Updated review: Initial arch wires used in orthodontic treatment with fixed appliances

Smiling young person showing arch wires in braces

Authors: Chang Liu, Zhi Wei, Fan Jian, Grant McIntyre, Declan T Millett, Wenli Lai, Yan Wang

What is the best first arch wire in a fixed orthodontic brace?*

Key messages

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.

Main results

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.

*This is a plain language summary of the review as published in the Cochrane Library. You can access the full review here: https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD007859.pub5/full#CD007859-abs-0002