Aetiology of Malocclusion Flashcards
- Define skeletal pattern - Appreciate the 3D aspects of skeletal relationships - Understand the interdependence of the skeletal pattern and soft tissues - Relate the form and function of the lips and tongue to incisor relationships - Give an account of normal and abnormal mandibular positions
Skeletal features consist of which bases?
Upper dental base
Lower dental base
Skeletal pattern depends on relationship between
upper and lower dental base
3 dimensions
Antero-posterior
Vertical
Transverse
Anteroposterior relationship classes definitions
I
II
III
I - Lower DB set back slightly to Upper
II - Lower DB set further back
III - Lower DB protrudes from line of 0 meridian/retrusion of maxilla
Maxilla has
More variation in terms of position of upper jaw
Regions of skull
Maxilla
Mandible
Skull
Vertical relationship features
FFMP definition and average value?
Columella to bottom of chin should =
FFMP - lower border of orbit –> EAM and and mandibular plane
approx 28 degrees on average
1/3 face height
Increased FFMP =
Increased likelihood of anterior open bite
Decreased FFMP =
Deep bite
Transverse features
Wider UA/LA can lead to
View from front
Wider UA or LA can lead to cross bite
Discrepancies are more obvious
Soft tissues
Lips and cheek
Nose
Gum line
Competency:
Gummy smile
Competent lips
Incompetent lips
Gummy smile can result from short lip length or vertical max. excess
Meet at rest
Do not meet at rest
Increases with age
Will meet if factor preventing it is removed
Lip line - location
Normally lower lip line rests midway up crown of upper incisors
Tongue - function
Creates resting force on teeth which opposes force from lips
In position of stability which influences tooth position
Tongue thrust
Creates seal either for adaptive or endogenous reasons
Correction of anterior open bite can resolve it
Endogenous thrust is rare - lisping or bimaxillary protrusion - can result in anterior open bite
Habits
Dummy/thumb sucking
Proclamation decreases with age due to loss of habit
Position will generally improve
Effect of thumb sucking
Reduced overbite or aob
Proclines upper incisors
Retroclines lower incisors
Posterior cross bite by reducing size of upper jaw
Labial frenum can be
Normal
Abnormal - low attachment –> diastema
Bonded retainer can stop spacing –> resorption of fibres
Dental cause of malocclusion and expand
Tooth/tissue ratio - crowding can be mild or severe
Crowding common in lower incisal area
Aetiology of crowding (x2)
Environmental - diet due to lack of occlusal wear - research showed wear below contact point allows for space for more teeth to erupt
Genetic - independent genetic control of tooth development and upper and lower jaw development
Spacing
Can be localised e.g midline diastema - can be closed but needs to be permanently retained
Conditions affecting number of teeth
Anodontia Hypodontia - no tooth bud Hyperdontia - mesiodens Supernumerary Macrodontia Microdontia
Abnormal form/position
Transposition
Impaction
Transposition - swapping of normal positions
Impaction - impaction between two teeth
Path of closure
Lateral displacement
Forward displacement
Lateral displacement - can occur with narrow upper arch/wide LA - teeth do not meet correctly Forward displacement - instancing class III incisors
Pathology
Cysts
Tumours
Trauma
Dentigerous cysts can prevent eruption
Tumours - knocking primary incisors–> intrusion
Trama
High lip line common in
Class II Div II due to retroclined upper incisors
A high lip line with a severe antero-posterior skeletal discrepancy and a Class II division 1 incisor
relationship shown by
A high lip line with a reduced lower face height will produce
A low lip line
Strap lower lip describes
One of the signs of a hyperactive lower lip
the lower lip is placed behind the upper incisors on the palate or the
teeth
produce a Class II(ii) incisor
relationship since the lower lip will be on the labial side of the upper incisors
The lower lip contacts the tongue thus dispersing the upper incisors.
a hyperactive lower lip. the significance of this condition is that any overjet
must be FULLY reduced in order to be stable.
the presence of a deep mentalis fold.
