Clinical Aspects Of Amalgam

Question 1

What is amalgam?

Answer 1

An alloy of silver, mercury and tin with other metals to modify the properties.

Question 2

How is amalgam made?

Answer 2

Alloy powder and liquid Mercury making a paste that sets hard.

Question 3

What do amalgam capsules contain?

Answer 3

Alloy powder, mercury and membrane separating the two.

Question 4

What are the two forms of alloy powder?

Answer 4

Spherical - made by spraying molten metal into fine mist

Lathe cut - creating an ingot of alloy and grinding down to a powder

Question 5

How do the two forms of amalgam differ in their handling?

Answer 5

Spherical - softer more flowable

Lathe cut - less flowable good for building up large amounts of missing tooth structure

Question 6

How do the powder and mercury mix.

Answer 6

The mercury surrounds the particles of powder that dissolve into a solution of mercury tin and silver. Metal ions fuse with each other to make new compounds.

Ag3Sn - gamma
Ag2Hg3 - gamma 1
Sn7Hg - gamma 2

Question 7

What is gamma 2?

Answer 7

Unwanted product Sn7Hg
Leads to corrosion
Cheap - changes shape under load
Decrease in strength 
BUT can seal the cavity against microleakage

Question 8

How do we reduce the amount of gamma 2?

Answer 8

Add copper, converts gamma 2 to a copper compound

Question 9

What is admixed amalgam?

Answer 9

Lathe cut, spherical and copper compound mixture of amalgam

Question 10

What is the composition of amalgam?

Answer 10

Silver - 65%
Tin - 29%
Copper - 6-13
Zinc - 2 max

Question 11

What does zinc do?

Answer 11

Added to prevent silver from oxidising during manufacture, acts as a scavenger for oxygen but not needed if produced in a vacuum.
Can cause a large expansion or the material as it sets

Question 12

How much mercury should amalgam contain?

Answer 12

Slightly more than 50% as less than makes the mixture too crumbly
Remove excess mercury by packing as it weakens the restoration, excess mercury is brought to the top.
Final restoration has less than 50%

Question 13

Advantages

Answer 13

Good compressive strength
Good wear resistance 
Kind to opposing teeth
Easy to use
Chemically set
Cheap
Radio-opaque - can see if there is secondary caries easily

Question 14

Disadvantages

Answer 14

Not adhesive - undercuts
Weak in thin sections deliberately have to remove more tooth tissue
Thermal conductor
Unaesthetic
Occasional lichenoid reactions

Question 15

Indications

Answer 15

Larger cavities in posterior teeth
Where heavy occlusal forces encountered - clenching
Where aesthetics aren’t important
High caries rate patients
Posterior restorations that extend subgingivally - moisture
Building up broken down teeth before crowning

Question 16

What is retention?

Answer 16

Prevention of being pulled out of the cavity vertically

Question 17

What is the cavity design for amalgam?

Answer 17

Infected dentine removed affected left
Clean walls
No unsupported enamel
Undercut
Cavo surface angle >90 angle between surface of the tooth and cavity
Width interproximally should be just wider than the contact area
Amalgam margin angle >70 degrees

Question 18

What do pins do?

Answer 18

Acts as a wall to help amalgam stay in place

Question 19

What are pits and grooves?

Answer 19

Retentive features for amalgam to lock in to

Question 20

What is a bonded amalgam?

Answer 20

Adhesive system containing mdp or 4-META forming a hybrid layer with dentine and a chemical bond to amalgam.
Wet uncurled RMGIC can have amalgam placed directly on top

Question 21

Advantages of polishing?

Answer 21

Less plaque retentive, reduces corrosion, looks nicer

Question 22

Disadvantages of polishing

Answer 22

Will not increase life expectancy of restoration

Heat generated may damage the pulp

Question 23

When is mercury vapour ingested?

Answer 23

When it is mixed, placed or removed

Released from filling when brushing and eating

Question 24

Problems with mercury and the environment

Answer 24

Can be converted by bacteria to methyl mercury in fresh and salt water, which is highly poisonous

Question 25

What was said at the minimata convention?

Answer 25

Phase down of amalgam by 2020 and ban mercury containing products
Call for a cease of teaching amalgam by 2015
Composite will become the most widely used type of material in posterior teeth

Question 26

Recommendations for phase down of amalgam

Answer 26

Shall only be used in pre dosed encapsulated form
Shall not be used for deciduous teeth in children under 15, pregnant women or breastfeeding women except when strictly necessary.
All dental facilities should be equipped with an amalgam separator
Report spills
Put empty capsules into pots that are named
Clean heads in designated sinks