Enamel Tissue: Histologic Structure and Clinical Considerations Flashcards
what is the hardest mineralized tissue in the body
Enamel
what part of the tooth is not a connective tissue
Enamel
what is enamel derived from
from specialized epithelial cells from the ectoderm
what is the cell that makes enamel
Ameloblasts
what stage doe enamel lack that other mineralized tissues have
No unmineralized or preenamel formation stage
stages of enamel growth
Immature stage (partially mineralized) Mature stage (fully mineralized)
when is enamel formed
The second mineralized fissue in the tooth(after dentin)
what organic substance is not found in enamel that other mineralized tissue has
No collagen fibers
what is enamel tissue
a composite biological mineral with apatite crystals ariented in a complex 3d pattern
what is the most clinically significant part of the tooth
Enamel
what is enamel equal to hardness in
Mild steel
what is the mohs mineral hardness of apatite
5
when is Enamel brittle
when no dentin support
why is enamel translucent
Thinness
Hue of enamel depends on
location level
surface conditions of enamel
Attraction to stain substances
Age changes
what is needed for enamel to maintain its integrity
Wet environment
what is the form of tooth wear that is normal
Attrition
what causes attrition
Slow wearing away of tooth substance under the stress of mastication
what causes abrasion
Non-normal wear
what causes erosion
Chemicals (see acid erosion)
what are the pathways in the enamel for diffusion of small molecules and water
Micro porosity
what on the pore walls can lead to carious lesions
Electrochemical effects
when mineral is returned to the molecular strucutre via saliva
Remineralization
when does cavitation occure
when demineralization exceedes remineralization
what makes up enamel by wieght
96% Inorganic
1% organic
3% water
what is the inorganic substance of enamel
Hydroxyappatie crystals
what separates Hydroxyapetite in enamel vs other mineralized tissue
Larger more impurities (fluoride, carbonate)
what makes up 90% of the organic substance of enamel
Amelogenin
roll of Amelogenin for enamel
Seed protein for normal mineralization
how are enamel proteins arranged
Lace like pattern throughout the volume of enamel, closely associated with the surface of the cystals
how is water distributed in the enamel
Micropores between crystals and proteins
what does the water form around the crystals in enamel
Hydration shell
importance of hydration shell in enamel
Ruote of F ions
Ca and P ion for remineralization
Whitening
Acidophic organisms (caries)
what happens to enamel as you age
Wears slowly (attrition) darkens Composition changes reduced porosity systemic age changes
ageing reduces porosity which means
Reduced susceptibility to cares
what does the composition of enamel change as you age
Fluoride increases
where is the DEJ scalloped
Coronally
why is the DEJ scalloped coronally
Adaptation to occlusial forces
where is the DEJ smooth
Cervical non-load bearing areas
what is the most common CEJ relationship
Cementum overlaps enamel
what is the second most common CEJ relationship
Cementum meets enamel
what is the least commone CEJ relationship
Does not meet enamel
how consistent are CEJ relationships
Can vary even on different sides of the tooth
What are the GRowth lines of enamel
Strae of Retzius
the numerous small transverse ridges on the exposed surface of enamel
Perikymata
what forms the PErikyma
The striae of Retzius form enamel grooves on the surfaces and the Perikyma form as the ridges
how long does it take for each perikyma to form
8-10 days
The structural unit of enamel
Enamel rods
size of enamel rods
diamter of 5-6 micrometers
length of 2.5 mm(wavey)
where are Hydroxyapatite crystals are more dense in the enamel rods
the center or core of the rod
what direction do enamel rodscrystals run
PArallel to the long axis of the rod
How Many Ameloblasts form each anemal rod
1 ameloblast
what is the outer surface of an enamel rod
Enamel sheath
density of crystal in the enamel sheath
less dense (more organic substance)
what direction do enamel crystals run in the enamel sheath
different directions
what makes up most of the organic material of the enamel sheath
Amelin
what is the stuff between sheaths of the enamel rods
Interrod substance
density of the cystals of the interrod substance
More dense that the sheath
what direction do the crystals of the interrod substance rub
In a different direction that those of the sheath
how many ameloblasts secrete interrod substance
2+
why are enamel rods wavy
For strength yo
why are enamel rods segnemented
Sometime the ameloblasts take a rest and therefore stop creating an interrod stritations
what direction do enamel rods lie in relation to the dentin
at a right angle
where do Enamel lamella extend
Extend in varying depths from the surface of enamel
what are Enamel Lamella filled with
Enamel protein
ORganic debris from the oral cavity
Clinical significance of enamel lamella
Can cary acidophhilic microorganisms for caries
Stain substances
where do Enamel tufts extend from
From the DEJ for a short distance into enamel
what is found in an enamel tuft
A greater concentration of enamel protein
Clinical significance of an enamel tuft
Contribute to the spread of caries at the DEJ
where do enamel spindles extend from
From the dentin to cross the DEJ into the enamel for a short distance
Clinical significance of an enamel spindle
Contribute to the spread of caries along the DEJ
How do enamel spindles form
Odontoblast shoot processes between the ameloblasts.
When dentin and enamel formation begins the process become embedded in the new enamel
what are Hunter-schreager brnads
Alternating dark and light bands of varying width, originating at the DEJ border and pass outward ending at some distance from the outer enamel surface
What causes the Hunter-Schreager bands to form
Different direction of enamel rods in adjacent layers
why do enamel rods change directions to form Hunter-Schreager bands
Minimize the risk of cleavage in the axial direction due to mastication
what forms the ameloblasts
Inner epithelial cells of the enamel organ
what forms the Odontoblasts
peripheral cells of the dnetal papilla
where does Odontoblast and ameloblast differentiation occur first
At the more coronla site of the future DEJ
what type of cell are ameloblasts
Columnar epithelail cells
what are Enamel pearls
Ectopic enamel formation
if tetracyclin stain is near the roots when was the antibiotic taken
Later in the pregnancy
what causes mulberry molars
Congenital syphilis
