Enamel I: structure and development Flashcards
Properties of Mature Enamel
- Acellular, non-vital,non-vascular
- ectodermal origin
- hardest (most mineralized) tissue in the body
- brittle
- somewhat dynamc tissue: de/re mineralized
more Properties of Mature Enamel
- translucent, range of colors
- covers crown of tooth
- thicker at crown, around 2.5mm, relatively thin at cervical line
- composed primarily of hydroxyapatite crystals
- small but essential protein component: organization of crystals
enamel composition
- organic: 1-2%distributed between HA crystals
- no collagen
- water 2-3%
- inorganic component: HA
Major enamel proteins:
amelogenins ameloblastins enamelin tuftelin etc
organization of enamel
enamel crystals
- closely packed, long, ribbon like
- many crystals packed together form both enamel rods and interrod enamel
enamel crystals mineral componet
HA, carbonatoapatite
carbon and magnesium incorporated more in the ____enamel, fluoride in the ____
inner, outer enamel
the outer enamel could be said to be more___ in the face of an acid attack
resilent
enamel crystals shape
hexagonal , 60-70 nm wide, 25-30 nm thick
enamel crystals length
long, may run entire length of enamel, in the mm range
Enamel Rods are
cylindrical accumulation of enamel crystals, line up along the long axis of the rod
Enamel Rods runs
perpendicular to the DEJ
Enamel Rods are organized
in rows which run in alternating directions. 1 ameloblast=1 rod
rod sheath is a
relatively protein rich area of enamelthat surrounds the rods
rod sheath runs
about 3/4 of the way around each rod, for the most part separating rod and interrod enamel
in the gaps of the rod sheath, enamel crystals are
continouos with the interrod enamel, linkin the two together
while crystal orientation is mainly parallel to the long axis of rods, except at the
gaps in the sheath area they bend outwards and become continuous with the interrod enamel
rod sheath proteins
ameloblasts and amelogenins
interrod enamel are the same basic composition as rods, simply different
enamel crystal orientation
interrod enamel fills gaps between
rods
formation of enamel-first
pre-dentin by odontoblast
ameloblast activation and deposition of enamel: initial depostion only around
30% mineralized, much larger organic component
as enamel matures, organic component
reduced, mineralization increases
ameloblasts maturation three general phases:
- pre secretory:mature from pre-ameloblasts to ameloblasts
- secretory:deposition of enamel
- maturation: reduction of organic matrix, increase mineralization via ion transport
ameloblast deposit organic matrix via
secretory vesicles, which exit the cell apically
depostition of enamel initially, the basal lamina
separating the pre dentin and ameloblast is penetrated by cell projections and broken down
enamel is laid down directly in
apposition to predentin/mantle (first) dentin
deposion of enamel big thing
tomes process
ruffled cells
infiltration and incorporation of calcium ions into crystals occurs during “rufflung”, lowered pH perhaps favors materialization. Secreation of proteolytic enzymes
smooth cells
allow diffusion out of protein fragments out of enamel which leak in between cells and laterally defuse though cell layer
