Aetiology of Malocclusion

Question 1

what are the 3 broad aetiologies of malocclusions

Answer 1

Skeletal - size, shape and relative position of upper and lower jaws
Muscular - form and function of the muscles that surround the teeth e.g lips, tongue and cheeks
Dento-alveolar - size of teeth in relation to size of jaws

Question 2

Cranial base angle

Answer 2

angle formed where the anterior cranial base and the posterior cranial base meet

Question 3

Class I occlusion

Answer 3

‘normal occlusion’
maxilla slightly in front of mandible
lower incisors occlude or lie directly below the upper central cingulum

Question 4

Class II occlusion

Answer 4

‘overjet’
mandible is posterior to maxilla
lower incisor edges lie posterior to the upper central cingulums
division 1 = upper incisors are proclined or normal
division 2 = upper incisors retroclined

Question 5

Class III occlusion

Answer 5

‘reversed overjet’
mandible is anterior to the maxilla
lower incisor edges lie anterior to the upper central cingulums

Question 6

dento alveolar compensation

Answer 6

refers to movement of dento alveolar structures to disguise skeletal discrepancies
e.g upper incisors procline and lower incisors retrocline in class IIIs making reverse overjet appear reduced

Question 7

Frankfort plane

Answer 7

lower orbital rim to the superior border of the external acoustic meatus

Question 8

mandibular plane

Answer 8

lower border of mandible

Question 9

where do the mandibular plane and the frankfort plane usually meet (in patients with normal skeletal relationship)

Answer 9

external occipital protuberance

Question 10

where is upper anterior face height measured from and to

Answer 10

glabella to base of nose

Question 11

where is lower anterior face height measured from and to o

Answer 11

base of nose to inferior surface of chin

Question 12

what is the average ratio of lower anterior face height : total anterior face height

Answer 12

TAFH = LAFH + UAFH (glabella to inferior border of chin)
average = 50% of TAFH

Question 13

what is the average FMPA angle and what is this

Answer 13

frankfort mandibular plane angle
usually 27 degrees +/- 4

Question 14

describe the skeletal tendencies of a ‘long facial type’

Answer 14

steeply inclined mandibular plane
Anterior open bite tendency
backward mandibular growth rotation
FMPA usually increased

Question 15

describe the skeletal tendencies of a ‘short facial type’

Answer 15

parallelism of jaws
deep overbite tendency
forward mandibular growth rotation
FMPA usually decreased

Question 16

Name 2 dento-alveolar discrepancies and a potential cause

Answer 16

Crowding - small jaws and normal teeth or macrodontia
Spacing - large jaws and normal teeth of microdontia