Daniela Sofia Wunsh
V course, 13 group
ORTHODONTIC TREATMENT POSSIBILITIES FOR PATIENTS
ALLERGIC TO NICKEL: A LITERATURE REVIEW
Master's Thesis
Supervisor:
Aistė Kavaliauskienė, Lector, PhD
LITHUANIAN UNIVERSITY OF HEALTH SCIENCES MEDICAL ACADEMY
FACULTY OF ODONTOLOGY THE CLINIC OF ORTHODONTICS
ORTHODONTIC TREATMENT POSSIBILITIES FOR PATIENTS
ALLERGIC TO NICKEL: A LITERATURE REVIEW
Master's Thesis
The thesis was done
by Student ... Supervisor...
(signature) (signature)
Daniela Sofia Wunsh, 5th year, group 13th Aistė Kavaliauskienė, Lector, PhD
30th April 2021 30th April 2021 Kaunas, 2021
EVALUATION TABLE OF THE MASTER’S THESIS
OF THE TYPE OF SYSTEMIC REVIEW OF SCIENTIFIC LITERATURE
Evaluation: ... Reviewer: ...(scientific degree. name and surname)
Reviewing date:
...
Compliance with MT
No. MT parts MT evaluation aspects requirements and
evaluation
Yes Partially No
1 Is summary informative and in compliance with the 0.3 0.1 0
Summary thesis content and requirements?
2 (0.5 point) Are keywords in compliance with the thesis 0.2 0.1 0 essence?
3 Introduc- Are the novelty, relevance and significance of the 0.4 0.2 0 work justified in the introduction of the thesis?
tion, aim
Are the problem, hypothesis, aim and tasks formed
4 and tasks 0.4 0.2 0
clearly and properly?
(1 point)
5 Are the aim and tasks interrelated? 0.2 0.1 0
6 Selection Is the protocol of systemic review present? 0.6 0.3 0
criteria of Were the eligibility criteria of articles for the
7 the studies, selected protocol determined (e.g., year, language, 0.4 0.2 0
search publication condition, etc.)
methods and Are all the information sources (databases with
8 strategy dates of coverage, contact with study authorsto 0.2 0.1 0
(3.4 points) identify additional studies) described and is the last
search day indicated?
Is the electronic search strategy described in such a way that it could be repeated (year of search, the
9 last search day; keywords and their combinations; 0.4 0.1 0
number of found and selected articles according to
the combinations of keywords)?
Is the selection process of studies (screening,
eligibility, includedin systemicreviewor,
ifapplicable, included in the meta-analysis)
described?
10 0.4 0.2 0
Is the data extraction method from the articles
11 (types of investigations, participants, interventions, 0.4 0.2 0
analyzed factors, indexes) described?
Are all the variables (for which data were sought
12 and any assumptions and simplifications made) 0.4 0.2 0
listed and defined?
Are the methods, which were used to evaluate the
13 risk of bias of individual studies and how this 0.2 0.1 0
information is to be used in data synthesis,
described?
14 Were the principal summary measures (risk ratio, 0.4 0.2 0
difference in means) stated?
Is the number of studies screened: included upon
15 assessment for eligibility and excluded upon giving 0.6 0.3 0
the reasons in each stage of exclusion presented? Are the characteristics of studies presented in the
16 Systemiza- included articles, according to which the data were 0.6 0.3 0 extracted (e.g., study size, follow-up period, type of
tion and
respondents) presented?
analysis of
Are the evaluations of beneficial or harmful
data
outcomes for each study presented? (a)simple
17 (2.2 points) 0.4 0.2 0
summary data for each intervention group; b) effect estimates and confidence intervals)
Are the extracted and systemized data from studies
18 presented in the tables according to individual 0.6 0.3 0
tasks?
19 Are the main findings summarized and is their 0.4 0.2 0
relevance indicated?
20 Discussion Arethe limitations of the performed systemic 0.4 0.2 0
(1.4 points) review discussed?
21 Does author present the interpretation of the 0.4 0.2 0
results?
22 Do the conclusions reflect the topic, aim and tasks 0.2 0.1 0
Conclusions of the master's thesis?
23 (0.5 points) Are the conclusions based on the analyzed material? 0.2 0.1 0
24 Are the conclusions clear and laconic? 0.1 0.1 0
25 Is the references listformed accordingtothe 0.4 0.2 0
requirements?
Are the links of the references to the text correct?
26 Are the literature sources cited correctly and 0.2 0.1 0
References precisely?
27 (1 point) Is the scientific levelMaster’s thesis? of references suitable for 0.2 0.1 0 Do the cited sources not older than 10 years old
28 form at least 70% of sources, and the not older than 0.2 0.1 0
5 years – at least 40%?
Additional sections, which may increase the collected number of points
29 Annexes Do the presented annexes help to understand the +0.2 +0.1 0 analyzed topic?
Practical
Are the practical recommendations suggested and
30 recommen- +0.4 +0.2 0
are they related to the received results?
dations
Were additional methods of data analysis and their
31 results used and described (sensitivity analyses, +1 +0.5 0
meta-regression)?
Was meta-analysis applied? Are theSelected
statistical methods indicated? Are theresults ofeach
meta-analysis presented?
32 +2 +1 0
General requirements, non-compliance with which reduce the numberof points
33 Is the thesis volume sufficient (excluding 15-20 pages <15 pages
annexes)? (-2 points) (-5 points)
34 Is the thesis volume increased -2 points -1 point
artificially?
35 Does the thesis structure satisfy the -1 point -2 points
requirements of master's thesis?
36 Is the thesis written in correct language, -0.5 point -1 points
scientifically, logically, and laconically?
37 Are there any grammatical, style or -2 points -1 points
computer literacy-related mistakes?
38 Is text consistent, integral, and are the -0.2 point -0.5 points
volumes of its structural parts balanced?
General
39 Amount of plagiarism in the thesis. >20%
require- (not evaluated)
ments Is the content (names of sections and sub-
40 sections and enumeration of pages) in -0.2 point -0.5 points
compliance with the thesis structure and
aims?
Are the names of the thesis parts in
41 compliance with the text? Are the titles of -0.2 point -0.5 points
sections and sub-sections distinguished
logically and correctly?
42 Are there explanations of the key terms -0.2 point -0.5 points
and abbreviations (if needed)?
Is the quality of the thesis typography
43 (quality of printing, visual aids, binding) -0.2 point -0.5 points
good?
*In total (maximum 10 points):
*Remark: the amount of collected points may exceed 10 points.
Reviewer’s comments: ___________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ __________________________________ _______________________
EVALUATION FORM OF THE MASTER’S THESIS
FOR THE MEMBER OF DEFENCE COMMITTEE
Graduate student Daniela Sofia Wunsh, of the year 2021, and the group 13 of the integrated study program of Odontology
Master’s Thesis title: Orthodontics Treatment Possibilities for Patient's Allergic to Nickel
Evaluation No. MT evaluation aspects
Yes Partially No
1 Has the student’s presentation lasted for more than 10 minutes?
2
Has the student presented the main problem of the Master’s
thesis, its aim and tasks? 3
Has the student provided information on research methodology
and main research instruments? 4 Has the student presented the received
results comprehensively?
5 Have the visual aids been informative and easy to understand?
6 Has the logical sequence of report been observed?
7
Have the conclusions been presented? Are they resulting from the
results?
8 Have the practical recommendations been presented?
9
Have the questions of the reviewer and commission’s members
been answered correctly and thoroughly?
10
Is the Master's thesis in compliance with the essence of the
selected study program?
Remarks of the member of evaluation committee of Master’s Thesis
______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________
Evaluation of the Master’s Thesis
_____________________________________________________________________________ Member of the MT evaluation committee:
________________ ___________________________ _____________________
TABLE OF CONTENTS
SUMMARY………...9
INTRODUCTION………….……….….………...10
1. SEARCH METHODS AND STRATEGY, SELECTION CRITERIA OF THE STUDIES…….13
2. SYSTEMATIZATION AND ANALYSIS OF DATA…...………....….25
3. DISCUSSION……….…...….………33 CONCLUSIONS……….………...…...36 PRACTICAL RECOMMENDATIONS……….………...…36 ACKNOLEDGEMENTS……….…….……….………36 REFERENCES……….………...….………..37 ANNEXES……….………..…………....………..……40
ABBREVIATIONS
Metal alloys
Composites:
GFRSMPU- Glass fiber reinforced shape memory polyurethane
SMPU- pure shape memory polyurethane FRC- fiber-reinforced composites
Thermo mechanical procedures EDM- electrical discharge machining PMEDM- powder-mixed EDM MRR- material removal rate
Tests:
SEM- scanning electron microscope, DSC- differential scanning calorimetry FEA- finite element analysis
LSCM- laser scanning confocal microscope ARI- Adhesive remnant index
LII- Little's irregularity index SS- stainless steel
Ni Ti- nickel titanium Co-Cr- cobalt chromium Ti-Mo- titanium-molybdenum
TiNbTaZr-niobium-titanium-tantalum-zirconium
SMA- shape memory alloy Ni- nickel
TMA- Titanium molybdenum alloy/ β titanium TiC- titanium carbide
Ti2O- titanium oxide Cu2O-copper oxide
MSW- multistranded stainless steel
Plastics:
SEP- super engineering plastics PEEK- polyether ether ketone PES- polyether sulfone
PVDF- polyvinylidene difluoride PMMA- Polymethyl methacrylate
9
SUMMARY
Title:
Orthodontic treatment possibilities for allergic to nickel patients.
Introduction:
The purpose of this study was to find orthodontic appliances suitable for patients with nickel allergy and compare their characteristics.
Materials and methods:
A search was done in PubMed database, publications which was suitable for the aim were analyzed and recruited if found relevant, after assessing the titles, abstracts, and full text. Articles included studies on humans and in vitro.
Results:
571 articles were found initially, in a search done in PubMed database. After checking titles and abstracts inclusion and exclusion criteria were applied. The articles left were checked for eligibility by reading full text. Eventually, 7 articles were chosen to be included in this review: 5 in vitro studies and 2 Randomized clinical trials. A total of 80 patients were enlisted in this systematic review.
Conclusion:
Current treatment alternatives include using super engineering plastics (SEP), Glass fiber reinforced shape memory polyurethane (GFRSMPU), niobium-titanium-tantalum-zirconium (TiNbTaZr) and adding TiC powder to shape memory alloy as alternative to conservative nickel containing archwires, and fiber reinforced composites (FRC) with spot covering technique as an alternative to conservative orthodontic retainer.
Keywords:
10
INTRODUCTION
Nickel allergy is one of the most common allergies in dentistry, especially in the orthodontic field. The prevalence of this type of allergy can reach up to 14.5% in the general population and is more common in females [1]. This type of reaction is considered as type IV hypersensitivity reaction (delayed type hypersensitivity), mediated by cytokines and chemokines, which eventually activate antigen specific Th1 lymphocytes that will lead to inflammatory reaction [2]. Nickel is widely used in orthodontic practice, it can be found in archwires, brackets and bands, whether nickel titanium (Ni Ti) or stainless steel (SS). Metal ion release happens mainly due to corrosion and aging, and though alloys used in dentistry must be as biocompatible as possible (having oxide layer to reduce the incidence of corrosion and being polished very well to remove the surface roughness of the material) the oral cavity is a complicated media for every metal. Friction, different pH levels that change due to the ingested food, microflora and various elements that form different solvents and salts can increase the corrosion potential, whether it is galvanic, pitting or other types of corrosion [3]. Corrosion will lead not only to nickel ions leak and accumulation in body fluids and periodontal tissues, but also to weakening of the alloy and reduce the efficacy of the orthodontic appliance [4]. Another problem is wearing of the metal that happens due to friction. Some friction is needed to achieve various tooth movements, but it can damage the surface composition of the metal. The saliva acts as a natural lubricant and can decrease the wearing of teeth and as well the material fixed to them, reducing the friction, and thus reducing the corrosion incidence [5].
When speaking about nickel ion release, the biggest release is from bands, followed by brackets and finally wires, and stainless steel is considered to be the alloy which releases nickel ions the most [6]. Titanium was the most biocompatible [7]. About the timing in which most of the ions are released, it is considered to be in the initial phase of the treatment, at about 4-5 months [8]. Most of the studies that evaluated the timing of most ions release were of short duration, but the study by Quadras et al (2019) [9] had a longer observation period- 1.5 years. During this period, they observed dramatic increase of nickel ions in saliva and blood serum, but they were still at the dietary limit and did not reach toxic levels. After removal of the orthodontic appliances, the nickel amount in blood and saliva supposed to return to normal values.During orthodontic treatment, especially with fixed orthodontic appliances, the patients are instructed to brush their teeth more often to remove plaque and to use fluoridated mouthwashes, pastes, and gels to eliminate formation of white spot lesions. This increasing amount of fluoride in the oral cavity leads to increase in the acidity and friction rate of the alloy, increasing corrosion incidence of orthodontic appliances, and to bigger Ni ion release [10]. The rate of corrosion of metals in presence of fluoride in the oral cavity depends on the type of alloy, coupling between different types of alloys (difference in electrical potential that will cause ions
11 movement between cathode and anode), and the active materials in the mouthwash/toothpaste and their amount [11]. At a study done by Pulikkottil et al (2016) [12] archwires from different materials (stainless steel, nickel-titanium, titanium molybdenum alloy, and low-friction TMA) were immersed in artificial saliva with and without fluoride (0.5% of NaF, like in commercial toothpastes) for 2 hours. Scanning electron microscope, atomic force microscopy and energy dispersive spectroscopy were used to analyze the surface data and Linear polarization test to evaluate the corrosion resistance. In their results, it was found that all the metals experienced reduce in the corrosion resistance, but titanium molybdenum alloy and low-friction TMA had higher corrosion resistance than the other metals. A study by Rafeeq et al (2014) [13] which evaluated metal ion release from 2 groups of stainless steel and Ni Ti archwires conducted similar results: fluoridated mouthwash caused a release of more nickel ions from both groups and higher ion release from Ni Ti archwires. Moreover, when coupled with Ni Ti wires, stainless steel brackets showed higher corrosion rate and nickel ion release when immersed in fluoride containing mouthwash [14].
