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Title: Oral Biology Year 1 1.0
Description: This Oral Biology study note is suitable for dental student who are needing a Year 1 study note. It covers topic 1 to topic 4 with pictures and detailed information. It is suitable for those who are preparing for dental school's examination.
Description: This Oral Biology study note is suitable for dental student who are needing a Year 1 study note. It covers topic 1 to topic 4 with pictures and detailed information. It is suitable for those who are preparing for dental school's examination.
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Topic 1: The Origin of Ectomesenchyme & Its Role in Tooth Development
1
...
Embryonic stage
Phases
Processes
Pre• Fertilized egg
implantation
↓
Phase
(After rapid divisions)
morula
↓
(After fluid accumulation & cells realign)
blastocyst
• Blastocyst: consists of trophoblast &
embryoblast
Embryonic
Phase
(2nd week)
•
•
Formation of bilaminar germ disc (day 8
of gestation)
2-layered disc:
o Epiblast layer: faces amniotic
cavity & columnar cells
o Hypoblast layer: faces yolk sac &
cuboidal cells
Pictures
Fetal period
3rd – 9th month
Embryo to fetus
Maturation to
existing structures
Embryonic
Phase
(3rd week)
•
•
•
Formation of
notochord
•
•
•
Gastrulation: Formation of trilaminar
germ disc
3-layered germ layers:
o Ectoderm
o Mesoderm
o Endoderm
Processes:
Increased proliferation of cells &
thickening in midline area
↓
Primitive streak (ends as primitive
node / pit)
↓
Forms 3 germ layers & notochord
↓
Epiblast cells migrate & displace
hypoblast cells of yolk sac: forms
endoderm
↓
Epiblast cells pack space between
ectoderm & endoderm: forms
mesoderm
↓
Remaining epiblast cells: forms
ectoderm
Beneath primitive streak
Epiblast cells enter node & migrate
between ectoderm & endoderm
(midline) towards cranial region: forms
notochord
Notochord:
basis for axial skeleton & CNS
development & intervertebral disc
Neurulation
•
•
•
•
•
•
•
Differentiate ectoderm to form brain &
spinal cord
Thicken ectodermal layer
↓
Neural plate
↓
(further growth & thickening +
deepen & invaginate centrally)
Neural groove
↓
(deepens further + forms raised
margin)
Neural fold
↓
Neural folds fuse
↓
A neural tube separates from
ectoderm
↓
Ectodermal cells at crest of neural
tube gets separated from
epithelium:
Neural crest cells
3 mesodermal aggregates:
o Paraxial mesoderm (break into
Somatomeres & Somites)
o Intermediate mesoderm
o Lateral plate mesoderm
Neural crest cells fx:
Migrate & differentiate within
developing embryo
NCC migrate to 1st branchial arch below
oral epithelium:
Known as ectomesenchyme
Ectomesenchyme cells develop into:
Dentine, pulp & tooth supporting
structures (cementum, PDL & alveolar
bone)
Mesenchyme =
Embryonic CT & it is derived from
mesoderm
•
•
Embryonic
Phase
(4th week)
•
•
•
•
•
•
•
Teacher Collins syndrome:
Failure of full facial development bc
NCC fail to migrate properly to facial
region
Depletion of NCC
↓
Prevents proper tooth development
Embryonic folding into embryo
Folding occurs at:
o Cephalic end
o Caudal end
o Lateral side
Head fold (at cephalic end):
Forms primitive stomodeum
Results of folding:
Positions of embryonic layers take on a
more recognizable placement for future
development of embryo
After folding:
o Ectoderm encapsulates embryo
↓
Forms surface epithelium
o Mesoderm fills in area between
ectoderm & endoderm except 2
embryonic membranes:
buccopharyngeal membrane &
cloacal membrane)
Stomodeum = Primitive mouth
Originates as a depressed area of
surface ectoderm & foregut endoderm
In early embryo:
Stomodeum is sealed off from primitive
gut by buccopharyngeal membrane,
separating stomodeum from primitive
pharynx & foregut
↓
th
4 week of prenatal:
Buccopharyngeal membrane
disintegrate + stomodeum is connected
to foregut
↓
Primitive mouth is deepens & enlarged
↓
Future development:
Stomodeum gives rise to oral cavity
Topic 2: Tooth Development
1
...
Genes
Questions
What controls initiation of
tooth development?
What controls position &
no
...
3
...
Hypothetical models explaining how different tooth shapes are determined
Theories
Field model
Descriptions
• Genes reside within ectomesenchyme in distinct but graded fields for
each tooth family
• Each fields express differing patterning homeobox genes
• Genes in oral epithelium provides signalling
• Coded pattern in ectomesenchyme might be expressed following an
epithelial signal
Clone model
• Each tooth class is derived from a clone of ectomesenchymal cells
programme by epithelium
• Ectomesenchyme assumes dominant role in crown formation
• For tooth initiation: both theories can be combined
5
...
d
...
d
...
d
Title: Oral Biology Year 1 1.0
Description: This Oral Biology study note is suitable for dental student who are needing a Year 1 study note. It covers topic 1 to topic 4 with pictures and detailed information. It is suitable for those who are preparing for dental school's examination.
Description: This Oral Biology study note is suitable for dental student who are needing a Year 1 study note. It covers topic 1 to topic 4 with pictures and detailed information. It is suitable for those who are preparing for dental school's examination.