4.4 Orthodontic Assessment, Indices & Referral
Key Takeaways
- Orthodontic assessment is structured as extra-oral (skeletal in three planes plus soft tissues), then intra-oral (teeth present, crowding, incisor and buccal segment relationships, overjet, overbite, centrelines, crossbites), then special investigations
- IOTN measures treatment need before treatment, while the Peer Assessment Rating measures the outcome: a PAR reduction of 30 per cent or more indicates improvement and a reduction of 22 points or more indicates a greatly improved result
- NHS orthodontic treatment is normally commissioned for IOTN Dental Health Component grade 4 or 5, or grade 3 with an Aesthetic Component of 6 or above
- Most patients are referred in the late mixed or early permanent dentition around age 11 to 12, but earlier referral is indicated for an unerupted incisor, a suspected ectopic canine, cleft lip and palate, severe skeletal discrepancy needing growth modification, and hypodontia
- Consent must cover decalcification, root resorption, relapse, gingival recession, pain, failure to achieve the planned result and the need for indefinite retention
The Structured Orthodontic Assessment
Outcome C2.10 asks for orthodontic diagnosis including the assessment of skeletal, dento-alveolar and soft tissues, and C2.11 for assessment of the development of the normal occlusion and deviations from it. The assessment runs outside in.
Extra-oral: skeletal pattern in three planes
| Plane | What is assessed | Normal |
|---|---|---|
| Anteroposterior | Relationship of maxilla to mandible, assessed clinically with the patient's Frankfort plane horizontal, or cephalometrically by the ANB angle | Class I; ANB about 3 degrees (± 2) |
| Vertical | Frankfort–mandibular planes angle (FMPA); lower anterior face height as a proportion of total anterior face height | FMPA about 27 degrees (± 4); lower anterior face height about 55% of total |
| Transverse | Facial symmetry, mandibular displacement on closing, arch width | Symmetrical, no displacement |
Extra-oral: soft tissues
Lip competence (competent, incompetent, potentially competent), lip line relative to the upper incisors, smile line and gingival display, nasolabial angle, tongue position and any habits such as digit sucking. Soft tissues determine the stability of a result: proclining lower incisors beyond the soft-tissue envelope invites relapse.
Intra-oral
Teeth present and absent, oral hygiene and caries status (an essential precondition for appliance therapy), crowding or spacing quantified per arch, incisor relationship, canine and molar relationships, overjet and overbite, centreline discrepancies, crossbites and any associated displacement.
Special investigations
A panoramic radiograph for teeth present, pathology and unerupted tooth position; upper standard occlusal and periapicals for localisation; a lateral cephalogram where skeletal assessment will change the plan, especially before growth modification or orthognathic surgery. The Eastman standard values worth recognising are SNA about 81 degrees, SNB about 78, ANB about 3, upper incisor to maxillary plane about 109 degrees and lower incisor to mandibular plane about 93 degrees.
Indices: IOTN and PAR
The two indices answer different questions and are frequently confused.
| Index | Question it answers | Structure |
|---|---|---|
| IOTN (Index of Orthodontic Treatment Need) | Does this patient need treatment? — used before treatment | Dental Health Component grades 1–5, recording the single worst feature using the MOCDO hierarchy (Missing teeth, Overjet, Crossbite, Displacement of contact points, Overbite); Aesthetic Component graded 1–10 against a photographic scale |
| PAR (Peer Assessment Rating) | How much did treatment improve the occlusion? — used before and after | Weighted scoring of contact point displacements, buccal occlusion, overjet, overbite and centreline, on study casts at start and finish |
NHS commissioning in England normally funds treatment at DHC grade 4 or 5, or grade 3 with an Aesthetic Component of 6 or above. Outcome C2.3 specifically names referral processes and orthodontic commissioning guidelines, so this threshold is examinable.
Interpreting PAR (outcome C2.9):
- A reduction of 30% or more in the PAR score indicates the case was improved.
- A reduction of 22 points or more indicates the case was greatly improved.
- A reduction of less than 30% is classified as worse or no different — a poor result regardless of how much effort went into it.
When to Refer (Outcomes C2.3 and C2.16)
| Timing | Trigger |
|---|---|
| As soon as identified | Cleft lip and palate (managed by the regional cleft team from birth), craniofacial syndromes |
| Age 7–9 | Unerupted permanent incisor when the contralateral tooth has been erupted for six months; suspected supernumerary; severe crossbite with displacement; poor prognosis first permanent molars needing timed extraction |
| Age 9–11 | Maxillary canine not palpable in the buccal sulcus by about age 11, or clear asymmetry between sides; hypodontia requiring joint planning |
| Age 11–12 | The routine referral point for most malocclusions, in the late mixed or early permanent dentition |
| Puberty (peak growth) | Class II skeletal discrepancy suitable for functional appliance growth modification |
| After growth completion | Severe skeletal discrepancy requiring combined orthodontics and orthognathic surgery |
A referral should record the IOTN grade, the presenting concern, oral hygiene and caries status, any relevant medical history, and the radiographs already taken — an incomplete referral wastes an appointment.
Risk and Benefit (Outcome C2.12)
Outcome C2.12 requires the candidate to assess the risk and benefit of orthodontics, and these risks form the consent discussion:
- Decalcification and white-spot lesions — the commonest complication of fixed appliances, driven by plaque around brackets; the reason caries risk must be controlled before bonding.
- Root resorption — some apical resorption occurs in most treated cases and is usually clinically insignificant; severe resorption is uncommon but more likely with long treatment, large movements, previous trauma and blunt or pipette-shaped roots.
- Relapse — the default outcome without retention. Patients must be told at the consent stage that retention is effectively indefinite.
- Gingival recession and periodontal damage, particularly with lower incisor proclination in a thin biotype.
- Pain and ulceration in the first days after placement and each adjustment.
- Loss of vitality in previously traumatised teeth.
- Failure to achieve the planned result, including the possibility of needing surgery or accepting a compromise.
- Time and compliance burden — typically 18–24 months of fixed appliance therapy with regular appointments.
Benefits are function, dental health where a crossbite with displacement or a traumatic overbite is being corrected, reduced trauma risk with a large overjet, and psychosocial gain. Where the malocclusion is mild and the patient's motivation is low, not treating is a legitimate option that must be offered.
Orthodontic Emergencies and Appliance Adjustment (Outcome C2.13)
Outcome C2.13 asks the candidate to suggest appropriate adjustments to an orthodontic appliance to render it comfortable and safe without compromising its effectiveness. General dental practitioners and dental core trainees see these problems out of hours, and the governing principle is to make the appliance safe without undoing the treatment, then inform the orthodontist.
| Problem | Immediate management |
|---|---|
| Protruding distal archwire | Cover with orthodontic wax as a temporary measure; if it is traumatising the mucosa, cut flush with the last bracket or tube using distal-end cutters and protect the fragment from being swallowed or inhaled |
| Loose bracket | If still threaded on the wire and not traumatic, cover with wax and arrange review; if detached, remove it and retain it for the orthodontist |
| Loose band | Remove it if it is mobile enough to be inhaled or swallowed; do not attempt to recement it |
| Displaced or unravelled ligature | Remove or replace the module; tuck a loose steel ligature under the archwire with a flat plastic instrument |
| Fractured or dislodged bonded retainer | Cover a sharp end with wax and arrange prompt review; unattached teeth relapse within days, so this is urgent rather than routine |
| Poking headgear or facebow | Discontinue use and arrange urgent review — headgear injury can be serious, which is why safety mechanisms are mandatory |
| Traumatic ulceration from a removable appliance | Identify the offending component, smooth or relieve the acrylic, and instruct the patient to keep wearing the appliance so that it still fits at review |
| Generalised discomfort after adjustment | Reassure: soreness for two to three days after each adjustment is expected; simple analgesia and a soft diet |
Two safety rules apply throughout: never cut a wire without securing the fragment against inhalation, and never make an adjustment that alters the prescribed tooth movement — if the only way to relieve the problem is to change the mechanics, contact the treating orthodontist.
A completed orthodontic case has a start PAR score of 30 and a finish score of 8. How should the outcome be classified?
A 12-year-old has an overjet of 5 mm with incompetent lips and an Aesthetic Component score of 4. Under normal NHS commissioning arrangements, would this case qualify for funded treatment?
A 9-year-old attends for a routine examination. The upper right permanent central incisor has not erupted, although the left central erupted eight months ago. What is the most appropriate action?
Which complication is the most common consequence of fixed appliance therapy in a patient with poor plaque control?