Enamel (Lecture 1) Flashcards
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
____: the process whereby a tooth develops from a few cells in the primitive oral cavity to an erupted tooth with crown and root
odontogenesis
____: enamel formation
amelogenesis
Enamel: a unique ____ tissue that covers the crown of the tooth
epithelial
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)
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
The terms (bud, cap, bell, crown) refer to the ____ in the dental organ.
morphological changes
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
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
During ____, inner dental epithelium folds according to tooth type
bell stage
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)
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
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
Enamel
____ tissue in the body
• Product of ____
• Extracellular matrix (secreted material) that contains ____
hardest
epithelial cells
no collagen
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
____: 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
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
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
- Ameloblasts develop from ____ and require communication with ____ (future odontoblasts) in order to differentiate.
- Ameloblasts change in shape and function during enamel development.
- The principle stages of enamel development are ____, ____ and ____.
inner dental epithelium ectomesenchyme cells secretion transition maturation
Summary
- Ameloblasts secrete a unique extracellular matrix containing enamel proteins (____, enamelin, ameloblastin and proteases (____ and ____).
- Ameloblasts secrete ____ and subsequently process and remove enamel proteins as the enamel ____.
- Ameloblasts also direct movement of ____ and ____ into developing enamel.
- Ameloblasts are lost before the tooth ____ into the oral cavity.
amelogenin MMP20 KLK4 first hardens calcium phosphate erupts
Summary
- Enamel is also influenced by environmental ____ and ____ during tooth development.
- Enamel is the ____ tissue in the body because of the high mineral amount and the ____ of mineral crystals.
- 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
