Aetiology of Malocclusion 1 - Skeletal Causes, Part 2 Flashcards
What is the Frankfurt plane?
Lower orbital rim to superior border of EAM
What is the mandibular plane?
Lower border of the mandible
Where do the frankfurt and mandibular plane meet?
Usually at the external occipital protuberance
What is the upper anterior face height?
Brow ridge (glabella) to the base of the nose
What is the lower anterior face height?
Base of nose (sub nasale) to inferior aspect of chin (soft tissue menton)
What is the average ratio of LAFH and TAFH?
50%
What is the average cephalometric value for the FMPA?
27º +/- 4º
What is the average cephalometric value for LAFH to TAFH and how is it calculated?
Nasion to anterior nasal spine
Anterior nasal spine to menton
55%
Describe the vertical jaw relationship for someone with a long facial type?
LAFH to TAFH proportion >55%
FMPA > 31º
Steeply inclined mandibular plane
Backward mandibular growth rotation
Anterior open bite tendency
Describe the vertical jaw relationship for someone with a short facial type
LAFH to TAFH proportion < 55%
FMPA < 23º
Tendency to parallelism of jaws
Forward mandibular growth rotation
Deep overbite tendency
What are arch width discrepancies?
Disproportion of maxillary and mandibular dental arches
What do arch width discrepancies cause?
Unilateral or bilateral buccal augment cross-bites
Often exaggerated by antero-posterior discrepancies
What is mandibular displacement and when does it happen?
Mandible forced to deviate to one side to achieve position of inter-cuspation
Occurs where inter-arch width discrepancy causes upper and lower posterior teeth to meet cusp to cusp
Possible association with TMD
What is the dental cause of facial asymmetries?
Displacement of normal mandible due to unilateral cross-bite
What causes true mandibular asymmetry?
Hemi-mandibular hyperplasia/elongation
Condylar hyperplasia
