Aetiology Of Malocclusion Flashcards
What 3 factors can cause 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 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
Why might mandibular displacement or cross biting occur?
To achieve ICP, mandible has to shift to one side, can be due to TMdysfunction
Why might someone have crowding or spacing?
Crowding
- small jaws, normal teeth
- large teeth (macrodontia)
Spacing
- large jaws
- small teeth (microdontia)
Incidence of class 1 molar occlusion?
30-35%
