Etiology of Malocclusion (Part I)

Question 1

List the predisposing factors to malocclusion:

Answer 1

1. disturbances in embryological development
2. heredity (genetics)
3. functional matrix (muscular/functional disturbances & habits)
4. traumas (especially mandibular fractures)

Question 2

Give an example of a functional matrix that may be a predisposing factor to malocclusion: (2)

Answer 2

muscular/functional disturbances & habits

Question 3

What trauma specifically is a predisposing factor to malocclusion?

Answer 3

mandibular fractures

Question 4

What three factors contribute to malocclusions?

Answer 4

1. genetic
2. environmental
3. other

Question 5

What do we use as a reference point for a normal skeletal relationship?

Answer 5

Cranial base

Question 6

We use the cranial base as a reference point for normal skeletal relationship, this includes: (2)

Answer 6

1. position & projection of upper jaw
2. position & projection of lower jaw

Question 7

Malocclusions occur in:

Answer 7

3 dimensions

Question 8

Angle classification is based on:

Answer 8

AP relationships

Question 9

List the relative percentages for the following:

-normal occlusion
-class I malocclusion
-class II malocclusion
-class III malocclusion

Answer 9

-normal occlusion: 30%
-class I malocclusion: 50-55%
-class II malocclusion: 15%
-class III malocclusion: 1-4%

Question 10

According to the intuitive theory what is the cause of a class I?

Answer 10

Jaw WITHOUT prognathism

Question 11

According to the intuitive theory what is the cause of a class II?

Answer 11

Maxillary prognathism

Question 12

According to the intuitive theory what is the cause of a class III?

Answer 12

Mandibular prognathism

Question 13

Class II malocclusion:

-mandibular ______
-40% present _____
-rarely _____

Answer 13

-mandibular retrognathism
-bimaxillary retrusion
-true maxillary prognathism

Question 14

T/F: A class II malocclusion is most commonly caused by a true maxillary prognathism

Answer 14

False, that is rare- typically caused by mandibular retrognathism

Question 15

What percent of class II malocclusions present with bimaxillary retrusion?

Answer 15

40%

Question 16

-Mandibular retrognathism
-40% present bimaxillary retrusion
-rarely true maxillary prognathism

Answer 16

Class II malocclusion

Question 17

Describe a typical skeletal class II: (3)

Answer 17

1. mandibular retrognathism
2. proclined upper incisors
3. deep bite

Question 18

Describe the typical bite for a skeletal class II:

Answer 18

Deep bite

Question 19

Describe the incisors for a typical skeletal class II:

Answer 19

proclined upper incisors

Question 20

-mandibular retrognathism
-proclined upper incisors
-deep bite

Skeletal class?

Answer 20

Typical skeletal class II

Question 21

-Jaws are well aligned in the antero-posterior dimension
-Vertical and transverse dimensions are variable

Answer 21

Class I malocclusion

Question 22

In a class I malocclusion, the jaws are well aligned in the ____ dimension, while the _____ & ____ dimensions are variable

Answer 22

anteroposterior; vertical & transverse

Question 23

Transverse dimension involves the: (3)

Answer 23

1. intermolar distance
2. intercanine distance
3. arch shape

Question 24

T/F: both the inter molar & inter canine distance are involved with the transverse dimension

Answer 24

True

Question 25

Class III malocclusion:

-maxillary ____
-mandibular ____
-usually a _____ of the two conditions
-______ dimension is variable causing a ____ to ____ bite

Answer 25

-maxillary retrognathism
-mandibular prognathism
-combination
-vertical dimension; deep bite to open bite

Question 26

-maxillary retrognathism
-mandiular prognathism
-usually, a combination of the two conditions
-vertical dimension is variable, deep bite to open bite

Answer 26

Class III malocclusion

Question 27

The prevalence of class III malocclusions depends on:

Answer 27

the population

Question 28

List the prevalence of class III malocclusions based on the following populations:

-southeast Asian:
-middle eastern:
-indian:
-european:

Answer 28

-southeast Asian: 15%
-middle eastern: 10%
-indian: 1%
-european: 1-4%

Question 29

Fundamentally, mandibular growth is induced by both genetic & environmental mechanisms which interact with each other to produce:

Answer 29

class III phenotype

Question 30

List the components involved that contribute to the mandibular growth seen in a class III relationship:

Answer 30

1. genes
2. environment
3. condylar cartilage (acted on by genes and environment)

Question 31

Fundamentally, mandibular growth is induced by:

Answer 31

both genetics & environmental mechanisms

Question 32

What is the etiology for an open bite?

Answer 32

multifactorial etiologies

Question 33

List some examples of the multifactorial etiology of an open bite: (4)

Answer 33

1. transitory
2. skeletal (genetic)
3. neuromuscular imbalance (CP)
4. combination sleep apnea

Question 34

What influences the neuromuscular imbalance seen in an open bite? (2)

Answer 34

1. oral habits
2. anterior tongue posture