CSA physical and mechanical properties Flashcards
What is tension?
Stretching the material tight
What is compression?
Subjecting material to compressive stress
What affects tension/compression?
extending or shrinking length of material
What are torsion/ sheer/ flexural modes?
ways in which we exhort tension & stress on a material
What is universal testing machine?
Deforms sample in regular & controlled way whilst monitoring the force applied
What is a stress strain cruve ?
o Stress = Force/ Area
o strain = Change in dimension/ Original length
What is elastic region on stress strain curve?
Stress proportional to strain & deformation is recoverable
What is slope in stress strain curve?
slope = young’s modulus (E)
higher modulus, stiffer the material
What is plastic region on stress curve >
Stress is no longer proportional to strain & deformation here isn’t recoverable
What is the point where elastic region & plastic region meet
Elastic limit/Proportional limit/Yield point
What factors do teeth have affecting them?
bone/ PDL (shock absorbers)/enamel/dentine
What is resilient ?
PDL not the actual brittle tooth , PDL adds toughness to system
What does cyclic loading lead to ?
fatigue
What does cyclic loading result in?
materials failing at lower stresses below their ultimate strength
What does cyclic loading do to teeth?
abfraction (enamel spooling/flaking) at the neck of tooth
Why is fatigue a problem with posts to fix crowns to dead teeth ?
bad designed post & core leads to failure of cement so post to flex & results in post becoming fatigued
Where are ware resistant areas on our teeth?
highly ware resistant collagen free regions on surface of teeth
What do we need to consider about wear resistance of restoration materials ?
some materials wear out opposing dentition – need material wears more easily than opposing tooth – no damage done to dentition
What are hard materials like?
more wear resistant and abrasive
What is knop hardness test?
diamond to create a small indentation on a surface
What is fracture toughness defined by?
griffith equation
Why do materials fail due to a crack
crack grows when stress applied
How to measure fracture toughness?
vickers hardness test
What do we do in LDI for fracture toughness?
place materials crack opposite a piston & then loaded until it fails – can’t generate large enough slab of enamel/dentine to carry out tests
what is impact toughness?
• Teeth undergoing trauma may result in impact
What do near white teeth reflect?
all wavelengths equally
Is enamel translucent?
quite translucent as It lets a lot of light through at the tips
When should dental shade guide be carried out
out in good lighting – good quality light source
• Traditionally this is north light (flat light) – can be obtained from electric light
