--- title: "Orthodontic Archwires: NiTi to Steel Progression UK" url: https://virtualconsultant.online/guides/orthodontic-archwires-explained-uk description: "Archwires move teeth by progressing from flexible NiTi for initial alignment to rigid stainless steel for precise finishing over months of treatment." updated: 2026-09-29T00:00:00Z publisher: Virtual Consultant Online --- Archwires Fixed Braces Orthodontic Mechanics # Orthodontic Archwires Explained UK Archwires move teeth by progressing from thin, flexible nickel-titanium wires used for initial alignment to thick, rigid stainless steel wires used for precise finishing, with each stage mirroring a phase of fixed brace treatment. Understanding what is happening at each stage helps make the process feel less mysterious. [Start Photo Assessment](https://virtualconsultant.online/evaluations/quote) [Compare Costs](https://virtualconsultant.online/costs) ## 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 [Orthodontic Bracket Types UK](https://virtualconsultant.online/guides/orthodontic-bracket-types-uk) [How Orthodontic Mechanics Work UK](https://virtualconsultant.online/guides/how-orthodontics-works-uk) [Orthodontic Review Appointment UK](https://virtualconsultant.online/guides/orthodontic-review-appointment-uk) [Braces Pain Management UK](https://virtualconsultant.online/guides/braces-pain-management-uk) This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist. ### Compare next steps [Orthodontist Near Me](https://virtualconsultant.online/locations/orthodontic-treatment-near-me) [Clear Aligners Near Me](https://virtualconsultant.online/treatments/clear-aligners-near-me) [Invisalign Near Me](https://virtualconsultant.online/locations/invisalign-provider-near-me) [Browse Locations](https://virtualconsultant.online/locations) ### Ready for a clearer starting point? Upload guided photos and receive an indication of likely treatment options and pricing before booking appointments. [Get an Online Quote](https://virtualconsultant.online/evaluations/quote) ### Frequently Asked Questions What are orthodontic braces wires made of? Orthodontic archwires are made from a small number of alloys chosen for their specific mechanical properties. Nickel-titanium (NiTi or nitinol) is used for initial levelling wires because of its superelasticity — it flexes greatly and returns to shape. Stainless steel is used for working and finishing wires because of its stiffness and ability to hold precise bends. Beta-titanium (TMA) sits between the two in stiffness and is used in some practices as a transitional or specialist wire. Some wires are coated in white resin for aesthetic reasons. Why does my wire get changed at appointments? Wires are changed as teeth move. The initial NiTi wire does its job of levelling and aligning, then needs to be replaced with a stiffer wire that can apply more specific forces to close spaces and detail positions. Each wire change moves treatment to the next stage. If the wire is not changed as the arch improves, treatment stagnates because a wire that is too flexible cannot produce the movements required in the working and finishing stages. What is NiTi in orthodontics? NiTi stands for nickel-titanium, a metal alloy also known as nitinol. It has two remarkable properties: shape memory and superelasticity. Shape memory means it returns to its original shape after being bent. Superelasticity means it can be deformed by a very large amount — enough to engage even severely crowded teeth — and still apply gentle, continuous force as it tries to recover. These properties make NiTi ideal for the initial levelling stage of fixed brace treatment. Do thicker wires hurt more? Moving to a larger or stiffer wire often causes more pressure and discomfort than the previous wire for the first one to three days. This is because a stiffer wire applies more force to teeth that have not yet reached their target position. The discomfort is normal and typically manageable with over-the-counter pain relief such as paracetamol or ibuprofen if needed. It settles as teeth respond to the new forces. Patients generally report that the very first wire change causes the most noticeable discomfort; subsequent changes tend to cause less. Can I see what wire I currently have? You can ask your orthodontist or orthodontic therapist at any appointment what wire is currently in place and what stage of treatment you are at. Many orthodontic practices document wire sizes in clinical notes and are happy to share this information. Knowing your wire sequence gives you a sense of how far through treatment you are — when you reach the final large rectangular stainless steel wire, you are typically in the finishing phase and approaching completion. What is the difference between round and rectangular archwires? Round wires contact only one surface of the bracket slot and let teeth rotate freely, making them suited to the initial levelling stage. Rectangular wires fill more of the bracket slot and engage all four walls, allowing the orthodontist to control the three-dimensional angulation and torque of each tooth. Full bracket-slot engagement with a rectangular wire is typically reserved for the later working and finishing stages of treatment. Explore your options Quick links Not sure where to start? Use these quick links to explore orthodontic treatments, typical costs, and helpful guides that explain what different options involve. Whether you're researching braces or clear aligners, comparing pricing, or just getting a feel for what comes next, you can browse at your own pace and come back when you're ready to request a quote. 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Upload guided photos and get a tailored recommendation for your teeth and bite. [Start Photo Assessment](https://virtualconsultant.online/evaluations/quote) [Find an Orthodontist](https://virtualconsultant.online/locations) Citation details Title Orthodontic Archwires: NiTi to Steel Progression UK Publisher Virtual Consultant Online Published 2026-05-28 Updated 2026-09-29 URL [https://staging.virtualconsultant.online/guides/orthodontic-archwires-explained-uk](https://staging.virtualconsultant.online/guides/orthodontic-archwires-explained-uk)