CSA physical and mechanical properties

Question 1

What is tension?

Answer 1

Stretching the material tight

Question 2

What is compression?

Answer 2

Subjecting material to compressive stress

Question 3

What affects tension/compression?

Answer 3

extending or shrinking length of material

Question 4

What are torsion/ sheer/ flexural modes?

Answer 4

ways in which we exhort tension & stress on a material

Question 5

What is universal testing machine?

Answer 5

Deforms sample in regular & controlled way whilst monitoring the force applied

Question 6

What is a stress strain cruve ?

Answer 6

o Stress = Force/ Area

o strain = Change in dimension/ Original length

Question 7

What is elastic region on stress strain curve?

Answer 7

Stress proportional to strain & deformation is recoverable

Question 8

What is slope in stress strain curve?

Answer 8

slope = young’s modulus (E)

higher modulus, stiffer the material

Question 9

What is plastic region on stress curve >

Answer 9

Stress is no longer proportional to strain & deformation here isn’t recoverable

Question 10

What is the point where elastic region & plastic region meet

Answer 10

Elastic limit/Proportional limit/Yield point

Question 11

What factors do teeth have affecting them?

Answer 11

bone/ PDL (shock absorbers)/enamel/dentine

Question 12

What is resilient ?

Answer 12

PDL not the actual brittle tooth , PDL adds toughness to system

Question 13

What does cyclic loading lead to ?

Answer 13

fatigue

Question 14

What does cyclic loading result in?

Answer 14

materials failing at lower stresses below their ultimate strength

Question 15

What does cyclic loading do to teeth?

Answer 15

abfraction (enamel spooling/flaking) at the neck of tooth

Question 16

Why is fatigue a problem with posts to fix crowns to dead teeth ?

Answer 16

bad designed post & core leads to failure of cement so post to flex & results in post becoming fatigued

Question 17

Where are ware resistant areas on our teeth?

Answer 17

highly ware resistant collagen free regions on surface of teeth

Question 18

What do we need to consider about wear resistance of restoration materials ?

Answer 18

some materials wear out opposing dentition – need material wears more easily than opposing tooth – no damage done to dentition

Question 19

What are hard materials like?

Answer 19

more wear resistant and abrasive

Question 20

What is knop hardness test?

Answer 20

diamond to create a small indentation on a surface

Question 21

What is fracture toughness defined by?

Answer 21

griffith equation

Question 22

Why do materials fail due to a crack

Answer 22

crack grows when stress applied

Question 23

How to measure fracture toughness?

Answer 23

vickers hardness test

Question 24

What do we do in LDI for fracture toughness?

Answer 24

place materials crack opposite a piston & then loaded until it fails – can’t generate large enough slab of enamel/dentine to carry out tests

Question 25

what is impact toughness?

Answer 25

• Teeth undergoing trauma may result in impact

Question 26

What do near white teeth reflect?

Answer 26

all wavelengths equally

Question 27

Is enamel translucent?

Answer 27

quite translucent as It lets a lot of light through at the tips

Question 28

When should dental shade guide be carried out

Answer 28

out in good lighting – good quality light source

• Traditionally this is north light (flat light) – can be obtained from electric light