Amelogenesis Flashcards
Enamel tissue is a composite ___ mineral with ___ crystals oriented in a complex three dimensional pattern.
biological; apatite
T/F. Amelogenesis occurs before dentinogenesis.
False, amelogenesis occurs AFTER dentinogenesis
During what stage of odontogenesis does amelogenesis occur?
the crown stage
Explain reciprocal induction as it relates to amelogenesis.
Dentin must be present for enamel to be formed and ameloblast must be present in order for dentinogenesis to occur.
In ___ ___, epithelial cells from the enamel ___ and ___ cells from the dental papilla interact.
reciprocal induction, organ; mesenchymal
T/F. Unlike the other 3 mineralized tissues, enamel does not have an unmineralized preenamel phase.
True.
What is the first step of amelogenesis?
secretion of an inmature or partially mineralized (30% inorganic and 70% organic and water) enamel
During the second step of amelogenesis, there is a influx of additional mineral conincident with the removal of organic material and water. Therefore, this phase is know as the ___ phase.
maturative
What three things are needed for enamel formation (and the other 3 mineralized tissues)?
ameloblast
alkaline phosphatase
rich blood supply
Where do ameloblast differentiate?
in the inner cells of the enamel organ
Where is alkaline phosphatase located?
in the stratum intermedium layer of the enamel organ
where is the rich blood supply located?
in the dental follicle part of the tooth germ
During amelogenesis, cells at the ___ most area of the ___ layer of the enamel organ are the first to differentiate into ameloblasts. This process continues apically toward the ___ ___ of the enamel organ.
coronal; inner; cervical loop
What are the two phases of the presecretory stage of amelogenesis?
- morphogenetic
2. histodifferentiation
During the ___ stage of tooth development, the shape of the crown is determined at the enamel ___. This represents the ___ phase of amelogenesis.
bell; knot; morphogenetic
In the morphogenetic phase, there is a ___ or ___ layer seen between the inner cells of the enamel organ and the peripheral cells of the dental papilla.
clear; acellular
During the ___ phase of amelogenesis, the inner enamel ___ cells differentiate into tall ___ ameloblasts. Their nuclei shift proximally toward the ___ ___.
histodifferentiation; epithelial; columnar; striatum intermedium
What cells is found at the distal end of the ameloblast?
odontoblasts
T/F. At the coronal area of the tooth germ, the ameloblasts and odontoblast interact limiting the clear layer that exists more inferiorly toward the cervical loop. This layer will disppear as the amelogenesis continues apically.
True.
What are the six phases of the secretory phase?
- inner immediately mineralized secretion
- interrod substance secretion
- rod secretion
- maturation phase
- outer immediately minteralized secretion
- final ameloblast secretion
The inner ___ phase is an ___-___ layer of inner ___ or strucureless enamel that immediately ___ upon secretion.
mineralized; ultra-thin; rodless; mineralized
What type of dentin is adjacent to the inner rodless enamel layer?
mantle layer of dentin
What happens during the interrod substance phase?
the distal end of the ameloblast changes from a smooth to a configuration termed Tomes’ process
___ processes of adjacent ameloblast secrete the ___ ___ that encircles this process.
Tomes’; interrod substance
What is the space that initally occupied by Tomes’ process termed?
Tomes’ pit
Interrod substance is partially mineralized. What is its composition?
70% organic and water
30% inorganic
What surrounds the wall of Tomes’ pits?
interrod substance
T/F. Tomes’ process stays as the ameloblast moves toward the future enamel surface. The processes turn into rods.
False, Tomes’ process moves out as the ameloblast move toward the future enamel surface. As the process withdraws, it secretes a partially mineralized rod into the pit.
What indicates that the ameloblasts are in the rod secretory phase?
the presence of Tomes’ pocesses and partially mineralized enamel
During the maturation phase, what happens to the distal end of the ameloblast?
it alternates between an even, smooth edge and an uneven, ruffled edge
What happens when the edge of the ameloblast is even?
They are resorbing or removing organic material and water
What happens when the edge of the ameloblast is uneven or ruffled?
They are secreting mineral salts (inorganic) int to the partially mineralized zone
When is maturation complete?
When the inorganic materail reaches 96%, organic reaches 1% and water becomes 3%.
During the alteration of the ameloblasts border during the maturation process, ___ ___ are no longer present.
Tomes’ processes
T/F. The inner, but not outer rodless enamel are mineralized immediately and not secreted by Tomes’ processes.
False, BOTH the inner and outer rodless enamel are mineralized immediately and not secreted by Tomes’ processes.
Why does the inner and outer rodless enamel not contain enamel rods?
they are not secreted by Tomes’ processes, which lay down the enamel rod
T/F. The outer mineralized phase is the last mineralized secretion of the ameloblasts but not its final secretion.
True.
What is secreted during the final ameloblast secretion phase?
the basal lamina
Is the basal lamina, mineralized or unmineralized?
unmineralized
What is the one phase of the postsecretory stage?
protection phase
What is the role of the reduced enamel epithelium?
remnant of the enamel organ and protector of enamel until tooth enters oral cavity
What forms the reduced enamel epithelium?
When the four cell layers of the enamel organ come together
What does the reduced enamel epithelium become during the emergence of the tooth from the oral cavity?
the junctional epithelium
How is the reduced enamel epithelium attached to the enamel surface?
by the basal lamina, the final secretion of the ameloblast
How long is the maturation phase, for each permanent tooth, from initiation to completion?
5 years
Immature enamel has a ___% organic and water and ___% inorganic make-up.
70; 30
What is the timeline for initial mineralization and completed mineralization for all primary teeth?
initial mineralization: 15 - 19 week IU
completed mineralization: 2 - 11 months PN
What is the timeline for initial mineralization and completed mineralization for all permanent teeth?
initial mineralization: birth - 9 years
completed mineralization: 5 - 14 years
