatment process. Archwires are thin, flexible wires inserted into the brackets attached to the teeth. They exert continuous pressure on the teeth, guiding them into the desired position over time. Archwires come in different materials, including stainless steel, nickel-titanium (NiTi), and beta-titanium alloys. Brackets are small attachments made of metal or ceramic that are bonded to the surface of each tooth. They serve as anchors for the archwire and help transmit forces from the wire to the teeth. Microimplants, also known as temporary anchorage devices (TADs), are small screws or mini-implants that are temporarily placed into the bone to provide additional anchorage during orthodontic treatment. These components are carefully selected and customized by orthodontists based on individual patient needs, treatment goals, and biomechanical principles. However, the use of orthodontic appliances, composed of archwires, brackets, and microimplants, presents a notable challenge in infection control due to the environment conducive to bacterial adhesion and biofilm formation [1]. Biofilm formation with increased levels of bacterial colonization on fixed orthodontic appliances poses significant risks to oral health, including dental caries, gingival inflammation, white spot lesions, and periodontal disease [2]. Plaque index values during orthodontic treatment were reportedly significantly higher than in the control group [3].

In response to this concern, the exploration of innovative solutions has accelerated, and a promising avenue involves integrating antimicrobial agents into orthodontic materials [4]. Among these agents, silver has gained recognition for its robust antimicrobial properties. In dentistry, acrylic resins used for removable dentures in prosthetics, composite resins in dental restorative treatment, root canal sterilization, composite materials used in orthodontic treatment, membranes used for guided tissue regeneration in periodontology, and titanium coatings applied in dental implant treatment can all contain silver nanoparticles [5,6]. The findings outlined in the study conducted by Sodagar et al showed that composite discs infused with 5% and 10% concentrations of silver/hydroxyapatite nanoparticles exhibit the formation of bacterial growth inhibition zones, demonstrating notable antibacterial efficacy against biofilms [7]. Silver, known for its potent antimicrobial properties, has been extensively studied as a coating material for orthodontic appliances [8–11]. This systematic review meticulously examined the existing literature on antimicrobial innovations in orthodontics, specifically focusing on coatings containing silver applied to archwires, brackets, and microimplants [12–14]. By synthesizing findings from a diverse array of studies, this review seeks to provide a comprehensive understanding of the efficacy of silver-based coatings in preventing microbial adhesion, colonization, and biofilm formation on orthodontic appliances.

Despite the potential benefits of silver-based coatings, a critical evaluation of the existing literature reveals gaps in understanding the extent to which these coatings effectively mitigate bacterial adhesion and biofilm formation on various orthodontic surfaces. While individual studies have demonstrated promising results, a systematic review is necessary to consolidate and analyze these findings comprehensively. The present review seeks to fill this gap by critically examining the methodologies, outcomes, and limitations of diverse studies, thereby providing a synthesized perspective on the antimicrobial efficacy of silver-coated orthodontic materials. The exploration of this topic is particularly timely given the increasing emphasis on infection control in dentistry and the continuous evolution of orthodontic materials and technologies.

With the overarching goal of advancing infection control measures in orthodontic practice, this systematic review posed the following research question: What is the current evidence regarding the antimicrobial efficacy of coatings containing silver on orthodontic archwires, brackets, and microimplants in preventing microbial colonization, adhesion, and biofilm formation? Therefore, this systematic review evaluated the literature on antimicrobial silver coatings on fixed orthodontic appliances, including archwires, brackets, and microimplants.

Material and Methods

SEARCH STRATEGY:

Two independent evaluators systematically conducted a thorough search in the databases PubMed, PubMed Central, Embase, Scopus, and Web of Science. The search query, initially prepared for PubMed; (“orthodontic*”) AND (”silver nanoparticle*” or “nano silver”) AND (“wire*” OR “archwire*”OR “braces” OR “bracket*” OR “miniimplant*” OR “microimplant*” OR “screw*” OR “surface” OR “appliance*”), was subsequently adapted for application to other databases, as illustrated in Figure 2. After completing a comprehensive search, all duplicate records were removed.

The present systematic review was structured according to the PICO framework [16] and focused on populations and interventions. Population: In vitro studies that investigate the incorporation of silver nanoparticles or layer enriched silver obtained by various methods into metal orthodontic devices, such as archwires, orthodontic brackets, and microimplants, to assess their potential antimicrobial capabilities. Intervention: Incorporation of silver particles onto the surface of metal orthodontic devices. The review compared these silver-coated devices against metal surfaces of orthodontic devices lacking silver agents, with the outcome of interest being the evaluation of antimicrobial activity. The research question being addressed was whether incorporating silver particles onto metal orthodontic devices enhances their antimicrobial activity in in vitro studies.

