REVIEW ARTICLE


https://doi.org/10.5005/jp-journals-10015-2066
World Journal of Dentistry
Volume 13 | Issue 4 | Year 2022

Effect of Nanoparticle Coatings on Frictional Resistance of Orthodontic Archwires: A Systematic Review and Meta-analysis


Mathew T Maliael1, Ravindra K Jain2, Srirengalakshmi M3

1-3Department of Orthodontics, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India

Corresponding Author: Mathew T Maliael, Department of Orthodontics, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Chennai, Tamil Nadu, India, Phone: +91 8880213792, e-mail dr.mathewthomasm@gmail.com

ABSTRACT

Aim: This review aims to perform a systematic evaluation of the literature and report on the effect of nanoparticle (NP) coating on frictional resistance (FR) of orthodontic archwires.

Background: Frictional resistance offered by archwires and brackets during orthodontic treatment can be minimized by surface treatment, and NP coating of archwires and brackets has been reported to reduce FR.

Review results: A total of ten in vitro studies were included in the qualitative analysis, and five studies were included in the quantitative analysis for this review; eight of the included articles identified a significant decrease in FR of the coated wires when compared to uncoated wires. The overall methodological quality of the included studies was moderate. There was a significant reduction in FR of NP coated SS wires (MD = −1.28N; 95% CI: −1.90, −0.67; p < 0.0001) and NiTi wires (MD = −0.19N; 95% CI: −0.28, −0.15; p < 0.00001) when compared with uncoated wires.

Conclusion: Both qualitative and quantitative assessment of the available literature suggests a significant reduction in FR of orthodontic archwires subjected to NP coating.

Clinical significance: Nanoparticle coating of archwires reduces FR; hence during orthodontic treatment coated archwires can be used to obtain better results.

How to cite this article: Maliael MT, Jain RK, Srirengalakshmi M. Effect of Nanoparticle Coatings on Frictional Resistance of Orthodontic Archwires: A Systematic Review and Meta-analysis. World J Dent 2022;13(4):417-424.

Source of support: Nil

Conflict of interest: None

Keywords: Friction, Nanoparticles, Orthodontic archwires, Orthodontics

INTRODUCTION

Sliding mechanics for tooth movement in orthodontics requires less chairside time and is efficient in controlling 3-dimensional movements of the teeth.1,2 A major disadvantage of sliding mechanics is FR at the bracket wire interface.3,4 Friction is an uncontrolled factor and is due to the load being applied at the contact points as the brackets move along the wire.1,2,5 The resistance to sliding is the sum total of the FR and binding. This resistance could prevent the attainment of optimal force levels to the supporting tissues during orthodontic mechanotherapy.6 Binding occurs when the wire contacts the edge of the bracket, causing notching and undergoing plastic deformation resulting in intermittent tooth movement.

This use of higher forces, in turn, could tax and strain the anchorage unit and result in anchorage loss.1,7 Also, other associated problems like root resorption and periodontal damage can occur due to the use of excessive orthodontic force.8-11 Various other factors such as the material characteristics of the wires and brackets used, the size of the wires, and the surface characteristics of the wire also have an impact on the FR.4,12-17

Nanoparticles (NP) were introduced in the 1990s and have been used to coat orthodontic wires with varying levels of success to improve the surface topography of orthodontic wires.18-21

Some authors have proposed that these coatings significantly decreased the FR of orthodontic archwires.3,22-24 Several authors have assessed and evaluated the frictional behavior of orthodontic wires coated with NP.3,22-24

It has been proposed that 50% of the applied orthodontic force is utilized to overcome FR,25 hence by lowering the FR during orthodontic treatment an improved hard and soft tissue response to orthodontic force can be expected.

Thus, the objective of this review was to perform a systematic evaluation of the available literature and assess and report on the effect of NP coating on the FR of orthodontic archwires.

MATERIALS AND METHODS

Research Question

Do NP coating of orthodontic archwires have an effect on FR?

Eligibility Criteria

Studies reporting on the FR of NP coated wires and have performed a comparison with the FR of uncoated orthodontic archwires, and performing the testing and evaluation of FR using a universal testing machine (UTM) were included in this review. The PICOS formulated for this review is as follows:

  • Population: Orthodontic archwires.

