Orthodontic Glossary UK
Plain-English definitions of orthodontic terms used in UK treatment. From IOTN and malocclusion to archwires and retention — every term explained.
About This Glossary
This glossary explains the clinical and everyday terms you may encounter during orthodontic treatment in the UK. Terms are drawn from NHS guidance, the British Orthodontic Society (BOS), and the General Dental Council (GDC). Each definition is written for patients — not clinicians.
If you are unsure about a term your orthodontist has used, use this glossary as a starting point. Always follow the specific advice of your treating clinician, as individual treatment plans vary.
Archwire
A thin metal or tooth-coloured wire threaded through the brackets on your teeth. The archwire applies gentle, continuous pressure to guide teeth into the desired position. Wires are changed periodically throughout treatment, typically progressing from flexible to stiffer materials as alignment improves.
Attachment (Aligner)
Small tooth-coloured composite resin bumps bonded to specific teeth when using clear aligners such as Invisalign or Spark. Attachments give the aligner something to grip against, enabling more precise or complex tooth movements that would otherwise be difficult. They are removed at the end of treatment and are not usually visible to others.
Band (Molar Band)
A thin metal ring cemented around a back tooth (usually a molar) to anchor orthodontic appliances. Bands are stronger than bonded brackets for teeth that need to bear significant force. They are fitted during the bonding appointment and removed at debond.
Bite Plane
A flat acrylic or resin surface built into a removable or fixed appliance that prevents the upper and lower back teeth from meeting. Bite planes are used to open the bite temporarily, allowing the back teeth to erupt and helping to correct a deep overbite. They can initially affect speech and eating.
Bond / Bonding
The process of attaching brackets directly to the surface of teeth using a dental adhesive. The tooth surface is lightly etched to help the adhesive grip, and the bracket is secured with a special bonding resin that sets under a blue curing light. The bond is strong enough to withstand normal eating and cleaning but can be released safely when braces are removed.
Bracket
A small metal, ceramic, or plastic fitting bonded to the front surface of each tooth. Brackets hold the archwire in place and transmit the wire's force to the tooth. They come in various materials — standard metal, clear ceramic, and tooth-coloured composite — and are a defining feature of fixed brace treatment.
Bruxism
The involuntary grinding or clenching of teeth, often during sleep. Bruxism can wear down tooth surfaces, damage brackets or aligners, and generate forces that complicate orthodontic treatment. It is commonly managed with an occlusal splint or night guard. Orthodontists will usually assess for bruxism before starting treatment.
CBCT Scan (Cone Beam CT)
A specialist three-dimensional X-ray that produces detailed images of the teeth, bone, and surrounding structures. CBCT scans are used for complex cases — such as impacted teeth, jaw surgery planning, or assessing root positions — and deliver a higher radiation dose than conventional X-rays. They are ordered only when clinical benefits outweigh the risks.
Cephalometric Analysis
A standardised method of measuring and analysing a lateral skull X-ray (cephalogram) to assess jaw position, tooth inclination, and facial profile. Measurements are compared to population norms to help plan orthodontic and surgical treatment. The analysis informs decisions about jaw surgery, extraction, and appliance mechanics.
Class I Malocclusion
A jaw and bite relationship in which the upper and lower molars are correctly positioned relative to each other (normal molar relationship), but the front teeth may be crowded, spaced, or irregularly positioned. Most orthodontic treatment cases are Class I. The upper and lower jaws are broadly in proportion, but individual teeth may need correcting.
Class II Malocclusion
A jaw relationship in which the lower jaw is positioned further back than normal relative to the upper jaw. This often results in protruding upper front teeth (overjet) and a receding chin. Class II malocclusion can be treated with functional appliances in growing patients, or with fixed braces and sometimes jaw surgery in adults.
Class III Malocclusion
A jaw relationship in which the lower jaw is positioned further forward than normal, often causing the lower front teeth to sit in front of the upper front teeth (underbite or reverse overjet). Mild Class III cases may be managed with braces alone, while severe cases typically require jaw surgery (orthognathic surgery) in addition to fixed braces.