The literature search was completed on February 15, 2024, with no limitations placed on publication dates to ensure a comprehensive review of relevant articles. The review process was conducted in an unbiased manner to maintain objectivity.

ELIGIBILITY CRITERIA:

We included in vitro studies that specifically evaluated the antimicrobial activity of silver nanoparticles when applied to the surface of metal orthodontic devices. We excluded literature reviews, systematic reviews, case reports, animal studies, and studies focused on the incorporation of silver nanoparticles into orthodontic bonding systems.

DATA EXTRACTION:

After eliminating duplicate publications, the first author (M.S.-D.) thoroughly examined the titles and abstracts of the remaining studies. Subsequently, the second author (L.S.-S.) also assessed all studies to identify potentially eligible ones. The full texts of the selected papers were carefully reviewed, and decisions regarding their inclusion or exclusion were made based on predetermined criteria. Any uncertainties or ambiguities that arose during this process were resolved through discussions between these 2 authors and the third author (K.W.). These allowed for a collaborative approach to addressing any disagreements or uncertainties, ensuring a comprehensive and reliable review process. To facilitate the comparative analysis of the chosen studies, a spreadsheet was generated in accordance with the Cochrane Collaboration guidelines. Cohen’s Kappa statistic was used to assess the level of agreement between authors.

QUALITY ASSESSMENT:

In this review, the quality assessment of included studies was conducted using the Newcastle-Ottawa Scale (NOS) [17]. The NOS scoring system assigns higher scores to studies demonstrating better methodological quality. The scale considers 3 domains: selection of study groups, comparability of groups, and assessment of outcomes or exposure. Each domain comprises criteria that are meticulously evaluated to calculate the overall quality score for each study. The assessment process was carried out independently by 2 reviewers (M.S.-D. and L.S.-S.), who engaged in discussions and consultations with a third author (K.W.) to resolve any uncertainties or disagreements. To quantify the level of agreement among the authors, the Cohen’s Kappa coefficient was calculated. This rigorous evaluation using NOS allowed for an objective assessment of the included studies’ methodological rigor and their contribution to the collective body of evidence.

STATISTICAL ANALYSIS:

Cohen’s Kappa coefficient was calculated using the R software package to assess the concordance between authors.

Results

SEARCH STRATEGY AND STUDY SELECTION:

The search strategy yielded a total of 702 potential articles, with contributions from various databases: 56 from PubMed, 420 from PubMed Central, 62 from Embase, 78 from Scopus, and 86 from Web of Science. After eliminating 193 duplicate records, the remaining articles underwent thorough analysis. Next, 469 papers were excluded as they did not meet the predefined inclusion criteria. Of the initial pool of 40 articles, 22 were excluded due to lack of relevance to the topic of the study. The final qualitative synthesis comprised 18 papers.

SYSTEMATIC REVIEW PROCESS:

The systematic review process was visually represented in the PRISMA Flow Diagram (Figure 1), offering a detailed depiction of each stage, including the initial search, screening, and selection. This diagram, following the PRISMA guidelines, provides transparency and clarity in outlining the systematic review’s progression. The agreement between the 2 reviewers demonstrated robust consistency, with a high Cohen’s Kappa coefficient of 0.97. The high level of agreement enhances the reliability and credibility of the systematic review’s findings.

ANTIMICROBIAL COATINGS ON ORTHODONTIC WIRES:

Several studies investigated the antimicrobial properties of orthodontic wires coated or modified with AgNPs (Tables 1, Table 2). Nafarrate-Valdez et al found that AgNPs significantly reduced the adhesion and growth capacity of S. mutans on conventional orthodontic archwires, demonstrating anti-adherent and antimicrobial properties [18]. The study utilized minimal inhibitory concentrations (MIC) and bacterial adherence testing, revealing a size of 30 nm for the AgNPs synthesized through chemical reduction. Bącela et al reported a significant reduction in S. mutans bacterial adhesion to stainless steel wires coated with TiO2: Ag, showing both antimicrobial activity and resistance to biofilm formation [19]. Gonçalves et al observed statistically significant reductions in biofilm formation by S. mutans and S. aureus on coated stainless-steel wires [20]. Gil et al found revealed that the incorporation of silver nanoparticles reduced bacterial presence by over 90% without altering colorimetric and mechanical properties or affecting nickel ions release from NiTi wires [21].

