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
What units is the mandible made up of?
- Condylar unit
- Angular unit
- Coronoid unit
- Alveolar unit
What does the condylar unit form?
- Forms articulation and contains largest secondary formation
Why does angular unit form?
- Forms in response to lateral pterygoid and masseter muscles
Why does coronoid unit form?
- Forms in response to temporalis muscle development (muscular processes)
Why does alveolar unit form?
- Only forms if teeth are developing
Why does body of mandible form?
- In response to inferior dental nerve
What are the 3 main sites of secondary cartilage formation in mandible?
- Condylar cartilage
- Coronoid cartilage
- Symphyseal
- Appear between 12 and 14 weeks
When does the coronoid cartilage disappear?
- Disappears long before birth
When does the sympheseal disappear?
- Just after birth
How long does growth of condylar cartilage continue for?
- 20years of age
At birth how does the mandible present and when does this fuse?
- At birth in two halves
- Midline symphysis fuses few months after
What are the key bits of info for prenatal growth?
- Ossification of the face and skull commences at about 7-8 weeks.
- The neurocranium encases the brain and the viscerocranium forms the face.
- The vault of the skull is formed intramembranously.
- The base of skull forms by endochondral ossification.
- Both the maxilla and the mandible develop intramembranously but are
preceded by a cartilagenous facial skeleton. - Meckel’s cartilage precedes the mandible and the nasal capsule is the primary
skeleton of the upper face
What is the definition of primary abnormality?
- Defect in structure of an organ or part of an organ that can be traced back to an anomaly in its development
- E.g. spina bifida, cleft lip, CHD
What is secondary abnormality?
- Interruption of normal development of organ that can be traced back to other influences
- E.g. Teratogenic agents or trauma
- Congenital abnormality not necessarily inherited
What is an example of teratogenic agents that can cause secondary abnormality?
Infection - rubella virus
Chemical - thalidomide
Chemical - lithium
What is an example of trauma that can cause secondary abnormality?
- Amniotic bands
What is the definition of deformation?
- Abnormalities that occur due to outer mechanical effects on existing structures
What is the definition of Agenesia?
- Absence of organ due to failed development during embryonic period
What is the definition of sequence?
- Single factor results in numerous secondary effects (Pierre robin)
What is the definition of syndrome?
- Group of abnormalities that can be traced to a common origin
What are some conditions of maxillary hypoplasia?
- Apert’s Syndrome* (acrosyndactyly)
- Crouzon’s Syndrome* (craniofacial dysostosis)
- Oral-Facial Digital Syndrome*
- Binder’s Syndrome
- Achondroplasia
- Down’s Syndrome
- Cleidocranial dysostosis*
- Foetal Alcohol Syndrome
- Cleft lip/palate*
*Can be associated with clefts
What are some conditions affecting mandibular?
- Treacher Collin’s Syndrome* (mandibulofacial dysostosis)
- Pierre-Robin*
- Stickler’s Syndrome*
- Van der Woude Syndrome*
- Turner’s Syndrome
- Hemifacial Microsomia
*Can be associated with clefts
What are some facial syndromes that can arise in first 8 weeks after conception?
Environmental - Foetal alcohol syndrome
Genetic
Multifactorial
- Hemifacial microsomia
- Treacher collins syndrome (mandibulofacial dysostosis)
- Clefts of lip and palate
How does Foetal alcohol syndrome present?
- Microcephaly (small head)
- Short palpebral fissures
- Short nose
- Long upper lip with deficient philtrum
- Small midface
- Small mandible
How and when does foetal alcohol syndrome occur?
- Occurs in high maternal intake of alcohol
- Occurs in 1:750-1000 live births
- Microform present in 1:300 live births
- Occurs on day 17 (very early and mother may not even know she is expecting)
What is hemifacial microsomia?
- Unilateral mandibular hypoplasia
- Zygomatic arch hypoplasia
- High arched palate
- Malformed pinna
- 3D progressive facial asymmetry
- Normal intellect , deafness, cardiac and renal problems
What is Treacher Collins (mandibulofacial dysostosis)?
- Deformity of 1st and 2nd branchial arches (day 19-28)
- Anti-monogloid slant palpebral fissures
- Colomboma of lower lid outer 1/3rd
- Hypoplastic or missing zygomatic arches
- Hypoplastic mandible with antigonial notch
- Deformed pinna, lead to conductive deafness
How common is Treacher Collins (mandibulofacial dysostosis)?
- 1:10,000 live births
What is a cleft lip or palate?
- When structures that form the upper lip or palate fail to join together in womb
- Fusion of maxillary process and fused medial nasal elevation
How common is cleft lip and/or palate?
- 1:700 live births
- 70% sporadic
- Males > females for cleft lip and opposite for palate
When does a cleft lip and palate occur in the womb?
Cleft lip = day 28-38
Cleft palate = 42-55
What are the types of clefts lip and palate?
- Normal
- Unilateral cleft of lip extending into nose
- Unilateral cleft lip and alveolus
- Bilateral cleft lip and alveolus
- Isolated cleft palate
- Cleft palate and unilateral cleft lip
What are the dental features of cleft lip and palate?
- Impacted Teeth
- Crowding
- Hypodontia
- Supernumeraries
- Hypoplastic teeth
- Caries
What is Achondroplasia?
- Problem with endochondrial ossification
- Defects in long bones leading to short limbs = dwarfism in 70%
- Defects in base of skull, retrusive middle third of face, frontal bossing, depressed nasal bridge
What is Crouzon’s?
- AKA craniofacial dysostosis
- Premature closure of cranial suture (esp coronal and lambdoid)
- Proptosis (shallow orbits), orbital dystopia and mild hypertelorism
- Retrusion and vertical shortening of face
- Prominent nose
- Requires surgical intervention and distraction osteogenesis
What are the dental features of Crouzon’s?
- Class III malocclusion
- Narrow spaced teeth
What is Apert’s?
- AKA Acrosyndactyly
- Premature closure of all cranial sutures
- Exophthalmos, hypertelorism
- Maxillary hypoplasia
- Parrot’s beak nose
- Syndactyly of fingers and toes
- Conductive deafness
What are the dental features of Apert’s?
- Class III occlusion
- Anterior open bite (AOB)
- Narrow spaced teeth
- Narrow high arched palate (30% have cleft palate)
What is hypertelorism?
- Abnormally large distance between eyes
What is exopthalmos?
- Bulging or protruding of eyeball/s
