Enamel Flashcards
mineral and organic percentage of enamel
96% Mineral and 4% organic and water
various ions (if present in enamel are)
strontium, magnesium, lead and fluoride.
the functional organizational unit of enamel are
rods and interrod. (rods are hexagonal and prism shaped in cross section)
shape of hydroxy in enamel and its width and thickness
its made up of ribbon like carbonate apatite crystals
width: 60-70 nm
thickness: 25-30 nm
hydroxy apatite is substituted with what in enamel
carbon (carbon apatite)
describe the shape of enamel rod
it is cylinder in shape with crystals in side with long axes that generally run longitudinal axis of the rod
describe the shape of inter rod
it surrounds each rod and its crystals run in a different directions than the rod
the boundary between rod and inter rod has ?
a space filled with organic matter called as rod sheath
circumferential rod area has?
the crystals of rod and inter rod are confluent with each other as there is no space or rod sheath between them.
how many steps of amelogenesis and overview of mineralization of the two steps
amelogenesis takes place in 2 steps
when first enamel forms its mineralized to only 30%
then the organic matrix breaks and the crystals grow, slowly the water is removed with the organic matrix and it mineralizes to 96%
ameloblast secrete what n is responsible for what
they secrete matrix proteins and are responsible for maintain the ecm for proper mineral deposition
stages of amelogenesis
presecretory stage
secretory stage
maturation stage.
overview of what happens in pre secretory phase
ameloblast differentiate, they quire their phenotype and prepare to secrete matrix protein
overview of secretory stage
(formative stage) they organize their whole enamel thickness, and highly ordered tissues.
overview of maturation stage
ameloblast influx ions for on going continuous mineralization
inner enamel epithelium cells traces the crown coronally. describe its cells
it cells are more columnar and their nuclei are arranged at the proximal end, adjacent to stratum intermedium
after dentin formation initiates what changes occur in ameloblast
they start secreting the enamel proteins, that immediately participate in the formation of a partially mineralized enamel layer without rods
important event for production of enamel is?
DEVELOPMENT of cytoplasmic extension on ameloblast called as the TOMES PROCESS
HIGHER mammals tomes process make>
junction between enamel and the ameloblast and give them a picket fence or saw toothed appearance
what happens after formation of enamel
post secretory transition ameloblast turn into squatter maturation cells.
cells in stratum intermedium stays stellate
outer enamel epi reorganize its layers
blood vessels invaginate these cells making a papillary layer
what happens to ameloblast after enamel is mature?
ameloblast stops doing its function of modulation and alternating appearance, it takes a low cuboidal appearance and and covers the enamel incase of a premature break
reduced enamel epithelium is constituted by
when enamel is mature the ameloblast layer and the adjacent papillary layer regress together and constitute the reduced enamel epi
reduced enamel epithelium future
the one present on incisally is destroyed and the one at the cervical region interreacts with oral epithelium to form junctional epithelium
2 stages of pre secretory stages
morphogenic phase
differentiation phase
morphogenic satge
the cells of inner enamel epithelium divide mitotically just at the cervical portion of the tooth and limited to it. these cells are cuboidal and have centered nuclei, poorly formed golgi elements and scattered mitochondria
what happens in differentiating phase
the inner enamel epi cells differentiate into ameloblast, their nuclei shift to proximal towards stratum intermedium
the basal lamina degrades when the formation of mantle dentine starts
Golgi complex shifts to supranuclear cytoplasm portion.
another junction complex is made at the distal end which compartmentalize the ameloblast into body with an extension called tomes process against which the enamel will be formed.
arranagemt of ameloblast after of them being polarized
they are tightly packed adjacent to each other, with junctional complex. these complex encircle the cells at distal and proximal ends. actin filaments radiate from these junctions into the ameloblast and make distal and proximal terminal webs
function of junctional complex between ameloblast
they keep the ameloblast tightly close together and sees what may or may not pass the enamel
explain the first part of secretory stage
(synthesis and transfer of proteins)
messenger RNA for enamel protein is translated by ribosomes present on the membrane of RER, THEN these proteins are transported to Golgi complex where these undergo posttranslational and released as secretory granules that migrate to distal extremity into the tomes process
tomes process when enamel is first formed
it has only the proximal part
secretory granules released against what n do what
they are released against the pre dentin, form a layer of enamel that is not mineralized and does not contain rods
the interrod and rod configuration is property of?
ameloblast and tomes process
what happens when distal portion of tomes process is made
the secretions of porteins is limited to two sites.
