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