  • Intervention: NP coating of orthodontic archwires.

  • Control/Comparison: Uncoated or noncoated on orthodontic archwires.

  • Outcome: FR.

Study design: In vitro studies

Studies that evaluated orthodontic brackets, bands, tubes, etc., were excluded from the review process. Clinical studies, microbial assays, and animal studies were also excluded from the review process.

Information Sources, Search Strategy, and Study Selection

A systematic search of the following scientific databases, PubMed, Google Scholar, Cochrane Library, Scopus, and LILACS was performed to identify relevant articles published from January 1990 to August 2021. Search strategies were developed for each database considering the varying vocabulary and syntax limits of each database. The following search terms were used [(NP) and (friction)] and (orthodontic wire). A manual search of various orthodontic journals of interest, including American Journal of Orthodontics and Dentofacial Orthopedics, Korean Journal of Orthodontics, European Journal of Orthodontics, Journal of Orthodontics, Orthodontic Waves, Taiwan Journal of Orthodontics, Journal of Indian Orthodontic Society, Dental Press Journal of Orthodontics and The Angle Orthodontist, was performed to identify further studies. Databases OpenGrey and GreyNet International were also searched to identify grey literature relevant to the research question. Only English language studies or studies that had an accompanying English language translation attached along with the full text were considered for review.

Two reviewers (MTM, RKJ) conducted the literature search independently, and any disagreements between these reviewers were settled in consultation with the third reviewer (SRL).

Data Collection Process

All studies meeting the selection criteria were included in the review. The selection process of included studies was reported in the PRISMA flow chart (Flowchart 1). A table for describing the study characteristics of the included articles was extracted, which included the following information: first author, year of publication, study design, sample size, outcomes in the studies (i.e., parameters assessed). The reference list of included articles was searched to identify any studies that were not identified through the initial database search.

Flowchart 1: PRISMA flow chart for study selection

Methodological Quality Assessment of the Included Studies

All included studies were analyzed to evaluate their methodological quality using a methodological evaluation described by Ehsani et al.26 (Fig. 1). All the studies had a moderate to good quality methodology (Table 1).

Table 1: Methodological quality of the included studies. (Score interpretation, 0–5: Poor methodological quality, 6–10: Moderate methodological quality, 11–15: Good methodological quality)
Study Objective Sample size Baseline Co-interventions Measurement Blinding Reliability Statistical test Confounding parameters Significance Clinical significance Score
Kachoei et al. 2013 * / * * * // ** ** * ** / 11
Behroozian et al. * / * * * // ** ** * ** / 11
Hammad et al. * / * * * // ** ** * ** / 11
Kachoei et al. 2016 * / * * * // ** ** * ** / 11
Redlich et al. * ^ * * * // ** ** * ** / 10
Redlich et al. (1) * ^ * * * // ** ** * ** / 10
Samorodnitzky-Naveh et al. * ^ * * * // ** ** * ** / 10
Sharma et al. * * * * * // ** ** * ** / 12
Kachoei et al. 2015 * / * * * // ** */ * ** / 10
Elhelbawy and Ellaithy * / * * * // ** ** * ** / 11

Fig. 1: Methodological evaluation used to evaluate risk of Bias and assess quality of evidence of the included articles26

RESULTS

Determination of the relevance, validation, and extraction of data from the included studies

After searching all of the above-mentioned databases, 165 articles were identified. After eliminating duplicates, 142 studies were evaluated for the title and abstract screening. Fourteen studies were considered to be relevant after screening the titles and abstracts. Full texts of these studies were sought for evaluation. Four studies were excluded after evaluation of the full text as two studies were unpublished thesis,27,28 one study did not have an English language translation attached to the full text (although an English language translation was attached along with the abstract)29 and the last study was not relevant to the research question.30 A total of 10 studies were included in the qualitative analysis.31-39 The search of the reference list of included studies also yielded no results. Five studies with similar methodologies and clear mention of sample size evaluated for FR were further included for quantitative analysis (Figs 2 and 3).31-34,40 The information from the included studies was collected and tabulated under the following subheadings: names of the authors, sample size, groups, coating technique employed, parameters evaluated, and results (Table 2).