Clear Aligner
A removable, transparent plastic tray custom-made to fit over the teeth and gradually move them into the desired position. Clear aligners such as Invisalign, Spark, and ClearCorrect are changed every one to two weeks. They are a popular alternative to fixed braces but require consistent wear of approximately 20–22 hours per day to be effective.
Crossbite
A misalignment in which one or more upper teeth bite inside the lower teeth rather than outside them. Crossbites can affect the front teeth (anterior crossbite) or back teeth (posterior crossbite) and may cause asymmetric jaw growth, uneven tooth wear, and jaw discomfort if untreated. Treatment options include expansion appliances, braces, or a combination of both.
Crowding
A condition in which there is insufficient space in the jaw for all the teeth to fit in their ideal positions. Crowding ranges from mild (small rotations or overlaps) to severe (teeth blocked entirely out of the arch). Treatment may involve creating space through expansion, interproximal reduction, or tooth extraction, followed by fixed braces or clear aligners.
Debond / Debonding
The process of removing fixed braces at the end of active treatment. The brackets are detached from the teeth using a special instrument, and the adhesive residue is polished away. Debonding is followed immediately by retainer fitting to prevent teeth from moving back.
Deep Bite
A type of malocclusion in which the upper front teeth overlap the lower front teeth excessively in a vertical direction. A deep bite can cause the lower teeth to bite into the roof of the mouth, tooth wear, and gum problems. Treatment often involves bite planes, braces with mechanics to intrude the front teeth, or clear aligners with attachments.
Dental Arch
The U-shaped curve formed by the row of teeth in either the upper (maxillary) or lower (mandibular) jaw. The shape and size of the dental arch influence how teeth align and how much space is available for them. Arch development and expansion are important considerations in orthodontic treatment planning.
Elastic Ligature
A small rubber ring used to hold the archwire inside a conventional bracket. Elastic ligatures come in a wide range of colours and are changed at each adjustment appointment. They can stain with food and drinks. Self-ligating brackets use a built-in clip instead of elastic ligatures.
Elastics (Rubber Bands)
Small rubber bands worn between the upper and lower teeth, attached to hooks on brackets or aligners. Elastics apply additional force to correct the bite relationship between upper and lower jaws. They are typically classified as Class II (pulling the lower jaw forward) or Class III (pulling the upper teeth back). Consistent wear is essential — missed hours significantly slow progress.
Expansion
The widening of the dental arch to create more space for crowded teeth or to correct a narrow arch. Expansion can be achieved with removable expansion plates, fixed palatal expanders (RPE/RME), or SARPE (surgically assisted rapid palatal expansion) in adults. The degree of expansion possible depends on age and bone maturity.
Fixed Appliance
Any orthodontic appliance that is bonded or cemented to the teeth and cannot be removed by the patient during treatment. Fixed appliances include metal braces, ceramic braces, lingual braces, palatal expanders, and transpalatal arches. They provide more consistent force than removable appliances because their effect does not depend on patient wear time.
Functional Appliance
A removable or fixed device that uses the forces generated by the muscles of the jaw and face to influence jaw growth. Functional appliances such as the Twin Block and Herbst are primarily used in growing children to correct Class II jaw relationships by encouraging the lower jaw to grow forward. They are most effective during the pubertal growth spurt.
GDC (General Dental Council)
The UK regulator for dental professionals. All orthodontists, dentists, and dental nurses practising in the UK must be registered with the GDC. Specialist orthodontists hold a recognised postgraduate qualification and are listed on the GDC specialist register. Checking GDC registration before starting orthodontic treatment is a key patient safety step.
Gingivitis
Inflammation of the gums caused by a build-up of plaque. Gingivitis is common during brace treatment because brackets and wires make cleaning more difficult. Symptoms include red, swollen, or bleeding gums. It is reversible with improved oral hygiene but can progress to more serious gum disease (periodontitis) if untreated. Orthodontists will not start treatment if active gum disease is present.
Hawley Retainer
A traditional removable retainer made from an acrylic plate and a wire that runs across the front teeth. Hawley retainers are durable and adjustable, but more visible than clear Essix or Vivera retainers. They are less commonly prescribed now but remain useful for cases requiring minor tooth position adjustments during the retention phase.
