Enamel I+II Flashcards
enamel is derived from :
ectoderm
collagen content of enamel :
0%
what structural feature sets enamel apart from other collagen based mineralized tissue ?
the fact that it has no collagen and has extremely long enamel crystals
why is it not possible to replace enamel biologically once the tooth erupts ?
because all the ameoloblasts (enamel secreting cells ) are dead by then
what is the natural color of enamel ?
bluish white tint . yellow at cervical rim
describe the thickness of enamel :
varies from 2.5mm over functional edge to feather edge at cervical line
enamel is relatively impermeable
what is the composition of enamel by weight ? (end of post secratory maturation phase)
96% inorganic hydroxyapatite crystals
1% organic protein
3% water
the enamel matrix is 1% Organic protein . what is that 1% composed of
90%amelogenins–> regulate growth in thickness and width of crystals
and 10% amelogenins –> (ameloblastin and enamelin)–> promote and guide the formation of the enamel crystals
the 10% non amelogenin composition of the organic matrix of enamel is composed of :
ameloblastin
enamelin
what is the composition of the inorganic matrix of enamel ?
-calcium phosphate (hydroxyapatite) crystals
-various ions like magnesium , potassium , sodium , and fluoride(if present during enamel formation they may be incorporated into the crystal structure )
studying enamel histologically requires the use of a ____ section
ground section
describe the structure of enamel crystals :
they are extremely long and hexagonal shaped they are also carbonated
they also measure 60-70 nm in width and 25-30nm in thickness
describe the structure and orientation of enamel rod
cylindrical shaped structure made up of crystals oriented in the same direction as the rod .
what is the inter-rod?
region surrounding rod to form key hole appearance. this region contain enamel crystals which are oriented in a different direction than those making up the rod
the basic structure of enamel consists of ___
rod (head)
inter rod (tail)
during the secretory phase , enamel is made up of ___
30% mineral
65% protein
5% water
in which stage does enamel have no rods
secretory stage
describe what happens in the secretory stage :
after deposition of mantel dentine , inner enamel epithelium differentiates into ameloblasts ( develops tomes process–> saw toothed appearance which allows secretion of enamel ) . ameloblasts then move backwards , secreting the initial enamel layer which is not fully mineralized
what happens during the post secretory transitional stage of amelogenesis ?
-25% of ameloblasts die
-tomes process disappears
-change of ameloblast morphology
what happens during the maturation stage of amelogenesis ?
-before tooth erupts enamel hardens by action of smooth ended(removal of polypeptide fragments and water) and ruffle ended ameloblasts (allow calcium ions to enter )
-ameloblasts assume a shorter cuboidal shape
-reduced enamel epithelium forms (stratum intermedium , stellate reticulum ,outer enamel epithelium )
what happens to the reduced enamel epithelium as the tooth passes through the oral epithelium ?
the part located incisally is destroyed while the part found more cervically interacts with the oral epithelium to form junctional epithelium .
what happens to the reduced enamel epithelium located more cervically ?
interacts with oral epithelium —> forming junctional epithelium
what are the 2 general families of proteinases involved in extracellular processing and degradation of enamel proteins ?
KLK4
MMP20
they cut amelogenin into small pieces to preform different functions in enamel formation
