1. Due to limited evidence, it is still unclear whether any first arch wire material or size is better than any other.
2. There is a need for large, well-planned studies. They should measure speed of alignment and side effects.
What is a fixed orthodontic brace?
The aim of orthodontic treatment is to correct crowded, twisted, buried, or protruding teeth. The people who receive orthodontic treatment are normally adolescents or adults. Fixed orthodontic braces (appliances) consist of brackets bonded to the teeth and connected to each other by arch wires, which exert force on the teeth to straighten or move them.
What is the first arch wire?
The first (initial) arch wire is inserted into brackets at the beginning of orthodontic treatment. Since the 1970s, several new types of initial arch wire have been developed, which show a range of different properties in the laboratory and which manufacturers claim offer benefits in terms of tooth alignment. New materials for initial arch wires include various mixtures (alloys) of nickel and titanium (NiTi).
What did we want to find out?
We wanted to find the best kind of first arch wire for orthodontists to use to correct crowded and twisted teeth. Our review evaluated whether different types (materials, sizes, or shapes) of first arch wires result in important differences, including faster alignment of teeth (speed of alignment, measured as tooth movement over time), and reduced side effects (e.g. pain and shortening of the tooth root) during treatment with braces.
What did we do?
We searched for studies that compared different types (materials, sizes, or shapes) of first arch wires among people who had upper or lower braces, or both. We compared and summarised their results, and rated our confidence in the evidence based on factors such as study methods and sizes.
What did we find?
We found 29 studies that involved 1915 people with 2581 first arch wires. The biggest study enroled 200 people and the smallest study enroled 14 people. The studies lasted from three days to six months. Eleven studies were funded. The studies varied in several aspects of orthodontic treatment, compared different materials and different sizes of first arch wires, and reported different results at different time points.
1. Multistrand stainless steel wires versus wires composed of other materials (6 studies): we do not know if multistrand stainless steel wires are better than wires made of other materials in terms of speed of alignment. There may be little or no difference between multistrand stainless steel wires and other wires in terms of pain.
2. Conventional NiTi wires versus superelastic NiTi wires (4 studies): there may be little or no difference between the two wire types in terms of their effect on alignment speed and pain.
3. Conventional NiTi wires versus thermoelastic copper-nickel-titanium wires (3 studies): we do not know if there is any difference between the two types of arch wires in speed of alignment.
4. Superelastic NiTi wires versus thermoelastic NiTi wires (12 studies): there may be little or no difference between superelastic NiTi wires and thermoelastic NiTi wires in terms of alignment speed. We do not know if there is a difference between the two wire types in terms of shortening of the tooth root. Superelastic NiTi wires compared with thermoelastic NiTi wires may take slightly longer to align the teeth and are probably slightly more painful.
5. Single-strand superelastic NiTi versus coaxial superelastic NiTi (3 studies): during the first four weeks after insertion of the first arch wires, speed of alignment is probably slower with single-strand superelastic NiTi wires compared with coaxial superelastic NiTi wires.
6. Different sizes of NiTi wires (2 studies): there may be little or no difference between different sizes of NiTi wires in terms of pain.
What are the limitations of the evidence?
We have limited confidence in the evidence because the results from the studies varied widely, and many studies enroled few people. Some studies did not clearly report how they were conducted, or whether the people taking part knew who had received which arch wire, which could have affected the study's results.
How up to date is this evidence?
The evidence is current to 4 July 2022. This is an update of a review first published in 2010 and last updated in 2018.
Superelastic NiTi wires probably produce slightly more pain after one day than thermoelastic NiTi wires, and single-strand superelastic NiTi wires probably have a lower alignment rate over four weeks compared with coaxial superelastic NiTi wires. All other evidence on alignment rate, root resorption, time to alignment, and pain is of low or very low certainty in all comparisons. Therefore, there is insufficient evidence to determine whether any particular arch wire material or size is superior to any other. The findings of this review are imprecise and unreliable; well-designed larger studies are needed to give better estimates of the benefits and harms of different arch wires. Orthodontists should exercise caution when interpreting the findings of this review and be prepared to adapt their treatment plans based on individual patient needs.
Initial arch wires are the first arch wires inserted into fixed appliance at the beginning of orthodontic treatment. With a number of different types of orthodontic arch wires available for initial tooth alignment, it is important to understand which are most efficient and which cause the least amount of root resorption and pain during the initial aligning stage of treatment. This is the third update of a Cochrane review first published in 2010.
To assess the effects of initial arch wires for the alignment of teeth with fixed orthodontic braces, in terms of the rate of tooth alignment, amount of root resorption accompanying tooth movement, and intensity of pain experienced by patients during the initial alignment stage of treatment.
