bds2 enamel morphology

Question 1

main features of enamel

Answer 1

hardest tissue in the body
resists abrasion
brittle and supported by dentine
covers the tooth crown
varies in thickness
translucent
transparency increases with mineralisation

Question 2

describe the regional variations in the thickness of enamel

Answer 2

surface enamel is more mineralised and harder than deeper enamel
hardness decreases from the cusp tip to the incisal edge to the cervical region

Question 3

summarise enamel rods ie prisms

Answer 3

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

Question 4

when is the orientation of crystallites in enamel rods determined

Answer 4

during enamel formation

Question 5

at what angle are crystallites produced

Answer 5

they are deposited at right angles to the ameldoblast membrane

Question 6

describe hydroxyapatite crystallites

Answer 6

Ca10(PO4)6(OH)2

hexagonal crystallites
larger in enamel than in dentine cementum and bone

Question 7

histology of the enamel rods

Answer 7

run a sinusoidal course
adjacent groups of rods have different orientations
periodic orientation causes banding patterns called hunter schreger bands

Question 8

what causes hunter schreger bands

Answer 8

periodic orientation of the enamel rods

Question 9

are hunter schreger bands found throughout enamel

Answer 9

no they are absent in outer enamel

Question 10

what are optical features of enamel

Answer 10

hunter schreger bands
gnarled enamel

Question 11

describe enamel tufts

Answer 11

these are hypo mineralised regions due to residual matrix proteins at the prism boundaries

Question 12

describe enamel lamella

Answer 12

incomplete maturation of groups of prisms create a fault line extending through the enamel thickness

Question 13

describe enamel spindles

Answer 13

odontoblast processes extend into the enamel forming the spindles

Question 14

what does enamel translucency mean

Answer 14

any content under the enamel will transfer its colour to the enamel

Question 15

compare the different regional thicknesses of enamel

Answer 15

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

Question 16

what does enamel maturation involve

Answer 16

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

Question 17

what is the orientation of crystallites in relation to the rods

Answer 17

parallel in most regions but in others they are inclined.

parallel are called rod regions
inclined are the inter rod regions

Question 18

relate acid etching to crystallite orientation

Answer 18

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

Question 19

what are cross striations

Answer 19

consequences of the daily growth of enamel

Question 20

what are brown striae of retzius

Answer 20

consequence of enamel growth at a weekly interval

Question 21

how does tooth whitening work

Answer 21

removal of organic content - makes enamel fragile

Question 22

what is tomes process

Answer 22

ameloblast projection for enamel production. arranges the crystallites to be either parallel or inclined

Question 23

describe the structure of a crystallite

Answer 23

hydroxyl group at the core with calcium on the outskirts and phosphate in between.

Question 24

describe the substitutions of crystallites

Answer 24

metals can sub the calcium

carbonate can substitute the phosphate

fluoride can substitute the hydroxyl

Question 25

relate the crystallites to acid attack

Answer 25

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

Question 26

what causes hunter schreger bands

Answer 26

the periodic orientation of the rods
they are not rods themselves they are just the orientation of crystallites

Question 27

are hunter schreger bands present throughout enamel

Answer 27

no they absent in outer enamel

Question 28

describe gnarled enamel

Answer 28

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

Question 29

relate brown striae of reties and perikymata

Answer 29

they are both a consequence of the weekly formation of enamel but perikymata are worn off after eruption

Question 30

how to differentiate spindles and tufts

Answer 30

spindles have a rounded end compared to tufts

Question 31

how are enamel spindles formed

Answer 31

when the odontoblasts are finished they will retrieve their process but in the case of spindles the process is left behind

Question 32

do fissures affect caries risk

Answer 32

yes they increase it