Aetiology Of Malocclusion Flashcards
What are the three overlying forms of malocclusion?
Skeletal - upper + lower jaws
Muscular - form and function of muscles
Dentoalveolar - size of teeth in relation to jaws
What planes can skeletal variation occur?
Anterio-posterior
Vertical
Transverse
What is:
SNA and avg value
SNA is maxilla relation to anterior cranial base = 81 degrees +- 3
Sella, naison, subspinale point
What is SNB and average value
SNB is mandible to anterior cranial base = 78 degrees +- 3
Sella, naison, supramentale point B
What is ANB and average value?
ANB relates mandible to maxilla = 3 degrees +- 2
What is a class 1?
Normal occlusion
What is a class 2? What are the common causes?
Mandible places too posterior to maxilla
Commonly, the mandible is too small or maxilla too large.
Mandible can be normally sized but positioned too far back due to obtuse cranial base angle
ANB >5
What is a class 3? Common causes?
Mandible Anteriorly positioned relative to maxilla
Most commonly - maxilla too small, mandible too large or combo
Can be due to acute cranial base angle causing mandibular protrusion
ANB 1 or negative
What is the Frankfurt plane?
Lower orbital rim to superior border of EAM
What is the mandibular plane?
Lower border of mandible
Where do Frankfurt and mandibular plane usually meet?
External occipital protuberance
What are the boundaries of the upper anterior face and lower anterior face? What is the ideal ratio?
Brow of ridge (glabella) to the base of nose
Base of nose to inferior aspect of chin
50:50
What is FMPA and its ideal value?
Frankfurt mandibular plane angle should be 27 degrees +- 4 degrees
What would result in someone having ‘long-face syndrome’
LAFH:UAFH >55%
FMPA > 31 degrees
What would result in someone having a short face
LAFH:UAFH <55%
FMPA >23 degrees