The daily intake of nickel ranges from 0.2 to 0.6 mg in humans. Some food products such as various fruits and vegetables contain high amount of nickel and do not cause hypersensitivity reaction, while ion release from orthodontic materials can be within dietary limit, but will promote allergic reaction [15][16]. Using this information, studies been done on the possibility to induce hyposensitization to patients with nickel systemic allergic reaction. Those studies used nickel oral hyposensitization in the form of slow increasing of Ni dietary intake with nickel containing water soluble granules and hard gelatin capsules (nickel sulphate or nickel sulfate hexahydrate), and later reintroduced the patients to nickel rich diet. There was a significant improvement of patients in tolerating nickel containing diet [17][18][19]. Another study done in 2002 in Denmark showed that wearing orthodontic appliances reduces the prevalence of nickel hypersensitivity [20]. Sadly. Until now there are no research done vice versa: will patients with ear piercing have less incidence of nickel allergy during orthodontic treatment?
Either way, even if nickel hyposensitization will work, it will be a time-consuming process with a lot of planning. Therefore, it is needed to think about alternatives for those patients. In previous years, gold brackets and archwires were recommended to allergic patients, but they are expensive, and the properties of gold might not have the characteristics needed for every stage of the treatment. Pure titanium and titanium alloys were suggested before. Titanium allergy, although rare, still might happen. due to the acidity in the oral environment caused by use of fluoridated pastes and mouthwashes, the alloy undergoes corrosion which result in release of ions and absorption of them in the body fluids [21]. Nickel free alloys are found in the market as well. A study done by Shintcovsk [22] et al in 2015, compared the chemical composition and surface characteristics of conventional and nickel free brackets. They evaluated the results, and despite having similar chemical composition,
12 the nickel free group demonstrated less polished surface, resulting in pits and uneven surface. As discussed before, it is not a good property for metal in the oral environment. Corrosion and ion release can still occur and might induce allergy to other ions which are not nickel.
Therefore, the aim in this review is to evaluate alternatives for conventional orthodontic appliances, which will be suitable for individuals suffering from nickel hypersensitivity.
Aim:
Review of modern treatment possibilities of patients who cannot use orthodontic devices made from standard materials due to nickel allergy.
Tasks:
● Find alternatives to nickel containing materials used in standard orthodontic appliances that will not cause allergic reaction to patients with nickel hypersensitivity.
● Evaluate the properties of alternative materials.
● Compare alternative materials properties with standard orthodontic materials containing nickel.
13
1. SEARCH METHODS AND STRATEGY, SELECTION CRITERIA OF THE
STUDIES
1.1 SEARCH METHODS AND STRATEGY
The protocol of this review was done following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement [23]. Local ethics committee approved this review (No. BEC-OF-96), present in Annex 1.
1.1.1 Focus question
The focus question was formulated using PICOS (population, intervention, comparison, and outcome) study design. It is presented in Table 1.
Table 1. PICOS table
Component Description
Population (P) Patients with nickel hypersensitivity.
Intervention (I) Alternatives to use of nickel-based alloys in orthodontics.
Comparison (C) Comparison between different materials used instead of nickel-based alloys.
Outcome (O) Orthodontic treatment that will not provoke hypersensitivity reaction. Study design (S) Randomized and non-randomized control trials, in vitro studies. Focus Question What alternatives can be used instead of nickel-based alloys?
1.1.2 Information sources
The information source used was PubMed database.
1.1.3 Types of Publications
The review included original articles, studies done on humans and in vitro published in electronic journals, in English language, between 2015-2020.
1.1.4 Types of studies
The review included randomized clinical trials and in vitro studies, written in the English language. The search was done manually, including studies published between the 1st of January 2015
14 and March 2021. The studies included were about dental materials which do not contain nickel, that can serve as orthodontic treatment alternative for patients with nickel hypersensitivity.
1.1.5 Population
5 articles were done in vitro, and 2 articles were randomized clinical trials done on healthy patients without known diseases or allergies. Even though the target population of this review was not directly checked, the results of both in vitro and clinical trials can serve as a good treatment option for nickel allergic patients.
1.1.6 Selection Criteria
The selection of articles was done according to the inclusion and exclusion criteria.
1.1.7 Inclusion criteria: ● Articles in English
● Articles that were published from 1st of January 2015 to 10th of March 2021 ● Randomized and nonrandomized clinical trials
● In vitro studies
1.1.8 Exclusion criteria:
● Articles in languages other than English ● Articles published before 2015
● Case reports, reviews and meta-analysis, editorials, study questionnaires ● Articles that do not fully open
● Clinical trials made on animals
1.1.9 Search
PubMed database was used for the search. The literature search was done according to the inclusion and exclusion criteria. Different keywords combinations were used to locate appropriate data. In addition, one article was incorporated which does not match the keywords used. First date of search was October 3rd, 2020 and last date March 10th, 2021.
15 Table 2. Summary of keywords combination and dates of search
Search dates Keyword's combinations Results
First date of search
03.10.2020 "Orthodontic treatment" AND "Contact stomatitis" OR "Allergic patients"
78 15.11.2020 "Nickel allergy" AND "Orthodontics" 147
23.11.2020 "Orthodontics" AND "Allergy" AND "Alternatives" 34 29.11.2020 "Orthodontics" AND "Allergy" OR
"Hypersensitivity" AND "Materials"
311
Last date of search
10.03.2021 "Orthodontic treatment" AND "Contact stomatitis" OR "Allergic patients"
81 "Nickel allergy" AND "Orthodontics" 151 "Orthodontics" AND "Allergy" AND "Alternatives" 36 "Orthodontics" AND "Allergy" OR "Hypersensitivity" AND "Materials"
317
1.1.10 Data items:
"Authors" and "Publication year"- revealed the authors and publication year. "Type of study"- described study type.
"Study group"- described the analyzed subject.
"Sample size"- showed the number of subjects of each study group. "Primary outcome"- explained the primary outcome of each study. "Secondary outcomes"- explained the secondary outcomes of each study.
"Storage media" and "Temperature"- described the environment and the temperature in which the study group was held.
"Observation period"- indicated the period in which the material was analyzed.
"Investigation method"- described the method in which the primary and secondary outcomes results were achieved.
"Gender"- showed the gender ratio of the study groups. "Age group"- showed the mean age group of the study group. "Aim of study- described the what the researchers wanted to check.
16 "Outcomes"- revealed the outcomes according to which the researchers based the results of their study.
"Results"- explained the result of the outcomes in each study group.
1.1.11 Methodological quality of studies (risk of bias)
2 tools were used for this procedure: the first one, modified CONSORT tool for assessing in
vitro studies [24], the second one JBI critical appraisal tool for assessing randomized control trials
[25]. Results are formulated in tables 3 and 4. Full protocol of questions to assess the quality of the studies are present in Annexes 2 and 3.
1.1.12 Synthesis of results
Appropriate data is formulated in tables 5 and 6.
1.1.13 Statistical analysis
The studies were heterogenic between each other, by study type and by the aims. Therefore, meta-analysis could not be performed.
1.2 SELECTION CRITERIA OF THE STUDIES
1.2.1 Selection of Studies
The search was done using PubMed database, and based on PRISMA [23] requirements. Specific keywords combinations were used: "orthodontics", "nickel allergy"," allergy materials", "materials alternatives", "hypersensitivity", "orthodontic treatment with contact stomatitis", "orthodontic treatment for allergic patients". One article which does not correspond to the keywords was added from PubMed database.