Hypodontia
A condition in which one or more teeth fail to develop (congenitally missing teeth). The most commonly absent teeth are upper lateral incisors, lower second premolars, and wisdom teeth. Orthodontic treatment for hypodontia typically involves either closing the gap or creating and maintaining space for a dental implant or bridge, depending on the tooth and the patient's overall dental situation.
IOTN (Index of Orthodontic Treatment Need)
A clinical scoring system used in the UK to determine whether a patient meets the threshold for NHS orthodontic treatment. The IOTN has two components: the Dental Health Component (DHC), which grades clinical need from 1 (no need) to 5 (great need), and the Aesthetic Component (AC), which scores dental appearance. NHS treatment is generally available for grades 4 and 5 of the DHC.
Impression
A mould of the teeth and surrounding tissues used to produce study models, retainers, or appliances. Impressions are taken using alginate or putty-like materials placed in a tray over the teeth. Many practices now use intraoral digital scanners instead, which are faster and more comfortable but serve the same purpose.
Intrusion / Extrusion
Intrusion is the movement of a tooth deeper into the jawbone (used to reduce the vertical height of a tooth), while extrusion is the opposite movement — pulling a tooth further out of the bone. Both movements require precise wire mechanics or aligner attachments and are used to level the bite and correct vertical discrepancies between teeth.
IPR (Interproximal Reduction)
The controlled removal of small amounts of enamel from the sides of teeth to create space. IPR is commonly used in aligner treatment as an alternative to extraction or expansion to relieve mild-to-moderate crowding. It is carried out using fine strips or discs and is considered safe within strict limits. Consent and documentation are important before any enamel is removed.
Jaw Surgery (Orthognathic Surgery)
Surgical repositioning of one or both jaws to correct severe skeletal malocclusions that cannot be treated with braces alone. Common procedures include Le Fort I osteotomy (upper jaw) and sagittal split ramus osteotomy (lower jaw). Orthognathic surgery is performed by an oral and maxillofacial surgeon and is combined with fixed brace treatment before and after the operation.
Lateral Cephalogram
A standardised side-on X-ray of the skull taken from a fixed distance with the patient's head in a set position. It allows the orthodontist to measure jaw angles, tooth inclinations, and skeletal relationships. Lateral cephalograms are routinely taken as part of orthodontic records and are used to plan treatment and compare results.
Ligation
The process of securing the archwire into a bracket using a ligature — either a small elastic ring or a thin stainless steel wire tie. Ligation holds the wire in the bracket slot and affects how much friction acts on the wire as teeth move. Self-ligating brackets use a built-in mechanism instead of a separate ligature.
Lingual Brace
A fixed brace system in which the brackets and wires are placed on the inside (tongue-side) surfaces of the teeth rather than the outside. Lingual braces are completely hidden from view when the patient smiles. They are more complex to fit and adjust than labial braces, typically cost more, and can affect speech initially. Popular systems include Incognito, WIN, and STb.
Lower Arch
The set of teeth in the lower jaw (mandible), held in a U-shaped arch. Treatment of the lower arch is often done concurrently with the upper arch to ensure the bite comes together correctly at the end of treatment. Some cases treat only one arch, depending on the specific clinical need.
Malocclusion
A collective term for any misalignment of the teeth or incorrect relationship between the upper and lower jaws. Malocclusion is classified by severity using systems such as IOTN in the UK. Common types include Class I (crowding/spacing with normal jaw relationship), Class II (overjet), and Class III (underbite). Malocclusion may affect chewing, speech, and oral hygiene.
Molar Band
See Band (Molar Band) above. A molar band is a stainless steel ring cemented around a back tooth to anchor orthodontic appliances or provide a strong attachment point for elastics and other anchorage mechanisms.
Myofunctional Therapy
A programme of exercises and habit training designed to correct abnormal muscle patterns affecting the tongue, lips, and face. Myofunctional therapy is used to address issues such as tongue thrust, mouth breathing, and thumb sucking that can contribute to or worsen malocclusion. It is often used alongside orthodontic treatment to help maintain results.
NiTi Wire (Nickel-Titanium)
A highly flexible superelastic wire made from a nickel-titanium alloy. NiTi wires are used at the start of treatment because their flexibility allows them to engage teeth even when they are significantly misaligned. They apply light, continuous forces that are gentler on teeth and more comfortable than stiffer wires. As treatment progresses, stiffer steel wires are typically introduced.
