Ortho - Malocclusion Flashcards
What 3 things can you do to reduce the levels of radiation from a lateral ceph?
Triangular collimator
Thyroid collar
Rare earth/ LANEX screen
What film speed is used on a lateral ceph?
60-70kV
What do the letters in SNA stand for?
Sella tursica - Which is a part of the sphenoid bone which holds the pituitary gland.
Nasion
A - the deepest concavity of maxillary alveolus
In a class 1 patient what are the SNA, SNB and ANB values on a lateral ceph?
SNA - 81 +- 3
SNA - 78 +- 3
ANB - 3+- 2
What is the Eastman correction?
This is to address inaccuracies.
For every degree the SNA value falls below 81 half a degree should be added to ANB and vice versa
What happens to the values of SNA, SNB and ANB on a lateral ceph, in a class ll patient?
SNA - stays the same
SNB - decreases < 78
ANB - increases >5
What happens to the values of SNA, SNB and ANB on a lateral ceph, in a class lll patient?
SNA - decreases
SNB - stays the same increase if mandible prognathic.
ANB - < 1 or negative
What is dento-alveolar compensation?
This is when dentoalveolar structures try and disguise skeletal discrepancies.
It forces the lips cheeks and tongue teeth towards a position of soft-tissue balance.
What is a common sign of dento-alveolar compensation?
Incisors being tipped towards one and other
What is the normal value for the FMPA on a lateral ceph?
27 degrees +- 4
What is the anterior face height ratio value normally (AFHR)
55% to the lower 45% to upper
In a patient with a long face what happens to the FMPA and AHFR?
FMPA > 31 degrees
LFHR > 55% of total face height
How does mandible grow in a patient with “long face”? and how does it present?
mandible grows down and backwards
Patients struggle to keep lips together.
Presents with shallow bite and anterior open bite.
May need surgical intervention
In a patient with a short face what happens to the FMPA and AHFR?
FMPA - < 23 degrees
LHFR < 55%
Presents with very deep bite
What can arch width discrepancies cause?
Posterior unilateral or bilateral crossbites
How can you expand the upper arch?
URA
mid-palatal screw
What is mandibular displacement? and what is it associated with?
This is when the teeth contact cusp to cusp but in order to achieve ICP, the mandible is displaced to one side.
Associated with TMD
What is transverse dento-alveolar compensation?
This is when the soft tissues mould the alveolar process during growth to maintain occlusion.
This disguises skeletal discrepancies
What are some types and reasons for facial asymmetry?
Dental cause - mandible is displaced due to a unilateral crossbite.
True Mandibular asymmetry, asymmetric growth of the mandible (Hemi-mandibular hyperplasia)
Hemifacial microsomia - incomplete growth of one side of the mandible
Dentoalveolar disproportion relates to discrepancies within the size of teeth and jaw, what can this cause?
Overcrowding - macrodont and small jaw
space - hypodontia and big jaw
What are the 5 broad categories of local causes for malocclusion?
1) Variation in tooth number
2) Variation in tooth size
3) Abnormal tooth position (ectopic)
4) Local abnormalities of soft tissues
5) Local pathology