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Dental material science > Amalgam > Flashcards

Amalgam Flashcards

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1
Q

What is the composition of amalgam

A

Dental Amalgam is an alloy formed by the reaction of
-mercury (liquid) ​
-silver, tin, copper & other metals (powder)

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2
Q

What are the metals within amalgam

A

Ag (silver) 70%
Sn (tin) 25%
Cu (copper) 3%
Zn (zinc) 1%
Hg (merury) 1%

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3
Q

What does copper do

A

Increases strength and hardness

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4
Q

How are lathe cut particles formed

A

By filling ingots

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5
Q

What are the types of particles

A

Lathe cut
Sperical, speroidal

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6
Q

How are spherical particles formed

A

By spraying molten metal into inhert atmosphere

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7
Q

What is the amalgam setting reaction

A

Ag3Sn + Hg ——-> Ag3Sn + Ag2Hg3 + Sn7Hg9

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8
Q

What forms the amalgam matrix

A

g1 and g2
(Ag2Hg3) and (Sn7Hg9)

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9
Q

What is the composition of Gamma, Gamma 1 and Gamma 2

A

g good strength & corrosion resistance​
g1 good corrosion resistance
g2 weak and poor corrosion resistance

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10
Q
A
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11
Q

What is the gamma phase

A

(Ag3Sn)

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12
Q

How many phases does amalgam have

A

3

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13
Q

What property does zinc have in amalgam

A

Oxidising agent

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14
Q

How does zinc interact with saliva and blood

A

interaction of zinc with saliva / blood -​

Zn + H2O ZnO + H2

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15
Q

What do the bubbles of H2 formed within amalgam cause

A

pressure build up causes expansion​

downward pressure cause pulpal pain​

upward - restoration sitting proud of surface

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16
Q

What are the advantages of spherical particles

A

less Hg required​

higher tensile strength​

higher early compressive strength​

less sensitive to condensation ​

easier to carve

17
Q

Name 5 amalgam properties

A

Strength
Creep
Thermal expansion
Radioplaque
Not Anticariogenic
Thermal conductivity
Rigidity

18
Q

What factors can decrease the strength of amalgam

A

undermixing

too high Hg content after condensation

too low condensation pressure

slow rate of packing increments do not bond​

corrosion

19
Q

What is creep

A

When a material experiences low-level stress levels (ie below elastic limit stress) which are applied repeatedly over a prolonged time period, it may FLOW, resulting in PERMANENT DEFORMATION

20
Q

Why does amalgam experience creep

A

Visco-elastic material

21
Q

What do the properties thermal expansion, thermal conductivity and thermal diffusivity mean for amalgam fillings

A

Thermal expansion - x 3 of tooth

Thermal Conductivity – high, may need to use liner / varnish in deep cavities

Thermal diffusivity – high, so when a transient thermal stimuli is applied (eg drinking tea) amalgam’s temperature rises quickly

22
Q

What is copper enriched amalgam

A

Doesnt contain the g2 phase, contains >6% copper

23
Q

What are the advantages amd disadvantages of enamel

A

Advantages
strong
hard
durable
radiopaque​
user friendly

Disadvantages​
corrosion​
leakage - does not bond​
poor aesthetics​
mercury:​
- perceived toxicity
- environmental impact

24
Q

Which amalgam has the least creep

A

Copper single composition

25
Q

Which amalgam has the greastest creep values

A

Traditional lathe

26
Q

Rate amalgam best - worst

A

Copper single
Copper dispersion
Traditional spherical
Traditional Lathe

27
Q

What are the benefits of copper enriched

A

Higher early strength​

Less creep​

Higher corrosion resistance​

Increased durability of margins

28
Q

What is the setting reaction of single composition copper amalgam

A

Ag-Sn-Cu + Hg ——> Ag-Sn-Cu + g1 + Cu6Sn5

29
Q

What does the first stage of the Dispersion Modified Setting Reaction produce

A

Gamma, Gamma 1 and Gamma 2

30
Q

What is the second phase of the Dispersion Modified ​
Setting Reaction

A

g2 + Ag-Cu ——> Cu6Sn5 + g1​
(takes several days)

31
Q

What is fully consumed within the Dispersion Modified ​
Setting Reaction

A

Gamma 2

32
Q

Why is the copper enriched amalgam setting reactions better

A

NO G2 PRODUCED
(all used up in dispersion)

33
Q

Why is gamma 2 not wanted

A

Most prone to corrosion

Dental material science (5 decks)

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