Initially, 570 results were found. After removing duplicates, 354 results left. Results older than 5 years, not corresponding to the topic and not fully available were excluded- 30 were left. Case reports and reviews were removed. Full text eligibility was assessed, and results that does not correspond to the research question were removed. Eventually 7 articles which met the inclusion criteria were included in the review. Schematic illustration of the study selection is shown in figure 1.
1.2.2 Quality of bias assessment
After selecting the studies, they were assessed for risk of bias. 2 tools were used for this procedure: the first one, modified CONSORT tool for assessing in vitro studies [28-32] suggested by
17 Faggion (2012) [24], the second one JBI critical appraisal tool for assessing randomized control trials [25], [26-27]. Both tools do not have a specific way to summarize if the risk is high or low, so there was no appropriate way to classify them of having high or low risk of bias. In general, there is no specific tool to assess in vitro studies, so it might be difficult to understand if they are reliable of not. No blinding, no appropriate statistical analysis done and no concrete explanation about sample design and allocation procedure make it even harder to have a perspective about those studies.
In this review, all included in vitro studies have probability to contain bias. In contrast, the randomized clinical control trials in this review followed some protocol to reduce the risk of bias. The study by Nordstrom et al. (2018) [26] had no risk of bias, but the study of Nagani et al. (2020) [27] had some risk of bias, thus becoming less reliable. Overall, to assess the in vitro studies, they need to be done on humans with proper study design. Risk of bias evaluation characteristics are shown in tables 3 and 4. Tables 5 and 6 present characteristics of each study.
18 Figure 1. PRISMA flow diagram
Additional record from PubMed database using different keywords
(n = 1) Records identified through PubMed
searching -Keywords used:
"orthodontics", "nickel
allergy", "materials", "alternatives",
"hypersensitivity", "orthodontic treatment", "contact stomatitis", "allergic patients" -Language: English (n = 570) Id e n ti fi cat ion
Filtered
Removal of duplication (n= 217)Records after duplicates removed (n = 354) Scr ee ni ng Records screened (n= 354) Records excluded
-Older than 5 years (n= 254) -Not relevant (67)
-Not full text (n= 3)
Filtered
El ig ib ili tyFull-text articles assessed for eligibility (n = 30)
Full-text articles reviewed and excluded:
-Case reports (n=7) -Reviews (n = 5)
Filtered
Studies included in qualitative synthesis (n = 18)
Excluded:
Studies not specific to the research question (n=11)
Filtered
In cl u d e d Studies included in quantitative synthesis (n = 7)19 Table 3. Risk of bias according to modified CONSORT tool suggested by Faggion [24]
Items Further explanation Maekawa et al. 2015 [28] Sfondrini et al. 2017 [29] Liu et al. 2018 [30] Lucchese et al. 2018 [31] Zhu et al. 2020 [32] Abstract Item 1 Partially yes Partially yes Partially
yes
Yes Partially yes Introduction Item 2a
background
Yes Yes Yes Yes Yes
Item 2b objectives and/or hypotheses
No Partially yes Partially yes
Partially yes No
Methods Item 3
Intervention
Yes Yes Yes Yes Yes
Item 4 Outcomes
Yes Yes Yes Yes Yes
Item 5 Sample size No No No No No Item 6 Sequence generation No No No No No Item 7 Allocation concealment mechanism No No No No No Item 8 Implementati on No No No No No Item 9 Blinding No No No No No Item 10 Statistical methods No Yes No Yes No Results Item 11 Outcomes and estimation No No No No No Discussion Item 12 Limitations
No Yes Yes Yes Yes
Other information Item 13 Funding No information No information Yes No information Yes Item 14 Protocol No No No No No
20 Table 4. Risk of bias according to JBI tool critical appraisal tool for assessing randomized control trials (25) Checklist Study design Studies Q13 Q12 Q11 Q10 Q9 Q8 Q7 Q6 Q5 Q4 Q3 Q2 Q1 + + + + + + + + + + + + + Randomized clinical trial Nordstrom et al. 2018 (26) + + + + + + + + - - + - + Randomized clinical trial Nagani et al. 2020 (27) + = yes, - = no
21 Table 5. characteristics of in vitro studies
Investigation method Observation period Storage media/ temperature Secondary outcomes Primary outcome Sample size Study group Type of studies Authors and publication year
Flexural strength: three-point bending test with universal testing machine 10 days – 1 month Flexural strength (metal wires): dry (37°C) Bending creep properties Flexural strength 4 PEEK plate SEP In vitro study Mekawa et al. (2015) [28] Bending creep properties (SEP): measuring permanent deformation
at the bending center Bending creep properties (SEP): distilled water at 37°C between 2 weeks- 1 month Water absorption 4 PES plate 4 PVDF plate
Water absorption (SEP) and PMMA: weight change, accelerated water absorption test Water absorption (SEP) and PMMA: distilled water at 37°C for 10 days Esthetics 5 SS Metal wires Co-Cr 5 5 Ti-Mo 5 Ni- Ti super-elastic wires
Esthetics (SEP)- by eye Universal testing machine, Nexygen MT software Unknown Dry Strength to bend the wire at maximum load Strength to
bend the wire at 0.1 mm deflection 10
Flat metallic wire retainer In vitro study Sfondrini et al. (2017) [29] 10 Round metallic wire
retainer
10 Spot bonded FRC retainer
10 Full bonded FRC retainer
Dispersity of
glass fibers in SMPU matrix: SEM scanning and images Unknown Thermo mechanical tests: temp of 24° C, 36° C and 50° C Examine dispersity of glass fibers in SMPU matrix Investigate thermo mechanical properties (tensile and 3 0% (pure SMPU) One extrusion (GFRSMPU) In vitro study Liu et al. (2018) [30] 3 5% 3 10%
22 Changes in the transition temperature: DSC apparatus Dispersity of glass fibers: -196° C in liquid nitrogen Determine changes in the transition temperature flexural modulus, stress relaxation effect) at different temp 3 15% 3 20% 3 25% 3 30% 3 35%
Tensile modulus test: universal machine Changes in the transition temp: between -50° C to 200 ° C in nitrogen atmosphere Investigate shape memory functions (recovery ratio and shape recovery force) 3 40% 3 0% (pure SMPU) Double extrusion (GFRSMPU)
Flexural modulus- three-point bending test with universal machine 3
5%
3 10%
Stress relaxation effect test: universal machine Shape recovery ratio- temp of 50° C, then 24° C for 1 hour, then 36° C 3 15% 3 20%
Shape recovery ratio: by equation
𝜃
180× 100, where θ describes the angle of the V shaped specimen 3 25% 3 30% 3 35% 3 40%
Shape recovery force: tooth movement rate on typodont models and nonlinear FEA Shape recovery force- temp of 50° C, then 24° C, then 36° C 3 0% (pure SMPU) Triple extrusion (GFRSMPU) 3 5% 3 10% 3 15% 3 20% 3 25% 3 30% 3 35% 3 40% Dry 2 5 mm
23 Max load and stress: three-point bending test with universal machine, Nexygen 4.0 MT software Evaluate FRC max stress according to length and storage condition Evaluate FRC
force max load according to length and storage condition 2 8 mm FRCs retainers (dry) In vitro study Lucchese et al. (2018) [31] 14 mm 2
Water absorption ability (FRC)- weight change with a precision balance T0- before T1- after 6h T2- after 12h T3- after 24h T4- after 48h T5- after 72h Distilled water at 37° C Water absorption ability (FRC) 2 5 mm FRCs retainers (wet) 2 8 mm 2 14 mm Dry 2 5 mm Multistrand stainless steel wire retainer 8 mm 2 2 14 mm PMEDM parameters: digital oscilloscope, x ray Unknown Deionized water Characterize surface roughness, surface morphology and microhardness Investigate the PMEDM parameters on the machining characteristics of NiTi SMA Unknown 0 TiC powder concentrations (g/L) In vitro study Zhu et al. 2020 [32] 3
