Aetiology of Malocclusion Flashcards
what are the general aetiological factors of malocclusion
skeletal/muscular/dentoalveolar
what are the skeletal factors of malocclusion
size, shape and relative positions of upper and lower jaws
what are the muscular factors of malocclusion
form and function of the muscles that surround the teeth
what are the dentoalveolar factors of malocclusion
size of teeth in relation to size of jaws
why does malocclusion result
due to disharmony between the components of the facial skeleton
what type of malocclusion is hereditary
class 3 occlusion
what are the possible environmental factors of skeletal variation
masticatory muscles, mouth breathing, head posture
what are the 3 views to consider when judging skeletal variation
antero-posterior
vertical
transverse
what is the skeletal relationship with a class 1 occlusion
mandible and maxilla related normally so that teeth erupt into class 1
how are lateral cephs made reproducible
due to cephalostat
what is a lateral ceph
standardised lateral radiograph of the face and base of skull
how are lateral cephs analysed
either hand traced onto paper or digitised using a computer
what is SNA in eastman analysis
maxilla to anterior cranial base
what is SNB in eastman analysis
mandible to anterior cranial base
what is ANB in eastman analysis
mandible to maxilla
what is the antero-posterior relationship in a class 2 occlusion
mandible placed posteriorly to maxilla
what causes the class 2 antero posterior relationship
mandible too small/maxilla too large
normal sized mandible but placed too far back (obtuse cranial base angle)
what is the antero-posterior relationship in a class 3 occlusion
mandible placed anteriorly relatively to maxilla
what causes the class 3 antero-posterior relationship
maxilla too small/mandible too large or both
normal sized jaw but acute cranial bae angle
what is dento-alveolar compensation
when dento-alveolar structures disguise skeletal discrepancies by inclining teeth towards position of soft tissue balance
in severe class 3 malocclusion what is the dento-alveolar compensation
proclined upper incisors
retroclined lower incisors
what is the frankfurt plane
lower orbital rim to superior border of external auditory meatus
what is the mandibular plane
lower border of mandible
where do the mandibular and frankfurt plane meet?
external occipital protuberance
how do you measure upper anterior face height
brow ridge to base of nose
how do you measure lower anterior face height
base of nose to inferior aspect of chin
what is the average ratio of lower anterior face height to upper anterior face height
50%
what is the average value of frankfurt mandibular plane angle
27 degrees
with a long facial type what is the proportion of LAFH to TAFH
> 55%
what are the features of long facial type
steeply inclined mandibular plane
backward mandibular growth rotation
anterior open bite
what is the proportion of LAFH to TAFH in short facial type
<55%
what are the features of short facial type
tendency to parallelism of jaws
forward mandibular growth rotation
deep overbite tendency
what does arch width discrepancies cause
unilateral or bilateral buccal segment cross bites
where does mandibular displacement occur
where inter-arch width discrepancy causes upper and lower posterior teeth to meet cusp to cusp
what happens to the mandible with mandibular displacement
it deviates to one side to achieve position of inter cuspation
what is the dental cause of facial symmetries
displacement of normal mandible due to unilateral cross bite
what is true mandibular asymmetry
hemi-mandibular hyperplasia/elongation
condylar hyperplasia
what is dento-alveolar disproportion
discrepancy between size of teeth and jaws
what is crowding caused by
small jaws and normal sized teeth
large teeth
what is spacing caused by
large jaws and normal sized teeth
small teeth
