OE L37 Facial Growth Flashcards
Which facial processes are present by week 5 of gestation?
- 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)
What 2 statistical analsyes are used to estimate the degree of variation in a phenotypic trait in a population?
- 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)
Is facial asymmetry caused by genetic or environemntal factors?
Mostly caused by environmental factors.
What influences face shape and facial growth?
- Environmental and biological contributions
- Sex
- Shared genetics and associated medical conditions
Which genes have been associated with craniofacial abnormalities?
- 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
Describe missense mutations associated with craniofacial abnormalities.
- Point mutation where single nucleotide change results in a codon that codes for a different amino acid
- E.g. Waardenburg syndrome (PAX3 gene)
Describe nonsense mutations associated with craniofacial abnormalities.
- Sense codon changed to chain-terminating codon
- E.g. Cleft lip and palate (SATB2)
- E.g. Scaphocephaly and micrognathia (KAT6A)
Describe insertion mutations associated with craniofacial abnormalities.
- Pierre Robin syndrome
Describe deletion mutations associated with craniofacial abnormalities.
- Van der Woude syndrome (deletion of chromosome 1q)
Describe duplication mutations associated with craniofacial abnormalities.
- Down’s syndrome (e.g. 3 copies of chromosome 21)
What is epigenetics?
Where environmental factors, e.g. toxins, influence gene function, either through methylation, histone modification or chromatin remodelling.
What is pleiotropy?
Where gene variants which influence facial morphology also have effects on other phenotypic traits e.g. cardiovascular, endocrine, respiratory, GI system
What are the major gender differences in facial development?
- Men tend to have a prominent nose, mouth and chin area
- Women tend to have rounder faces with more prominent eyes and cheeks
How can asthma affect facial features?
- Shorter mid facial distance
- Wider inter alar distance
How can sleep breathing disorders affect facial features?
- Increased face height
- Decreased nose width
- Decreased nose prominence
- Retrognathic mandbile
How much of the total face height does the lower face occupy?
48%
What is the remodelling explanation for the changing facial morphology due to growth?
Bone remodelling during growth changes the facial profile.
Bone deposition and resorption in various areas allows the face to project downwards and forwards.
What is the suture theory for the changing facial morphology due to growth?
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
What is the nasal septum theory for the changing facial morphology due to growth?
Idea that the nasal cartilage causes forward protrusion of the nose and anterior part of the maxilla.
Several genes associated with the nasal septum.
What is the condylar/mandibular growth rotations explanation for the changing facial morphology due to growth?
- 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
What is the functional matrix theory for the changing facial morphology due to growth?
Craniofacial growth is dependent on the demands of related functional matrices.
What is the dento-alveolar compensation explanation for the changing facial morphology due to growth?
- Teeth compensate for skeletal discrepancies
- E.g. Small mandible means mandibular incisors grow high to meet the upper incisors
What is the servosystem explanation for the changing facial morphology due to growth?
Craniofacial growth is dependent on growth signals, hormonal factors and feedback mechanisms. Multi-factorial.
What is the part-counterpart relationship explanation for the changing facial morphology due to growth?
States that the bones of the craniofacial complex work together to produce a balanced and symmetrical growth.
Does the face grow after puberty?
Yes
Do growth hormones and testosterone affect craniofacial growth?
Yes, if administered during childhood they will accelerate statural and craniofacial growth.
Do funtional appliances affect craniofacial growth?
Current research suggests that funcitonal appliances have no or minimal effect on the growth of the facial skeleton.