Surface roughness: laser scanning confocal microscope (LSCM) 5 7 10 Surface morphology: SEM Thickness and composition of
the recast layer Microhardness:
microVickers hardness tester Thickness of recast layer: SEM Composition of recast layer: SEM
SEP- super engineering plastics, PEEK- polyether ether ketone, PES- polyether sulfone, PVDF- polyvinylidene difluoride, PMMA-Polymethyl methacrylate, SS- stainless steel, Co-Cr- cobalt chromium, Ti-Mo- titanium-molybdenum, Ni- Ti – nickel titanium, GFRSMPU- Glass fiber reinforced shape memory polyurethane, SMPU- pure shape memory polyurethane, SEM- scanning electron microscope, DSC- differential scanning calorimetry, FEA- finite element analysis, FRC- fiber-reinforced composites, TiC- titanium carbide, SMA- shape memory alloy, EDM- electrical discharge machining, PMEDM- powder-mixed EDM, LSCM- laser scanning confocal microscope
24 Table 6. characteristics of Randomized clinical trials
M- male, F- female, NiTi- nickel-titanium, TiNbTaZr- niobium-titanium-tantalum-zirconium, FRC- Fiber reinforced composite, MSW- multistranded stainless steel Investigation Method Results Observation period Outcomes Aim of the study Age group (mean±SD) Gender Study group Sample size Type of studies Authors and publication year Digital scanner, 3Shape OrthoAnalyzer software. I: Little’s Irregularity Index: 3.6 mm Transverse width less than 1 mm T0- before treatment T1- after 4-6 months T2- after 8-12 months from point T0 Little’s Irregularity Index for teeth alignment and transverse width Compare efficacy of NiTi and TiNbTaZr archwires during initial stage of alignment I: 16.50±3.27 I: 6M; 8F I: NiTi archwires (14) 28 Randomized clinical trial Nordstrom et al. (2018) [26] II: Little’s Irregularity Index: 2.48 mm Transverse width less than 1 mm II: 15.43± 2.31 II: 5M; 9 F II: TiNbTaZr archwires (Gummetal) (14) Adhesive remnant index (ARI)
I: bond failure rate: 42.94% Failure pattern: Type 0- 45 62.5%) Type 1- 18 (85.7%) Type 2- 3 (20%) Type 3- 1 (12.5%) Every 3 months for 1 year Primary: bond failure rate Secondary: failure pattern Evaluate number and type of bond failure between FRC and MSW retainers I: 20.88 ± 3.45 I: 4M; 22 F I: FRC (27) 52 Randomized clinical trial Nagani et al. (2020) [27]
II: bond failure rate: 31.41% Failure pattern: Type 0- 27 (37.5%) Type 1- 3 (14.3%) Type 2- 12 (80%) Type 3- 7 (87.5%) II: 22.15 ± 3.68 II: 4M; 22 F II: MSW (27)
25
2. SYSTEMIZATION AND ANALYSIS OF DATA
2.1 Individualization according to appliance2.1.1 Archwire alternatives
A study done by Maekawa et al. (2015) [28] compared the properties of super engineering plastics (SEP) and standard metal archwire [e.g., stainless steel (SS), cobalt chromium (Co-Cr), titanium molybdenum- β titanium alloy (Ti Mo) and super elastic Ni Ti]. SEP is used in the medical field and has good thermal and mechanical properties, compared to conventional plastics. Since they do not contain metal, they do not have the risk of corrosion. The properties of polyether ether ketone (PEEK), polyether sulfone (PES) and polyvinylidene difluoride (PVDF) were investigated in this study. Among them, PEEK has the highest tensile and bending strength, PES has high mechanical strength and esthetics and is biocompatible enough to be used for dentures, and PVDF is the strongest in fluoroplastic category, has high chemical stability and good esthetics.
Three points bending test was done to the metal and SEP specimen to check their flexibility. The wires were deflected by 2 mm and returned to original position, at a temperature of 37° C. The results showed that SS and Co-Cr have highest flexure strength (means we need to apply more power to deflect them by 2 mm- more rigid), but also highest permanent deformity (1 mm- half of the deflection). Ni Ti had no permanent deformation at all, and the flexural strength was similar to that of PES by mean results. More specifically, PEEK and PES tolerated more load than Ni Ti, but deformed more than Ni Ti (0.2 mm and 0.1 mm, respectively), thus being less flexible. Regarding the bending strength, SEP wires were almost double the width of the metal ones (cross-sectional dimensions of 1.0×1.0 mm square for SEP, 0.40×0.55 mm for the metal wires), meaning that they were able to produce higher strength only when having bigger volume- the material itself is not very strong. Bending creep (relaxation tests) were done to check the deformation of SEP material over time, under constant load. The specimens were held at the same position as for three-point bending test, at a temperature of 37° C in distilled water, for time varying between two weeks and 1 month. Then, permanent deformation was checked again. PVDF and PES had higher deformation than PEEK after two weeks and one month.
Water absorption test was done for the SEP and Polymethyl methacrylate (PMMA) the specimens were polished and invested in 37° C distilled water for 10 days. Later they were removed from water and dried overnight at room temperature. Another test was done: specimens were immersed in distilled water and autoclaved for 10 days, and 121° C temperature and 2 atmosphere pressure. The results showed that after 10 days in distilled water without autoclaving, PVDF results was almost no water absorption, PEEK absorbed a little more water, and PMMA and PES absorbed
26 much larger water volume. When comparing to autoclaving, the results were almost the same. The reason for no water absorption by PVDF is its hydrophobic nature.
Esthetic tests were done as well, indicating that PES and PVDF had better color comparing to opaque beige PEEK.
Liu et al. (2018) [30] observed the thermo mechanical properties of glass fiber reinforced shape memory polyurethane (GFRSMPU). Lately, there have been attempts to use shape memory polymer (SMP) as an alternative to orthodontic archwire due to its good shape memory and other desirable characteristics such as large deformation, good heat preservation, etc. The disadvantage of this material is its low stiffness compared to other metal wires. Therefore, some fillers need to be added to the pure SMP for better characteristics, for example adding of carbon particles to create composite shape memory polyurethane (SMPU).
In this study, the researchers suggested to employ fiber glass to improve the mechanical properties of SMPU. To do that, they mixed short cut glass fiber powder with pure SMPU particles in different weight fraction (between 0% and 40%) and extruded the specimen under 207° C. Before the extrusion, the glass fibers were surface treated with silane coupling agent to improve the bonding strength between the glass fiber and SMPU particles. Single, double, or triple extrusion composites were made to investigate how mixing time influences their properties. Later they were refrigerated in liquid nitrogen in -196°C to be more prone to fracture and were fracture by hand. SEM scanned the broken specimen to assess the microstructure and glass fiber disparity in the composites (equal distribution of the fibers is a desirable outcome). The best result was for 30 wt.% in double and triple extrusion. There was no significant reason between them, so we can conclude that double extrusion is enough since triple extrusion requires more resources and is more expensive.