Table 2: Characteristics table of included studies
S. no. Author, journal, year Sample size Groups Coating technique Parameters evaluated Observations and results
1 Kachoei et al. 2013 40 Intervention—20 ZnO-NP coated 0.016 SS and 20 numbers of 19 × 25 SS wires
Control—20 Uncoated 0.016 SS and 20 19 × 25 SS wires.
(Elastomeric ligation, 022 UR1 SS brackets for 19 × 25 wires used and 018 UR1 SS brackets for 0.016 wires)
Electrodeposition of ZnO-NP. UTM was used to assess FR at 0°, 5°, and 10° angulation. A significant difference in FR between groups (p < 0.001). ZnO-NP coated wires had exhibited reduced FR.
2 Behroozian et al. 120 Group 1–30 coated wires and coated brackets
Group 2–30 coated wires and uncoated brackets
Group 3–30 coated bracket and uncoated wires
Group 4–30 uncoated wires and brackets
(19 × 25 SS wire, elastomeric ligation, and 022 UR1 ceramic brackets used)
Electrodeposition of ZnO-NP. UTM was used to assess FR at 0° angulation and artificial saliva was dropped every 3 seconds to simulate oral conditions. Significant intergroup differences between group 1 and 3 (p < 0.05). Coated brackets and coated wire exhibited the highest FR.
3 Hammad et al. 20 Intervention—10 ZnO-NP coated 16 × 22 NiTi wires
Control—10 Uncoated 16 × 22 NiTi wires.
(Elastomeric ligation and 022 SS brackets used)
Electrodeposition of ZnO-NP. UTM was used to assess FR at 0° angulation. No significant difference among the groups (p = 0.183). Coated wires exhibited no reduction in FR.
4 Kachoei et al. 2016 20 Intervention—10 ZnO-NP coated 0.016 NiTi wires
Control—10 Uncoated 0.016 NiTi wires
(Elastomeric ligation and 018 SS U1 brackets used)
Chemical deposition of ZnO-NP. UTM was used to assess FR at 0°, 5°, and 10°angulations. Coated wires exhibited reduced FR and this difference was significant statistically (p < 0.001).
5 Redlich et al. Intervention—NiP + IF-WS2 -NP 19 × 25 SS coated wires
Control - uncoated 19 × 25 SS wires
(Elastomeric ligation, 022 UR1 SS brackets)
Electrodeposition of NiP + IF-WS2-NP. UTM was used to assess FR at 0°, 5°, and 10° angulation. Coated wires exhibited reduced FR and this difference was significant statistically (p < 0.001 at 5° and 10°; p < 0.05 at 0°).
6 Redlich et al. (1) Intervention—Ni + IF-WS2-NP 19 × 25 SS Coated wires
Control - uncoated 19 × 25 SS wires
(022 self-ligating SS brackets)
Electro-co-deposition of Ni + IF-WS2-NP. UTM was used to assess FR at 10° angulation. Coated wires exhibited a 60% reduction in FR when compared to uncoated wires.
7 Samorodnitzky-Naveh et al. Intervention—Co + IF-WS2-NP coating on NiTi wires (4 preformed brands and one straight wire brand)
Control—uncoated wires of the same type.
(Self-ligating SS brackets)
Electro-co-deposition of Co + IF-WS2-NP. UTM was used to assess FR at 2° and 3.8° angulation. Coated wires exhibited reduced FR and this difference was significant statistically (p < 0.0007 at 2°; p < 0.0001 at 3.8°).
8 Sharma et al. 40 Group 1–10 Ag–NP coated 17 × 25 SS wires.
Group 2–10 uncoated 17 × 25 SS wires.
Group 3–10 Ag–NP coated 19 × 25 SS wires.
Group 4–10 uncoated 19 × 25 SS wires.
(Elastomeric ligation and 022 SS U1 brackets used)
Physical vapor deposition of Ag–NP. UTM was used to assess FR at 0° angulation. Coated 19 × 25 SS wires exhibited a significant reduction in FR (p = 0.032). No significant difference in FR between coated and uncoated 17 × 25 SS wires.
9 Kachoei et al. 2015 160 Intervention—40 ZnO-NP coated 0.016 SS and 40 numbers of 19 × 25 SS wires
Control—40 uncoated 0.016 SS and 40 19 × 25 SS wires.
(Elastomeric ligation, 022 UR1 SS brackets for 19 × 25 wires used and 018 UR1 SS brackets for 0.016 wires)
Chemical deposition of ZnO-NP. UTM was used to assess FR at 0°, 5°, and 10° angulations. Coated SS wires exhibited significantly reduced FR at all angulations.
10 Elhelbawy and Ellaithy 70 Group 1–uncoated wires and brackets
Group 2– coated wires and brackets (ZnO-NP)
Group 3– coated wires and brackets (CTS-NP)
Group 4–uncoated wires and coated brackets (ZnO-NP)
Group 5–uncoated wires and coated brackets (CTS-NP)
Group 6–coated wires (ZnO-NP) and uncoated brackets
Group 7–coated wires (CTS-NP) and uncoated brackets
(Elastomeric ligation, 022 UR1 SS brackets, 19 × 25 SS wires)
Dip coating UTM was used to assess FR at 0° angulation. All groups except the uncoated wire and uncoated bracket group exhibited a significant decrease in FR.