the first site of protein secretions
secretions from the first site (proximal part of the process, close junctional complex, along the periphery of the cell)along with ameloblast make a enamel partition that delimit a pit which is continuous over the enamel and is known as INTERROD
SECOND site of protein secretions
provides matrix that takes part in the formation of enamel rod
future of tomes porcess as enamel thickens
the distal tomes process is lengthened, squeezed by the rods against the interrod cavity and in last its squeezed out of existence to from the enamel sheath
why the outer third of enamel shape is altered
when the outer layer of enamel is formed the shape of distal tome process is altered, and that why outer 3rd of the enamel has a rectilinear trajectory
final enamel contains no rods. why>
rods are made by the distal tomes process which is no more when final enamel is made so it has no roads
define enamel layer in terms of presence of rods
it is prismatic (interrod/rod) layer sandwiched between aprismatic layers (rodless)
what happens in transitional stage
ameloblast shorten, decrease in their volume and undergo programmed apoptosis
principal activity of ameloblast
removal or water and organic matrix to allow intro to inorganic material
what is modulation
the cyclic creation, loss and re creation of a ruffled bordered which highly invaginated or a smooth border, ( the cells alternate between possessing a smooth or ruffled border)
modulation occur how and where
occurs in wave on the crown of the developing tooth from the least mature site to the most mature ( apical incisal direction in continuous erupting teeth and cervical incisal direction in limited eruption)
modulation is related to
maintaining environment for mineral accretions and loss of organic matter
what fixes the acidification going on cause of mineral accretions
ruffled border secrete bicarbonate ions, which alkalinizes the enamel fluid, present reverse demineralization of growing crystallites, and maintain for matrix degrading enzymes
ruffled ended border contains?
lysosomes, calcium binding proteins, and membrane associated calcium adenosinetriphosphatases
main mechanism or organic matter remoeval
degradation enzyems that work extracellularly and degrades proteins into small peptides
what happens when to ameloblast when transitional stage is completed
they deposit an atypical basal lamina on now their flattened apex, this layer is adherent to enamel surface with ameloblast joined with hemidesmosomes
when tomes process is made
differentiation phase of presecretory phase
what is amelogenin? what does it do? and what happens if not present
- found as main secretory protein in forming enamel, it stops secreting when enamel attains full thickness
- inhibits lateral growth of crystals
- hypoplastic thin enamel
ameloblastin ? what happens if mutated?
found in secretory stage to the outer surface at (dej)
- ameloblast express ameloblast throughout maturation stage but it doesn’t cross basal lamina and enter the mature enamel
- terminal differentiation ameloblast detach from dentin and enamel formation abort.
enamelin found where and do what
- found on growing enamel surface
- linger within enamel, binds to mineral and inhibit crystal growth
- modulatory affect on crystal elongation and mineral formation
- if absent no proper enamel layer
enamelysin
ca dependent metalloproteinase
found in secretory stage
degrades ameloblast and enamelin into large fragments
- if not present hypo matured thin enamel layer
enamel matrix serine protease
found on enamel this attained full thickness, lost tomes process and started the modulation cycle
degrades amelogenin and nonamelogenin into tiny polypeptides
- if not present hypo mineralized enamel
general arrangement of rods in enamel
they run perpendicularly to the surface of enamel, vertically at the cusp tip and horizontally at the cervical
what are the 2 patterns that complicate the arrangement of rods in enamel
they follow an irregular course bending right and left transversely and up and down the vertical plane.
inner 2/3rd of enamel has rods intertwining each other have dissimilar orientation but similar general direction
striae of retzius are generally cause by
weekly enamel production which results in structural change of rods
another proposal for the cause of straie of rezius
they are made due to the incremental growth of enamel, so more cells are added to the growing enamel to compensate for the increase in size
these cells under go decussation and take a more coronal position
why striae or retzius is found after birth
neonatal line found in enlarged retzius, is because of physiological changes occurring at birth ( incremental lines also occur due to disturbance like fever)
gnarled enamel
rods at the cusp time are twisted around each other to form what is called gnarled enamel
enamel tuft
best seen in transverse direction, arise from DEJ to short distance into enamel, branches and have more amount of enamel proteins
enamel tuft has what protein and how its made/cause
they have tuft protein which is developmentally made due to different orientations of group of rods coming from different regions of scalloped DEJ
lamella in enamel
arise from varying depts. from enamel surface and have longitudinal linear oriented defects that contains organic matter
enamel spindles
some developing odontoblast process gets trapped in ameloblast when enamel is formed and they make the enamel spindle.
3condition affecting enamel formation
febrile disease
tetracycline induced disturbance
fluoride ion
febrile disease
enamel formation is disturbed so u can see a distinctive bands of malformed enamel
tetracycline induced disturbance
tetracycline antibiotics are incorporated in mineralization that causes enamel to form bands of brown pigmentation or whole enamel is pigmented
can also result in hypoplasia and absence of enamel
fluoride ions
intake of fluoride ions more than 5ppm interferes with ameloblast making mottled enamel that can be seen as hypo mineralized white patches and altered enamel
