aetiology og malocclusion: skeletal factors

Question 1

3 dimensions of skeletal pattern and describe each

Answer 1

antero-posterior (skeletal class)

vertical: facial proportions
transverse: facial asymmetry, arch width discrepancy

Question 2

define skeletal CLASS

Answer 2

Classification of the antero-postero relationship of the dental bases which support the teeth and alveolar processes

Question 3

define skeletal class 1

Answer 3

maxillary dental base lies 2-3mm anterior to mandibular dental base when teeth in occlusion

Question 4

define skeletal class 2

Answer 4

maxillary dental base more than 2-3mm anterior to mandibular dental base when teeth in occlusion

Question 5

3 causes of skeletal class 2

Answer 5

• retrognathic mandible
• prognathic maxilla
• both

Question 6

likely skeletal class if cranial base angle is

a. obtuse
b. acute

Answer 6

a. obtuse: class 2

b. acute: class 3

Question 7

define skeletal class 3

Answer 7

mandibular dental bases more anterior than the maxillary dental bases

Question 8

how should the pt be sitting to measure skeletal class

Answer 8

upright with the head in the free postural position

Question 9

3 causes and % of causes of skeletal class 3

Answer 9

retrognathic maxilla (25%)
prognathic mandible (25%)
combination of both (50%)

Question 10

what is dentoalveolar compensation

Answer 10

when the antero-posterior jaw relationship is class 2 or 3 but the soft tissues are favourable –> lips and tongue guide erupting teeth in to better positions than the skeletal class would suggest

Question 11

describe dentoalveolar compensation in class 2 (3)

Answer 11

retroclined upper incisors
proclination of lower incisors –> class I incisors, class 2 base
both

Question 12

dentoalveolar compensation in class 3 (3)

Answer 12

proclined upper incisors
retroclination of lower incisors
both

Question 13

what radiograph is needed to see skeletal class

Answer 13

lat cephalometric

Question 14

what 2 points on the faced are used in cephalometric analysis

Answer 14

sella (depression in sphenoid bone containing pituitary gland)
nasion (intersection of nasal bone and frontal bone)

Question 15

what do SNA and SNB measure

Answer 15

SNA: how far forward/back upper incisors are (A= dental bases of maxillary incisors
SNB: how far forward/ back lower incisors are (B= dental bases of mandibular incisors)

Question 16

describe the distribution of cephalometric analysis

Answer 16

normal distribution (most people skeletal class I, very sk3 and sk2 to each side

Question 17

median ANB (SNA-SNB) (degrees)

Answer 17

3.4 degrees

Question 18

4 outcomes of diagnosing wrong skeletal class

Answer 18

• failure to achieve desired occlusion
• poor dental aesthetics
• poor facial aesthetics
• instability of result

Question 19

describe average facial proportions (vertical)

Answer 19

1/3: top of head to top of ear
1/3: top of ear to bottom of nose
1/3: bottom of nose to bottom of chin

Question 20

describe the frankfort plane

Answer 20

top of eam- inferior margin of orbit. HORIZONTAL

Question 21

what does the mandibular plane measure

Answer 21

top of eam to bottom of chin

Question 22

normal value of

a. frankfort-mandibular angle
b. maxillary plane- mandubular angle

Answer 22

a. frankfort-mandibular angle: 27+- 5 degrees

b. maxillary plane- mandubular angle: 27+- 5 degrees

Question 23

what points mark

a. upper anterior face height B
b. lower anterior face height A

Answer 23

a. upper anterior face height: superior margin of orbit/ eyebrow - maxillary plane/ bottom of nose
b. lower anterior face height: maxillary plane/ bottom of nose - bottom of chin

Question 24

which of these changes with face height

Answer 24

lower face height A

Question 25

usual value of A/B

Answer 25

50-55

Question 26

2 probs of inc face height

Answer 26

aesthetics: wide separation of lips
malocclusion: reduced overbite/ anterior open bite (negative overbite)

Question 27

reduced lower face height

a. facial features 2
b. occlusal tendencies 2
c. soft tissues 1

Answer 27

a. facial features 2: reduced lower face height, prominent chin (look overclosed, edentulous)
b. occlusal tendencies 2: increased overbite, hard to correct
c. soft tissues 1: lips completely cover teeth

Question 28

where frankfort plane and mandibular angle meet

a. on average
b. with reduced face height
c. with increased face height

Answer 28

a. on average: at back of head
b. with reduced face height: way behind back of head
c. with increased face height: anterior to back of head

Question 29

2 intra oral features associated with asymmetry

Answer 29

centre line discrepancies
posterior crossbites (in buccal segments)