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| IMC Wiki | Index of Orthodontic Treatment Need (IOTN)

Index of Orthodontic Treatment Need (IOTN)

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IOTN, Richmond (Manchester)

  • The IOTN is a clinical index to assess orthodontic treatment need.
  • Requirements of medical indices:
    • Clinical validity and reliability
    • Objectivity and provision of quantitative data that can be analyzed
    • Quick to obtain
    • Acceptable for patient and clinician
  • For use directly on the patient (or on plaster models with minor modification) 74 dentists took part in the validation.
  • See: PAR Index:developed specially for model analysis; both indices were developed by groups of British orthodontists.
  • Most important goals of orthodontic treatment (British Dental Association, 1954):
    • Improvement of physical function
    • Prevention of tissue destruction
    • Correction of aesthetic defects
    • Controversial:
      • Caries prophylaxis
      • Periodontal prophylaxis
      • TMJ prophylaxis
  • The IOTN combines aesthetic components and dental health components:
    • Aesthetic components (AC)
    • Dental health components (DHC)

Aesthetic components (AC)

  • Using a series of 10 color photos the degree of 'dental attractiveness' is assessed.
  • The patient should be involved in the subjective assessment.
    • Grade 1 = aesthetically optimal dentition
    • Grade 10 = aesthetically worst imaginable dentition
      • Grade 1-4 = no or slight treatment need
        #pic# #pic# #pic# #pic#
      • Grade 5-7 = moderate or borderline treatment need
        #pic# #pic# #pic#
      • Grade 8-10 = treatment need
        #pic# #pic#
Assessment using single-color plaster models or black and white photos has the advantage that the assessment is not influenced by oral hygiene, periodontal status and any tooth discoloration (do not be influenced by this during intraoral assessment!).

Dental health components (DHC)

  • Based on the Swedish Medical Health Board index (Linder Aronson, 1974)
  • They are classified into 5 grades.
  • Grade 1 = no treatment need (e.g., contact point displacements of less than 1 mm)
  • Grade 5 = treatment need (e.g., cleft lip/palate or reverse sagittal overjets greater than 9 mm)
Only the worst occlusal feature is scored.

The hierarchical scale has two purposes:
  1. The dentition is assessed systematically, thus ensuring that all relevant occlusion anomalies are recorded.
  2. If two or more occlusal anomalies are of the same DHC grade, the most severe one is scored.
Hierarchical scale:
  1. Missing teeth (including aplasia, displaced and impacted teeth)
  2. Overjets (including reverse sagittal overjets)
  3. Crossbite
  4. Displacement
  5. Overbites (including open bites)
Mnemonic acronym: MOCDO
Grade 1 No treatment need
Grade 2 Minor anomaly, no treatment need
Grade 3 Borderline treatment need
Grade 4 Treatment need
Grade 5 Treatment need

Grade 1: No treatment need

1. Extremely minor malocclusion with contact point displacements of less than 1 mm

Grade 2: Minor anomaly, no treatment need

2.a Overjet > 3.5 mm and ≤ 6 mm (with competent lip closing)
2.b Reverse overjet between 0 and ≤ 1 mm
2.c Anterior or posterior crossbite with 1 mm discrepancy between RCP and ICP
2.d Contact point displacements > 1 mm and ≤ 2 mm
2.e Anterior or posterior open bite > 1 mm and ≤ 2 mm
2.f Increased overbite of ≥ 3.5 mm (without gingival contact)
2.g Class II or class III occlusion without other anomalies (up to half a premolar width)

Grade 3: Borderline treatment need

3.a Overjet > 3.5 mm and ≤ 6 mm (incompetent lip closing)
3.b Reverse overjet between 1 and ≤ 3.5 mm
3.c Anterior or posterior crossbite with > 1 mm and ≤ 2 mm discrepancy between RCP and ICP
3.d Contact point displacements > 2 mm and ≤ 4 mm
3.e Lateral or anterior open bite > 2 mm and ≤ 4 mm
3.f Deep overbite with gingival contact or contact with palatal mucosa (but without trauma)

Grade 4: Treatment need

4.h Less severe hypodontia requiring prerestorative orthodontics or orthodontic space closure to obviate the need for prosthetic restoration
4.a Overjet > 6 mm and ≤ 9 mm
4.b Reverse overjet > 3.5 mm (without masticatory or speech problems)
4.m Reverse overjet > 1 mm and ≤ 3.5 mm (without masticatory or speech problems)
4.c Anterior or posterior crossbite with > 2 mm discrepancy between RCP and ICP
4.l Posterior lingual crossbite with no functional occlusal contact in one or both buccal segments
4.d Major contact point displacements > 4 mm
4.e Extreme lateral or anterior open bite > 4 mm
4.f Increased and complete overbite with gingival or palatal trauma
4.t Partially erupted teeth, tipped and impacted against adjacent teeth
4.x Existence of supernumerary teeth

Grade 5: Treatment need

5.i Impeded tooth eruption (3rd molars) attributable to crowding, displacements, supernumerary teeth, retained deciduous teeth and all pathological reasons
5.h Extensive hypodontia with restorative impact (more than 1 congenitally missing tooth in any quadrant) requiring prerestorative orthodontics
5.a Increased overjet > 9 mm
5.m Reverse overjet > 3.5 mm with masticatory problems and speech disorders
5.p Cleft lip and palate and other craniofacial anomalies
5.s Retained deciduous teeth