To analyze the changes in transition temperature (important for activation of the shape memory characteristic) due to adding glass fibers, differential scanning calorimetry (DSC) was used. This test was performed in different temperatures ranging from-50 °C to 200 °C in the nitrogen atmosphere, in a process of heating, cooling, and heating again. The temperature needed for activation of pure SMPU is approximately 36 °C, and the results showed that even with the addition of glass fiber fillers (between 25- 40 wt.%) the temperature stays approximately the same, indicating that the oral environment which has similar temperature is suitable for activating of shape memory process. To investigate the tensile, flexural modulus and stress relaxation, Tensile tests, three-point bending tests, and stress relaxation tests were done, respectively, at temperatures of: 24 °C, 36° C and 50 °C, with different glass fibers concentration, and at dimension of 50 mm×5 mm×1.6 mm. Proper outcome is described as stiffer material than pure SMPU (0 wt.%), which will give sufficient orthodontic force. Adding of glass fibers was assumed to provide this outcome due to their stiffness. Regarding tensile strength, there is direct connection between ductility and hardness; less elastic
27 material will be harder, thus easier to break. Tensile strength increased with increasing glass fibers concentration, seen more significantly after 25 wt.%. 24° C was the most suitable temperature, and triple extrusion most suitable mixing time (almost with no difference of that of double extrusion). The flexural modulus showed similar results: increase of glass fiber concentration led to higher flexural strength. Relaxation is also important factor for orthodontic material: we would like the material to relax slower, to have more force between reactivations. Stress relaxation tests were done at 36 °C, with a load of 10 mm/min for 1 hour. When applying the load, the stress was linearly increased in the beginning, but after reaching the maximum load, it gradually decreased to a plateau. Higher glass fiber concentration sustained higher stress. To check the shape recovery ratio, preliminary tests were done first. Specimen with 0, 10 and 30 wt.% were bent to a V shape at 50° C and held for 1 hour in 24° C. The results of these preliminary tests showed that with increasing of glass fiber concentration, the recovery ratio was lower, and none of the specimen reached full recovery in 24 hours. When checking on typodont models, the researchers analyzed 0 wt.% glass fiber concentration (pure SMPU) and 30 wt.% GFRSMPU. They stretched the archwires made of GFRSMPU to fit the shape of the dental arch at 50° C, cooled to 24 °C and stimulated the archwires at 36° C. The archwires were placed into brackets bended to the typodont teeth and analyzed for recovery of lingually displaced upper lateral incisor (3 mm). Nonlinear finite element analysis (FEA) was done to analyze the result: the SMPU spent 2 hours to align the tooth, while the 30 wt.% specimen needed only one hour for the same work. We can conclude that adding glass fibers in this concentration improves the shape recovery time by 50 %. The magnitude of the orthodontic force was also bigger for the 30 wt.% specimen than SMPU (108g compared to 55), which is important in producing different tooth movements which require bigger force (e.g., translation).
Nordstrom et al. (2018) designed a clinical trial to compare the efficiency in clinical implementation of Ni Ti and niobium-titanium-tantalum-zirconium (TiNbTaZr- Gummetal, noble β titanium) archwires during initial orthodontic alignment in adolescents. Subjects from The Ohio State University Orthodontic Clinic were recruited voluntarily to this trial and randomly allocated in to 2 groups: one receiving treatment with Ni Ti archwires (control group), and the other with Gummetal. Allocation to groups was done with a computer. Only 12- 20 years old patients were in this study, with fully erupted permanent teeth, no dental trauma history or use of bisphosphonates, no metal allergy, no root abnormalities and periodontal disease, not treated by extractions, and having Little's irregularity index (LII) bigger than 2 mm. 28 patients were divided into 2 groups. The researchers chose a difference of 1 mm tooth movement as significant enough from a clinical point of view.
0.022-inch slot straight wire brackets were bonded to patients' teeth (by a resident). Both archwires had a diameter of 0.016-inch. Before applying the archwires, the maxillary and mandibular arches were studied, and Gummetal arches were contoured to the dental arch shape based on study
28 models. Ni Ti archwires could not be contoured, so were adjusted according to canine width. After bracket bonding, archwires were inserted and religated after 4-6 weeks, and 4-6 weeks more. Digital scanning was done before treatment and at each appointment to measure Little's irregularity index, and transverse width of digital models (by a blinded researcher), each measurement was carried twice. LII is originally used as an objective method to assess mandibular teeth alignment for epidemiological studies, but is not suitable for measuring vertical displacement, means that infra and supra erupted teeth were not investigated properly [33]. Since Ni Ti is used in initial treatment stage, in which vertical modifications are done to align teeth, it could not be assessed properly due to inaccessibility of the measuring method. Therefore, transverse width measurement was carried out, indicating that with time, vertical malocclusion was corrected and the result of it is increase in transverse width of the arch. The results showed that there was no significant difference between the archwires. Decrease of LII was seen in the anterior area and in full arch in both jaws (initially maxilla presented greater initial irregularity), and transverse width change was not significant. ANOVA statistical test that was carried for the results, showed that if the LII difference was increased to 2 mm and transverse width to 2.5 mm, the results would be more significant. Also, after removing the archwires the Gummetal showed more permanent deformation than Ni Ti, means it is having less shape memory and can be less effective than Ni Ti archwires when dealing with severely displaced teeth. Nevertheless, since the experiment observation period was only few months, maybe if given enough time the Gummetal will be able to produce same results as Ni Ti, because they both produce light continues forces which are crucial for the initial alignment phase.
The study done by Zhu et al. (2020) [32] is based on the idea that to improve biocompatibility, it is needed to have a protective layer that will act against corrosion [e.g., titanium oxide (Ti2O) layer in Ni Ti alloys]. Some processes need to be done to assure the stability of this layer, one of them is suggested at that article. They used titanium carbide-powder-assisted micro-electrical discharge machining (PMEDM) to evaluate the improvement of surface characteristics of the nickel titanium shape memory alloy (Ni Ti SMA). Creating a thinner recast layer, (which is made of debris and is undesirable) and proper material removal rate (MRR) to remove the excess of material considered as positive outcomes. They did it by creating a micro electrode from Brass sheet and another one from Ni Ti SMA alloy (the workpiece) by low-speed wire electrical discharge machining (EDM) machine CNC system, and formed microcavities with a depth of 100 µm (using micro EDM). The Ni Ti SMA specimen had the length of 100 mm, a width of 300 mm, and a thickness of 0.5 mm. Prior to the experiment, they analyzed the surface characteristics; scanning electron microscope (SEM) was used to evaluate the surface morphology, laser scanning microscope to measure surface roughness, and microVickers hardness tester to measure surface hardness under a load of 100 g for 10 s. To conduct this experiment, they used different powder concentration, voltage, and pulse duration. The TiC
29 powder was added to a solution of deionized water, micropump was used to mix the powder evenly. The microelectrode was connected to an amplifier and a pump generator. What they found out, is that adding TiC powder does improve the discharge characteristics of Ni Ti SMA in EDM, significantly. Regarding material removal rate, which was calculated as the ratio between the volume of material removal and the processing time (mm 3/min), it increases when the powder ratio is higher. But, if increasing the ratio to more than 5 g/L, the removal rate decreases. Speaking of surface roughness, the optimal powder concentration was the same, 5 g/L (causing surface roughness of 0.828 µm)- when increasing the concentration until that number the surface roughness decrease, and larger concentration will increase surface roughness. When increasing the voltage, surface roughness increases as well- so best result was seen in 60 V- only 1.609 µm. Increase in pulse width and voltage cause increase in surface roughness, but longer pulse width and higher voltage are crucial for better removal rate. According to this reason, most optimal pulse width is 4 µs and voltage of 80 V (0.828 µm). Higher surface roughness can lead to bigger corrosion and material wear, as mentioned earlier.
