Lecture 5: Amelogenesis Flashcards
what is reciprocal induction?
the prerequisite that although dentin must be present for enamel to be formed, it is also true that ameloblasts must be present in order for dentinogenesis to occur
what are the two steps of creating the structurally identifying or majority part of enamel?
- secretion of immature or partially mineralized enamel (once the width is large enough the second step occurs)
- significant influx of additional mineral coincident with the removal of organic material and water (secretory and maturative phases)
three things that enamel formation needs
- ameloblasts (inner cells of enamel organ)
- alkaline phosphatase (stratum intermedium layer)
- rich blood supply (dental follicle)
which cells are the first to differentiate into ameloblasts?
cells at the coronal most area of the inner layer of the enamel organ
(process continues apical toward the cervical loop of the enamel organ)
what are the 3 main stages of amelogenesis?
- presecretory stage (morphogenetic)(histodifferentiation)
- secretory stage (6 phases)
- postsecretory stage (protective phase)
phase of amelogenesis in which a clear or acellular layer is seen between the inner cells of the enamel organ and peripheral cells of the dental papilla
morphogenetic phase [presecretory 1]
*ameloblasts elongate and touch the peripheral cells of dental papilla which induce odontoblasts
phase of amelogenesis in which there is a lack of clear layer above odontoblasts (both odontoblasts and ameloblasts can be seen here)
histodifferentiation phase [presecretory 2]
phase of amelogenesis in which there is inner rodless ultra-thin layer enamel. immediately mineralized upon secretion. continuous layer completely mineralized. enamel rods do NOT touch dentin here
inner mineralized phase [secretory 1]
phase of amelogenesis in which the distal end of the ameloblasts changes from a smooth configuration to TOME’S PROCESSES
interrod substance secretion phase [secretory 2]
- tome’s processes of adjacent ameloblasts secrete the interred substance that encircles tomes processes (TOMES PIT)
- tomes process is at distal end of ameloblast
- the interred substances are partially mineralized (immature enamel)
phase of amelogenesis in which tome’s process moves out of the pit as the ameloblast moves toward the future enamel surface. as the process withdrawals it secretes a partially mineralized rod into the pit. this continues until the length of the immature interrod substance and rod is reached
rod secretion phase [secretory 3]
- at this point it is still all partially mineralized enamel
- the presence of tomes processes and partially mineralized enamel indicate that ameloblasts are in the rod secretly phase
phase of amelogenesis in which the distal end of the ameloblasts alternates between an even (smooth edge that is reabsorbing or removing organic material) and an uneven (ruffled edge secreting minerals and salts (inorganic) into the partially)
maturation phase [secretory 4]
- maturation is complete when percentage of inorganic material reaches 96%, organic = 1%, and water = 4%
- once the alternation begins, tomes process is no longer present
phase of amelogenesis in which like the inner, the outer enamel is mineralized immediately and is not secreted by tome’s processes (bc it does not contain enamel rods)
outer mineralization phase [secretory 5]
- now the entire space between inner and outer enamel is mature enamel and fully mineralized
- this is the last MINERALIZED SECRETION of ameloblasts but NOT its final secretion
phase of amelogenesis in which a basal lamina is secreted just on top of the outer rodless enamel
final ameloblast secretion phase [secretory 6]
- basal lamina is the LAST SECRETION of ameloblasts
- everything on top of this will be used for the reduced enamel epithelium in the protective phase
phase of amelogenesis in which the 4 cell layers of the enamel organ come together to form the “reduced enamel epithelium” which is the protective layer of the enamel that becomes the “junctional epithelium” once the tooth enters the oral cavity
protective phase [postsecretory]
*the reduced enamel epithelium is attached to the enamel surface by a basal lamina (the final secretion of the ameloblasts)
how long does the maturation phase take for a tooth?
5 years