Facial Growth Flashcards
1
Q
Why is facial growth important?
A
- Size, shape and position of underlying jaws determines position of teeth and therefore malocclusion
2
Q
Why is the study of facial growth important to orthodontists?
A
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
3
Q
What are the two phases of life in utero?
A
Embryonic - 1-8weeks
Foetal - 8 weeks to term
4
Q
When can cranio-facial abnormalities form?
A
- Very early on in pregnancy as all the limbs and organs inc face have formed within first two months
5
Q
What time frame is the embryo most sensitive with respect to deformities?
A
- 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%
6
Q
When do the neural folds fuse?
A
- Fuse to form neural tube
- Towards end of week 3
- Failure to fuse will lead to spina bifida
7
Q
What does the neural tube develop into?
A
- Develop into brain and spinal cord
- Failure to develop will lead to anencephaly
8
Q
What is anencephaly?
A
- Cerebral hemispheres and cranial vault absent
9
Q
What do neural crest cells do?
A
- Undergo extensive migration within developing embryo
- Differentiate into many cell types e.g. spinal and autonomic ganglia, Schwann cells, adrenal medulla, meninges of brain
10
Q
What does the neural crest derived ectomesenchyme do?
A
- Contribute to branchial arch cartilage, bone and connective tissue proper
- Also dental tissues like pulp, dentine, cementum and periodontal ligament
11
Q
When does the formation of the face occur?
A
- During first eight weeks after fertilisation
- Environmental factors may lead to sig malformations in this time
12
Q
How are defects in the face related to the brain?
A
- Defects of face particularly in midline closely related to defects in anterior parts of brain
13
Q
What causes severe facial deformities?
A
- Most of face forms from migrating neural crest cells in fronto-nasal process or branchial arches
- Interference with this causes deformities
14
Q
What can lead to cleft formation?
A
- Failure of fusion between various facial processes or between palatine processes
15
Q
How can cleft lip and alveolus occur independently of cleft palate?
A
- Upper lip and anterior part of palate have different embryological origins from posterior palate
- Fuse at different times
16
Q
When are the facial processes fused?
A
- Weeks 5-7
17
Q
What two parts are the skull divided into?
A
Neurocranium -forms protective case around brain
Viscerocranium - skeleton of face
18
Q
What can the neurocranium be divided into?
A
- Flat bones of vault
- Develop intramembranously and endochondral elements of base of skull
19
Q
What are the intramembranous bones?
A
- Vault of skull
- Maxilla
- Most of mandible
20
Q
What happens during bone formation of the intramembranous
A
- 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
21
Q
What do the cartilages that make the base of the skull undergo?
A
- Endochondral ossification from multiple centres
- Starts with basi-occiput at 10-12 weeks
22
Q
At birth where do cartilaginous growth centres remain?
A
- Remain between sphenoid and occipital bones and nasal septum
23
Q
When does intramembranous ossification of vault occur?
A
- Third month
24
Q
When does the growth of the skull stop?
A
- Continues until 7th year
- Some sutures remain open until adulthood
25
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
26
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
27
What units is the mandible made up of?
- Condylar unit
- Angular unit
- Coronoid unit
- Alveolar unit
28
What does the condylar unit form?
- Forms articulation and contains largest secondary formation
29
Why does angular unit form?
- Forms in response to lateral pterygoid and masseter muscles
30
Why does coronoid unit form?
- Forms in response to temporalis muscle development (muscular processes)
31
Why does alveolar unit form?
- Only forms if teeth are developing
32
Why does body of mandible form?
- In response to inferior dental nerve
33
What are the 3 main sites of secondary cartilage formation in mandible?
- Condylar cartilage
- Coronoid cartilage
- Symphyseal
- Appear between 12 and 14 weeks
34
When does the coronoid cartilage disappear?
- Disappears long before birth
35
When does the sympheseal disappear?
- Just after birth
36
How long does growth of condylar cartilage continue for?
- 20years of age
37
At birth how does the mandible present and when does this fuse?
- At birth in two halves
- Midline symphysis fuses few months after
38
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
39
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
40
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
41
What is an example of teratogenic agents that can cause secondary abnormality?
Infection - rubella virus
Chemical - thalidomide
Chemical - lithium
42
What is an example of trauma that can cause secondary abnormality?
- Amniotic bands
43
What is the definition of deformation?
- Abnormalities that occur due to outer mechanical effects on existing structures
44
What is the definition of Agenesia?
- Absence of organ due to failed development during embryonic period
45
What is the definition of sequence?
- Single factor results in numerous secondary effects (Pierre robin)
46
What is the definition of syndrome?
- Group of abnormalities that can be traced to a common origin
47
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
48
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
49
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
50
How does Foetal alcohol syndrome present?
- Microcephaly (small head)
- Short palpebral fissures
- Short nose
- Long upper lip with deficient philtrum
- Small midface
- Small mandible
51
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)
52
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
53
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
54
How common is Treacher Collins (mandibulofacial dysostosis)?
- 1:10,000 live births
55
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
56
How common is cleft lip and/or palate?
- 1:700 live births
- 70% sporadic
- Males > females for cleft lip and opposite for palate
57
When does a cleft lip and palate occur in the womb?
Cleft lip = day 28-38
Cleft palate = 42-55
58
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
59
What are the dental features of cleft lip and palate?
- Impacted Teeth
- Crowding
- Hypodontia
- Supernumeraries
- Hypoplastic teeth
- Caries
60
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
61
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
62
What are the dental features of Crouzon's?
- Class III malocclusion
- Narrow spaced teeth
63
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
64
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)
65
What is hypertelorism?
- Abnormally large distance between eyes
66
What is exopthalmos?
- Bulging or protruding of eyeball/s
