L7: Enamel Structure & Biomechanical Properties

Question 1

What is the thickness of enamel?

Answer 1

Incisors: 0-2mm
Molars: 2.6mm

Question 2

What is the microscopic structure of enamel?

Answer 2

Clusters of prisms containing around 1000 crystallites;

The prisms are then arranged in larger groups, with interprismatic enamel in-between

Question 3

What is the difference between the crystal alignment in enamel and Dentine?

Answer 3

Enamel: anisotropic
Dentine: insotropic

Question 4

Cross-sectional enamel has a _________ elastic modulus than surface enamel

Answer 4

Lower

Question 5

The higher the load applied, the _______ the elastic modulus measured

Answer 5

Lower

Question 6

What is the elastic modulus?

Answer 6

Stress over strain

Measures a substances resistance to being elastically deformed when a stress is applied to it

Question 7

what is the visual representation of enamel?

Answer 7

grayish/bluish white

- appears yellowish white as it semi-translucent and reflects colour of underlying dentine

Question 8

what is the thikness of the enamel of molars and incisors?

Answer 8

incisor: 2mm
molar: 2.6mm

Question 9

enamel is selectively permeabe

T/F

Answer 9

T

water can travel through enamel at 4mm3 /cm2 /24hrs

Question 10

microscopic properties of enamel

Answer 10

Clusters of needle-like crystals into prisms containing around 1000 crystallites

Question 11

what type of enamel is found between enamel prisms?

Answer 11

Interprismatic enamel

Question 12

What is used to identify the nanostructure of enamel?

Answer 12

Synchrotron x-ray diffraction

Question 13

what does an anisotropic structure mean?

Answer 13

organised, oriented, direction of prisms

Question 14

what does an isotropic structure mean?

Answer 14

having a property which has the same value in different directions

Question 15

dentine has a isotropic/anisotropic structure?

Answer 15

isotropic

Question 16

enamel has a isotropic/anisotropic structure?

Answer 16

anisotropic

Question 17

what is fracture toughness

Answer 17

Fracture toughness is a quantitative way of expressing a material’s resistance to brittle fracture when a crack is present.

Question 18

what does a high fracture toughness mean?

Answer 18

a high fracture toughness shows improved clinical performance and reliability

Question 19

what happens to a tooth during a fracture?

Answer 19

Crack propagation and subsequent fracture leads to ultimate structural failure

Question 20

what does a high crystallite thickness of enamel mean?

Answer 20

high stress resistance

Question 21

how is the wear resistance of enamel increased?

Answer 21

Rods are oriented in a way to reduce wear by increasing hardness

Question 22

what increases the fracture toughness of enamel?

Answer 22

Inter-rod structure to holt cracks

Question 23

What is present around the enamel prisms?

Answer 23

A protein sheath

Question 24

What is the function of a protein sheath?

Answer 24

1) protein macromolecule chains may deform (polymer-like behaviour)
2) Thermodynamically unstable therefore will return to initial form and position on release of load (elastic behaviour)