12 - Class 2 Division 1 Malocclusion Flashcards
What is the most common malocclusion
Class II div I
Identify class II div I
- incisors are proclined
- increase in overjet
- commonly these patients have class 2 molar relationship and class 2 canine relationship
Class II div I incisor relationship
British standards classification definition:
Upper incisors can be proclined or of normal inclination
- Tendency to incomplete bite
- Tendency to crossbite
Skeletal aetiology:
Examination:
- clinical
- radio graphic
- study models
NEED TO CONSIDER THESE generally:
Skeletal aetiology of class II div I malocclusion
Step in appearance of the mandible - Either:
- Maxilla too far forward
- Mandible too far back
If discrepancy between point A and B is more than 3 -4mm than skeletal class 2
- Increase in vertical proportions
- As the vertical proportion increases, the lip incompetence also increases
Skeletal factors: A-P Class II: Maxillary protrusion / Mandibular retrusion
Aetiology is either maxillary protrusion or mandibular retrusion or size of jaws
Identify
Cephalometric measurements can identify position of upper jaw in relation to cranial base and lower jaw in relationship to cranial base and so relationship of maxilla to mandible
As pt skeletal class II - we can see patients lip trained behind upper incisors and so proclining upper incisors - so this pt has multi factorial aetiology:
- position of maxilla to mandible
- soft tissue trap
Class 2 - Angle ANB is :
Analysis of SNB and SNA indicates?
Mandible is retrognathic if it is less than normal SNB
Maxilla is prognathic if it is more than normal SNA
Must check mandible AND maxilla to identify which jaw is causing class II
In this case mandible is in normal position but maxilla is prognathic:
Skeletal vertical assessment
What 2 things do we check?
Increased vertical dimension leads to:
Decreased vertical dimension leads to:
Check frankforts mandibular plane angle + Lower face height
How are skeletal vertical facial assessments carried out ?
Vertical assessments done from a point called Glabella (most prominent point between the eyebrows) to a point called Subnasale (below the nose) to soft tissue menton
Clinically pt should have 50% between Glabella and subnasale and 50% between subnasale and soft tissue menton to have a well balance face - as shown below:
For this patient
If we assess this patient in vertical dimension - Frankfort mandibular plane angle and lower face height - mild skeletal 2 when we look at her profile
There’s an increase in vertical proportions between subnasale and soft tissue menton
So intraorally we are not suprised to see she has increase in overjet and there’s a reduced incomplete bite (DIFFERENT to anterior open bite)
Skeletal vertical dimension
2 Cephalometric values that represent vertical dimension:
If these are average, increased or decreased what are the effects:
- Lower face height (LFH) - measure radiographically
- MMPA - maxillary mandibular plane angle
Skeletal factors: Transverse assessment
Affects occlusal relationships - Posterior Crossbites
- If there is a discrepancy between the width of the upper and lower jaw, you get a posterior crossbite
- Crossbite can also be caused by mandibular displacement.
- To examine this:
- Check clinically for mandibular displacement
- DPT for mandibular asymmetry
- PA skull
- DPT - if skeletal problems will be differences in ramus height between L and R, differences in thickness of the mandible
- BUT IF MANDIBULAR DISPLACEMENT - When the patient opens, the chin will become symmetrical
- If the chin is not centred when opening, then there will be a skeletal issue causing the displacement and may need orthognathic surgery to correct
Transverse Assessment:
- Posterior Crossbites
- If there is a discrepancy between the width of the upper and lower jaw, you get a posterior
crossbite - Crossbite can also be caused by mandibular displacement.
- To examine this:
Aetiology: Habit
Disruption of soft tissue equilibrium by digit causes class II division I malocclusion
The effect on the occlusion of thumb sucking depends on a number of factors:
- Age of the patient
- Number of hours per day – Greater than 6 hours will affect dentition
- Manner in which thumb/finger is sucked
Tongue is depressed + Cheeks compress the upper arch and constricts the arch
This creates a cusp to cusp relationship between both arches, which is uncomfortable for the patient
The mandible deviates to one side to relive this discomfort
Classically asymmetrical anterior open bite as shown below:
Possible effects of a habit are:
Aetiology : Soft Tissue
Soft tissue influence depends on:
Soft tissue influence depends on:
- Skeletal
- AP and vertical
- Lips
- Length
- Tone
- Activity
- Swallowing pattern
Aetiology: Soft Tissue
Clinical assessment of soft tissue:
Left to right pics:
1. Mild class II - overjet mild
2. More class II - greater overjet
3 - tight lower lip - leading to retroclination of lower incisors and so overjet is increased
But when you look at facial profile they dont look as if they’re different in terms of AP skeletal relationship
Intra-oral dental examination of class II
What can you see - features of CLASS II
Well aligned arches
Some teeth need to come through
Classical increase in overjet - cheek retractors show extent of the overjet
Mandibular position of class II Div I
Ask pt to bite on back teeth when assessing overjet
Facial growth in class II div I
What is favourable vs unfavourable facial growth?
Variable - can be either:
1. Favourable:
- Downward and forward
- Profile improves
- Unfavourable – 2 patterns:
1) Upwards and forwards – Deep bite
2) Downwards and backwards – Open bite (and more class II)
