Orthodontic Archwires Explained UK

What are orthodontic archwires?

An archwire is the continuous metal wire that runs from the back of your mouth on one side to the back on the other, passing through the slot of every bracket along the way. When the wire is placed into the bracket slots, it is usually in a shape that does not perfectly match your current tooth arrangement. As the wire tries to return to its natural arch form, it exerts gentle, continuous forces on each tooth through the bracket. Over time — typically weeks to months — these forces cause the bone around the tooth roots to remodel, allowing teeth to move to new positions. The wire is the source of the force; the brackets are the handles that translate that force to individual teeth. Without the archwire, brackets alone produce no movement.

Nickel-titanium (NiTi) — the first stage

The first wires placed in fixed braces are almost always made from nickel-titanium alloy (NiTi), also known as nitinol. NiTi has two critical properties that make it ideal for the early stage of treatment. First, it has superelastic behaviour — it can be deformed by a large amount and still return to its original shape. This means even a severely crowded arch can have a wire engaged into all bracket slots, and the wire will gently straighten as it recovers. Second, it exerts light, continuous forces rather than large intermittent ones, which is both more comfortable and more biologically effective for tooth movement. The trade-off is that NiTi wires are too flexible to be used for fine detail, space closure, or torque control — they are levelling and aligning wires only.

Stainless steel — the working and finishing stage

As the arch levels and aligns through the NiTi stages, stiffer stainless steel (SS) archwires are introduced. Stainless steel is far less flexible than NiTi and does not have shape-memory superelasticity, which means it holds the precise bends and shapes the orthodontist places in it. This precision is essential for the middle and later stages of treatment: closing extraction spaces, applying torque (rotating teeth in three dimensions), detailing individual tooth positions, and coordinating upper and lower arch widths. Stainless steel wires can be bent chairside to produce highly specific tooth movements that would be impossible with NiTi. The stiffer the wire, the better it transmits the forces from elastic bands, springs, and other auxiliaries.

Round versus rectangular wires

Archwires come in two cross-sectional shapes: round and rectangular. Round wires contact only one surface of the bracket slot and allow teeth to rotate freely within the slot. This makes them ideal for the initial levelling stage when teeth need to move into alignment without restriction. Rectangular wires fill more of the bracket slot and engage all four walls, which allows the orthodontist to control the three-dimensional angulation and torque of each tooth. Full bracket-slot engagement — called full expression — is only possible with a rectangular wire that closely matches the slot dimensions. Most orthodontic bracket slots are either 0.018 inch or 0.022 inch in width; the final wire used in finishing is typically close to but slightly smaller than the full slot size.

Wire size progression

Treatment typically follows a defined wire progression, moving from small-diameter round NiTi to large rectangular stainless steel over the course of months. A typical sequence for a 0.022 slot bracket might begin with a 0.012 or 0.014 round NiTi for initial levelling, progressing to a 0.016 or 0.018 round NiTi as alignment improves, then to a 0.016x0.022 or 0.018x0.025 rectangular NiTi, and finally to a 0.019x0.025 stainless steel wire for space closure, torque, and finishing. The exact sequence varies between orthodontists and between cases — some skip steps if alignment is fast, others add intermediate sizes for specific reasons. Wire changes usually happen at adjustment appointments every 6 to 10 weeks.

Heat-activated NiTi

A specialist type of NiTi called heat-activated NiTi (HANT or HANT NiTi) is used in some practices. This wire is soft and flexible at room temperature but becomes stiffer when it warms to mouth temperature — around 37 degrees Celsius. This property allows the orthodontist to place the wire in highly crowded teeth easily and then have it exert greater force once in the mouth. Heat-activated NiTi is often used in patients with severe initial crowding where standard NiTi cannot be fully engaged into all brackets. It is more expensive than standard NiTi but can reduce the number of initial wire changes needed.

Beta-titanium (TMA) wires

Between NiTi and stainless steel in the wire progression sits a material called beta-titanium, commercially sold as TMA (Titanium Molybdenum Alloy). TMA has roughly half the stiffness of stainless steel but is more formable than NiTi and holds bends well. It is often used as a transitional wire between rectangular NiTi and full stainless steel, or in specific clinical situations where a slightly lower force level is needed during space closure or torquing. TMA is less commonly used in routine NHS orthodontics due to cost, but is a standard option in private and university-based orthodontic care.

What happens at adjustment appointments?

At most adjustment appointments, the orthodontist or orthodontic therapist will remove the ligatures or release the self-ligating clips holding the wire in place, assess tooth movement, and decide whether to replace the wire with the same wire, a larger wire, or a different material. They may also add or adjust bends in a stainless steel wire, change the position of auxiliaries such as power chains or springs, or replace worn or discoloured elastic ligatures with fresh ones. It is common to feel increased pressure or mild discomfort for one to three days after a wire change, particularly after moving to a larger size. This settles as the teeth respond to the new forces.

Coated and white aesthetic wires

Several manufacturers produce white or tooth-coloured archwires for patients who want a more discreet appearance. These are typically stainless steel or NiTi wires coated in an epoxy resin or nylon material. White wires are popular with adults and are widely available in UK orthodontic practices, including NHS settings where aesthetic appliances are used. The main limitation is that the coating can chip or discolour over time, particularly at the bracket contact points where friction is highest, and the coating slightly reduces friction management compared with metal wires. They are not available as the final working wires in all practices because the coating reduces precision in some detailed finishing movements.

Useful related pages

This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist.