• IOTN- Index of Orthodontic Treatment Need
• PAR score- Peer Assessment Rating
• ICON- Index of complexity, outcome and need

The IOTN is used to assess the eligibility of a patient for orthodontic treatment under the NHS.

IOTN description: Link- https://ewellorthodontics.co.uk/IOTN-Chart.pdf

IOTN is composed of two main components: Aesthetic Component and Dental Component

Aesthetic component (AC) (see link): Consists of 10 standard photographs from Grade 1 (most aesthetically pleasing) to Grade 10 (least aesthetically pleasing).

Dental component (DC) (see link):

• Grade 1: No orthodontic treatment need
• Grade 2: No orthodontic treatment need
• Grade 3: Borderline treatment need
• Grade 4: Treatment required (eligible for NHS treatment)
• Grade 5: Very great need (eligible for NHS treatment)

Only the worst occlusal feature is recorded, based on the hierarchal grade of MOCDO (M-highest ranking, O-lowest ranking):

• Missing teeth
• Overjet
• Crossbite
• Displacement (of contact point)
• Overbite

NOTE: If a patient presents with a DC of grade 3 they are borderline treatment need. They are only eligible for orthodontic treatment under the NHS if they have an AC of grade 6 or above.

1. Skeletal Pattern

This refers to the position of the mandible in relation to the maxilla.

Class 1: Mandible lies 2-3mm behind the maxilla

Class 2: Mandible lies >3mm posterior to the maxilla.

• In relation to class 1 the maxilla appears to be more protruded.
• Caused by a retrognathic mandible, prognathic maxilla or both

Class 3: Mandible lies <2 mm posterior to the maxilla.

• In relation to the maxilla, the mandible appears protruded in comparison to class 1.
• Caused by a prognathic mandible, retrognathic maxilla or both

2. Frankfort Mandibular Plane Angle (FMPA)

This is the angle between the Frankfort plane and the Mandibular plane.

• Frankfort plane– Superior point of external auditory meatus to the inferior point of the orbital rim.
• Mandibular plane– Lower border of the mandible

The FMPA is reduced when the angle lies behind the occiput and indicates the patient has a shorter face.

The FMPA is increased when the angle lies in front of the occiput and indicates the patient has a longer face.

3. Vertical Assessment – Lower Anterior Facial Height

Facial height is split into 3 parts:

• Trichion -> Glabella
• Glabella -> Subnasale
• Subnasale -> Menton

In a well-balanced face the distance between the 1/3rds are equal

4. Transverse Assessment – Asymmetry

Assess the transverse section of the face for gross asymmetries.

• Assess the patient from directly in front, or look at the patient from directly above.
• Draw an imaginary line through the pupils and through the middle of the face and assess for any asymmetry.

5. Soft Tissues – Nasiolabial Angle

The nasiolabial angle measures the relative protrusion of the upper lip. The nasiolabial angle is formed from the midline of the labial surface of the upper lip and the inferior border of the nose.

Increased nasolabial angle – >110°

Average nasolabial angle – 90-110°

Reduced nasolabial angle – <90°

6. Soft Tissues – Lip Competence

• Competent lips-  When the lips meettogether at rest without muscular activity.
• Incompetent lips-  When the lips do not meet when the mandible is in the rest position and muscles of facial expression are at rest.
• Habitually competent lips- When the lips are held together by a small amount of muscle activity.

1. Incisor Relationship

Class 1- When the lower incisor edges occludes with, or directly below the cingulum plateau of the upper incisors.

Class 2- When the lower incisor edges occlude posterior to the cingulum plateau of the upper incisors. There are two divisions:

• Class 2 division 1-  The upper incisors are of average inclination or proclined.
• Class 2 division 2-  The upper incisors are retroclined, with a minimal overjet and increased overbite.

(In a patient with a class 2 div 2; the overjet is measured using the centrals)

Class 3- When the lower incisor edges occlude in front of the cingulum plateau of the upper incisors.

2. Overjet

• Horizontal distance between the labial surface of the lower incisors and upper incisal edge.
• Average overjet: 2-3 mm.
• Measure from the most prominent incisor

3. Overbite

The overlapping vertical distance between the upper incisal edge and lower incisal edge.

