Aetiology of Malocclusion - Skeletal Elements Flashcards
where is malocclusion most common
western developed countries - mix of gene pools from different populations
what are the general factors to malocclusion
skeletal
muscular
dento-alveolar
what does the skeletal aspect of malocclusion mean
size, shape and relative positions of the upper and lower jaws
what does the muscular aspect of malocclusion mean
form and function of the muscles that surround the teeth - lips, cheeks and tongue
what does dentoalveolar aspects of malocclusion mean
size of the teeth in relation to the size of the jaws
what are the components of the facial skeleton
maxilla (attached to anterior cranial base)
mandible (articulates with posterior cranial base)
maxillary and mandibular alveolar processes
what aspects affect the transverse facial variation
width of the jaws
width of cranial base
what causes variation in facial skeleton
genetic and environmental factors
hereditary
what occlusion class is hereditary
class III
what are possible environmental factors of skeletal facial variation
masticatory muscles
mouth breathing
head posture
what are the three planes of space for facial skeletal examination
AP
transverse
vertical
what is a class I AP relationship
mandible related normal to maxilla such that the teeth erupt in class I - slight convex profile
what are lateral cephalograms
standardised radiographs of the face and base of skull
they are reproducible
what is the technique for a lateral cephalogram
frankfort plane horizontal
what is the eastman analysis
AP and vertical values from a lateral cephalostat that is recorded
what is the SNA angle of a lateral cephalogram
the SNA is the angle between the sella turcica (S), the (A) maxi concavity above upper incisor (B) is max concavity below bottom incisor
what is the SNA of a normal occlusion
3
what are reasons for a class II jaw relationship
mandible too small or maxilla too large
mandible normal sized but placed too far back due to obtuse angle of cranial base
what are the values usually for a class II
SNA close to normal
SNB decreased
what are reasons for the jaws to be in class III occlusion
maxilla too small or mandible too large
normal sized jaws but mandible placed too far forwards
what are the values for a class III relationship
SNA decreased if maxilla deficient
SNB normal or increased if mandible prognathic
what is dento-alveolar compensation
soft tissues disguise skeletal discrepancies by tilting teeth towards one another
what reference planes do you need to look at vertical relationship of jaws
Frankfort plane (lower orbital rum to superior border of EAM)
mandibular plane
where does the Frankfort plane and mandibular plane ususally meet
external occipital protuberance
what proportional measurements do you look at in vertical jaw relationship
upper anterior face height
lower anterior face height
what should the ratio of UAFH to LAFH be
equal (50-50)
what is the gonion
angle of mandible
what should be the angle between the Frankfort plane and mandibular plane in a normal jaw relationship
27 degree
what would happen to the frankfort plane - mandibular plane angle in a long face
increased
what would happen to the frankfort plane - mandibular plane angle in a reduced face
decreased
what does transverse jaw relationship look at
disproportion of maxillary and mandibular arch sizes - deals with crossbites
what is posterior cross bite most often associated with
class III malocclusion
what is mandibular displacement
occurs when inter-arch width discrepancies causes upper and lower teeth to meet cusp to cusp and the mandible is forced to deviate to achieve position of inter-cuspation
what is dento-alveolar compensation in transverse plane
eg upper molars flare out and lower molars roll in due to small maxilla
what are causes of asymmetry
dental
true mandibular asymmetry
what is dental cause of asymmetry
displacement of normal mandible due to unilateral cross bite
what are causes of true mandibular asymmetry
hemi-mandibular hyperplasia/ elongation
condylar hyperlasia
what is dento-alveolar disproportion
discrepancy between size of teeth and jaws
what can cause crowding
large teeth and small jaws
what can cause spacing
large arch and small teeth