We searched Cochrane Oral Health's Trials Register, CENTRAL, MEDLINE, Embase, and two ongoing trials registries on 4 July 2022.
We included randomised controlled trials (RCTs) of different initial arch wires used to align teeth with fixed orthodontic braces. We included people with full-arch fixed orthodontic appliances on the upper arch, lower arch, or both arches.
Two independent review authors were responsible for study selection, data extraction, and assessment of risk of bias in included studies. We contacted corresponding authors of included studies to obtain missing information. We resolved disagreements by discussion between the review authors.
Our main outcomes were alignment rate (movement of teeth in mm), root resorption, time to alignment, and intensity of pain measured on a 100-mm visual analogue scale (VAS). We pooled data from studies with similar interventions and outcomes using random-effects models. We reported mean differences (MDs) with 95% confidence intervals (CIs) for continuous data, risk ratios (RRs) with 95% CIs for dichotomous data, and alignment rate ratios with 95% CIs for time-to-event data.
Two independent review authors assessed the certainty of evidence. We resolved disagreements by discussion between the review authors.
We included 29 RCTs with 1915 participants (2581 arches) in this review. Studies were generally small (sample sizes ranged from 14 to 200 participants). Duration of follow-up varied between three days and six months. Eleven studies received funding, six received no funding, and 12 provided no information about funding sources. We judged eight studies at high risk of bias, nine at low risk, and 12 at unclear risk. We grouped the studies into six main comparisons.
Multistrand stainless steel wires versus wires composed of other materials
Six studies with 409 participants (545 arches) evaluated multistrand stainless steel (StSt) wires versus wires composed of other materials. We are very uncertain about the effect of multistrand StSt wires versus other wires on alignment rate (4 studies, 281 participants, 417 arches; very low-certainty evidence). There may be little to no difference between multistrand StSt wires and other wires in terms of intensity of pain (MD −2.68 mm, 95% CI −6.75 to 1.38; 2 studies, 127 participants, 127 arches; low-certainty evidence).
Conventional nickel-titanium wires versus superelastic nickel-titanium wires
Four studies with 266 participants (274 arches) evaluated conventional nickel-titanium (NiTi) wires versus superelastic NiTi wires. There may be little to no difference between the different wire types in terms of alignment rate (124 participants, 124 arches, 2 studies; low-certainty evidence) and intensity of pain (MD −0.29 mm, 95% CI −1.10 to 0.52; 2 studies, 142 participants, 150 arches; low-certainty evidence).
Conventional nickel-titanium wires versus thermoelastic copper-nickel-titanium wires
Three studies with 210 participants (210 arches) evaluated conventional Ni-Ti versus thermoelastic copper-nickel-titanium (CuNiTi) wires. We are very uncertain about the effects of the different arch wires on alignment rate (1 study, 66 participants, 66 arches; very low-certainty evidence). There may be little to no difference between conventional NiTi wires and thermoelastic CuNiTi wires in terms of time to alignment (alignment rate ratio 1.30, 95% CI 0.68 to 2.50; 1 study, 60 participants, 60 arches; low-certainty evidence).
Superelastic nickel-titanium wires versus thermoelastic nickel-titanium wires
Twelve studies with 703 participants (936 arches) evaluated superelastic NiTi versus thermoelastic NiTi wires. There may be little to no difference between superelastic NiTi wires and thermoelastic NiTi wires in alignment rate at four weeks (MD −0.28 mm, 95% CI 0.62 to 0.06; 5 studies, 183 participants, 183 arches; low-certainty evidence). We are very uncertain about the effects of the different wires on root resorption (2 studies, 52 participants, 312 teeth; very low-certainty evidence). Superelastic NiTi wires compared with thermoelastic NiTi wires may result in a slight increase in time to alignment (MD 0.5 months, 95% CI 0.21 to 0.79; 1 study, 32 participants, 32 arches; low-certainty evidence) but are probably associated with a slight increase in intensity of pain (MD 6.96 mm, 95% CI 1.82 to 12.10; 3 studies, 94 participants, 138 arches, moderate-certainty evidence).
Single-strand superelastic nickel-titanium wires versus coaxial superelastic nickel-titanium wires
Three studies with 104 participants (104 arches) evaluated single-strand superelastic NiTi versus coaxial superelastic NiTi wires. Use of single-strand superelastic NiTi wires compared with coaxial superelastic NiTi wires probably results in a slight reduction in alignment rate at four weeks (MD −2.64 mm, 95% CI −4.61 to −0.67; 2 studies, 64 participants, 64 arches, moderate-certainty evidence).
Different sizes of nickel-titanium wires
Two studies with 149 participants (232 arches) compared different types of NiTi wires. There may be little to no difference between different sizes of NiTi wires in terms of pain (low-certainty evidence).