Orthodontic treatment is undertaken worldwide to correct crowded, twisted, buried or prominent front teeth. This treatment is normally given in adolescence or adulthood. Fixed orthodontic appliances, otherwise known as braces, consist of brackets bonded to the teeth. The brackets are connected by arch wires, which exert forces on the teeth to straighten them. The first, or initial, type of arch wire, inserted at the beginning of treatment, is for correcting crowded and twisted teeth. Over recent years, a number of new materials have been developed, which show a range of different properties in the laboratory and which manufacturers claim offer benefits in terms of tooth alignment. These include mixtures of nickel and titanium (NiTi).
What was the research?
A systematic review to find out the best kind of wire arches for orthodontists to use when putting braces on people’s teeth to make them straighter. Our review evaluated whether different types of initial arch wires result in important differences, such as faster straightening of teeth. We also looked at whether the type of arch wire used reduced side effects, such as pain and the shortening of the tooth root.
Who conducted the research?
The research was conducted by a team led by Yan Wang of West China Hospital of Stomatology, on behalf of Cochrane Oral Health. Chang Liu, Fan Jian, Grant T. McIntyre, Declan T. Millett, Joy Hickman and Wenli Lai were also on the team.
What evidence was included in the review?
We included 12 randomised controlled trials, with 799 participants, all of whom had upper or lower full arch fixed braces, or both.
What did the evidence say?
We found moderate-quality evidence that coaxial superelastic nickel-titanium (NiTi) can produce greater tooth movement over 12 weeks than single-strand superelastic NiTi. We found moderate-quality evidence that there is no difference in pain at day 1 between multistrand stainless steel versus superelastic NiTi arch wires. There is insufficient evidence from our included studies to know if any other particular initial arch wire material is better or worse than another, or if they function equally well, with regard to speed of straightening, pain or tooth shortening in people undergoing orthodontic treatment.
How good was the evidence?
The studies evaluated different initial arch wires, but they were poorly conducted or reported, or both, and their results are likely to be biased. The studies 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 studies reported both potential benefits (straightening) and harms (pain or side effects such as tooth root shortening).
What are the implications for orthodontists and the general public?
Moderate-quality evidence shows that coaxial superelastic nickel-titanium (NiTi) can produce greater tooth movement over 12 weeks than single-strand superelastic NiTi. Moderate-quality evidence also suggests that there may be no difference in pain at day 1 between multistrand stainless steel versus superelastic NiTi arch wires. Other than these findings, there is insufficient evidence to determine whether any particular arch wire material is superior to any other in terms of alignment rate, time to alignment, pain and root resorption.
What should researchers look at in the future?
This review suggests a need for more well-designed randomised controlled trials (RCTs) in order to determine which initial arch wire is most effective.
Wang Y, Liu C, Jian F, McIntyre GT, Millett DT, Hickman J, Lai W. Initial arch wires used in orthodontic treatment with fixed appliances. Cochrane Database of Systematic Reviews 2018 , Issue 7 . Art. No.: CD007859. DOI: 10.1002/14651858.CD007859.pub4
This post is an extended version of the review’s plain language summary, compiled by Anne Littlewood at the Cochrane Oral Health Editorial Base.