Introduction
This 3-arm parallel, double-blind study aimed to evaluate the alignment efficiency of 3 different diameters of superelastic nickel-titanium (NiTi) archwires during the initial phase of orthodontic treatment.
Methods
Ninety-three patients with nonextraction treatment in the mandibular arch (using 0.022-in Roth prescription brackets) were randomly allocated into 3 groups: 0.012-in NiTi (group 1), 0.014-in NiTi (group 2), and 0.016-in NiTi (group 3). The alignment change was measured using the modified Little’s irregularity index before archwire placement and every 4 weeks. The alignment efficiency of the 3 groups was analyzed.
Results
Ninety patients were analyzed (group 1: n = 29, group 2: n = 31, and group 3: n = 30; overall mean age, 16.6 years). The overall Wald test analysis revealed that wire type was not statistically significant ( P = 0.91), whereas time exhibited significance as expected ( P <0.001). Furthermore, the interaction between wire type and time was not significant ( P = 0.93). The time-adjusted estimated difference between 0.014-in and 0.012-in was −0.49 (95% confidence interval, −2.83 to 1.85; P = 0.68). The time-adjusted estimated difference between 0.016-in and 0.012-in was −0.45 (95% confidence interval, −2.95 to 2.05; P = 0.72). No harm was observed.
Conclusions
The clinical performance of 3 different sizes of NiTi archwires was similar. In addition, 0.014-in and 0.016-in NiTi archwires demonstrated better performances in aligning any irregularities because of a greater number of wire deformations in the 0.012-in group.
Registration
IR.TBZMED.REC.1395.1039.
Protocol
The protocol was not published before trial commencement.
Funding
None.
Highlights
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The study examined performance of different sized NiTi wires in alignment phase.
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All 3 sizes of NiTi wires demonstrate comparable effectiveness in addressing irregularities.
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0.014-in and 0.016-in NiTi wires may be preferable due to fewer wire deformations.
Optimal forces delivered by archwires are required not only to achieve controlled tooth movement but also to minimize patient discomfort and pathologic effects on the teeth and their surrounding structures. Material properties and geometric factors, such as the cross-sectional shape, length (ie, interbracket span), and diameter, could influence the force delivery performance of archwires. As a wide variety of archwires are available, it is crucial to understand the properties of archwires and select the most appropriate and efficient one, especially during the initial aligning stage of treatment.
Nickel-titanium (NiTi) archwires have gained popularity for their ability to deliver a light, continuous load over an extended period. Several clinical trials have compared the alignment efficacy of different types of NiTi archwires. , , However, a recent Cochrane systematic review reported that there is insufficient evidence to determine any particular archwire as the most efficient one in terms of alignment rate and efficacy.
Nowadays, superelastic NiTi archwires are commonly used by orthodontists as initial archwires during the first stage of treatment. However, to the best of our knowledge, no randomized clinical study has evaluated the clinical performance of different sizes of superelastic NiTi archwires in the initial stage.
Specific objectives or hypotheses
This study primarily aimed to compare the alignment efficacy of different sizes of superelastic NiTi archwires by measuring the amount of tooth movement that occurred at 4, 8, and 12-week intervals.
Material and methods
Trial design and any changes after trial commencement
This study was a randomized, double-blind, 3-arm, parallel clinical trial. The trial was approved by the Ethics Committee of Tabriz University of Medical Sciences (ID no. IR.TBZMED.REC.1395.1039).
Participants, eligibility criteria, and setting
Selection of participants was based on the following inclusion criteria: nonextraction treatment in the mandibular arch, presence of all permanent dentition (excluding third molars), crowding in which all the teeth could be bonded and engaged, no quad-helix or other palatal expansion devices; no extraoral appliances, no history of previous orthodontic treatment, no considerable medical history (systematic disease) or craniofacial abnormality, no active periodontal disease, no notable skeletal asymmetry, no previous extraction; no blocking out of the tooth that could not be bonded at the beginning of treatment; and no missing or spacing.
The trial setting was a private orthodontic office of one of the authors (A.S.). All participants signed an informed consent to participate in this study after clarifying the purpose of the intervention. Participants were enrolled in the study after providing written informed consent.
