What Is an IOTN Score? IOTN Explained UK

What is the IOTN?

The Index of Orthodontic Treatment Need was developed at the University of Manchester in the late 1980s and has been used by the NHS as its primary eligibility tool ever since. It provides a standardised framework for clinicians to assess how much a patient's dental misalignment affects their dental health and aesthetics, and therefore whether treatment is justified at public expense. IOTN has two separate components — the Dental Health Component (DHC) and the Aesthetic Component (AC) — with the DHC as the main measure and the AC deciding borderline grade 3 cases. The index is not used to design treatment; it is used purely to determine whether NHS funding applies. Private treatment is available regardless of IOTN grade.

Dental Health Component (DHC) grades 1 to 5

The DHC uses a five-point scale, with each grade defined by specific measured features. Grade 1 means no treatment need: only minor irregularities. Grade 2 means little need, such as an overjet of 3.5 to 6 mm with lips that close comfortably, or teeth displaced by 1 to 2 mm. Grade 3 means moderate, borderline need, such as an overjet of 3.5 to 6 mm with lips that do not close, a reverse overjet of 1 to 3.5 mm, or teeth displaced by 2 to 4 mm. Grade 4 means great need, including an overjet over 6 mm up to 9 mm, teeth displaced by more than 4 mm, a deep bite that damages the gum, or less extensive missing teeth. Grade 5 means very great need, including an overjet over 9 mm, teeth prevented from erupting (such as impacted canines), extensive hypodontia, and cleft lip and palate. Grades 4 and 5 qualify for NHS treatment; grade 3 qualifies only with an Aesthetic Component of 6 or more, which is what the shorthand 3.6 means.

How the IOTN score is measured

The clinician examines the teeth and measures overjet (how far the upper front teeth sit ahead of the lower) and overbite (how much they overlap vertically), checks for crowding and how much space is missing, and looks for crossbites, open bites, rotations, and missing, extra or impacted teeth. The DHC grade is set by the single most severe feature found, not an average, so one significant finding such as a large overjet or an impacted canine can place a case in grade 4 or 5 even if everything else is mild. The Aesthetic Component is then scored by matching the front teeth to the ten-photograph scale. The whole assessment takes a few minutes within a normal examination.

Aesthetic Component (AC) scale 1 to 10

The AC uses a set of ten standardised photographs of dental arrangements ranked from 1 (most attractive) to 10 (least attractive). The clinician compares the patient's smile to this scale and assigns a score. Scores of 1 to 4 indicate no or slight treatment need. Scores of 5 to 7 indicate moderate treatment need. Scores of 8 to 10 indicate a great treatment need. The AC matters for NHS eligibility only in grade 3 cases: a DHC grade 3 combined with an AC of 6 or more qualifies. A high AC score on its own does not qualify a patient whose DHC is grade 1 or 2.

NHS eligibility threshold

The standard NHS threshold is IOTN DHC grade 3.6 or above: a DHC grade of 4 or 5, or a DHC grade 3 with an Aesthetic Component of 6 or more. Grade 3 cases with an AC below 6, and all grade 1 and 2 cases, do not qualify. In practice the DHC is weighted so that certain features automatically trigger the grade ceiling: a large overjet, impacted permanent teeth, traumatic overbite, and hypodontia are among the features that push a case to Grades 4 or 5. Eligibility applies to under-18s referred through normal NHS channels, and treatment must start before the patient turns 18. Eligible under-18s pay nothing. Adults are very rarely eligible for NHS orthodontics except under specific clinical exceptions such as jaw surgery cases or those with certain developmental conditions.

Who assesses the IOTN?

The IOTN is assessed by a qualified dental professional, most commonly a specialist orthodontist or an orthodontic therapist working under one. General dental practitioners can also carry out an IOTN assessment when referring a patient to an orthodontic service. In NHS settings, the referring GDP usually provides an initial IOTN estimate, and the orthodontist carries out a formal assessment at the first appointment. It is the orthodontist's assessment that determines eligibility, not the GDP's referral opinion. Self-referral to NHS orthodontics is not available in England and Wales; a GDP referral is required for most patients.

What happens if the IOTN score is too low?

If the formal IOTN assessment finds a score below the NHS threshold, the patient is discharged from the NHS waiting list and private treatment becomes the only funded option. The orthodontist should explain the result and what features contributed to the score. Patients who are borderline — particularly at the upper end of Grade 3 — may be reassessed at a later date if eruption of permanent teeth changes the clinical picture. It is also worth noting that an IOTN assessment is not a refusal of treatment; it is a statement that the NHS does not fund treatment at that level of need. Private orthodontic treatment can address mild to moderate malocclusion that does not reach the NHS threshold.

Private treatment if your IOTN score is below the threshold

Private orthodontics has no IOTN requirement: a clinician assesses your case on its own merits. Many teenagers and adults with grade 2 or 3 crowding, spacing or mild bite problems still benefit from treatment. Typical UK private fees are £1,500 to £3,500 for metal braces, £2,000 to £4,500 for ceramic braces, £4,000 to £8,000 for lingual braces, £2,500 to £5,500 for Invisalign, and £1,500 to £5,500 for supervised clear aligners. Clear aligners are a common choice for mild grade 2 to 3 cases that do not need complex bite correction, and most practices offer payment plans.

Limitations of IOTN

IOTN was designed in the late 1980s and has been criticised in the research literature for several reasons. The aesthetic component relies on photographs of smiles that do not reflect modern dental aesthetics and may not capture the full psychological impact of dental appearance on individual patients. The DHC does not adequately capture functional problems such as TMJ symptoms or speech difficulties that may be genuinely related to the malocclusion. The index also does not account for the patient quality of life impact, which can be significant even in mild cases. Despite its limitations, IOTN remains the standard tool because it provides consistent, evidence-based, comparable assessments across a very large and variable NHS system.

Devolved nation variation

IOTN thresholds and NHS orthodontic provision vary across the four UK nations. In Scotland, NHS orthodontics is administered through the Scottish Dental Service and IOTN thresholds are broadly similar to England, though local health board variation exists. In Wales, the NHS Wales threshold broadly mirrors England. In Northern Ireland, the Health and Social Care system uses IOTN but commissioning decisions are made regionally. It is always worth checking with a local orthodontic service or GP dental practice to understand the threshold that applies in your area, as eligibility can differ meaningfully between postcodes and commissioning regions.

Useful related pages

IOTN scoring is carried out by a qualified dental professional after a clinical examination. Scores estimated online or from photographs are indicative only; NHS eligibility is decided by the orthodontic provider at assessment.