Physical And Mechanical Properties

Question 1

How do you establish the most important property of a material?

Answer 1

Once you have defined the task a material has to fulfill

Question 2

What are the two simple modes of stress?

Answer 2

Tension and compression

Question 3

What what is tensile strength?

Answer 3

Stretching force

Question 4

What is compressive strength?

Answer 4

Compressive force

Question 5

Which forces are a combination of compressive and tensile modes?

Answer 5

Torsion, shear and flexible modes

Question 6

What is torsion?

Answer 6

Twisting

Question 7

What is shear strength?

Answer 7

Ability to resist forces that cause material’s internal structure to slide against itself

Question 8

What is flexural strength?

Answer 8

Bending

Question 9

Why is the tooth a complex material to test the strength of?

Answer 9

It is a composite - made up of multiple components

Question 10

What does a universal testing machine do?

Answer 10

It deforms the sample tested in a known and controlled way whilst monitoring the force

Question 11

What does anistrophic mean?

Answer 11

Having a physical property which has a different value when measured in different directions

Question 12

Where are the loads directed in enamel?

Answer 12

Along the the length of the prism

Question 13

What form will the material being tested in the UTM need to be in?

Answer 13

A regular and reproducible specimen

Question 14

What could affect if a tooth is used for a sample?

Answer 14

The history of the tooth. - damage, etc

Question 15

Describe what is shown in the elastic region

Answer 15

Initially the stress is proportional to strain

Deformation is recoverable

Question 16

What is shown in the plastic region?

Answer 16

Permanent deformation

Question 17

What is the point where the elastic and plastic regions meet?

Answer 17

The elastic limit, proportional limit or yield point

Question 18

What is the highest value for stress termed?

Answer 18

Strength

Question 19

What is Young’s modulus?

Answer 19

The slope of the elastic region - modulus of elasticity

Question 20

What is a complaint material?

Answer 20

A material with a low stiffness

Question 21

What does a higher Young’s modulus mean?

Answer 21

The stiffer the material

Question 22

Which tooth tissue is easily deformed?

Answer 22

PDL - relatively easily elastic ally deformed.

Question 23

What is aberfraction of the tooth?

Answer 23

Where cyclic loading had lead to enamel spooling at the neck of the tooth

Question 24

Fatigue is a major problem in regards to which device?

Answer 24

Posts - used to fix crowns to devitalised teeth which have their pulps extracted

Question 25

What affects the highly ware resistant enamel?

Answer 25

Our diets and bad oral habits

Question 26

What assumptions can we make about hard materials?

Answer 26

That they have higher ware resistance and are more abrasive

Question 27

Name and explain a hardness scale

Answer 27

- Mohs’ hardness scale - 1 to 10 talc to diamond - scratch one material with another - the less hard material is scratched

Question 28

How do we define fracture toughness?

Answer 28

The Griffith Equation

Question 29

What does the growth of a crack/fault lead to?

Answer 29

Failure | All materials have flaws/cracks

Question 30

How do you increase rapture toughness?

Answer 30

Make the path of crack more difficult

Question 31

How does the structure of the tooth increase fracture toughness but what is the issue with the nature of the tooth?

Answer 31

Cracks are deflected from common paths | Tooth is anisotropic - higher fracture toughness on one plane as oppose to another

Question 32

Explain the know test vickers test

Answer 32

An indent with equal length diagonals and cracks emanating from their tips are measured Notoriously hard to do correctly

Question 33

How do you test fracture toughness with a biaxial flexure rig?

Answer 33

- indent is placed opposite top loading piston - sample loaded till it fails maximum load - other variable then used to calculate fracture toughness Unfortunately cant generate big enough disks of enamel or dentine

Question 34

How does an impact tester work?

Answer 34

- hammer strikes specimen - specimen will break on absorbing some energy from the hammer - hammer travels less high - measure difference in pendulum travel - calculate energy absorbed -> impact energy

Question 35

Which wavelengths do (near) white teeth reflect?

Answer 35

All wavelengths- reasonably well

Question 36

Why does the inside colour of the tooth effect its appearance?

Answer 36

Enamel is quite translucent - esp at tips

Question 37

What does value mean?

Answer 37

How light or dark a colour is

Question 38

What is important to make sure of when matching shades/colours?

Answer 38

Quality of light source - natural north light - flat and even - possible Edith electric light