Aetiology Malocclusion - Skeletal Cause

Question 1

Aetiology of malocclusion - which more common cause problem - dental or skeletal?

Answer 1

Dental

Question 2

What is the skeletal pattern and how does it affect occlusion?

Answer 2

Relationship of upper and lower dental bases

Discrepancies between max and hand will affect occlusion

Question 3

What planes should you assess skeletal pattern in?

Answer 3

3 planes as all affect position of teeth

1. Antero-posterior
2. Vertical - common
3. Transverse - less common

Question 4

How does anteroposterior plane affect class I pattern?

Answer 4

Basal bone of mandible normal in relation to maxilla
Ideal profile
Soft tissue - line forehead to upper lip generally perpendicular

Question 5

How does antero-posterior plane affect class II pattern?

Answer 5

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

Question 6

How does anteroposterior plane affect class III pattern?

Answer 6

Basal bone of mandible in pre-normal to maxilla

Maxilla set back, mandible set forwards OR combo

Question 7

What is aetiology of class II skeletal pattern?

Answer 7

86% mandibular retrusion

14% maxilla protrusion

Question 8

What is aetiology of class III skeletal pattern?

Answer 8

Variable
34% maxillary retrusion
40% mandibular protrusion
26% combination

Question 9

How assess vertical dimensions?

Answer 9

Using FMP angle - lower face height

Question 10

What would you see with increased FMP angle?

Answer 10

Increased lower face height = reduced overbite/ anterior open bite

Question 11

What would you see with decreased FMP angle?

Answer 11

Decreased lower face height = deep overbite

Question 12

How tx variable FMP angle?

Answer 12

Hard to tx w/o favourable growth

Question 13

What is Frankfort plane?

Answer 13

From lower bored of orbit through external auditory meatus against mandibular plane
Should converge back of head = 28 degree

Question 14

What can discrepancies in transverse dimensions cause?

Answer 14

Cause discrepancies between width of mandible and maxilla

Often see cross bite/ scissor bite

Question 15

Why is it important to consider soft tissues?

Answer 15

Forces are usually balanced - if instability present = movement of teeth
Teeth in zone of stability between lips and cheek

Question 16

How does lip length affect aesthetic?

Answer 16

Short upper lip - cause incompetent lips

Question 17

How does lip line affect aesthetic?

Answer 17

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

Question 18

Difference between adaptive and edogenous tongue issues?

Answer 18

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

Question 19

How can habits affect occlusion?

Answer 19

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

Question 20

How can labial frenum affect occlusion?

Answer 20

Cause diastema - fibres of frenum can prevent teeth meeting