The recast layer is determined by few factors, one of them is the pulse discharge energy. It promotes heat that is important to the formation of the recast layer, and higher pulse width will result in thickest recast layer- which is undesirable. when increasing powder concentration, the recast layer width decreases, but after 5 g/L it increases. Regarding microhardness: when the material is hard it is more brittle, but it is also more resistant to wearing. The researchers checked the microhardness of the most desirable results (80 V voltage, 4 µs pulse width and 5 g/L powder concentration) and found out that the microhardness can reach 438.7 HV after micro-EDM, which is a good result. Moreover, when analyzing the surface treated with EDM with the characteristics mentioned below, it was found that the surface contained different oxide layers (Ti2O, Cu2O (copper oxide), TiC and Ni Ti phases). This emphasizes that this machining process can increase biocompatibility of the material studied.
2.1.2 Retainer alternatives
Sfondrini et al. (2017) compared properties of spot bonded FRC retainers with conventional full bonded FRC retainers and spot bonded stainless steel metallic wires (flat and round). FRC are considered stiffer than metallic retainers, maybe due to the bonding technique or due to the fiber additives which enhance their mechanical and physiological properties. This rigidity can decrease physiological tooth movement and lead to ankylosis. Spot bonded FRC retainer technique suggests covering the retainer with composite material only on the teeth, and to leave the fiber exposed in the interproximal areas, like in metallic wires. In this study, the FRC contained glass fiber additives with a diameter of 0.75 mm, thicker than the SS retainers (flat: 0.673 mm × 0.268 mm, round: 0.394 mm). 10 specimens were divided into 4 groups: flat metal wire, round metal wire, FRC spot bonded technique, FRC full bonded technique. The length of each specimen was 28 mm. They were bonded
30 to Frasaco dental model from canine to canine, on acrylic teeth with light cured flow composite (after applying one step self-etched bonding material. Composite material covered only the teeth, except the full coverage group in which covered the interproximal areas as well. Tooth 31 was not fixed to the model to allow vertical movement. The other teeth 33-43 were fixed to the model. The strength to bend the wire was measured at 0.1 mm deflection and at maximum load (until the material breaks) by universal machine. Data was recorded by computer software and statistics were done: Kolmogorov Smirnov test to measure normality, ANOVA for analysis of variance and Tukey test to evaluate difference in deflection.
For 0.1 deflection, the results showed that both metal wires and spot bonded FRC had the lowest flexure strength- means they are less rigid. No significant difference was seen among them (𝑃 < 0.05). However, full bonded FRC had significantly higher flexure strength (𝑃 < 0.001). At maximum load, no significant difference (𝑃 < 0.05) was seen between both metal wires and spot bonded FRC- they tolerated less stress then full bonded FRC. Full bonded FRC tolerated higher load values, but without significance (𝑃 < 0.05). We can conclude that spot bonded FRC has no significant difference from metal wires in its flexural properties and can be used as an alternative to them.
Luccese et al (2018) [31] examined the properties of FRC retainers and compared them to multistrand stainless steel twisted orthodontic retainers, with different length spans. The FRC were composed of glass fibers, thermoplastic polymer, and light-cured resin matrix, and their diameter was 0.75 mm, SS wires diameter was 0.55 mm.
The FRC and SS wires were cut to length of 5 mm, 8 mm, and 14 mm. Another subdivision was done for the FRC specimens according to the storage condition: dry and wet. Eventually, 3 groups were established: FRC held in dry condition (subdivided into 5, 8, 14 mm- 2 specimens in each length), FRC held in wet condition (subdivided into 5, 8, 14 mm- 2 specimens in each length), and SS (subdivided into 5, 8, 14 mm- 2 specimens in each length). Initially, the FRC specimens were cut to 20 mm before polymerization. Polymerization was done by halogen light according to the manufacturer. After polymerization, all FRC specimens were stored in dry conditions.
The specimens that were going through wet storage condition were weighed with a precision balance before being inserted to distilled water at 37° C, to check their water absorption. After 6, 12, 24, 48 and 72 hours the specimens were weighed once again to check how much water was absorbed. Their maximal water absorption capacity was reached after 2 days.
After that, flexural tests were done to SS and FRC specimens using three-point bending test, by measuring the force needed to deflect the specimen by 1 mm, and the maximum load the specimen can withstand. ANOVA was used to assess differences at maximum load and maximum stress. During maximum load test, none of the specimen broke completely, only micro cracks were seen. There was a significant difference between the SS and FRC wet and dry storage and specimen length
31 in both tests (𝑃 < 0.001). Less load was needed to deflect longer specimen (14 mm) by 1 mm, and they appeared more elastic. When comparing SS and dry storage FRC under same length and deflection, the SS had significantly lower mechanical properties (𝑃 < 0.001) than the dry storage FRC- it was able to withstand less load but was also more elastic. Wet storage FRC showed more similar result to SS. Since the ideal outcome is to find material that will be able to replace SS wires- we can conclude that wet storage FRC can be used for this purpose; it has similar elastic modulus as SS and can withstand even higher load, not to mention dry storage FRC is impossible to imply in the oral cavity due to wet environment.
Nagani et al. (2020) [27] compared the bond failure rate in mandibular canine to canine retainer in FRC and multistranded stainless steel (MSW) retainers.
It was a randomized clinical trial with allocation of 1:1. They calculated that the sample size needs to be at least 56 subjects to gain significant result. Therefore, they recruited 60 subjects, in case some will drop out. The subjects were randomly divided to 2 groups via computer program. Inclusion criteria included subjects who do not need extractions, younger than 45 years, with normal facial appearance and moderate crowding, treated by MBT fixed appliance system, who agreed to a visit every 3 months for a follow up of one year. Exclusion criteria were poor oral hygiene and congenitally missing anterior teeth.
