Properties of dental tissues

Question 1

what does this measure?

Answer 1

tensile strength

Question 2

what does this measure?

Answer 2

compressive strength

Question 3

what does this measure?

Answer 3

diametral tensile strength

Question 4

what does this measure?

Answer 4

3 point flexural strength

Question 5

what is stress?

Answer 5

force per unit area acting on a material

Question 6

what is strain?

Answer 6

fractional change in dimension caused by the forced

Question 7

compare stress and strain up to the yield point

Answer 7

stress is proportional to strain

Question 8

what is youngs/elastic modulus?

Answer 8

ratio of stress/strain when stress is proportional to strain

Question 9

what is the hardness of a material?

Answer 9

its ability to resist deformation

Question 10

how is the hardness of a material measured?

Answer 10

with an indenter
Larger indent = softer material

Question 11

remember enamel is an Epithelial product formed by ameloblasts

Question 12

what percentage of enamel is in-organic/mineral -> hydroxyapatite?

Answer 12

96%

Question 13

how thick is enamel?

Answer 13

2mm max

Question 14

is enamel vital?

Answer 14

no

Question 15

what are the properties of enamel?

Answer 15

hard and brittle

Question 16

what do you use to cut enamel?

Answer 16

High speed air turbine with diamond or tungsten carbide bur

Question 17

what is the hardness of enamel in GPa?

Answer 17

3-7GPa

Question 18

what is the elastic modulus of enamel in GPa?

Answer 18

84.4GPa

Question 19

where are the maximum properties of enamel?

Answer 19

on the surface
decrease towards the ADJ

Question 20

hardness and elastic properties of enamel are dependant on what?

Answer 20

position in prism/rod
Ca2+ content
age

Question 21

how does position in prism/rod effect enamel hardness and elastic properties?

Answer 21

In prism sheath: hydroxyapatite crystals not tightly packed together

Prism core: hydroxyapatite crystals packed tightly in the same orientation

hardness and elastic properties are higher in core as higher hydroxyapatite content

Question 22

how does Ca2+ content effect enamel hardness and elastic properties?

Answer 22

higher Ca2+ content enriches the enamel increasing its hardness and elastic properties

Question 23

how does age effect the enamel hardness and elastic properties?

Answer 23

Increases with age as post-eruption, enamel undergoes maturation due to oral environment rich in Ca2+ to enrich the hydroxyapatite

Question 24

in dentine what is the % by weight of in-organic mineral - hydroxyapatite?

Answer 24

70% hydroxyapatite

Question 25

in dentine what is the % by weight of organic - collagen?

Answer 25

20%

Question 26

what do you use to cut carious dentine?

Answer 26

bladed bur or hand excavator

Question 27

what do you use to cut sound dentine?

Answer 27

diamond bur (high speed) or bladed bur (high/low speed)

Question 28

what factors impact the properties of dentine?

Answer 28

tubule size and density and dentine types

Question 29

what is the hardness of dentine?

Answer 29

0.5-1.4GPa
○ Highest between tubules as highly mineralised
Decreases from ADJ to pulp

Question 30

what is the elastic modulus of dentine?

Answer 30

Between tubules (peritubular dentine): 40-42GPa
§ More likely to fracture

Intertubular dentine: 17GPa

Question 31

what happens to the flexural strength as you go deeper into dentine?

Answer 31

felxural strength decreases as it becomes more tubular
- more peritubular dentine
- less intertubular dentine

Question 32

understand this

Question 33

understand this