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Flashcards in Enamel (Lecture 1) Deck (44)
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1

Reconstructed early oral cavity

At about ____, the primary epithelial band forms in presumptive upper and lower jaws at future dental arch. • The band thickens by ____ proliferation perpendicular to the surface.

5 weeks
epithelial

2

____: the process whereby a tooth develops from a few cells in the primitive oral cavity to an erupted tooth with crown and root

odontogenesis

3

____: enamel formation

amelogenesis

4

Enamel: a unique ____ tissue that covers the crown of the tooth

epithelial

5

Cap stage of tooth development

The bud splits into a ____ structure due to proliferation.
• The epithelium forms the ____.
• ____ cells aggregate beneath the enamel organ, to form the ____. •
The ____ forms.

cap-like
enamel organ
ectomesenchymal
dental papilla
dental follicle (sac)

6

Timing of developmental stages

Primary epithelial band:
Bud stage:
Cap:
Bell:
Crown:

5 weeks, initiation
6-8, in-growth
8-12, morphogenesis
12-16, differentiation
18, mineral forms

7

The terms (bud, cap, bell, crown) refer to the ____ in the dental organ.

morphological changes

8

Bell Stage
• During bell stage, the undersurface of the enamel organ ____, and ____ begins.
• Epithelial cells assume different appearances in preparation for formation of the ____

deepens
cellular histo-differentiation
hard tissue

9

Bell Stage: Epithelial cell differentiation

4 epithelial cell types during bell stage are
• Outer dental epithelium (EDE) – ____
• Stellate reticulum (SR) – ____
• Stratum intermedium (SI) - ____
• Inner dental epithelium (IDE) - ____

cuboidal cells
star-shaped cells
several flattened layers
short columnar

10

During ____, inner dental epithelium folds according to tooth type

bell stage

11

Ameloblasts and Odontoblasts

• Precursors (____) stop proliferation
• Epithelial and ____ signal to each other using secreted proteins as instructions for differentiation
• Cells elongate and change organelle components for secretory function
• Begin to secrete ____

inner dental epithelial and ectomesenchymal cells
ectomesenchymal cells
extracellular matrix (ECM)

12

Late Bell/Early crown stage

During bell stage, ____ folds according to tooth type
The ____ reduces in thickness at locations of ____
Differentiation continues down the slopes of ____

inner dental epithelium
stellate reticulum
mineral formation
developing crown

13

After first dentin is secreted and mineralizes, ameloblasts secrete first enamel toward the ____
• Ameloblasts then retreat ____, forming ____, which creates structure in enamel
• Are in contact with ____, which contains alkaline phosphatase
• Ameloblasts & SI are considered a ____

basement membrane
peripherally
tomes' process
stratum intermedium (SI)
functional unit

14

Enamel

____ tissue in the body
• Product of ____
• Extracellular matrix (secreted material) that contains ____

hardest
epithelial cells
no collagen

15

As ameloblasts change in morphology, their ____ change as well. Each ameloblast goes through all stages, but at different times.
• ____ ameloblasts produce most of the enamel matrix
• ____ is a short stage where secretion slows, and many ameloblasts die by apoptosis. Remaining cells shorten and excess organelles are digested

functions
secretory
transition

16

____: Maturative ameloblasts secrete a basal lamina on the enamel surface and attach to it by ____
• Maturative ameloblasts remove proteins from developing enamel & replace organic material with ____
• ____ ameloblasts continue to modify enamel composition.

maturation
hemidesmosomes
calcium and phosphate
protective

17

Maturation stage ameloblasts

Exist in ____ morphologies
• ____ ameloblasts permit
removal of peptides and water
• ____ ameloblasts transport calcium and phosphate to the enamel
• Cells cycling between stages are undergoing ____

two
smooth-ended
ruffle-ended
modulation

18

Reduced Dental Epithelium

• As mineralized dentin and enamel form, the ____ compresses, and ____ is no longer visible
• The remaining layers of the enamel organ form the ____

dental organ
stellate reticulum
reduced dental epithelium

19

Secretory Stage:

Amelogenins (____ of ECM)
-Amelogenins are small ____ proteins with conserved amino acid sequence
-Amelogenins assemble; they regulate ____
-Amelogenins are ____ Genes on X and Y chromosomes Proteolysis produces ____;
____ produces many mRNAs that encode amelogenin proteins

90%
hydrophobic
crystal growth and enamel thickness
heterogeneous
peptides
alternative splicing

20

Secretory Stage: Non-amelogenins (____ of ECM)
-____ – acidic; found at ____; involved in crystal nucleation
-____ – (amelin, sheathlin)
found in rod sheath
interaction between cell and ECM
expressed in secretory, maturation, by HERS
-____ – protease that processes enamel proteins during ____

10%
enamelin
DEJ
ameloblastin
MMP20 (matrix metalloproteinase 20)
secretory stage

21

Stages of Amelogenesis

____ Stage
• Ameloblasts shorten and organelles rearrange • Some ameloblasts die - apoptosis

____ Stage
• ____ is secreted and degrades most remaining enamel proteins
• Protein is removed from developing enamel; calcium and phosphate are added

transition
maturation
KLK4 protease

22

Enamel Composition

Secretion
Protein:
Mineral:
Water:

Maturation
Protein:
Mineral:
Water:

66%
29%
5%

4%
95%
1%

23

Enamel structure: Hydroxyapatite

• Formula is ____
• A unit cell is the ____ repeating unit
• Unit cells stack to form the repeating unit of the ____
• ____ can substitute for OH-

Ca10(PO4)6(OH)2
smallest
lattice
fluoride

24

The ____ is a space created by groups of crystals that orient at ____.
• Small amounts of protein remain in the rod sheath (e.g., ____).
• The rod sheath separates ____.

rod sheath
angles
sheathlin
enamel rods (prisms)

25

Rod sheaths

Before ____ extends, enamel rods are not formed.
• Secretory granules containing enamel proteins are released from the ____.
• The membrane of the granule fuses with the cell membrane, and the contents are released outside the ameloblast by ____

Tomes' process
ameloblast
exocytosis

26

Rod sheaths

Crystals in rod and interrod enamel are similar in ____ and ____ but diverge in ____

structure
composition
orientation

27

Striae of Retzius and lamellae

• ____ are daily increments of enamel secretion.
• ____ are prominent striations or developmental lines in enamel.
• ____ end at the enamel surface in shallow furrows called ____.
• ____ are faults in the enamel mineral, probably due to ____.

cross-striations
striae of retzius
striae
perikymata
lamellae
incomplete mineralization

28

Enamel Tufts

Enamel tufts extend from the ____ into enamel. They are ____ structures that contain the protein ____

DEJ
feather-like
tuftelin

29

Enamel Spindles

Enamel spindles are formed when ends of ____ are embedded in enamel during ____

odontoblast processes
development

30

Physical characteristics of enamel

• ____ due to the high mineral content.
• Also ____, but the underlying ____ provides resilient support
• ____ and varies in thickness, from 2.5 mm at the tip of cusp to very thin at the ____

very hard
brittle
dentin
translucent
cervical line