Amelogenesis
True or False: Enamel can be regenerated
FALSE
in longitudinal section how do striae or retzius appear?
a series of dark lines from DEJ to tooth surface
many _______ ________ forms of amelogenin exist, and the different forms have different function
alternatively spliced
what are the two proteins that cleave amelogenin at different times during enamel ofrmation?
MMP-20 and KLK-4
where do ameloblasts primarily deposit enamel?
a mineralization front very near the ameloblast cell membrane
when the tooth erupts into the oral cavity, what cell layer is lost?
ameloblast cell layer
when are amelogenin fragments removed?
during final enamel mineralization
Teeth develop as __________ appendages in the vertebrate embryo
ectodermal
how often the ameloblasts cycle between rough ended and smooth ended?
eight hours
what is the hardest substance in our body, comparable to mild steel?
enamel
what do amelogenin nanospheres direct?
enamel crystal growth
extremely long and parallel-organized hydroxyapatite crystals
enamel crystals
the protein/organic component of the enamel is made up of what proteins
enamel matrix proteins, dentin/bone proteins, proteinases
enamel mineralizes in specific patterns called
enamel rods
tightly packed mass of hydroxy apatite crystals
enamel rods
these form from odontoblast processes that become trapped in the developing enamel and extend from DEJ
enamel spindels
these project from DEJ a short distance and are hyperpolymerized areas with greater protein
enamel tufts
The early development of teeth resembles what morphologically, as well as molecularly?
other organs such as hairs and glands.
during the maturation stage there is gradual completion of mineralization which results in lost of how much initially secreted protein and water?
over 90%
enamel formation occurs...
over an extended period of time
circumferential, horizontal shallow furrows that run on the surface of the enamel
perikymata
tomes processes lie parallel/perpendicular to the enamel rods
perpendicular
how enamel crystals typically organized?
perpendicular to each other
the thin layer of cells between the stellate reticulum and the inner enamel epithelium
stratum intermedium
what do perikymata result from?
striae of retzius extending onto the surface of the tooth
what occurs in amelogenin supramolecular assembly?
subunits and linear of chains of nanospheres form
where is the cyclic process of modulation observed in ameloblasts?
the apical end of the ameloblasts
what causes enamel to be the hardest and toughest material in the human body?
the hierarchical micro-architecture of the enamel and the rods consisting of more than 10,000 hydroxyapatite crystallites
enamel
the substance that covers the crown of the tooth
what is the color of enamel effected by?
the underlying dentin
when enamel formation is complete and tooth erupts into the oral cavity what will happen to the ameloblast cells?
they will die
why does the outer-most layer of enamel not have a rod structure (aprismatic)?
tomes processes dictate the rod shape
cytoplasmic extensions of ameloblasts that extend into enamel
tomes' processes
what color is enamel?
translucent light yellow to gray-white color
enamel is made at the same time as dentin is made through ____________
dentinogenesis
what surrounds the forming rod and the distal portion of the tomes' processes
interrod enamel
since the cementum is relatively soft it does not wear well against environmental assaults. t/f it abrades away rapidly whenever what?
it is exposed to the oral environment
these extend varying lengths from enamel surface and are filled with organic material (proteins)
lamellae
enamel is composed of what?
large rod containing inter rod layer sandwiched by two thin rodless initial and final layers
does cementogenesis occur early or later on in tooth development?
late
at what stage of tooth development is the dental lamina disintegrating, tooth formation is not connected to oral epithelium, and dentin and enamel are beginning to form at the crest of the inner enamel epithelium?
late bell stage
what is the neonatal line a result of ?
marked environmental change at birth
stage in which ameloblasts remove degraded proteins (by proteases) which matures the enamel mineral
maturation
the interrod and rod growth sites are associated with what?
membrane infoldings on the proximal and distal portions of the tomes' processes
the gardening process of enamel
mineralization
amelogenin self-assembles into ____________ with multiple amelogenin molecules
nanospheres
what happens during maturation proper?
- bulk removal of water and organic material from enamel - additional inorganic material is introduced - modulation
amelogenin processing occurs through how many pathways?
2
how thick is enamel?
2.5 mm to feather edge
how much does enamel grow everyday?
