Aetiology Malocclusion - Skeletal Cause Flashcards
Aetiology of malocclusion - which more common cause problem - dental or skeletal?
Dental
What is the skeletal pattern and how does it affect occlusion?
Relationship of upper and lower dental bases
Discrepancies between max and hand will affect occlusion
What planes should you assess skeletal pattern in?
3 planes as all affect position of teeth
- Antero-posterior
- Vertical - common
- Transverse - less common
How does anteroposterior plane affect class I pattern?
Basal bone of mandible normal in relation to maxilla
Ideal profile
Soft tissue - line forehead to upper lip generally perpendicular
How does antero-posterior plane affect class II pattern?
Basal bone of mandible post-normal to maxilla
Maxilla tends to be normal
Soft tissue - line forehead to upper lip perpendicular but lower lip set back
How does anteroposterior plane affect class III pattern?
Basal bone of mandible in pre-normal to maxilla
Maxilla set back, mandible set forwards OR combo
What is aetiology of class II skeletal pattern?
86% mandibular retrusion
14% maxilla protrusion
What is aetiology of class III skeletal pattern?
Variable
34% maxillary retrusion
40% mandibular protrusion
26% combination
How assess vertical dimensions?
Using FMP angle - lower face height
What would you see with increased FMP angle?
Increased lower face height = reduced overbite/ anterior open bite
What would you see with decreased FMP angle?
Decreased lower face height = deep overbite
How tx variable FMP angle?
Hard to tx w/o favourable growth
What is Frankfort plane?
From lower bored of orbit through external auditory meatus against mandibular plane
Should converge back of head = 28 degree
What can discrepancies in transverse dimensions cause?
Cause discrepancies between width of mandible and maxilla
Often see cross bite/ scissor bite
Why is it important to consider soft tissues?
Forces are usually balanced - if instability present = movement of teeth
Teeth in zone of stability between lips and cheek
How does lip length affect aesthetic?
Short upper lip - cause incompetent lips
How does lip line affect aesthetic?
Normal lip line - lower lip rests middle upper incisor
Low lip line - lower lip rest behind lower incisor -push upper forward
High lip line - retroclined upper incisors - lower lip sits above crown lower incisor - can push back upper
Difference between adaptive and edogenous tongue issues?
Adaptive e.g thumb sucking- cause anterior-open bite (correction AOB resolve tongue thrust) (tongue thrust cause AOB close via seal when swallow)
Endogenous - rare - can be associated w/ lisping
How can habits affect occlusion?
Dummy or digit sucking - effect permanent dentition
Reduced overbite or anterior open bite
Proclined upper incisors
Retroclined lower incisors
Posterior cross bite - change equilibrium of forces
How can labial frenum affect occlusion?
Cause diastema - fibres of frenum can prevent teeth meeting
