Initial arch wires for tooth alignment in orthodontic treatment with fixed appliances

Orthodontic treatment is undertaken worldwide, mainly in adolescents and adults to correct crowded, rotated, buried or prominent front teeth. Fixed orthodontic appliances (braces) consist of brackets bonded to the teeth that are connected by arch wires which exert forces on the teeth. The first (initial) type of arch wire, inserted at the beginning of treatment, is for correcting crowding and rotations of teeth.

Over recent years a number of new materials (various metal alloys, or mixtures, of nickel and titanium (NiTi)) have been developed which show a range of different properties in the laboratory and which manufacturers claim offer benefits in terms of tooth alignment. Clinical trials of these products in people undergoing orthodontic treatment are required to understand whether different types of initial arch wires actually result in important differences, such as faster alignment, reduced pain or reduced side-effects, during orthodontic treatment. The Cochrane Oral Health Group undertook this review of existing studies to identify and assess the evidence for the effects of initial arch wires of different materials, shape and size of cross-section for alignment of teeth with fixed orthodontic braces in relation to alignment speed, root resorption and pain intensity.

The most recent search of studies was done on 2 August 2012. We found nine trials with 571 participants all of whom had upper and/or lower full arch fixed orthodontic appliances. The trials evaluated different initial arch wires, but all of these studies were poorly conducted and/or reported and the results are likely to be biased. All of the trials also varied in a number of other aspects of orthodontic treatment, compared different types of initial arch wires and reported different outcomes at different times. None of the trials reported both potential benefits (alignment) and harms (pain or side-effects such as root resorption). There is no evidence from these studies that any particular initial arch wire material is better than another in people undergoing orthodontic treatment.

Authors' conclusions: 

There is no reliable evidence from the trials included in this review that any specific initial arch wire material is better or worse than another with regard to speed of alignment or pain. There is no evidence at all about the effect of initial arch wire materials on the important adverse effect of root resorption. Further well-designed and conducted, adequately-powered, RCTs are required to determine whether the performance of initial arch wire materials as demonstrated in the laboratory, makes a clinically important difference to the alignment of teeth in the initial stage of orthodontic treatment in patients.

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Background: 

Initial arch wires are the first arch wires to be inserted into the fixed appliance at the beginning of orthodontic treatment and are used mainly for the alignment of teeth by correcting crowding and rotations. With a number of different types of orthodontic arch wires available for initial tooth alignment, it is important to understand which wire is most efficient, as well as which wires cause the least amount of root resorption and pain during the initial aligning stage of treatment. This is an update of the review 'Initial arch wires for alignment of crooked teeth with fixed orthodontic braces' first published in the Cochrane Database of Systematic Reviews 2010, Issue 4.

Objectives: 

To assess the effects of initial arch wires for alignment of teeth with fixed orthodontic braces in relation to alignment speed, root resorption and pain intensity.

Search strategy: 

We searched the following electronic databases: the Cochrane Oral Health Group's Trials Register (to 2 August 2012), CENTRAL (The Cochrane Library 2012, Issue 7), MEDLINE via OVID (1950 to 2 August 2012) and EMBASE via OVID (1980 to 2 August 2012). We also searched the reference lists of relevant articles. There was no restriction with regard to publication status or language of publication. We contacted all authors of included studies to identify additional studies.

Selection criteria: 

We included randomised controlled trials (RCTs) of initial arch wires to align teeth with fixed orthodontic braces. Only studies involving participants with upper and/or lower full arch fixed orthodontic appliances were included.

Data collection and analysis: 

Two review authors were responsible for study selection, validity assessment and data extraction. All disagreements were resolved by discussion amongst the review team. Corresponding authors of included studies were contacted to obtain missing information.

Main results: 

Nine RCTs with 571 participants were included in this review. All trials were at high risk of bias and a number of methodological limitations were identified. All trials had at least one potentially confounding factor (such as bracket type, slot size, ligation method, extraction of teeth) which is likely to have influenced the outcome and was not controlled in the trial. None of the trials reported the important adverse outcome of root resorption.

Three groups of comparisons were made.

(1) Multistrand stainless steel initial arch wires compared to superelastic nickel titanium (NiTi) initial arch wires. There were four trials in this group, with different comparisons and outcomes reported at different times. No meta-analysis was possible. There is insufficient evidence from these trials to determine whether or not there is a difference in either rate of alignment or pain between stainless steel and NiTi initial arch wires.

(2) Conventional (stabilised) NiTi initial arch wires compared to superelastic NiTi initial arch wires. There were two trials in this group, one reporting the outcome of alignment over 6 months and the other reporting pain over 1 week. There is insufficient evidence from these trials to determine whether or not there is any difference between conventional (stabilised) and superelastic NiTi initial arch wires with regard to either alignment or pain.

(3) Single-strand superelastic NiTi initial arch wires compared to other NiTi (coaxial, copper NiTi (CuNiTi) or thermoelastic) initial arch wires. The three trials in this comparison each compared a different product against single-strand superelastic NiTi. There is very weak unreliable evidence, based on one very small study (n = 24) at high risk of bias, that coaxial superelastic NiTi may produce greater tooth movement over 12 weeks, but no information on associated pain or root resorption. This result should be interpreted with caution until further research evidence is available. There is insufficient evidence to determine whether or not there is a difference between either thermoelastic or CuNiTi and superelastic NiTi initial arch wires.

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