Enamel (Lecture 1) Flashcards by J L

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

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

odontogenesis

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____: enamel formation

amelogenesis

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

epithelial

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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)

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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

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

morphological changes

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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

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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

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During ____, inner dental epithelium folds according to tooth type

bell stage

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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)

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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

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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

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Enamel

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

hardest
epithelial cells
no collagen

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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

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____: 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

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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

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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

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

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

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

Enamel Composition

Secretion
Protein:
Mineral:
Water:

Maturation
Protein:
Mineral:
Water:

66%
29%
5%

4%
95%
1%

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

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)

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

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

structure composition orientation

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 ```

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

DEJ feather-like tuftelin

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

odontoblast processes | development

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 ```

Enamel Demineralization ``` • Three acid etching patterns. – Type I – ____. • Preferential removal of ____. – Type II. • Reverse of type I – ____ removed. – Type III – ____ • ____ pattern. ```

``` most common rods interrod enamel least frequent irregular and indiscriminate ```

Changes in enamel * During aging, enamel can erode as it is not ____ * When ____ is adsorbed onto the crystals, enamel becomes more resistant to ____, which helps resist caries. * Excess ____ interferes with enamel development, leading to ____

``` regenerated fluoride acid dissolution fluoride fluorosis ```

``` • Fluoride-induced defects. – Fluoride ions are incorporated into the ____, preventing caries. – Excess fluoride interferes with ____. – ____ results. – ____ enamel. – Chalk white or brown in color. – Very resistant to caries. – Tooth form is ____. ```

``` hydroxylapatite crystals amelogenesis fluorosis or mottled enamel hypomineralized normal ```

Summary 1. Ameloblasts develop from ____ and require communication with ____ (future odontoblasts) in order to differentiate. 2. Ameloblasts change in shape and function during enamel development. 3. The principle stages of enamel development are ____, ____ and ____.

``` inner dental epithelium ectomesenchyme cells secretion transition maturation ```

Summary 4. Ameloblasts secrete a unique extracellular matrix containing enamel proteins (____, enamelin, ameloblastin and proteases (____ and ____). 5. Ameloblasts secrete ____ and subsequently process and remove enamel proteins as the enamel ____. 6. Ameloblasts also direct movement of ____ and ____ into developing enamel. 7. Ameloblasts are lost before the tooth ____ into the oral cavity.

``` amelogenin MMP20 KLK4 first hardens calcium phosphate erupts ```

Summary 8. Enamel is also influenced by environmental ____ and ____ during tooth development. 9. Enamel is the ____ tissue in the body because of the high mineral amount and the ____ of mineral crystals. 10. Genetic mutations in genes encoding enamel proteins or proteases lead to the inherited enamel defect ____.

``` fluoride fever hardest orderly orientation amelogenesis imperfecta ```

Age Changes in Enamel • Attrition. – Enamel is ____. – Attrition of enamel may expose dentin. – Pits and fissures may be eliminated. • Color. – Darkness ____ w/age. – Thinning of enamel. – Extrinsic staining.

non-vital | increases

Age Changes in Enamel ``` • Permeability. – ____ with age. – ____ pore size between crystals; crystals ____ in size; • Water content. – ____ with age. – ____ pore size forces water out. ```

``` decreases decrease increase decrease decreasing ```

Age Changes in Enamel ``` • Nature of surface layer. – Changes due to ionic exchange with oral environment. – Fluoride ion most prevalent. • Topical application. • Brittleness - ____ w/age. ```

increases

``` Age Changes in Enamel • Decreased ____ of caries. – ____ Fluoride ion content. – Loss of ____ susceptible to caries. – Change in diet – less ____ consumed by adults. ```

incidence increased surface areas refined carbohydrates

Disturbances in Enamel Formation * ____ – amelogenesis imperfecta (AI). * Ameloblasts are very susceptible to changes in their environment. * Minor physiologic changes → structural changes visible only ____. * ____ insults → damage or death of ameloblasts with easily visible defects.

genetic dysplasias histologically severe

Disturbances in Enamel Formation • Febrile disease-induced defects. – ____ causes disturbance in enamel formation. – Enamel formed during this time period is ____. – Enamel formation returns to normal with ____.

fever malformed remission of fever

``` Disturbances in Enamel Formation • Tetracycline-induced defects. – Tetracycline antibiotics are incorporated into all ____ (enamel, dentin, cementum and bone). – ____ band of pigmentation. – Severity ____ to dose and duration. – Tooth form is ____. ```

mineralizing tissues brown, yellow, or gray proportional normal

emdogain = ____

shit