SS, stainless steel; NiTi, nickel titanium; ZnO-NP, zinc oxides; UR1, maxillary right central incisor; U1, maxillary central incisor; UR2, maxillary right lateral incisor; UR3, maxillary right canine; UR4, maxillary right first premolar; Ag–NP, silver nanoparticles; NiP + IF-WS2-NP, inorganic fullerene like tungsten disulfide nanoparticles embedded in the nickel-phosphorus film; Ni + IF-WS2-NP, inorganic fullerene like tungsten disulfide nanoparticles embedded in nickel film; Co + IF-WS2-NP, inorganic fullerene like tungsten disulfide nanoparticles embedded in cobalt film; CTS-NP, chitosan nanoparticles; UTM, universal testing machine; FR, frictional resistance

Fig. 2: Forest plot for FR difference between nanoparticle coated SS wires and uncoated wires at 0° angulation between the bracket and the wire

Fig. 3: Forest plot for FR difference between nanoparticle coated NiTi wires and uncoated NiTi wires at 0° angulation between the bracket and the wire

Results of the Methodological Quality Assessment

Based on the methodological evaluation as given by Ehsani et al.,26 (Fig. 1) quality of methodology of the included studies was assessed. Six of the included studies had a good quality of methodology,31-34,38,40 and four studies had a moderate quality of methodology35-37,39 (Table 1). The overall quality of the methodology of the included studies was moderate.

Results of Individual Studies

Eight of the included studies32-37,39,40 reported a significant reduction in the FR of orthodontic archwires coated with NP. The studies by Hammad et al.,31 and Behroozian et al.38 reported no significant difference in the FR between NP coated and uncoated archwires (Table 2).

Quantitative Synthesis of Included Studies

For SS wires, a random-effects meta-analysis of the pooled data on the effect of NP coating for FR showed a significant reduction in NP coated wires (p < 0.0001) with a mean difference of −1.28N (95% CI, −1.90, −0.67) compared to uncoated wires with a significant heterogeneity (I = 87%) (Fig. 2).

For NiTi wires, the meta-analysis of the pooled data on the effect of NP coating for FR showed a significant reduction in the FR of NP coated wires (p < 0.0001), with a mean difference of −0.19 N (95% CI, −0.30, −0.09) compared to controls and no heterogeneity (I = 0%) (Fig. 3).

DISCUSSION

Nano particles have been utilized to coat orthodontic brackets and wires to improve their properties and surface characteristics. According to Rapoport et al. and Cizaire et al. NP decrease the frictional coefficient by acting as a spacer and improving the surface topography of the wires.41,42 This decreased friction could help mitigate and reduce some of the adverse effects of orthodontic treatment and also aid in shortening the treatment duration.

