Highlighted review: What are the best materials to use for the first arch wire in a fixed brace?

Yan Wang, Chang Liu, Fan Jian, Grant T McIntyre, Declan T Millett, Joy Hickman, Wenli Lai

Plain language summary: What are the best materials to use for the first arch wire in a fixed brace?

Review question
We wanted 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, reduced pain or reduced side effects, such as the shortening of the tooth root during treatment with braces?

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 (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 crowded and twisted teeth.

Over recent years, a number of new materials (various mixtures ('alloys') 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. This is an update of the review entitledInitial arch wires for alignment of crooked teeth with fixed orthodontic braces, which was first published in 2010.

Study characteristics
We searched for studies on 5 October 2017. We were interested in 'randomised controlled trials' (RCTs), which are studies in which participants are assigned randomly to the interventions being compared. We found 12 RCTs with 799 participants, all of whom had upper or lower full arch fixed braces, or both.

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).

Main results
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.

Quality of the evidence
There was moderate-quality evidence that coaxial superelastic NiTi can produce greater tooth movement than single-strand superelastic NiTi, and that there is no real difference in pain whether whether arch wires are made with multistrand stainless steel or superelastic NiTi. The quality of the evidence for all other comparisons and outcomes was low or very low.

Overall, the evidence about initial arch wires in orthodontic treatment is very limited, with comparisons often assessed by one small study with problems in its design. The findings are imprecise and unreliable so more research is needed.

Read the full review 

Citation: 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.