ANTIMICROBIAL COATINGS ON ORTHODONTIC BRACKETS:

Studies on orthodontic brackets revealed promising results (Tables 1, 2). Ghasemi et al reported a significant decrease in bacterial colony counts on coated bracket, with results being statistically significant (P<0.05) [22], while Ameli et al demonstrated strong antibacterial efficacy of brackets coated with hydroxyapatite and silver nanoparticles against S. mutans [23]. Jasso-Ruiz observed reduced bacterial adhesion in all groups with AgNPs compared to control groups [24], and also found significant inhibitory effects on microbial growth with AgNPs-coated brackets against S. aureus and E. coli [11]. Moreover, Zeidan et al reported greater antibacterial effects for all types of coated brackets compared to uncoated ones [13]. Ryu et al found a significant decrease in bacterial growth on silver-coated specimens, achieving an approximate 60% reduction [25].

ANTIMICROBIAL COATINGS ON ORTHODONTIC MICROIMPLANTS:

Research on microimplants showed positive outcomes (Table 2). Subramanian et al reported antibacterial effects of Ti-BP-AgNPs against Lactobacillus and S. aureus, with a slightly smaller zones of inhibition against S. mutans [9], while Fathy Abo-Elmahasen et al [26] observed antimicrobial activity against various microorganisms, including Gram-positive, Gram-negative, and fungal strains, in tested microimplants. Venugopal et al noted strong antimicrobial activity of Ti-BP-AgNPs microimplants against 3 bacterial cultures [14].

SURFACE CHARACTERIZATION METHODS:

In the reviewed studies, various surface characterization methods were employed to analyze the coated orthodontic materials (Table 1). Scanning electron microscopy (SEM) was frequently utilized to examine the surface morphology and structure, providing detailed images at the microscale. Transmission electron microscopy (TEM) allowed for even finer visualization, offering insights into the nanoscale features of the coatings.

BACTERIAL STRAINS TESTED:

Regarding the bacteria tested, different studies assessed the antimicrobial efficacy of silver-coated orthodontic materials against various strains (Table 1). For instance, S. mutans, a common bacterium associated with dental caries, was a recurrent choice for evaluating bacterial adhesion and biofilm formation [10,18–20,23,22,25,27,28]. Other bacteria tested included S. aureus, E. coli, L. monocytogenes, and Lactobacillus, representing a spectrum of Gram-positive and Gram-negative bacteria with different pathogenic characteristics [9,13,20,27,28].

QUALITY ASSESSMENT OF STUDIES:

Table 3 succinctly summarizes the outcomes of the quality assessment, demonstrating a high level of agreement among evaluators (Cohen’s Kappa coefficient 0.94). The majority of studies achieved a creditable score of 7/9 on the NOS assessment [17], indicating overall good quality. Despite this positive trend, a noticeable heterogeneity persists across various aspects, encompassing study designs, sample characteristics, and methodologies. The aggregate exploration of silver-containing coatings in orthodontics was shown in the reviewed studies; however, the variety of materials used made meta-analysis impossible.

SUMMARY OF FINDINGS:

In summary, the incorporation of AgNPs into orthodontic wires, brackets, and microimplants demonstrated significant antimicrobial effects against various bacteria, particularly S. mutans. The coated surfaces exhibited reduced bacterial adhesion, inhibited biofilm formation, and, in some cases, showed statistically significant decreases in bacterial colony counts.

Discussion

STRENGTHS AND LIMITATIONS:

One strength of the present systematic review is its comprehensive analysis of diverse studies, encompassing various orthodontic materials and coating techniques. The inclusion of in vitro studies allowed for a focused assessment of the antimicrobial effects of silver coatings. The use of the Newcastle-Ottawa Scale for quality assessment adds rigor to the evaluation of study methodologies. Nonetheless, the diversity in study designs, methodologies, and outcome measures introduces a level of heterogeneity that may lead to variability in result interpretation and impose constraints on the generalizability of the findings. Additionally, the review primarily focuses on in vitro studies, and extrapolating these findings to clinical settings requires caution. Future research could address these limitations by using standardized methodologies and conducting well-designed clinical trials to validate the effectiveness of silver-coated orthodontic materials.

Conclusions

The present systematic review provides strong evidence supporting the antimicrobial efficacy of silver-coated orthodontic materials. The results may contribute to infection control measures in orthodontic practice, thus opening the way for further research and potential clinical applications of AgNPs. Ultimately, while AgNPs offer promising antimicrobial properties, their potential impact on patients’ health should be carefully considered and balanced with the need for effective infection control in orthodontic practice.Początek formularza