Facial Growth Flashcards
Why is facial growth important?
- Size, shape and position of underlying jaws determines position of teeth and therefore malocclusion
Why is the study of facial growth important to orthodontists?
Insight into growth of face so can;
- Predict changes
- Utilise growth to correct malocclusion
- Time our orthodontics and surgery
- Understand development of facial anomalies
- Measure changes in growth and treatment using cephalometry
What are the two phases of life in utero?
Embryonic - 1-8weeks
Foetal - 8 weeks to term
When can cranio-facial abnormalities form?
- Very early on in pregnancy as all the limbs and organs inc face have formed within first two months
What time frame is the embryo most sensitive with respect to deformities?
- 10% within first 4 weeks leads to miscarriages
- Drops to 1% within 8 weeks (foetal period)
- By end of embryonic period (8 weeks) neural tube defects drop from 2.5% to 0.1%
When do the neural folds fuse?
- Fuse to form neural tube
- Towards end of week 3
- Failure to fuse will lead to spina bifida
What does the neural tube develop into?
- Develop into brain and spinal cord
- Failure to develop will lead to anencephaly
What is anencephaly?
- Cerebral hemispheres and cranial vault absent
What do neural crest cells do?
- Undergo extensive migration within developing embryo
- Differentiate into many cell types e.g. spinal and autonomic ganglia, Schwann cells, adrenal medulla, meninges of brain
What does the neural crest derived ectomesenchyme do?
- Contribute to branchial arch cartilage, bone and connective tissue proper
- Also dental tissues like pulp, dentine, cementum and periodontal ligament
When does the formation of the face occur?
- During first eight weeks after fertilisation
- Environmental factors may lead to sig malformations in this time
How are defects in the face related to the brain?
- Defects of face particularly in midline closely related to defects in anterior parts of brain
What causes severe facial deformities?
- Most of face forms from migrating neural crest cells in fronto-nasal process or branchial arches
- Interference with this causes deformities
What can lead to cleft formation?
- Failure of fusion between various facial processes or between palatine processes
How can cleft lip and alveolus occur independently of cleft palate?
- Upper lip and anterior part of palate have different embryological origins from posterior palate
- Fuse at different times
When are the facial processes fused?
- Weeks 5-7
What two parts are the skull divided into?
Neurocranium -forms protective case around brain
Viscerocranium - skeleton of face
What can the neurocranium be divided into?
- Flat bones of vault
- Develop intramembranously and endochondral elements of base of skull
What are the intramembranous bones?
- Vault of skull
- Maxilla
- Most of mandible
What happens during bone formation of the intramembranous
- Bone deposited into primitive mesenchymal tissue
- Needle-like bone spicules form
- They radiate from primary ossification centres to periphery
- Progressive bone formation results in fusion of adjacent bony centres
What do the cartilages that make the base of the skull undergo?
- Endochondral ossification from multiple centres
- Starts with basi-occiput at 10-12 weeks
At birth where do cartilaginous growth centres remain?
- Remain between sphenoid and occipital bones and nasal septum
When does intramembranous ossification of vault occur?
- Third month
When does the growth of the skull stop?
- Continues until 7th year
- Some sutures remain open until adulthood
When do the fontanelles close and why?
- Fusion incomplete at birth which leaves fontanelles to allow flexibility in skull during birth
- Anterior fontanelle closes 2 years
- Posterior closes 1 year
- Growth occurs at fibrous sutures in response to intracranial pressure
When does maxilla and mandible form and what structures do they develop adjacent to?
- Form at 6 weeks intramembranously
- Develop next to nasal capsule and Meckel’s cartilage
