Amelogenesis Flashcards
what is enamel tissue?
composite biological mineral with apatite crystals oriented in a complex three dimensional pattern
what is amelogenesis?
occurs after dentinogenesis during the crown stage of odontogenesis
what is reciprocal induction?
what is the example in this instance?
dentin must be present for enamel to be formed, but ameloblasts must be present in order for dentinogenesis to occur.
between epithelial cells of the enamel organ and mesenchymal cells of the dental papilla
what is unique about enamel unlike the other 3 mineralized tissue?
enamel does not have an unmineralized preenamel phase
2 step enamel process
first step: secretion of an immature or partially mienralized (30% inorganic and 70% organic and water) enamel
second step: significant influx of additional mineral coincident with the removal of organic material and water
enamel formation requirements
specialized cell: ameloblast: differentiated inner cells of the enamel organ
alkaline phosphatase: located in the stratum intermedium layer of enamel organ
rich blood supply: located in the dental follicle part of tooth germ
life cycle of inner epithelial cell of enamel organ
cells at the coronal most area of the inner layer of the enamel organ are the first to differentiate into ameloblasts. process continues apical toward the cervical loop of the enamel organ
phases of presecretory stage
morphogenetic phase
histodifferentiation phase
phases of secretory stage
1.inner immediately mineralized secretion:ultra thin inner rodless enamel layer
2. interrod substance secretion (initially immature or partially mineralized
3. rod secretion (initially immature or partially mineralized)
4. maturation phase (interrod substance and rods become mature (fully mineralized)
a. removal of organic substance until 1% is reached and removal of water until 3% is reached
B. influx of mineral salts (inorganic substance) until 96% is reached
5. outer immediately mineralized secretion: ultra thin outer rodless enamel layer
6. final ameloblast secretion phase. basal lamina: non-mineralized
postsecretory stage phases
- protective phase- reduced enamel epithelium: former 4 epithelial layers of enamel organ
morphogenetic phase
clear or acellular layer is seen between the inner cells of the enamel organ and peripheral cells of dental papilla
histodifferentiation phase
area of inner cells where differentiation begins- proceeds cervically. along acellular layer of tooth germ are forming odontoblasts and ameloblasts- columnar epthelial cells
inner mineralized phase- ultra thin layer
inner rodless or structureless enamel: immediately mineralized upon secretion. distal end of ameloblast is smooth or even here
interrod substance secretion
distal end of the ameloblast changes from smooth to tome’s process
tomes processes of adjacent ameloblast secrete interrod substance that encircles tomes processes. space originally occupied by tomes process is termed tomes pit
interrod substance is partially mineralized: 70% organic and water and 30% inorganic
walls of pits are surrounded by interrod substance of enamel
rod secretion stage
tomes process moves out of the pit as ameloblast moves toward future enamel surface. as the process withdraws it secretes a partially minerallized rod into the pit- continues until the length of immature interrod substance and rod is reached
maturation phase
distal end of ameloblast altermnates between an even or smooth edge or uneven or ruffled edge
when the edge is even- ameloblast is resorbing or removing organic material and water
when uneven or ruffled- ameloblast is secreting mineral salts (inorganic) into the partially mineralized
maturation is complete when percentage of inorganic material reaches 96% organic reaches 1% and water becomes 4%
outer mineralized phase: outer rodless enamel
like the inner, the outer rodless enamel is mineralized immediately is not secreted by tomes processes bc it does not contain enamel rods
final mineralized secretion of ameloblast**
final ameloblast secretion stage (basal lamina)
final secretion of ameloblasts non- mineralized structure
proctective phase
4 cell layers of enamel organ comes together to form the “reduced enamel epithelium” the protective layer of the enamel that becomes the junctional epithelium during emergence of tooth into oral cavity
reduced enamel epithelium is attached to the enamel surface by a basal lamina
timeline of initial mineralization of all permanent teeth
birth to 9 years
timeline of completed mineralization of all permanent teeth
5 to 14 years