Patients undergone through debonding, deep scaling and curettage, composite remnants were removed, and teeth surface was cleaned with a tungsten carbide burr using low speed handpiece. One operator bonded all lingual retainers to all subjects. One group received FRC retainers (diameter 2 mm) and the other MSW retainers (diameter 0.0175 inch). The mandibular anterior teeth were isolated, and a dental floss was used to measure the inter-canine distance. Then, the retainer was cut to the appropriate length and treated with adhesive primer. The teeth were etched with phosphoric acid 37% for half a minute, washed and dried. Same adhesive primer was applied to each tooth and light cured for 15 seconds, and flowable composite was applied. The retainer was adapted to the lingual teeth surface, excess composite was removed, and each tooth was light cured for another 15 seconds. The patients were instructed to follow strict hygiene regimen. The patients were evaluated at each visit for bond failure rate and type of failure by adhesive remnant index (ARI): 0- no resin left on enamel surface, 1- less than 50% resin left on enamel surface, 2- more than 50% resin left on enamel surface, 3- all resin left on enamel surface. If during the visit detachment was observed, the subject could approach immediately for repair, and bond failure was recorded.
Initially, 60 subjects were recruited, out of whom 6 were excluded and 2 were lost to follow up, which left 52 subjects- smaller amount then what was calculated for appropriate statistical analysis. Nevertheless, both groups had equal number of 26 subjects. Statistics were done using
32 Statistical Package for Social Sciences (SPSS), and bond failure rate and pattern were compared using Chi square test with p-value < 0.05 as significant.
Total number of bond failures in both groups were 37.17%. In FRC group, Bond failure rate was 42.94%, and in MSW group bond failure rate was 31.41%. The difference of bond failure rate was significant (p= 0.012). Type 0 failure pattern occurred 45 times in FRC group (62.5%), 27 times in MSW group (37.5%), and a total of 72 times in both groups. Type 1 failure pattern occurred 18 times in FRC group (85.7%), 3 times in MSW group (14.3%), and a total of 21 times in both groups. Type 2 failure pattern occurred 3 times in FRC group (20%), 12 times in MSW group (80%), and a total of 15 times in both groups. Type 3 failure pattern occurred 1 time in FRC group (12.5%), 7 times in MSW group (87.5%), and a total of 8 times in both groups.
We can conclude that the most frequent failure pattern was type 0, and it occurred more often in FRC group. But type 2 and 3 failure patterns were observed more in MSW group- means they have higher bond strength. When FRC fails, less resin is left on the enamel surface, maybe due to the rigidity of the material, or because it covers more surface area. Other reasons can be poor moisture control, insufficient etching, or destructive oral environment, which weakens the bond between FRC resin matrix and additive fibers. This study is more trustworthy, since it is a randomized clinical trial, and has less risk of bias.
33
3. DISCUSSION
As mentioned before, the appliances which release the biggest amount of nickel are orthodontic bands, followed by brackets and archwires [6]. Today, bands are not needed for every orthodontic procedure, and since currently there is no specific alternative to stainless steel bands, we can try simply not to incorporate them when treating a susceptible patient. Some studies suggest use of gold bands, but they are quite expansive [34]. Regarding brackets, the market is full of nonmetallic brackets: ceramic, polycarbonate, sapphire, and other types. Their main advantage is their higher esthetic value comparing to standard metal brackets, and the fact they do not contain metal. They also have disadvantages: they are more fragile and are more difficult to debond from the tooth surface, leaving micro cracks on the enamel. Gold and titanium brackets are recommended as well [6], [3]. Also, at a study done by Downarowicz et al. [8] it was mentioned that the biggest amount of nickel is released during the first 4-5 months of initial stage of orthodontic treatment, in which usually Ni Ti flexible archwires are used, but at another study it was mentioned that nickel release is the highest in stainless steel alloys, which are used as a form of archwires in much later stages of treatment [6]. Either way, we need to consider alternative to both materials: Ni-Ti and stainless steel archwire.
Regarding nickel containing archwires, few solutions can be found: we can try to find alternative material with similar or better thermo mechanical characteristics as the original nickel containing metal, or we can employ the traditional archwires with some modifications done in them: processing characteristics to ensure oxide layer stability and reduce corrosion and wear, or coat them in different materials as suggested in another study [34].
Alternatives to Ni Ti can be SEP, FRC or TiNbTaZr.
FRC are becoming more popular in dentistry, and studies have done to check their abilities to function as archwires. The composite material (resin, polyurethane, or any other matrix material) provide the chemical and thermal stability, while the fibers give the mechanical strength. Fibers can be made of glass, carbon, polyaramid and polyethylene, and glass is one of the favorite choices- high tensile strength, high elastic modulus, good adhesion between composite resin and fibers and easy handling [35], [36].
An example to FRC is GFRSMPU, a combination of glass fibers and SMPU. The ideal ratio between glass fibers and SMPU is found to be 30 wt.%, and double extrusion mixing provides good results. They have shape memory which is activated at 36° C, they can tolerate high stress, they are stiff enough to produce various tooth movements (can produce force of 108 g), and they relax slower- meaning the orthodontic force will not decline to 0 between activations [30]. They can be used as an alternative to Ni Ti archwires, but not SS. Further investigations of matrix- fibers ratio and the types and combination of materials need to be done to find suitable alternative to SS archwires.
34 SEP are characterized by good esthetics, relatively low water absorption, they are more flexible than SS wires (like Ni Ti) but have less permanent deformation and can tolerate more load than Ni Ti. Out of SEP tested, PEEK had the most optimal results [28]. But they have a big disadvantage: to get those results, the width needs to be two times bigger than SS wires. It means that the material itself is strong only when having a large amount of it. Thicker archwire may complicate eating, speaking and oral hygiene, and will result in bigger plaque accumulation and caries risk.
TiNbTaZr archwires gained similar results to Ni Ti archwires, with one disadvantage: it has more permanent deformation than Ni Ti- means it has less shape memory. The clinical result will be less movement for severely displaced teeth. Since the study lasted only few months, we do not know if it will still be possible to get adequate result for this kind of problem; maybe the archwire just needs more time to gain the same result, or maybe the reason for that is that TiNbTaZr archwires are less flexible. According to the investigations in that study, both archwires had low stiffness, low elastic modulus, and both generated light force, which are desirable properties [26].
Some processing procedures can be done to improve the material's characteristics. As mentioned by Zhu [32] non-conventional machining such as EDM can be mixed with TiC powder to improve the surface characteristics of Ni Ti SMA wires. Less surface roughness and more polished surface, adequate hardness (not too brittle but strong enough not to wear) and thick oxide layer were established with the most optimal conditions: 80 V voltage, 4 µs pulse width and 5 g/L powder concentration.
Coating can be done with TiO2, Teflon and other materials, and can not only prevent metal ion release, but also to reduce bacterial adhesion to the archwires, thus reducing plaque incidence. It can also act as a barrier between the metal of the archwire and the saliva and the solvents found in it, thus providing a solution to the high fluoride amount in the oral cavity, as mentioned earlier.
Fixed orthodontic retainers are passive: they do not need to produce any force for tooth movement, only to be bonded well and to be rigid enough to hold the teeth in one place. For those reasons, SS retainers are very popular. In the recent years, FRC retainers were incorporated, not only for orthodontic use, but to stabilize teeth after trauma or reduce pathological movement for periodontologically compromised teeth. The idea of retaining is that when few teeth are connected, not only that they stabilize each other, they also prevent unwanted movement.
Teeth tend to move back to their natural place, so usually the retainers are fixed for a lifetime. When using such a long-term method, problems can occur. One of them is the use of MRI. When scanning with MRI machine, all metals must be removed from the body not to distort the results. When using nonmetallic retainers, we can avoid the need to remove the retainer prior to the scanning. They are also more esthetic than metal retainers.
