H - DMS Flashcards

1
Q

How to from martensite?

A

Quenching of austenite

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2
Q

What percentage of Cr is there in SS?

A

13%

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3
Q

Ideal properties of impression material?

A
Low viscosity
Low viscoelasticity
Low stiffness 
Low thermal Expansion
Low polymerisation shrinkage 
High tear resistance 
High surface detail
Dimensionally stable
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4
Q

What is weld decay in SS?

A

Occurs between 500-900 degrees
Chromium carbide precipitate at the grain boundaries
Alloy brittle
Minimise by low carbon content In steel

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5
Q

What are the pros and cons of self-cured PMMA compared with heat-cured?

A
Pros 
Much quicker to make 
Less thermal contraction
Cons 
irritant to tissues - unreacted monomer 
Water absorption and expansion
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6
Q

Examples of temp materials are direct/indirect? short/long term?

A

PMMA - indirect, long
PEMA - direct, short
Bis-arcylic composite - direct, long

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7
Q

Requirement of wires, (desirable properties)

A

Must be springy - High EL YM
Stiffness
High ductility -
Corrosion resistance - resistance to reactions within their environment

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8
Q

What is sintering in dental ceramics?

A

When a crown is heated in a furnace above glass transition temp
Ceramic particles fuse to form a solid mass

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9
Q

What is kaolin? and what is it replaced with in dental ceramics?

A

A soft white clay which makes other ceramics opaque

Replaced with silica and feldspar

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10
Q

The function of alumina core?

A

High flexural strength, prevents cracks propagating through ceramic material

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11
Q

How does yttria (yttrium oxide) work in zirconia core

A

Crystal structure changes shape if a crack appears

causes slight expansion to close the crack

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12
Q

Sintered vs milled ceramics?

Which is stronger

A

Milled

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13
Q

Causes of endodontic instrument fracture?

A

Torsional stress

Cyclic stress/fatigue - generation of tension/compression forces leads to failure

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14
Q

Properties of NiTi Endo instruments?

A

Super elasticity

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15
Q

Ideal properties of obturation material?

A
Dimensionally stable 
Seals canal 
non-irritant
Bacteriostatic/cidal 
radiopaque 
Doesn't discolour tooth
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16
Q

What stops the transition to martensite in austenitic SS?

A

Sufficient Cr and NI

17
Q

By what mechanism can porcelain bond to metal?

A

Chemical - electron sharing in oxides
Stress skin effect - slight differences in thermal contraction leads to compressive forces
mechanical - surface irregularities

18
Q

Process of lost wax technique?

A

Wax pattern made
investment material passed around it
Wax then eliminated
Molten alloy forced into mould via channels in investment material

19
Q

Why do investment materials need to be porous?

A

As if porous it prevents incomplete casting by allowing escape of gases

20
Q

Types of luting agents?

A

GIC
Composite luting agents
Conventional cements e.g zinc phosphate
RMGIC - however, HEMMA expands when wet