Enamel

Question 1

composition of enamel

Answer 1

96% inorganic, HAP
1% organic, NON-COLLAGENOUS proteins
3% h20

Question 2

where is enamel thickest

Answer 2

insical edge/ cusp

Question 3

what are the major diseases of enamel

Answer 3

dental caries, genetic conditions grouped as amelogensis imperfecta

Question 4

is enamel HAP pure

Answer 4

no, it contains impurities- carbonate

Question 5

enamel HAP are hexagonal in cross-section. what are the dimensions of the HAP crystal in enamel

Answer 5

width= 60- 90nm

depth=25-30nm

Question 6

how is HAP arranged in enamel

Answer 6

each HAP crystal is bigger than bone and dentine. millions of HAP crystals packed into a prism.
each prism runs from the EDJ to the tooth surface in a sinosodial path therefore meet at varying lengths.
each prism is perpendicular to the EDJ

Question 7

what are the incremental lines of enamel

Answer 7

1. Daily cross striations= 5um periodicity, circadian rhythm, less prominent
2. Striae of Reitzus= irregular striations, superimosed on daily lines, more prominent but less frequent

Question 8

what are the patterns of prisms in enamel

Answer 8

1. circular

2. keyhole

Question 9

what is inter-prismatic enamel

Answer 9

enamel which runs in between the enamel prisms

Question 10

list all the structures found at the ADJ part of enamel

Answer 10

tufts
lamellae
spindles
hunter-schreger bands

Question 11

what are tufts

Answer 11

structures that contain tuftelin protein

recur at every 100um intervals along the ADJ

Question 12

why do tufts form

Answer 12

when residual organic enamel protein collects

Question 13

what are lamella

Answer 13

a layer/ line running through the full thickness of enamel

Question 14

why do spindles form

Answer 14

result of odontoblast processes (dentin forming cells) inserting themselves in between the ameloblasts during early enamel formation and disrupting it

Question 15

where are hunter-schreger bands seen in enamel

Answer 15

inner 2/3 of enamel

Question 16

what is a-prismatic enamel

Answer 16

‘absence of prisms’

Question 17

where is aprismatic enamel found

Answer 17

in newly erupted teeth, the outer layer

Question 18

why does aprismatic enamel occur

Answer 18

there is an outer layer region in newly erupted teeth where all the prisms are aligned at right angles to the tooth surface, are parallel to one another

Question 19

what do spindles look like

Answer 19

dark, cigar shaped

Question 20

where are spindles commonly seen

Answer 20

under cusps of teeth

penetrate 50um deep into enamel

Question 21

what is gnarled enamel

Answer 21

part of enamel with abnormal, disordered prisms

Question 22

why has gnarled enamel evolved

Answer 22

to break up lines of shear where maximum force hits the crown

Question 23

why has gnarled enamel evolved

Answer 23

to break up lines of shear where maximum force hits the crown

Question 24

what do the stria of reitzus look like

Answer 24

‘tree rings’ which run obliquely across prism, lateral borders of crown, under cusps

Question 25

what is perkymata

Answer 25

caused by stria of reitzus which form a depression running around the tooth