OE L37 Facial Growth

Question 1

Which facial processes are present by week 5 of gestation?

Answer 1

• Frontonasal process (forehead, eyelids)
• Medial and lateral nasal processes/placodes (nose, part of upper lip, philtrum, upper incisors, alae and base of nose)
• Maxillary process (lateral parts of upper lip, canines, premolars and molars, cheeks)
• Mandibular process (lower lip, lower jaw and teeth)

Question 2

What 2 statistical analsyes are used to estimate the degree of variation in a phenotypic trait in a population?

Answer 2

• Narrow sense heritability: used to determine resemblance between relatives
• Broad sense heritability: reflects proportion of phenotypic variation due to genetic values that may include effects due to dominance and epistasis (H^2 value of 1 = complete genetic involvement, 0 = none)

Question 3

Is facial asymmetry caused by genetic or environemntal factors?

Answer 3

Mostly caused by environmental factors.

Question 4

What influences face shape and facial growth?

Answer 4

• Environmental and biological contributions
• Sex
• Shared genetics and associated medical conditions

Question 5

Which genes have been associated with craniofacial abnormalities?

Answer 5

• Face height: FREM1
• Face width: PAX1,3,7, MSX1, PTCH3, NOG
• Eye depth: PAX3
• Vertical nose height: PRDM16
• Nasal prominence: PRDM16, SOX9
• Forehead: TBX15, THADA

Question 6

Describe missense mutations associated with craniofacial abnormalities.

Answer 6

• Point mutation where single nucleotide change results in a codon that codes for a different amino acid
• E.g. Waardenburg syndrome (PAX3 gene)

Question 7

Describe nonsense mutations associated with craniofacial abnormalities.

Answer 7

• Sense codon changed to chain-terminating codon
• E.g. Cleft lip and palate (SATB2)
• E.g. Scaphocephaly and micrognathia (KAT6A)

Question 8

Describe insertion mutations associated with craniofacial abnormalities.

Answer 8

• Pierre Robin syndrome

Question 9

Describe deletion mutations associated with craniofacial abnormalities.

Answer 9

• Van der Woude syndrome (deletion of chromosome 1q)

Question 10

Describe duplication mutations associated with craniofacial abnormalities.

Answer 10

• Down’s syndrome (e.g. 3 copies of chromosome 21)

Question 11

What is epigenetics?

Answer 11

Where environmental factors, e.g. toxins, influence gene function, either through methylation, histone modification or chromatin remodelling.

Question 12

What is pleiotropy?

Answer 12

Where gene variants which influence facial morphology also have effects on other phenotypic traits e.g. cardiovascular, endocrine, respiratory, GI system

Question 13

What are the major gender differences in facial development?

Answer 13

• Men tend to have a prominent nose, mouth and chin area

- Women tend to have rounder faces with more prominent eyes and cheeks

Question 14

How can asthma affect facial features?

Answer 14

• Shorter mid facial distance

- Wider inter alar distance

Question 15

How can sleep breathing disorders affect facial features?

Answer 15

• Increased face height
• Decreased nose width
• Decreased nose prominence
• Retrognathic mandbile

Question 16

How much of the total face height does the lower face occupy?

Answer 16

48%

Question 17

What is the remodelling explanation for the changing facial morphology due to growth?

Answer 17

Bone remodelling during growth changes the facial profile.

Bone deposition and resorption in various areas allows the face to project downwards and forwards.

Question 18

What is the suture theory for the changing facial morphology due to growth?

Answer 18

Disproven theory.

• Idea that sutures push bone apart, but sutures are passive, it is the development of the brain which pushes bone outwards
• However, early fusion of skull bones can cause distortion of the crnaium

Question 19

What is the nasal septum theory for the changing facial morphology due to growth?

Answer 19

Idea that the nasal cartilage causes forward protrusion of the nose and anterior part of the maxilla.
Several genes associated with the nasal septum.

Question 20

What is the condylar/mandibular growth rotations explanation for the changing facial morphology due to growth?

Answer 20

• Bjork and Skeiller identified 4 stable landmarks in the mandible
• They found that when they superimposed serial radiographs on these structures the mandible went through a growth rotation

Question 21

What is the functional matrix theory for the changing facial morphology due to growth?

Answer 21

Craniofacial growth is dependent on the demands of related functional matrices.

Question 22

What is the dento-alveolar compensation explanation for the changing facial morphology due to growth?

Answer 22

• Teeth compensate for skeletal discrepancies

- E.g. Small mandible means mandibular incisors grow high to meet the upper incisors

Question 23

What is the servosystem explanation for the changing facial morphology due to growth?

Answer 23

Craniofacial growth is dependent on growth signals, hormonal factors and feedback mechanisms. Multi-factorial.

Question 24

What is the part-counterpart relationship explanation for the changing facial morphology due to growth?

Answer 24

States that the bones of the craniofacial complex work together to produce a balanced and symmetrical growth.

Question 25

Does the face grow after puberty?

Answer 25

Yes

Question 26

Do growth hormones and testosterone affect craniofacial growth?

Answer 26

Yes, if administered during childhood they will accelerate statural and craniofacial growth.

Question 27

Do funtional appliances affect craniofacial growth?

Answer 27

Current research suggests that funcitonal appliances have no or minimal effect on the growth of the facial skeleton.