Amalgam

Question 1

Define amalgam

Answer 1

An alloy containing mercury

Question 2

What is amalgam an alloy of?

Answer 2

Mercury

Question 3

Why is mercury an unusual metal?

Answer 3

It is liquid at room temperature s can form cloys at room temp

Question 4

What is the freezing point of mercury?

Answer 4

-39

Question 5

What is mercury used I?

Answer 5

Thermometers
Manometers
Tilt switches
Treatment for STDs

Question 6

Why is the use of mercury causing contention?

Answer 6

As it is a cumulative toxin

Question 7

Name the most dangerous state of mercury?

Answer 7

The organic state and mercury vapour

Question 8

How can mercury be rendered ‘‘safe’’?`

Answer 8

By combining it into an alloy or intermetalic compound

Question 9

What happens to a dental amalgam once it has been placed the patients mouth?

Answer 9

It becomes inert

Question 10

What is the maximum mercury exposure level according t the WHO?

Answer 10

300 mg per week
and/or
air concentration of the vapour of 25 mg/m3

Question 11

What is the half life of mercury?

Answer 11

60 days

Question 12

Name the components that make up dental amalgam

Answer 12

Liquid mercury (Hg)
Powder metal alloy

Question 13

What is the powder that makes up dental amalgam

Answer 13

It is an alloy of the remaining ingredients with the exact composition depending on manufactures preferences.

Question 14

What reaction occurs when amalgam and mercury mix together?

Answer 14

Hg + Ag3Sn -> Ag3Sn + Ag2Hg3 + Sn7Hg

Question 15

What is the gamma 1 phase fo dental amalgam,?

Answer 15

Ag2Hg3

Question 16

What is the gamma 2 phase for dental amalgam?

Answer 16

Sn7Hg

Question 17

What does dental amalgam contain small concentrations of?

Answer 17

Copper

Question 18

How much copper may be found in dental amalgam?

Answer 18

Below 6% and has little effect n the microstructure

Question 19

What is the gamma 1 phase also referred to as?

Answer 19

The matrix as it holds the structure together

Question 20

What has the gamma 2 phase been identified as?

Answer 20

Being susceptible to corrosion

Question 21

Why is corrosion bad in relation to dental amalgam ?

Answer 21

The products of corrosion tend to distort restorations particularly the mains and this can lead to marginal failure
Also corrosion causes staining of the surrounding tissues

Question 22

What are the remaining products of corrosion made of?

Answer 22

They are tin based

Question 23

What do we use to mix amalgam?

Answer 23

An amalgamator

Question 24

Why is vigorous mixing necessary?

Answer 24

It is required since mercury doesn’t wet the amalgam alloy very well

Question 25

State the 3 forms the amalgam alloy can be shaped into?

Answer 25

Lathe cut
Spherical
Mix of both

Question 26

How can we rid of gamma 2?

Answer 26

By adding more copper

Question 27

What % by weight of copper is added to the amalgam alloy?

Answer 27

12%

Question 28

Wat reaction occurs when copper is adde into a solution of gamma 2alloy?

Answer 28

Gamma 1 and Cu6Sn5 are made

Question 29

Where is th copper added in the amalgam?

Answer 29

Can be directly incorporated into the amalgam alloy such that the alloy is of 2 intermetalic compounds AgSn and Cu3Sn can be added in s fine powder

Question 30

What is the problem with amalgam?

Answer 30

1. It doesn’t adhere to the tooth
2. Not aesthetic as silver in colour
3. May be a need for a therapeutic liner or base material if cavity is large
4. Poor tensile strength
5. Send visit required 2 hours later to polish
6. Forms a corrosion layer
7. Creep may occur

Question 31

What type of retention occur in amalgam?

Answer 31

Entirely mechanical retention

Question 32

As amalgam can only adhere to the tooth mechanically what does th cavity require?

Answer 32

An undercut

Question 33

Describe the spherical morphology of amalgam?

Answer 33

It is thought to lead to th amalgam flowing better during condensation and so reduction in the amount of Hg needed to make workable material