bds2 enamel morphology Flashcards
main features of enamel
hardest tissue in the body
resists abrasion
brittle and supported by dentine
covers the tooth crown
varies in thickness
translucent
transparency increases with mineralisation
describe the regional variations in the thickness of enamel
surface enamel is more mineralised and harder than deeper enamel
hardness decreases from the cusp tip to the incisal edge to the cervical region
summarise enamel rods ie prisms
the basic unit of enamel is called an enamel rod
5 micrometers by 2.5mm in length
run from the amelodentino junction to the surface
contain many hydroxyapatite crystallites
orientation varies within and along the rod
the head and tail regions are composed of the same hydroxyapatite crystals
the distinction is caused by variation in the orientation of the crystallites in different parts of the rod
when is the orientation of crystallites in enamel rods determined
during enamel formation
at what angle are crystallites produced
they are deposited at right angles to the ameldoblast membrane
describe hydroxyapatite crystallites
Ca10(PO4)6(OH)2
hexagonal crystallites
larger in enamel than in dentine cementum and bone
histology of the enamel rods
run a sinusoidal course
adjacent groups of rods have different orientations
periodic orientation causes banding patterns called hunter schreger bands
what causes hunter schreger bands
periodic orientation of the enamel rods
are hunter schreger bands found throughout enamel
no they are absent in outer enamel
what are optical features of enamel
hunter schreger bands
gnarled enamel
describe enamel tufts
these are hypo mineralised regions due to residual matrix proteins at the prism boundaries
describe enamel lamella
incomplete maturation of groups of prisms create a fault line extending through the enamel thickness
describe enamel spindles
odontoblast processes extend into the enamel forming the spindles
what does enamel translucency mean
any content under the enamel will transfer its colour to the enamel
compare the different regional thicknesses of enamel
thicker at incisal edge and in the cusps
thinner at the cervical margin
when comparing the cusps of molars and deciduous molars, there is less enamel in the primary because the molar is in the mouth for less time than the permanent molar
what does enamel maturation involve
removal of the surface of the tips and the cusps require more resilience and this will benefit from the hardness
it is important to remember that the cervical region is less hard and will have certain problems.
when restoring the cervical regions, this may be at the highest rate
what is the orientation of crystallites in relation to the rods
parallel in most regions but in others they are inclined.
parallel are called rod regions
inclined are the inter rod regions
relate acid etching to crystallite orientation
etch is more effective in the inter rod region because the etch works better on the sides of the crystallites compared to the tips of the crystallites
what are cross striations
consequences of the daily growth of enamel
what are brown striae of retzius
consequence of enamel growth at a weekly interval
how does tooth whitening work
removal of organic content - makes enamel fragile
what is tomes process
ameloblast projection for enamel production. arranges the crystallites to be either parallel or inclined
describe the structure of a crystallite
hydroxyl group at the core with calcium on the outskirts and phosphate in between.
describe the substitutions of crystallites
metals can sub the calcium
carbonate can substitute the phosphate
fluoride can substitute the hydroxyl
relate the crystallites to acid attack
when the crystallites have a high carbonate concentration they are more susceptible to acid atack. if there is fluoride in the diet, and an acid attack occurs, during remineralisation the fluoride will be incorporated
what causes hunter schreger bands
the periodic orientation of the rods
they are not rods themselves they are just the orientation of crystallites
are hunter schreger bands present throughout enamel
no they absent in outer enamel
describe gnarled enamel
an optical illusion caused by concentration of rods in the cusps. because the rods are concentrated they look inter twined and moving like they are going around one another
relate brown striae of reties and perikymata
they are both a consequence of the weekly formation of enamel but perikymata are worn off after eruption
how to differentiate spindles and tufts
spindles have a rounded end compared to tufts
how are enamel spindles formed
when the odontoblasts are finished they will retrieve their process but in the case of spindles the process is left behind
do fissures affect caries risk
yes they increase it