The objective of this review was to evaluate the evidence of the use of NP coatings on the FR of orthodontic archwires. NP coatings are garnering ever more popularity as coating materials. Although many in vitro studies were conducted no qualitative analysis was performed. Among the studies included in this review, eight of them reported a significant reduction in the FR of orthodontic archwires coated with NP,32-37,39,40 and the other two studies31,38 reported no significant difference in the FR of coated archwires. Quantitative analysis using a random effects model to evaluate the effect of NP coating on FR was done separately for both stainless steel (SS) and nickel-titanium (NiTi) wires. A significant mean difference of −1.28N between NP coated and non-coated wires favoring NP coating was obtained for SS wires, and a significant mean difference of −0.19N between NP coated and uncoated wires favoring NP coating was obtained for NiTi wires.

The overall methodological quality of the included studies was judged to be assessed to be of moderate. The studies by Redlich et al.35,37 and Samorodnitzky-Naveh et al.36 have not mentioned the sample size evaluated, and sample size calculation was also not performed; thus, these studies were assigned a moderate quality of methodology. In the study by Kachoei et al.,39 a moderate quality of evidence was assigned as the study failed to clearly state the statistical significance of the evaluated outcome. In the study by Sharma et al., the sample size calculation based on the reference article has been clearly mentioned.32 In the studies by Hammad et al., Behroozian et al., and Kachoei et al.33,34,38 sample size calculation was not performed, but the sample size was mentioned, so it becomes difficult to assess whether the sample size is sufficient or not.

A major variability of studies included in the qualitative analysis is the different types of NP used for coating. Although predominantly zinc oxide NP is evaluated in the studies,31,33,34,38-40 Chitosan NP,40 Silver NP32 and inorganic fullerene-like tungsten disulfide NP were also evaluated by the studies. Only two studies31,38 that evaluated Zinc Oxide NP identified no significant difference in FR. Another difference among the included studies in the review is the techniques used for coating archwires which are different in all the included studies. Six studies utilized electrodeposition,31,33,35-38 two studies utilized chemical deposition,34,39 one study used physical vapor deposition,32 and the one study utilized the dip-coating technique.40 Each author claims that the technique used in their study is more advantageous, although a direct comparison to evaluate all the different techniques for coating wires used is not possible within the purview of this review. The studies have all evaluated the coating procedures using scanning electron microscopy, X-ray diffraction, or energy dispersive spectroscopy. Kachoei et al.39 identified the particles post coating to be of spherical shape and have a diameter of 42 nm. Redlich et al.35 obtained a coating thickness of 4–6 µm. Redlich et al.37 also verified that the coatings were durable even after multiple cycles of friction testing.

Some confounders that can impact the resistance to sliding include the type of ligation, the material of the bracket, dimension and cross-section of the wire, in-built second-order angulation, material, and the cross-sectional dimension of the wire.3,4,12-17 Most confounders were eliminated in all the studies for testing FR except in the study by Behoorzian et al.38 where ceramic brackets were used, and in the studies, conducted by Redlich et al.,35 and Samorodnitzky-Naveh et al.,36 who used SS self-ligating brackets. This variability could have had an impact on the results as ceramic brackets tend to offer higher FR when compared to SS brackets,43,44 and self-ligating brackets tend to offer lower FR than brackets with conventional ligation.45,46 In all of the included studies, the FR was evaluated using a UTM, calibration of the testing machine was similar in five studies33,34,38-40 and varied in the other five studies.31,32,35-37

Nanoparticle coatings have significant advantages of improving the FR of orthodontic wires and antimicrobial activity,47-51 but the evidence on the biocompatibility and biosafety of these coatings is still inconclusive.20,52,53

LIMITATIONS

A major limitation of this review is that the in vitro studies cannot replicate the complex interactions occurring in the oral cavity. Studies reporting on coating with different types of NP are included in the review, and a direct comparison among these different coatings is not available. Variable methodologies adopted in the studies and a very limited number of studies included in the meta-analysis further limit the results of the present review. Further clinical studies should be conducted based on the limitations of the available literature.

CONCLUSION

Considering the limitations of this review and with moderate-quality evidence, it can be concluded that the use of NP to coat orthodontic archwires has a beneficial effect on reducing the FR of these archwires.

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