Facial Growth I 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
Why is the study of facial growth important to orthodontists
It provides insight into the growth of the face
Allows us to understand development of facial anomalies
To measure changes in growth and tx using cephalometry
Why is insight into the growth of the face important
predict changes
utilize growth to correct malocclusion
time our ortho and surgery
What are the 2 phases in utero
embryonic
foetal
When does the embryonic stage occur
1-8 weeks
When does the foetal stage occur
8 weeks to term
What forms within the first two months
all of the limbs, organs including the face have formed within the first 2 months and embryo has a characteristic human form
What can the external environment influence cause
cranio facial abnormalities very early on in pregnancy
What occurs at stage 1
its around 0.1-0.15mm in size and its an egg
What occurs in stage 2
0.1-0.2mm
the egg keeps dividing into more and more cells
up to about 8-16 cells and they float down the fallopian tubes
called the morula
What occurs in stage 3
same size made of up to 62 cells in total cells divide to make a cyst/blastocyst there is an inner cell mass before pre-implantation the egg hatches and loses its zone halucida and starts to get first of germ layers
What has happened by stage 6
there is a germ disc made up of ectoderm and inside is the endoderm and you also have the primitive node and streak
the ectoderm has a third layer called mesoderm and they form everything
about 4 weeks in you get somites which are blocks of material at the back and get grooves forming first which form neural tube
What is neural crest cell migration important for
development of the face
What does the neural folds fuse to form
neural tube, towards the end of week 3
failure to fuse will lead to spina bifida
What does the neural tube develop into
brain and spinal cord
What does failure of neural tube development had to
anecephaly
in which cerebral hemispheres and cranial vault are absent
During the folding of the neural plate, what cells develop
neural crest cells develop from the ectoderm along the edge of the groove
What is the importance of neural crest cells
they undergo extensive migration within the developing embryo and ultimately differentiate into many cell types e.g spinal and autonomic ganglia etc
What are neural crest cells derived from
ectomesencyhme
What do the the ectomesenchyme contribute to
branchial arch cartilage
bone
connective tissue proper
dentalm tissues
By stage 12 what has formed
beginning of pharyngeal arches
maxillary process of first arch and mandibular process too
By stage 13 what has formed
fourth pharyngeal arch
What happens by stage 15
has folded over
When does formation of the face occur
first 8 weeks after fertilization
What are defects of the face linked to
defects of the face, particularly in the midline, may be closely related to defects of the anterior parts of the brain
What does most of the face form from
migrating neural crest cells
either in the fronto-nasal process or the branchial arches
interference with this migration can lead to severe facial abnormalities
What does failure of fusion between the various facial processes/palatine processes result in
cleft formation
Why can cleft lip and alveolus occur independently of cleft palate
upper lip and anterior part of palate have different embryological origins from the posterior palate and they fuse at different times
At week 4 what forms
migrating neural crest cells form the frontonasal processes and laterally the branchial arches
At week 5-7 what is seen in the facial processes
extension and fusion of the facial processes
What can the skull be divided into
neuro and viscerocranium
What is the neurocranium
forms a protective case around the brain
What is the viscerocranium
forms the skeleton of the face
What can the neurocranium be divided into
flat bones of the vault which develop intramembranously
endochondreal elements of the base of the skull
What happens in intrammebranous bone formation
bone is deposited directly 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 progressively radiate from the primary ossification centre to the periphery
progressive bone formation results in fusion of adjacent bony centres
What happens in endochondral bone formation
bones are preceded by a hyaline cartilage ‘model’
forms the base of the skull
several centers of ossification which eventually fuse
How does the base of the skull grow and form
a series of cartilages form the base of the skull
these undergo endochondral ossification from multiple centers starting with the base-occiput at 10-12 weeks
at birth, cartilaginous growth centers remain between the sphenoid and occipital bones and in the nasal septum
When does the intramembranous ossification of the vault of the skull commence
in third month in several centers
Describe how the intramembranous ossification of the vault of the skull forms fontanelles
the fusion is incomplete at birth leaving widening known as fontanelles to allow flexibility in the skull during birth