• Average–  1/3 – 2/3 overlap
• Increased overbite– >2/3 overlap
• Decreased overbite– <1/3 overlap

Incomplete overbite- An incisor relationship in which the lower incisors fail to occlude with either the upper incisors or the mucosa of the palate when buccal teeth are in occlusion.

Complete overbite-  the lower incisors occlude with either the upper incisors or the mucosa of the palate.

Traumatic overbite- When the lower incisor occludes it causes trauma to the upper incisors or mucosa of the palate.

4. Open bite

Anterior open bite– An occlusion in which the upper incisors do not overlap the lower incisors in the vertical plane and do not occlude with them when the posterior teeth are in maximum intercuspation.

Posterior open bite- An occlusion in which there is a lack of overlap in the posterior segments when the anterior teeth are occluding.

5. Centreline

• The centreline of the upper central incisors and lower incisors should be coincident with the middle of the face.
• When carrying out an orthodontic assessment record the direction and length of the discrepancy in mm.

6. Molar Relationship

Angles classification is used to assess the molar relationship:

• Class 1:  The mesiobuccal cusp of the upper first permanent molar occludes with the mesiobuccal groove of the lower first permanent molar.
• Class 2: The mesiobuccal cusp of the upper first permanent molar occludes anterior to the mesiobuccal groove of the lower first permanent molar.
• Class 3: The mesiobuccal cusp of the upper first permanent molar occludes posterior to the mesiobuccal groove of the lower first permanent molar.

7. Canine Relationship

• Class 1– Maxillary permanent canine occludes with distal ½ of mandibular canine and mesial half of mandibular first premolar.
• Class 2- Distal surface of mandibular canine is distal to the mesial surface of maxillary canine by at least the width of a premolar.
• Class 3- Distal surface of mandibular canine is mesial to mesial surface of maxillary canine by at least the width of a premolar.

8. Crossbite

A crossbite is a buccolingual discrepancy between the relationship of the maxillary arch and mandibular arch.

The three following features should be taken into consideration when describing a crossbite:

• Anterior/posterior?
• Buccal/lingual?
  • Buccal crossbite– Buccal cusps of the mandibular teeth occlude palatal to the palatal cusps of the upper teeth
  • Lingual crossbite– Buccal cusps of the mandibular teeth occlude buccal to the buccal cusps of the maxillary teeth
• Bilateral/ unilateral?

9. Arch Alignment

Arch alignment is assessed by crowding and spacing

Step 1:

• Split the arch into 3 segments, anterior and right and left buccal segments.
• The 8’s are not included.
• Much easier to do on study models than in the mouth.

Step 2:

• Measure the mesio-distal width of the tooth and the space available

• Measure the spaces between each contact point and add them together (space available)
• Measure the mesio-distal width of the teeth and add them together
• If the canines and premolars have not erupted use an average of 21mm per lower quadrant and 22mm per upper quadrant for their space requirement.

Step 3:

Add the scores for each tooth and record the crowding for each segment. (MD width- space available)

• 0-4mm – Mild crowding
• >4mm-8mm – Moderate crowding
• >8mm – Severe crowding

1. Age 7-8: presence and position of permanent incisors

2. Age 8: Assess prognosis of the first permanent molars

3. Age 9: Palpate for the canines

4. If the normal eruption sequence deviates from normal by longer than 6 months/if there is 6 months difference in eruption of contralateral teeth- investigate

5. Early detection of a skeletal discrepancy will mean treatment can coincide with pubertal growth spurts – Intervention orthodontics

1) Class I molar relationship

2) Correct mesio-distal angulation– Gingival portion of crown is distal to the occlusal portion

3) Correct bucco-lingual angulation– Two rules:

• Upper Incisors– Gingival portion of labial surface of crown is lingual to the incisal portion
• For All Other Teeth- Gingival portion of buccal surfaces are buccal to the incisal/occlusal portion

4) No spaces

5) No rotations

6) Curve of Spee– Measured from lower molars to incisors and should be <1.5mm

1. Littlewood, S.J. and Mitchell, L., 2019. An introduction to orthodontics. Oxford university press.
2. Andrews, L.F., 1972. The six keys to normal occlusion. Am J Orthod, 62(3), pp.296-309.