Aetiology of Malocclusion

Question 1

What are the four components of facial skeleton ?

Answer 1

Maxilla base.
Mandibular base.
Alveolar processes of upper and lower.
Maxillary complex (attached to anterior skull base).
Mandibular complex (attached to posterior skull base).

Question 2

What malocclusion is most commonly associated with genetic aetiology ?

Answer 2

Class III malocclusion.

Question 3

What are 3 examples of environmental etiological factors affecting malocclusions ?

Answer 3

Muscles of mastication.
Mouth breathing.
Head posture.

Question 4

Describe a Class I malocclusion.

Answer 4

Mandible related normally to maxilla so teeth erupt into normal occlusion. Jaws are normally the correct size.

Question 5

Describe a Class II malocclusion.

Answer 5

Mandible placed posteriorly relative to maxilla.

Question 6

What can be the anatomical reasons for a Class II malocclusion ?

Answer 6

Mandible too small - most common.
Maxilla too large.
Obtuse cranial base angle - normal mandible but set far back in skull base.

Question 7

Describe a Class III malocclusion.

Answer 7

Mandible placed anteriorly relative to maxilla.

Question 8

What can be the anatomical reasons for a Class III malocclusion ?

Answer 8

Maxilla too small - most common.
Mandible too large.
Acute cranial base angle - with normal jaw size.

Question 9

What is dental alveolar compensation ?

Answer 9

Forces from lips, cheeks, tongue incline teeth towards position of soft tissue balance - leads to disguising of malocclusion with soft tissue envelope.

Question 10

What is a lateral cephalogram ?

Answer 10

Standardised (reproducible) lateral radiograph of face and skull base.

Question 11

What makes a lateral cephalogram reproducible ?

Answer 11

Patient at set distance from cephalostat between cone and film.

Question 12

When would a cephalogram be beneficial in orthodontic treatment ?

Answer 12

Monitoring growth.
Severe malocclusions.

Question 13

What does the SNA angle show ?

Answer 13

Relationship of maxilla to anterior cranial base.

Question 14

What does the SNB angle show ?

Answer 14

Relationship of mandible to anterior cranial base.

Question 15

What does the ANB angle show ?

Answer 15

Relationship of maxilla to mandible.

Question 16

How is the SNA angle measured ?

Answer 16

Angle between lines -
- Between sella turcica and nasion.
- Between nasion and maximum concavity of upper incisors.

Question 17

How is the SNB angle measured ?

Answer 17

Angle between lines -
- Between sella turcica and nasion.
- Between nasion and maximum concavity of lower incisors.

Question 18

How is the ANB angle measured ?

Answer 18

Difference between upper and lower maximum concavity lines.

Question 19

What is the normal SNA angle for a Class I malocclusion ?

Answer 19

81 degrees (+/- 3 degrees).

Question 20

What is the normal SNB angle for a Class I malocclusion ?

Answer 20

78 degrees (+/- 3 degrees).

Question 21

What is the normal ANB angle for a Class I malocclusion ?

Answer 21

3 degrees (+/- 2 degrees).

Question 22

If the maxilla is prognathic in a Class II malocclusion, will the SNA angle be increased or decreased compared to the standard values ?

Answer 22

Increased.

Question 23

If the mandible is prognathic in a Class III malocclusion, will the SNA angle be increased or decreased compared to the standard values ?

Answer 23

Decreased.

Question 24

What value will ANB angle be in a Class II malocclusion ?

Answer 24

> 5 degrees.

Question 25

What value will ANB angle be in a Class III malocclusion ?

Answer 25

<1 (-) degrees.

Question 26

What is the Frankfort plane measured between ?

Answer 26

Lower orbital rim to superior border of external auditory meatus.

Question 27

What is the mandibular plane measured against ?

Answer 27

Lower border of mandible.

Question 28

Where should mandibular and Frankfort plane meet ?

Answer 28

External occipital protuberence.

Question 29

What angle can be measured between mandibular and Frankfort plane ?

Answer 29

Frankfort-mandibular plane angle - FMPA.

Question 30

What two anatomical features is upper anterior face height measured between ?

Answer 30

Glabella to base of the nose.

Question 31

What two anatomical features is lower anterior face height measured between ?

Answer 31

Subnasale to soft tissue menton.

Question 32

What is the average ratio between LAFH and UAFH ?