Interventions
The patients were treated by the same orthodontist (A.S.) using 0.022-in Roth prescription brackets (Ulti-Mim; Ortho Classic, McMinnville, Ore). The archwires (0.012-in, 0.014-in, and 0.016-in superelastic NiTi wires [Highland Metals Inc, Franklin, Ind] as initial archwire) were engaged in all teeth with elastomeric ligatures (American Orthodontics, Sheboygan, Wisc). The 3 sizes of archwires used in this study were similar and the same product line from the same manufacturer. The clinician decided whether to fully or partially engage the teeth with elastomeric ligatures.
Outcomes (primary and secondary) and any changes after trial commencement
The primary outcome was to compare the alignment efficacy of different sizes of superelastic NiTi archwires. At the beginning of the study and before placement of brackets (T0), alginate impressions were taken for study models, and irregularity of mandibular teeth was measured on study models from the right first molar to the left first molar in millimeters and a modified Little’s irregularity index (LII) was calculated for each cast. , It was calculated by measuring the horizontal linear displacement of anatomic contact points of each tooth from the adjacent anatomic point and summing the 11 displacements together ( Fig 1 ). All the measurements were made by 1 investigator (S.T.), who was not directly involved in patient treatment and was blind to the type of archwire to which the patient was allocated using a digital caliper (at 0.01 mm). Impressions were taken again (every 4 weeks), and the irregularity index was recalculated 4 (T1), 8 (T2), and 12 weeks (T3) later. Archwires of each group were retied in these 4-week intervals. Wire deformations were also assessed clinically by looking at the archwires extraorally. In case of permanent wire deformations, the archwires were replaced by new ones. In case of broken brackets (if patients informed the office), patients were recalled a maximum of 3 days after their calls to rebond these brackets.
Sample size calculation
The sample size was calculated as 28 subjects for each group. This gave the study a power of 80% to detect a difference of 1.5 mm in irregularity indexes between the NiTi archwire groups (based on a pilot study’s standard deviation of 1.9 mm [9 participants in each group in the pilot study]). An additional 10% was included to account for potential dropouts.
Interim analyses and stopping guidelines
Not applicable.
Randomization (random number generation, allocation concealment, and implementation )
A computer-generated randomization list ( https://sealedenvelope.com/simple-randomiser/v1/lists ) was used to develop a simple nonstratified randomization with an equal allocation ratio (0.012-in, 0.014-in, and 0.016-in superelastic NiTi wires as initial archwire). The randomization sequence was concealed in sealed opaque envelopes. The archwire types were written and placed in a sealed opaque envelope for allocation. This was performed by an office assistant who was out of the study.
Blinding
During this double-blind study, the participants and outcome assessor were blinded to the treatment allocation, and the operator was also blinded until the envelope seals were broken.
Statistical analysis (primary and secondary outcomes and subgroup analysis)
Descriptive statistics
Descriptive statistics were presented as mean and standard deviation or frequency and percentage for gender, age, and average amount (in millimeters) of LII for each group of treatment.
Reliability statistics
Reliability statistics were presented as LII. The Dahlberg formula and the relative Dahlberg error were used to test the reliability of 56 study models measured twice with a 2-week interval.
Inferential statistics
Generalized estimating equations regression models were used to test the differences in mean LII between time points and adjusted differences by gender and age of the patients.
An overall Wald test was used to assess the overall effect of wire type, time, and the interaction between wire type and time on LII.
The statistical analyses were performed using R (version 4.2.3; R Foundation for Statistical Computing, Vienna, Austria). The level of statistical significance was set at 0.05.
Results
Participant flow (including flow diagram, early stopping, and periods)
A total of 102 patients were invited to participate in this clinical trial; 6 of those were excluded because they did not meet the inclusion criteria. Three patients declined to participate in the trial. Therefore, 93 patients were randomly allocated to 3 groups at the beginning of the trial. The Consolidated Standards of Reporting Trials flowchart of the participants for this trial is shown in Figure 2 .
Baseline data (including baseline table)
Sample demographics and characteristics for the groups are shown in Table I . Baseline characteristics, including age, gender, and initial LII, were comparable between groups.
| Characteristics | Group 1 (0.012-in NiTi) | Group 2 (0.014-in NiTi) | Group 3 (0.016-in NiTi) |
|---|---|---|---|
| Gender | |||
| Male, n (%) | 25 (83) | 26 (84) | 26 (84) |
| Female, n (%) | 6 (17) | 5 (16) | 5 (16) |
| Age, y | 16.87 ± 4.94 | 17.51 ± 5.34 | 18.93 ± 6.28 |
| LII at T0 (mm) | 10.93 ± 4.26 | 11.06 ± 3.95 | 11.10 ± 4.64 |
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