Amelogenesis

Question 1

what is enamel tissue?

Answer 1

composite biological mineral with apatite crystals oriented in a complex three dimensional pattern

Question 2

what is amelogenesis?

Answer 2

occurs after dentinogenesis during the crown stage of odontogenesis

Question 3

what is reciprocal induction?

what is the example in this instance?

Answer 3

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

Question 4

what is unique about enamel unlike the other 3 mineralized tissue?

Answer 4

enamel does not have an unmineralized preenamel phase

Question 5

2 step enamel process

Answer 5

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

Question 6

enamel formation requirements

Answer 6

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

Question 7

life cycle of inner epithelial cell of enamel organ

Answer 7

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

Question 8

phases of presecretory stage

Answer 8

morphogenetic phase

histodifferentiation phase

Question 9

phases of secretory stage

Answer 9

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

Question 10

postsecretory stage phases

Answer 10

1. protective phase- reduced enamel epithelium: former 4 epithelial layers of enamel organ

Question 11

morphogenetic phase

Answer 11

clear or acellular layer is seen between the inner cells of the enamel organ and peripheral cells of dental papilla

Question 12

histodifferentiation phase

Answer 12

area of inner cells where differentiation begins- proceeds cervically. along acellular layer of tooth germ are forming odontoblasts and ameloblasts- columnar epthelial cells

Question 13

inner mineralized phase- ultra thin layer

Answer 13

inner rodless or structureless enamel: immediately mineralized upon secretion. distal end of ameloblast is smooth or even here

Question 14

interrod substance secretion

Answer 14

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

Question 15

rod secretion stage

Answer 15

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

Question 16

maturation phase

Answer 16

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%

Question 17

outer mineralized phase: outer rodless enamel

Answer 17

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**

Question 18

final ameloblast secretion stage (basal lamina)

Answer 18

final secretion of ameloblasts non- mineralized structure

Question 19

proctective phase

Answer 19

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

Question 20

timeline of initial mineralization of all permanent teeth

Answer 20

birth to 9 years

Question 21

timeline of completed mineralization of all permanent teeth

Answer 21

5 to 14 years