Answer 32

LAFH - 55% UAFH - 45%

Question 33

In a patient with an anterior open bite, what will FMPA and LAFH values be vs. normal values ?

Answer 33

Increased FMPA. Increased LAFH.

Question 34

What are five causes for transverse relationship variation ?

Answer 34

Arch discrepancies. Mandibular displacement. Transverse dento-alveolar discrepancy. Facial asymetry. Arch size discrepancy.

Question 35

What is an example of arch discrepancies ?

Answer 35

Unilateral or bilateral crossbite.

Question 36

What causes mandibular displacement ?

Answer 36

Inter-arch width discrepancy causing upper and lower posterior teeth to meet cusp to cusp. Mandible has to deviate to gain ICP.

Question 37

What are 3 examples of true facial asymmetries i.e. not to do with tooth position ?

Answer 37

Condylar hyperplasia. Hemi-mandibular hyperplasia or elongation.

Question 38

What are the four causes of malocclusion ?

Answer 38

Skeletal pattern. Dental. Soft tissue. Other i.e. habits.

Question 39

What is the definition of local causes of malocclusion ?

Answer 39

Localised problem or abnormality within either arch, usually confined to 1/2 or several teeth producing malocclusion which tends to get worst with time.

Question 40

What are 5 local causes of malocclusion ?

Answer 40

Variation in tooth number. Variation in tooth size or form. Abnormalities of tooth position. Local abnormalities of soft tissues. Local pathologies.

Question 41

What is the definition of hypodontia ?

Answer 41

Developmental absence of one or more teeth.

Question 42

Is hypodontia more common in males vs. females ?

Answer 42

Females - 3:2.

Question 43

What teeth are most commonly affected by hypodontia ?

Answer 43

Upper laterals and second premolars.

Question 44

What is the definition of retained primary teeth ?

Answer 44

A difference of more than 6 months between shedding of contra-lateral teeth - disruption in sequence of eruption.

Question 45

What are the five reasons which a primary tooth may be retained ?

Answer 45

Absent successor. Ectopic successor or dilacerated. Infra-occluded (ankylosed) primary molars. Dentally delayed in terms of development. Pathology/supernumerary.

Question 46

What are two treatment options for retained primary teeth ?

Answer 46

1. Maintain primary tooth as long as possible if good prognosis. 2. XLA deciduous tooth really to encourage spontaneous space closure in crowded cases.

Question 47

What is the definition of infra-occluded primary molars ?

Answer 47

Process where tooth fails to achieve or maintain its occlusal relationship with adjacent teeth. Can be measured slight (<2mm from occlusal surface), moderate (inter-proximal contact) and severe (below inter-proximal).

Question 48

What are 4 causes for early loss of primary teeth ?

Answer 48

Trauma. PA pathology. Caries. Resorption of successor.

Question 49

What is a balancing extraction ?

Answer 49

Extraction tooth from the opposite side of same arch - designed to minimise midline shift.

Question 50

What is a compensating extraction ?

Answer 50

Extraction of tooth from opposing arch of the same side - designed to maintain occlusal relationship.

Question 51

What is the impact of early loss of primary canines ?

Answer 51

Unilateral loss in crowded arch - causes midline shift. Consider balancing extraction.

Question 52

What teeth are most commonly ectopic ?

Answer 52

8s, 3s, 6s, 1s.

Question 53

From what age should ectopic maxillary canines be palpated to check position ?

Answer 53

9+ years old.

Question 54

What % of ectopic canines are palatally placed ?

Answer 54

80%

Question 55

What can be 4 signs of ectopic canines in clinical assessment ?

Answer 55

Visualisation/palpation of obvious bumps of 3. Inclination of 2. Mobility of c or 2. Colour of c or 2.

Question 56

What 2 radiographs are required for radiographic assessment of ectopic canines ?

Answer 56

OPT and upper anterior oblique occlusal. Use parallax technique.

Question 57

What are the 3Ps in assessment of ectopic canines ?

Answer 57

Presence, position, pathology.

Question 58

For are six management options of ectopic canines ?

Answer 58

1. Prevention. 2. Extraction of c to encourage improvement in position of 3 - interceptive orthodontic treatment. 3. Retain 3s and observe - accept position. 4. Surgical exposure and orthodontic alignment. 5. Surgical extraction. 6. Autotransplantation.