Facial Growth Flashcards
How does the mandible develop
Intra-membranous ossification
What are the two phases and durations of life in utero?
Embryonic = 1-8 weeks
Foetal = 8 weeks to term
When are deformities most likely to happen?
In the embryonic period.
External environmental influences can cause craniofacial abnormalities in this period as facial structure has typically already formed in the first 8 weeks
How does an embryo begin to form up to the neural tube stage?
- Egg released
- Fertilised by sperm in fallopian tube
- Cells in the morula (surrounded by zona pellucida) proliferates to form blastocyst
- Inner cell mass within blastocyst is what forms the human, rest forms the placenta
- Zona pellucida breaks and egg leaves, now have the germ layers begin forming - ectoderm, mesoderm, endoderm
- Neural plate gives rise to neural fold and groove as the ectoderm elevate and connect, eventually forming the neural tube and crest
How does the neural tube form? What does failure to fuse cause?
Forms by neural folds migrating together to form the tube. These migrating Neural crest cells eventually come together until the groove forms a tube.
Failure leads to spina bifida
What does the neural tube develop into in a human? What does incorrect neural tube development cause?
Forms brain and spinal cord
Failure to develop will lead to anencephaly (absence of cerebral hemispheres and cranial vault)
What forms the pharyngeal arches?
Ectomesenchyme
Cranial neural crest cells that are migrating
What cells form the majority of the face?
Migrating Neural crest cells
Why can cleft lip and alveolus form independently of cleft palate and vice versa?
Upper lip and anterior palate have different embryological origin to the posterior palate
What are the 5 protruberances in the development of the face, caused by cranial neural crest cells? What happens to them?
Frontonasal prominence
2 x maxillary prominence
2 x mandibular prominence
As development carries on, they move forward and towards the midline, and form the upper and lower jaws
What is intramembranous ossification? Where does this occur?
Bone is directly deposited from centres of ossification
These bone spicules radiate from ossification centres to the periphery
This fuses adjacent ossification centres
Neurocranium, maxilla and most of mandible
What is endochindrial ossification? Where does this occur?
Hyaline cartilage framework is systematically replaced by bone.
Long bones and base of skull where there are foramina
What is unique about the intramembranous ossification of the maxilla and mandible?
Although they form via intramembranous ossification, they form adjacent to a cartilaginous framework typical of endochondrial ossification
Maxilla = nasal capsule
Mandible = meckels cartilage
What would occur if one is born with no masseter or medial pterygoid?
The angle of the mandible will not form on that side as there is no reason to be there.
Same apples for the coronoid area if one is born without temporalis
The body of the mandible forms due to the interdental nerve
What are the secondary cartilages that form? Implications for one?
Condylar cartilage
Coronoid cartilage
Symphyseal cartilage
Condylar cartilage grows until around 20 yrs old, abnormal growth on one side can cause asymmetry
When does ossification of the face and skull begin?
7-8 weeks
What is a primary abnormality?
Defect in structure of an organ that can be traced back to an anomaly in development
E.g. spina bifida
What is hemifacial microsomia? Causes? Complications?
Multi-factorial, so idiopathic cause
Spectrum disorder
3D progressive facial asymmetry
Unilateral mandibular, zygomatic arch, ear hypoplasia
No intellectual impairment, but cardiac and renal problems along with deafness
What is crouzons? Craniofacial dysostosis
Premature closure of cranial sutures - especially coronal and lamboid
Leads to shallow orbits so the eyes look bulging
Retrusion and vertical shortening of the mid face
Prominent nose
Class 3 occlusion
How does the mandible grow?
Grows downwards and outwards
Growth occurs at the condylar cartilage via bone remodelling with deposition mainly posteriorly and laterally
