Facial Growth 1 Flashcards
Why is facial growth important?
The size, shape and position of the underlying jaws determines the position of the teeth and therefore the malocclusion
What are the phases of life in utero?
Embryonic - 1-8 weeks
Foetal - 8 weeks to term
Describe neural crest cells
During folding of neural plate, cells develop from the ectoderm called neural crest cells
These migrate and differentiate into different cell types
What happens if the neural tube fails to fuse or form?
If fails to fuse - spina bifida
If fails to form - anencephaly
When does formation of the face occur?
First eight weeks after fertilisation
What causes cleft formation?
Failure of fusion between facial processes
When do the third and fourth pharyngeal arches develop?
Third and fourth - 5th week
Describe intramembranous bone formation
Bone is deposited into primitive mesenchymal tissue
Intramembranous bones include the vault of the skull, the maxilla and most of the mandible
Needle-like bone spicules form which radiate from the primary ossification centres to the periphery
Describe endochondral bone formation
Bones are preceded by hyaline cartilage
Forms the base of the skull
Several centres of ossification which eventually fuse
How does the base of the skull develop?
Series of cartilages forms the base of the skull
These undergo endochondral ossification starting at 10-12 weeks
At birth cartilaginous growth centres remain
How is the vault of the skull formed?
Intramembranous ossification starts in the third month in several centres
Fusion is incomplete at birth leaving fontanelles to allow flexibility in the skull
Growth occurs at fibrous sutures in response to intracranial pressure
Growth of the skull continues until the seventh year
What are the embryonic facial cartilages?
The maxilla and mandible develop adjacent to pre-existing cartilaginous skeletons - the nasal capsule and Meckel’s cartilage
What are the different mandibular processes and what stimulates their developments?
Condylar unit - forms articulation
Coronoid unit - lateral pterygoid and masseter
Angular unit - temporalis
Alveolar unit - if teeth are developing
Body - IAN
What are the main sites of secondary cartilage formation in the mandible?
Condylar cartilage
Coronoid cartilage
Symphyseal
When does ossification of the face and skull commence?
7-8 weeks
What is primary abnormality?
Defect in the structure of an organ or part of an organ that can be traced back to an anomaly in it’s development
Eg - spina bifida, cleft lip
What is a secondary abnormality?
Interruption of the normal development of an organ that can be traced back to other influences
Eg - infection (rubella), trauma - amniotic bands
What is a deformation?
Anomalies that occur due to outer mechanical effects on existing structures
What is agenesia?
Absence of an organ due to failed development during the embryonic period
What is a sequence?
Single factor results in numerous secondary effects
Eg - Pierre-Robin
What is a syndrome?
A group of anomalies that can be traced to a common origin
Eg - Trisomy 21 in Down’s syndome
Give examples of maxillary facial syndromes
Down’s syndrome
Cleft lip/palate
Achondroplasia
Give examples of facial syndromes affecting the mandible
Treacher Collin’s syndrome
Pierre-Robin
Stickler’s syndrome
Give some features of foetal alcohol syndrome
Small head
Short nose
Small mandible
Mild mental retardation