NHS Band 3
The NHS dental charge band that covers complex dental treatments, including orthodontic treatment for eligible patients. From 1 April 2026, the NHS Band 3 charge in England is £332.10 for a full course of orthodontic treatment, regardless of how many appointments it involves. This charge is set by NHS England and is reviewed periodically. Some patients are exempt from charges.
Open Bite
A malocclusion in which the upper and lower front teeth do not meet when the back teeth are biting together. Anterior open bite is often associated with thumb sucking, tongue thrust, or skeletal jaw differences. Treatment includes habit appliances, braces, and sometimes jaw surgery in severe cases. Posterior open bite, where the back teeth do not meet, is less common.
OPG (Orthopantomogram)
A panoramic dental X-ray that produces a single flat image showing all the teeth, roots, and surrounding bone in both jaws. OPGs are routinely taken before orthodontic treatment to assess tooth positions, root shapes, and the presence of impacted or missing teeth. They are also called a DPT (dental panoramic tomograph) or panoramic radiograph.
Overbite
The vertical overlap of the upper front teeth over the lower front teeth. A small overbite (approximately 2–4 mm) is normal. A deep overbite occurs when the overlap is excessive and may cause the lower teeth to bite into the roof of the mouth. Treatment involves bite planes or brace mechanics to reduce the vertical overlap.
Overjet
The horizontal distance between the upper front teeth and the lower front teeth, measured from the front surfaces of the lower incisors to the back of the upper incisors. An increased overjet (protruding upper teeth) is one of the most common reasons for NHS orthodontic referral under IOTN grading. A reverse overjet occurs in Class III cases where the lower teeth protrude further than the upper teeth.
Palatal Expander
A fixed or removable appliance placed across the roof of the mouth (palate) to gradually widen the upper jaw. Fixed expanders such as the Rapid Maxillary Expander (RME or RPE) use a key turned by the patient or parent to open the midpalatal suture, creating new bone. Expansion is most effective in children and adolescents before the suture fuses. In adults, surgically assisted rapid palatal expansion (SARPE) may be needed.
PDL (Periodontal Ligament)
The connective tissue fibres that attach a tooth root to the surrounding bone socket. The PDL absorbs chewing forces and enables the small movements necessary for orthodontic tooth movement. When pressure is applied to a tooth, the PDL fibres on one side compress and on the other side stretch, stimulating bone remodelling that allows the tooth to move gradually.
Power Chain
A continuous elastic chain (resembling a chain of rings) used to link several brackets together and apply a closing force to reduce spaces between teeth. Power chains are used to close extraction spaces, close gaps after tooth loss, or consolidate alignment at the end of treatment. They are replaced at adjustment appointments as the elastic loses force over time.
Records (Orthodontic)
The collection of clinical information gathered before treatment begins. Orthodontic records typically include photographs (intraoral and extraoral), X-rays (OPG and lateral cephalogram), digital scans or study models, and clinical measurements. Records are used to plan treatment, document starting point, monitor progress, and compare outcomes after treatment.
Relapse
The partial or complete return of teeth to their pre-treatment positions after orthodontic treatment. Relapse is a natural tendency driven by the periodontal ligament fibres and surrounding tissues. It is managed with long-term retainer wear. The risk of relapse never fully disappears, which is why most orthodontists recommend retainers be worn indefinitely.
Retention
The phase of orthodontic treatment after active tooth movement has been completed. During retention, removable or fixed retainers hold the teeth in their new positions while the surrounding bone and tissues stabilise. Most orthodontists recommend retainers for life — at minimum every night — to prevent relapse. Retention is as important as the active treatment phase.
Retainer
An appliance worn after active orthodontic treatment to hold the teeth in their corrected positions. Retainers can be removable (Essix clear retainers, Hawley retainers, Vivera retainers) or fixed (a thin wire bonded to the back of the front teeth). Most patients need to wear retainers long-term — initially full time, then nightly. Fixed retainers provide more reliable retention but require careful cleaning.
