histology of enamel e lecture Flashcards
what is the strength of enamel like
very brittle and hard wearing
what does enamel rely on for its strength
the underlying dentine
what is enamel made from
almost pure mineral- and organic material which is non collagenous protein
only 4% is water
what mineral is in enamel
hydroxyapatite- but much larger in enamel than dentine
where is the enamel thickest
A incisal edge or in the cusp of a molar
where is the enamel thin
at the knife edged margin of the cervical margin
how are the hydroxyapatite crystals arranged
they are arranged in prisms or in rods
how long is the crystals
runs from the enamel to the dentine and is approx 5 micro milimetres in diameter
what lies on top of the hydroxyapatite crystals
brown lines called the striae of Retzius
how are the striae of retzius arranged
they are arranged more irregular at the cusp but more regular towards the cervical margin
other structures can form due to
optical effects produced by the overall prisms
what happens if all the top enamel is removed by acid
ribbons of protein can often be seen to run down the exposed dentine surface – this is tuft protein
what do tuft proteins represent
areas between prims and residual enamel proteins
what shape is the ADJ
scalloped in appearance
how do the prisms run in the enamel
in a sinusoidal path to the surface with all the prisms running parallel to each other
how do enamel tufts form
high protein content retained at the prism boundaries and, because of the superimposition, give the appearance of a tuft of grass
where do spindles originate
at the ADJ AND PROJECT INTO the enamel
what shape are spindles
distinct cigar shapes
how can the visibility of tufts and spindles change
due to the changing of the focus and therefore it becomes visible and then no longer visible
what are the striae of retzius
they are incremental growth lines that run obliquely to the enamel prisms
what depressions are the striae of retzius associated with
they are associated with depressions called perikymata
where are perikymata found more commonly
towards the outer regions of the enamel and the cervical margin which can be regularly spaced
what do straie form the markings of
they form the markings of the enamel at a particular time in the crowns development
what does the scalloping of the ADJ aid
aid-resists shearing forces
and aids the retention of the enamel on the underlying dentine
how does the ADJ resist shearing forces
by providing a more irregular and greater surface area
what is the enamel spindle continuous with
with the dentinal tubules
how do enamel spindles form
They are thought to arise because of growth of odontoblast processes across the forming ADJ into the developing enamel during crown development
what angle do the enamel prims run on the outer surface
the enamel prims run at 90 degrees to the ADJ
what angle do the enamel prisms run at the cusp
the prisms run at a much more disorganised fashion and therefore are known as gnarled enamel
why is gnarled enamel good-
can resist harder shearing forces at the cusp
how do hunter schrenger bands run
run at slightly different paths which can form the visible enamel tufts
what is a fissure lesion-
it is a lesion where it is much smaller than the underlying enamel and dentine lesion
why does a fissure lesion occur-
- largely due to the divergent pathway of the prisms away from the fissure
what does the smooth surface lesion contain-
the translucent zone
the lesion body
the dark zone
surface zone
why might the striae of retzius and the cross striations lines become more prominent-
due to the partial demineralisation of the enamel which makes them appear more distinct than in normal enamel
the translucent zone-why
t appears translucent because it takes up media into its relatively uniform sized pores
how are the uniform sized pores in the translucent zone produced-
by early acid demineralisation
how much mineral is lost in the translucent zone-
around 1%
how much mineral is lost in the body of the lesion-
greater than 20%
what happens in the dark zone
some remineralisation has occurred and therefore the pores are different sizes. some are small and inhibit the ingressing of the imbibing fluid. this causes light to scatter therefore dark colouring
what might the dark zone also have
high protein content
what % of mineral has been lost in the dark zone
5%
the surface zone
looks relatively intact so that the demineralisation can look like its sub surface
the presence of the surface zone is-
independant of fluoride conc
what may also be present in the surface zone
micro channels may be present in the surface zone
