Orthodontics Flashcards
OverJet
The horizontal distance from the labial surface of the lower incisors to the palatal surface of the upper incisors.
Normal is 2-4mm
Overbite
The vertical distance from the incisal edges of the upper and lower central incisors.
Normal value: 2-4mm
Crowding - classification of severity
Mild <4mm
Moderate 5-9mm
Severe >9mm
Common developmentally absent teeth
Combined : 2% in caucasians
Lower Second Premolar
Upper Lateral Incisor
Upper second premolar
3 molars
Types of Supernumaries
Conical
Tuberculate
Supplemental
Odontome
Porion
Upper margin of boney external auditory meatus
Pogonion
Most anterior point of mandible/bony chin
Sella
Midpoint of the sella turcica i.e. the pituitary fossa (on lateral ceph)
Nasion
The intersection of the frontal bone and the nasal bones
Holdaway Line
A line drawn from the anterior soft tissue chin up through the upper and lower lips
Rickett’s E plane
A line drawn through the soft tissue chin up through the tip of the nose
Menton
Most inferior point of the anterior mandible at the symphysis
Gonion
The lowest point on the curvature of the angle of the mandible where the body of the mandible meets the ramus
ANS
Anterior Nasal Spine
PNS
Posterior Nasal Spine
A Point (sub-spinale)
Deepest point of the curvature of the anterior maxilla (between the ANS and the alveolar crest of the upper central incisor)
B Point (sub-mentale)
The deepest point on the curvature of the anterior mandible (between the pogonion and the alveolar crest of the lower central incisors)
Maxillary Plane
A plane from the ANS to the PNS
Mandibular Plane
Gonion to Menton
Functional Occlusal Plane (FOP)
A line passing through the occlusion of the premolars (or Es) and the permanent molars
*Used in WITS analysis
Frankfort Plane
A line drawn from the porion (most superior part of the boney EAM) to the orbitale (the most inferior portion of the orbital rim)
ANB angle
The angle from point A to the Nasion to point B
Calculated by determining the difference between the SNA and the SNB
2-4 degrees = skeletal base I
>4 degrees = skeletal base II
<2 degrees = skeletal base III
SNA/SNB compensation for sella or nasion abnormality
The Eastman Correction
First ensure the position of the sella is normal:
Measure angle SN to maxillary plane which should be 8deg +/- 3deg
SNA normal value is 81 degrees (caucasian)
For every degree > 81deg subtract 0.5deg from SNB
For every degree < 81deg add 0.5deg to SNB
The Eastman Analysis
SNA and SNB
Determine ANB
Apply Eastman Correction
Draw mandibular plane (Go-Menton) Draw maxillary plane (ANS to PNS) Angle between them is MMPA Measure the lower face height Assess angulation of Incisors Measure inter-incisal angle
Maxillary-Mandibular Plane
27deg +/- 4
If this angle is significantly >32 deg then lower facial height is increased
If this angle is < 23 then the anterior lower facial height is reduced
Lower face height percentage
Should be 55%
Lower third should be 33% or equal to midface
Angulation of Incisors
Measured by drawing a line through the long axis of the tooth and the respective alveolar plane
Upper incisors = 109deg
Lower incisors = 93 deg
If the angles are reduced then the teeth and retroclined vs increased and they are proclined
N.B. The lower incisal angle is inversely proportional to the MMPA i.e. is 93 deg where the MMPA is 27deg
Inter-incisal angle
Intersection of the long axes of the upper and lower incisors
= 133-135 deg
SNA
Gives the AP position of the maxilla
Normal value is 81deg
SNB
Gives the AP position of the mandible
Normal value is 78 deg
African Variation in Eastman Analysis
SNA - 85
SNB - 80
ANB - 5
MMPA - 28
Upper incisal angle 118
Lower incisal angle 96
Chinese variation in Eastman Analysis
SNA- 83
SNB- 80
ANB- 3
MMPA- 28
Upper incisal angle- 113
Lower incisal angle- 96
Ballard’s Conversion Tracing
The Lines are drawn as for measuring incisal angles
The upper incisor is then tipped to it’s ideal 109deg about a point 1/3 from it’s root apex
The lower incisor angle and the MMPA need to equal 120deg
This new ideal position of the lower incisor is drawn and projected until it meets the upper incisor
This will represent the angles incisor classification and removes any dental compensation
WITS analysis
- Uses the FOP
- A perpendicular line drawn from A point to the FOP
- A perpendicular line drawn from B point to the FOP
- Measure the difference between where these lines meet the FOP
Within 1mm = skeletal I
If A-FOP is >1mm ahead of B-FOP = skeletal II
If B-FOP is >1mm ahead of A-FOP = skeletal III
Index of Orthodontic Treatment Need (IOTN)
To determine need for orthodontic treatment
2 elements:
Dental component (1-5) Aesthetic component (1-10)
IOTN dental component grading
Grade 2-5
Increased over jet (lip competence)
Grade 2-4
Reverse overjet (S&M difficulties) Overbite (ST trauma) Crossbite Open bite Displacement
Grade 4 Reverse overjet with S&M difficulty Lingual crossbite Impacted partially erupted teeth Uncomplicated Supernumerary teeth
Grade 4 and 5
Hypodontia
Grade 5
Impeded eruption of teeth
Submerged deciduous teeth
Cleft lip and palate
IOTN grade 1
No treatment need
Extremely minor malocclusion including displacements of <1mm
IOTN Grade 2
Minimal need for treatment
Increased overjet 3.5mm to 6mm with competent lips
Reverse Overjet 0-1mm
Anterior or posterior crossbite of <1mm
Anterior or posterior open bite 1-2mm
Increased overbite >3.5mm (no gingival contact)
Displacement of teeth 1-2mm
*uncomplicated pre or postnormal occlusions
IOTN grade 3
Borderline need for treatment
Increased overjet 3.5mm to 6mm but with incompetent lips
Reverse overjet 1-3.5mm
Anterior or posterior crossbites 1-2mm
Lateral or anterior open bite 2-4mm
Increased and incomplete overbite without gingival trauma
Displacement of 2-4mm
IOTN 4
Treatment required
Increased over jet >6mm
(but <9mm)
Reverse overjet 1-3.5mm (with S&M issues)
Reverse overjet >3.5mm (with no S&M issues)
Anterior or posterior crossbites >2mm
Lateral or anterior open bites >4mm
Posterior lingual cross bite (with no functional buccal contact)
Increased and complete overbite with ST trauma
Displacement of >4mm
Mild to mod hypodontia (less than one tooth in each quadrant)
Partially erupted teeth, tipped and impacted against other teeth
Existing supernumerary teeth
Leeway space
Surplus space for the permanent successors (3,4 & 5) left by the discrepancy in width with the deciduous predecessors (c, d & e)
1-1.5mm in the maxilla
2-2.5 in the mandible
IOTN 5
Treatment Required
Increased overjet >9mm
Reverse overjet >3.5mm
With speech or masticatory difficulties
Extensive hypodontia (>1 tooth missing per quadrant)
Impeded eruption of any teeth for any cause (except 3rd molars)
Submerged deciduous teeth
Cleft lip and palate
