Odontogenesis Flashcards
what happens during initiation?
underlying ectomesenchymal cell induce the overlying ectoderm (oval epithelium) to proliferate, forming a localized thickening at the site of each tooth celled the dental lamina
when does initiation occur?
starts at 6 weeks in utero
when does the bud stage occur?
starts at 8 weeks in utero
what happens during the cap stage?
the enamel organ begins to form, which is composed of a single layer of cells at the convex region (outer enamel epithelium, OEE) and the concave region (inner enamel epithelium, IEE). Between the two epithelial layers is loosely arranged stellate reticulum. Some cells of the stellate reticulum become densely packed near the IEE and are known as the enamel knot. The dental papilla is composed of condensed ectomesenchymal cells located within the concavity of the enamel organ. The dental follicle (dental sac) is the capsule-like encasing of mesenchyme surrounding the enamel organ.
tooth germ
enamel organ, dental papilla, dental follicle
when does the bell stage happen?
it starts at week 11 in utero
what happens during the bell stage?
morphodifferentiation and histodifferentiation of specific cells. the enamel organ is now well-defined and composed of the following: OEE (outermost layer of the enamel organ), IEE (innermost layer of the enamel organ), stratum intermedium (forms directly lateral to the IEE), stellate reticulum (becomes more sparsely arranged due to increased proteoglycan synthesis). the enamel knot disappear. The cells in the IEE become tall and columnar (now called preameloblasts) first. The cells of the dental papilla closest to the IEE become tall and columnar (now called preodontoblasts) after the preameloblasts are formed. The dental lamina disintegrates.
When does the appositional stage start?
At week 14 in utero
What happens during the appositional stage?
the reduced enamel epithelium (REE) forms when the stellate reticulum collapses, merging OEE with IEE. Odontoblasts secrete dentin matrix first. Ameloblasts secrete enamel matrix after dentin is first formed. Root formation begins. The dental papilla forms the pulp tissue. The dental follicle forms cementum, alveolar bone, and PDL.
what happens during root formation?
Begins at the cervical loop (where the OEE and IEE join) after enamel is first formed. As the cervical loop elongates, HERS is formed, which shapes the roots and ultimately surrounds the majority of the dental papilla. As radicular dentin is formed HERS begins to disintegrate, leaving behind patches of epithelial cells called epithelial rests of Malassez. The collapse of HERS enables ectomesenchymal cells of dental follicle to contact dentin and differentiate into the formative cells of periodontium: cementoblasts, osteoblasts, and fibroblasts.
When does the cap stage occur?
It starts at week 9 in utero.
What happens during eruption?
As the tooth erupts into the oral cavity, the reduced enamel epithelium (REE) fuses with the oral epithelium, forming the dentogingival junction (epithelial attachment). This later migrates apically along the tooth into its normal position in which the most apical cells of the JE are at the CEJ. A delay in the apical migration is known as delayed (altered) passive eruption.
What is the chronological order of enamel and dentin formation?
- differentiation of ameloblasts.
- differentiation of odontoblasts.
- deposition of dentin matrix.
- deposition of enamel matrix.
what happens after IEE cells differentiate into preameloblasts?
differentiation of preodontoblasts from mesenchymal cells of the dental papilla
What disintegrates following tooth formation?
dental lamina
ameloblasts
HERS
reduced enamel ep.
What is the precursor for ameloblasts?
inner enamel ep.
what is the precursor for HERS?
outer enamel ep.
What is the precursor for reduced enamel ep?
IEE, OEE, stratum intermedium, stellate reticulum
What is the precursor for junctional ep?
reduced enamel ep.
What is the precursor for root formation?
HERS
what is the precursor for pulp?
dental papilla
what is the precursor for dentin
dental papilla
what is the precursor for alveolar bone?
osteoclasts
what is the precursor for cementum?
cementoblasts
what is the precursor for the periodontal ligament
fibroblasts
What does the dental sac differentiate into?
cementoblasts
fibroblasts
osteoclasts
what is the precursor for dental sac and dental papilla?
ectomesenchyme
what forms the dental lamina?
oral epithelium
original precursor cells of enamel
epithelial cells
original precursor cells of dentin, pulp, cementum
ectomesenchymal cells
ectoderm
tissues covering the outside of the body / epidermis, hair, nails, etc
mesoderm
connective tissues / heart, muscle, blood cells, bone, dermis, etc
endoderm
tissues lining inside the body / lung, stomach, intestine, liver, etc
what forms from the neural crest
sensory ganglia
connective tissues of head and neck (bone, cartilage, muscles, tooth, etc)
enamel organ
(aka dental organ) proliferation of epithelial cells
dental papilla
condensation of ectomesenchymal cells
dental sac
(aka dental follicle) capsule like condesation of ectomesenchymal cells
future tooth product of enamel organ
enamel
future tooth product of dental papilla
dentin
pulp
future tooth product of dental sac
cementum
periodontal ligament
alveolar bone
connective tissues of gingiva
tooth germ
enamel organ + dental papilla + dental follicle
purpose of inner enamel ep
generates enamel
purpose of the cervical loop
root formation
purpose of the stella reticulum
protect inner enamel ep.
purpose of enamel knot
location of cusp
when are the enamel knot, enamel cord, and enamel navel present
during the cap stage
differentiation of ameloblasts
older, taller polarized (cusp tip)
younger, shorter, unpolarized (root)
dentin =
collagen + hydroxyapaptite crystals
enamel =
amelogenin +hydroxapatite crystals
amelogenin
resorbable –> allows further packing of crystals –> inorganic component, hardness
promote calcificaiton
alkaline phosphatase (supply phosphate) pyrophosphatase (hydrolyze phosphate)
inhibit calcification
pyrophosphate
matrix vesicles
contain essential components
contain seed of crystal
released from odontoblasts to collagen matrix
what reverses calcification
acid
sharpey’s fiber
collagen fibers of periodontal ligament embedded in cementum
cementoblasts
secrete cementoid (matrix) and mineralize cementum on root dentin
enervation in cap stage
axons enter the dental follicle
enervation in bell stage
axons enter dental papilla following the initiation of dentinogenesis
remnants of odontogenic epithelial cells
epithelial rests of Malassez
remnant of HERS
located in periodontal ligament
hardest tissue found in the oral cavity
enamel
the dental lamina
is derived from ectoderm
collagen is not the major component of matrix of
enamel
what is present in bell stage
OEE, IEE, stellate reticulum, stellate intermedium
cementogenesis starts prior to
formation of apical foramen
odontoblasts are characterized by
possessing long cytoplasmic processes which lie within dentinal tubules
pulp chamber of a mature tooth contains
blood vessels and nerves
