EX1; Enamel Tissue Flashcards
True or False
Enamel is the second hardest of the 4 mineralized tissues in the body
False; it IS THE hardest of the tissues
What is different about the ectodermal derived tissue that forms enamel
it is epithelium;
the other tissues of the tooth are connective tissue
What is different about the mineralization stages of enamel
it does not have an unmineralized or pre enamel formation stage
it has an immature (partially mineralized) and mature (fully mineralized)
Enamel is considered what because the ameloblast completes its enamel formative cycle once the correct thickness is achieved
finite
True or False
Enamel is the second mineralized tissue to appear
True; dentin is the first
Enamel is subject to what due to genetic and external factors (age changes, habits, smoking, etc.)
malformations
Enamel does not contain what compared to other tissues
enclosed cells; acellular, aneural, avascular, and alymphatic
*What is the definition of enamel
a composite biological mineral with apatite crystals oriented in a complex three dimensional pattern
What is apatite on the Mohs mineral hardness scale
5
What does enamel need to maintain its integrity
a wet environment
What forces is enamel subject to
attrition (normal)
abrasion
erosion
These are pathways for the diffusion of small molecules such as water and bactera
micropores (microporosity)
What is the inorganic, organic, and water weight of enamel
96% inorganic
1% organic
3% water
What is the principal mineral component of enamel
calcium hydroxyapatite (fluro exchanged when there is fluoride present)
What is the main protein (90%) composing the organic component of enamel
amelogenin
Enamel is the only tooth tissue that does not contain what
collagen fibers
How is the water distributed throughout enamel
via micropores between the crystals and proteins
What are the CEJ relationships
cementum overlaping enamel (most commong)
cementum meeting enamel
cementum does not touch enamel (least common)
What are the different configurations of the DEJ
scalloped
smooth
This DEJ configuration is better adapted for occlusal forces
scalloped; in the coronal area
This DEJ configuration is better for non-load bearing areas
smooth; in the cervical areas
These are growth lines found on enamel
lines of Retzius
These are ridges (wave-like) on the exposed surfaces of enamel centered between the lines of Retzius (grooves)
perikymata
This is the structural unit of enamel
enamel rods
Where are the HA crystals most dense in the enamel rod
in the center or core of the rod running parallel
What forms the enamel rods
ameloblast (one ameloblast = one rod)
This is the outer surface of the rod
enamel sheath
How are the HA crystals of the enamel sheath arranged
they are less dense (more organic %) and run in different directions
What substance is in the highest percentage of the organic material of the enamel sheath
amelin
This is located between the sheath of rods
interrod substance
How are the HA crystals arranged in the interred substance
crystals are more dense and run at different directions than the sheath
What create the interred substance
two or more ameloblasts
What causes the different optical properties of the structural components of enamel
density of crystals and the direction in relation to each other
What are the direction of the rods compared to the dentin
they are at a 90º angle
Ea\ch enamel rod is built up of segments separated by dark lines that give it a striated appearance, hence this name
interrod striations
These extend from varying depths of the SURFACE of ENAMEL and consist of longitudinally orientated defects filled with enamel protein or organic debris (ribbon like)
enamel lamella
What is the clinical significance of enamel lamella
access by acidophilic microorganisms (caries) and to stain substances
These project from the DEJ for a short distance into enamel and contain a greater concentration of enamel protein (tuftelin)
enamel tufts
What is the clinical significance of enamel tufts
contributes to the spread of caries at the DEJ
These extend from the DENTIN across the DEJ into the enamel for a short distance
enamel spindle
What is the clinical significance of enamel spindles
contributes to the spread of caries at the DEJ
What makes up the enamel spindles
odontoblast processes extending between ameloblast and when enamel begins to form, it become embedded in the enamel
What are the three hypomineralized enamel structures
enamel lamella
enamel tuft
enamel spindle
These are alternating dark and light bands of varying width which originate at the DEJ and pass outward ending some distance from the outer enamel surface
Hunter-Schreager bands
What causes Hunter-Shreager bands
different directions of enamel rods in adjacent layers
What is induced by the change of enamel rod direction
functional adaptation;
minimizing the risk of cleavage in the axial direction under mastication
Where does differentiation of the inner epithelial cells of the enamel organ into ameloblasts and of the peripheral cells into odontoblasts begin
on the coronal most site of the DEJ