4 micrometes
what are the cells that make the enamel called?
ameloblasts
in the secretory phase at what will be known as the DEJ, what occurs?
ameloblasts actively secrete enamel proteins that accumulate and participate in the formation of a partially mineralized initial layer of enamel
tomes processes are the interdigitation of what?
ameloblasts and enamel rods
once the full thickness of enamel matrix is secreted what happens?
ameloblasts become shorter and loose the tomes' processes/ resemble original shape.
the process of enamel formation
amelogenesis
this is the major enamel matrix protein, the structural protein that binds calcium, and helps direct enamel crystal formation
amelogenin
the partially mineralized initial layer that is formed in the secretory phase does not have rods so it is called...
aprismatic enamel
where are enamel spindles most frequently found?
at cusp tips
enamel rods do not directly contact dentin. why?
because ameloblasts move away from the dentin surface
when does maturation begin?
before matrix has reached full thickness
where does mineralization begin and what is the path by which it spreads?
begins at DEJ and move out to incisal edge. starts at occlusal/incisal region of tooth and moves toward CEJ
is amelogenin an inhibitor or organizer of crystal growth?
both
the specific function of modulation is unknown, but we do know that it is related to what?
calcium transport
what does cementum form from?
cementoblasts
the cementum meets the enamel in a line that surrounds the tooth called the
cementoenamel junction
cementum formation
cementogenesis
a relatively soft bony tissue that covers the root surface in a thin layer whose main function is to act as an attachment layer for the periodontal ligament
cementum
what do enamel tufts and lamella arise from?
changes in the direction of groups of rods
in the pre-secretory stage what shape are the cells?
columnar
in cross-section how to striae of retzius appear?
concentric rings
periodic banding across the enamel rod that results from daily growth of the enamel
cross striations
what do pre-ameloblasts look like?
cuboidal, undifferentiated
in late bell stage dentin and enamel are beginning to form at the crest of the inner enamel epithelium. this is the future site of what?
cusp tip
what modulation occurs in the maturation stage?
cycles between ruffled and smooth ended ameloblasts
enamel rods are ______ with special relation to interrod region cervical to it
cylindrical
enamel must have the support of the resilient underlying ______
dentin
if caries destroy _______, enamel is fractured easily
dentin
Tooth morphogenesis is a process that is regulated by sequential and reciprocal interactions between the _________ and _______ tissues and during this morphogenesis the simple oral ectoderm thickens, buds, grows and folds to form the complex shape of the tooth crown
epithelial and mesenchymal
start to finish of enamel formation can be how long?
five years
striae of retzius have incremental weekly rhythmic _______ _______
growth lines
in what direction do crystals run?
head parallel to the longitudinal axis of the rod in the head and tail at the flaring of crystals
striae of retzius are most common in what teeth?
human permanent teeth
mineral is added during maturation called
hydroxyapatite
96% of the tooth enamel consists of mineral (primarily calcium phosphate = ____________), with water and organic material (__________) composing the rest
hydroxyapatite, proteins
during the initial mineralization of enamel some organic material is removed by proteases. when does this occur? how much of the final mineral content is achieved at this point?
immediately as it is laid down; 25-30%
the cycling of modulation occurs in waves starting where?
in the least mature area and traveling to the most mature
prior to enamel formation, cells of the inner enamel epithelium are called what
pre-ameloblasts
stage in which the ameloblasts form, polarize, and mature
presecretory stage
ameloblasts have three stages of development. what are they?
presecretory, secretory, maturation
enamel crystals are organize in bundles called ______
prisms
what are the three major components of enamel?
protein, mineral, water
in the presecretory phase the nuclei become aligned where, making the cells polarized.
proximal end
during the transitional phase from secretory to maturation stages what happen to ameloblasts?
reduce height and volume and 25% of the cells die via apoptosis
what do proteinases do?
remove the proteins secreted in the matrix by degradation
tomes processes give what kind of appearance to the enamel/ameloblast junction?
saw tooth
the process of forming the enamel matrix
secretion
what part of enamel formation is relatively quick? what part is relatively long?
secretion, mineralization
stage in which ameloblasts produce the enamel matrix proteins, including amelogenin
secretory stage
what do the membrane infoldings represent?
sites where secretory granules release enamel matrix proteins extracellularly for growth in length of enamel crystals that result in an increase in the thickness of the enamel layer
what is the neonatal line?
special, accentuated striae of retzius
at any given time, different parts of the tooth may be at a different what?
stage of enamel formation
how is the striae of retzius identified?
using ground sections of calcified teeth
at what point in development do neonatal line show up?
when child is born
enamels seems like a ________ ________ in the electron microscope
woven fabricprisims