When does the anterior and posterior fontanelle close
A - 2 years
P - 1 year
How does growth occur at the fibrous sutures of the vault
in response to intracranial pressure
When does growth of the skull continue until
seventh year
some of the sutures remain open until adulthood
What are the embryonic facial cartilages and what is their relevance
maxilla and mandible form intramembranously but develop adjacent to pre-existing cartilaginous skeletons - nasal capsule and Meckel’s cartilage (6 wks)
How does the mandible develop
as several units all responding to different growth stimuli
What are the different mandibular units
condylar unit
angular unit
coronoid unit
alveolar unit
What does the condylar unit form
the articulation
contains the larges secondary cartilage formation
What does the angular unit form in response to
LP and masseter muscles
What does the coronoid unit respond to
temporalis muscle development (muscular processes)
What does the alveolar unit formation depend on
development of teeth
What does the body of the mandible form in response to
IDN
What are the 3 main sites of secondary cartilage formation in the mandible
condylar cartilage
coronoid cartilage
symphyseal end of each half of the bony mandible
When do the cartilages appear in the mandible
12-14 weeks IU
When do the mandibular cartilages disappear
condylar - before birth
symphesal - just after birth
When does growth at condylar cartilage stop
20 YO
What are the two halves of the mandible fused by
midline symphysis
fuses few months after
When does ossification of the face and skull commence
7-8 weeks
What is a primary abnormality
defect in structure of an organ or part of an organ that can be traced back to an anomaly in development
e.g spina bifida, cleft lip, CHD
What are secondary abnormalities
interruption of the normal development of an organ that can be traced back to other influences e.g teratogenic agents, trauma, amniotic bands
What are teratogenic agents
infection e.g rubella
chemical e.g thalidomide
chemical e.g lithium
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 embryonic period
What is sequence
single factor results in numerous secondary effects e.g pierre robin
What is a syndrome
group of anomalies that can be traced back to a common origin
What are facial syndromes where maxillary hypoplasia is seen
Apert's syndrome croutons syndrome oral-facial digital syndrome binder's syndrome achondroplasia down's syndrome cleidocranial dystosis foetal alcohol syndrome cleft lip/palate
What are conditions where there is mandibular problems
treacher colin's syndrome pierre robin stickler's syndrome van der wood syndrome turners syndrome hemifacial microsomia
What are environmental facial syndromes arising from early problems with facial developments (1-8 wks)
foetal alcohol syndrome
What are multifactorial facial syndromes arising from early problems with facial developments (1-8 wks)
hemifacial microsomia
treacher colins syndrome (mandibulofacial dysostosis)
clefts of lip and palate
What do those with foetal alcohol syndrome habve
microcephaly
mild mental retardation
What are the typical facies having of those with foetal alcohol syndrome
short palpebral fissures short nose long upper lip with deficient philtrum small midface small mandible
What is femifacial microsomes
unilateral mandibular hypoplasia, zygomatic arch hypoplasia, high arched palate, malformed pinna
but clonal spectrum (ear tags only, to complete lack of condyle, coronoid and ramus)
normal intellect, deafness cardiac and renal problems
What is the theoretical cause of hemifacial microsomia
neural crest cell migration
What is the cause of treacher collins
deformity of 1st and 2nd branchial arches
day 19-28
What are features of treacher collins
anti-mongoloid slant palperable fissure coloboma of lower lid outer1/3 hypoplastic or missing zygomatic arches hypoplastic mandible with antimonial notch deformed pinna, conductive deafness
What is the genetic etiology of cleft lip /palate
monozygotic twins
syndromes
familial patterns
What is the environment etiology of cleft lip and palate
social deprivation smoking alcohol anti epileptics multivitamins reduce
What are dental features of cleft lip
impacted teeth crowding hypodontia super numeraries hypoplasitc teeth caries
Why does cleft palate not have dental features
it does not cross over the alveolus, cleft lip does
What is achondroplasia
problem with endochondrial ossification
defects in long bones, short limbs (dwarfism)
defects in base of the skull, restrusive middle third of face, frontal bossing, depressed nasal bridge
What is cruouzon’s
premature closure of cranial sutures (esp coronal and lamdoid)
What is the features of Crouzon’s
proptosis (shallow orbits) orbital dystopia mild hypertelorism recursion and vertical shortening of the midface prominent nose class III malocclusion narrow spaced teeth
What’s Apert’s
premature closure of almost all cranial sutures
What are features of Apert’s
exopthalmos hypertolarism maxillary hypoplasia class III occlusion, AOB, narrow spaced teeth parrot's beak nose syndactyly of finger and toes
