IOTN scoring explained

How IOTN works

The Index of Orthodontic Treatment Need (IOTN) is a two-component scoring system used by NHS orthodontists across the UK to assess who qualifies for NHS-funded treatment. It was introduced to ensure eligibility decisions are made consistently and based on clinical need rather than subjective judgement.

The Dental Health Component (DHC) is the primary scoring tool. It grades the severity of malocclusion on a 5-point scale based on defined clinical measurements. DHC grade is determined by the single most severe dental feature present. The grades are: Grade 1 — no need; Grade 2 — little need (mild malocclusion); Grade 3 — borderline need (moderate); Grade 4 — treatment need (severe); Grade 5 — very great need (most complex cases).

DHC grade 5 features include: increased overjet greater than 9mm; severe hypodontia (missing teeth) requiring restorative and orthodontic treatment; impacted teeth other than third molars; extensive hypodontia; cleft palate. These represent the most severe structural and health-impacting malocclusions.

DHC grade 4 features include: increased overjet greater than 6mm but not more than 9mm; reverse overjet greater than 3.5mm with masticatory or speech difficulties; anterior or posterior crossbite with greater than 2mm discrepancy between RCP and ICP; severe displacements of teeth greater than 4mm; extreme lateral or anterior open bites greater than 4mm; increased complete overbite with significant gingival trauma. These represent cases where dental health is clearly compromised.

DHC grade 3 is the borderline category. It includes cases with: increased overjet greater than 3.5mm but not exceeding 6mm; increased overbite greater than 3.5mm without gingival contact; reverse overjet of 1mm to 3.5mm; anterior crossbite with up to 2mm discrepancy; moderate displacements of teeth greater than 2mm; increased lateral or anterior open bites of greater than 2mm. For grade 3 cases, the Aesthetic Component (AC) is also assessed.

The Aesthetic Component (AC) uses a 10-photograph scale developed by Bjorn Kohler. The images depict dentitions of increasing aesthetic impairment, rated 1 (best) to 10 (most impaired). The AC is used for grade 3 DHC cases to determine whether the aesthetic impact is sufficient to justify NHS treatment. AC scores of 6–10 at grade 3 DHC typically qualify.

Grades 1 and 2 do not qualify for NHS funding. Grade 1 (no need) has no clinical malocclusion features. Grade 2 (little need) includes minor irregularities, small overjets, mild hypodontia, and minor spacing issues that don't meet the severity thresholds for clinical need. These cases can be treated privately and are often well-suited to clear aligners at reasonable cost.

It is important to understand that IOTN scoring is a clinical assessment, not a patient-reported score. You cannot self-assess your IOTN grade with certainty — a dentist examination is required. However, understanding the system in advance helps you have a more informed conversation at your assessment appointment.