Self-Ligating Bracket
A bracket with a built-in clip or door mechanism that holds the archwire in place without the need for separate elastic ligatures. Self-ligating systems such as Damon, In-Ovation, and Empower are often marketed as faster or more comfortable than conventional brackets. Clinical evidence comparing outcomes with conventional brackets is mixed — both systems can achieve excellent results in skilled hands.
Space Maintainer
A fixed or removable device used to hold open the space left by a prematurely lost baby tooth until the permanent tooth erupts. Without a space maintainer, adjacent teeth may drift into the gap and block the permanent tooth from erupting in the correct position. Space maintainers are most commonly used in children.
Study Models
Three-dimensional casts of the teeth and gums made from dental impressions or digital scans. Study models are part of the orthodontic records taken before treatment begins and allow the clinician to analyse the bite, measure tooth positions, and plan treatment in detail. Digital study models stored as 3D files have replaced physical plaster casts in most modern practices.
TMA Wire (Titanium Molybdenum Alloy)
A speciality orthodontic wire with properties between NiTi and stainless steel — flexible enough to apply light forces while being stiff enough to allow precise three-dimensional tooth control. TMA is commonly used for detailed finishing in the later stages of fixed brace treatment. It is more expensive than standard stainless steel wire.
Torque
A rotational force applied to a tooth to tip its root in or out relative to the crown. Controlling torque is important for achieving a correct bite, ideal tooth angles, and stable long-term results. Different bracket prescriptions are designed with specific torque values built in, and torque can be further adjusted by bending the archwire or using specific aligner attachments.
Treatment Coordinator
A non-clinical team member at an orthodontic practice who guides patients through the treatment journey — from initial enquiry and consultations to financial planning and booking appointments. Treatment coordinators are not clinical professionals and cannot provide clinical advice, but they are a key point of contact for administrative and process-related questions.
Twin Block
A two-piece removable functional appliance used to correct Class II malocclusion (protruding upper teeth / receding lower jaw) in growing patients. The upper and lower blocks interlock at an angle when biting together, holding the lower jaw in a forward position. Worn almost full-time, the Twin Block stimulates the lower jaw to grow forward and is most effective during the pubertal growth spurt.
Upper Arch
The set of teeth in the upper jaw (maxilla), arranged in a U-shaped arch. Upper arch treatment often addresses crowding, spacing, overjet, or alignment of the front teeth. The upper arch is typically treated concurrently with the lower arch in a full fixed brace or aligner course.
Vivera Retainer
A proprietary brand of clear removable retainer manufactured by Align Technology (the makers of Invisalign). Vivera retainers are made from a thicker, more durable material than standard Essix retainers. They are prescribed as a series of four retainers per arch and are often recommended after Invisalign treatment, though they can be used after any form of orthodontic treatment.
Wire Change
The replacement of the archwire with a new wire at an adjustment appointment. Wire changes are a routine part of fixed brace treatment and typically happen every 6–10 weeks. Wires are progressively upgraded from flexible, light wires at the start of treatment to stiffer, more rectangular wires as treatment progresses, enabling more precise tooth movement and torque control.
Related Resources
Orthodontic terms: questions
IOTN stands for the Index of Orthodontic Treatment Need. It is a two-part scoring system used in the UK to judge how much a patient's teeth and bite need treatment, and it is the measure used to decide whether treatment is funded by the NHS. The glossary entry explains the grades and what each part measures.
Malocclusion is the clinical term for teeth that do not fit together properly when the jaws close, such as crowding, spacing, an overbite, an underbite or a crossbite. It covers a wide range, from mild alignment differences to problems that affect chewing or speech, which is why a clinician assesses each case individually.
Brackets are the small fittings bonded to the teeth, and the archwire is the thin wire that runs through them. The archwire applies gentle, continuous pressure, and the orthodontist changes it over the course of treatment to guide teeth into position. Together they make up the main parts of a fixed brace.
Teeth can drift back towards their old positions after braces or aligners come off, which is called relapse. A retainer holds teeth in their new positions while the tissues around them settle. Your orthodontist will explain whether you need a fixed or removable retainer and how long to wear it.
No. The glossary explains terms in plain English so you can follow appointments and quotes, but it cannot diagnose or recommend treatment. If a term describes something you think applies to you, ask your orthodontist or dentist, who can examine you and explain what it means for your own teeth.
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