Amalgam

Question 1

What is amalgam?

Answer 1

Dental amalgam is an alloy made by mixing mercury with silver tin alloy.

Question 2

Amalgam consists of?

Answer 2

Mercury combined with powdered silver-tin alloy

Question 3

Why mercury suitable to be used in dentistry?

Answer 3

Liquid at room temperature and is able to form workable mass when mixed with alloy. This behaviour makes it suitable

Question 4

What is amalgamation reaction?

Answer 4

• Reaction between mercury and alloy which follows mixing
• It results in formation of hard restorative material of silver grey appearance
• The colour generally limits its use in those cavities where appereance is not of primary concern

Question 5

Why mercury in dental amalgam should be purified?

Answer 5

• it is purified by distillation
• to ensure elimination of impurities so that it does not affect setting characteristics and physical properties of amalgam

Question 6

Composition of amalgam?

Answer 6

• MAJOR COMPONENTS: Silver, tin, copper

* MINOR COMPONENTS: zinc, mercury, palladium

Question 7

What is silver tin compound and its importance?

Answer 7

• Ag and Sn react to form Ag3Sn intermatellic compound
• this compound is known as Y phase
• its advantage is, it readily undergoes amalgamation reaction with mercury.

Question 8

Role of copper in amalgam?

Answer 8

• most conventional alloys contain arround 5% copper

* it gives strengthening effect on set amalgam

Question 9

Role of zinc in amalgam?

Answer 9

• is a scavenger during production of alloy
• alloy is formed by melting of all constituent metals together at elevated temperature so for this purpose there is tendency for oxidation to occur
• oxidation of Sn,Cu or silver would affect properties of alloy and amalgam
• zinc reacts rapidly with oxygen and forms slag of ZnO which is easily removed

Question 10

How oxidation is prevented in zinc free alloys?

Answer 10

By carring out procedure in inert atmosphere

Question 11

What are pre amalgamated alloys?

Answer 11

Alloys which contain3% mercury

Question 12

Which 2 methods are used to produce powder particles?

Answer 12

1) lathe cut: amalgam powder made by grinding and milling.
* Size~ 1-40um
* irregular shape

2) atomization: molten alloy is sprayed into column filled with inert gas
* equal size particles
* spherical shape

Question 13

Which 2 heat procedures carried out on lathe cut alloys?

Answer 13

•Before lathe cutting:
1) homogenisation heat treatment:
*alloy ingot is heated at 420C for several hours
*the resulting alloy contains homogeneous grains of Ag3Sn compound
* large grains of Y phase
•After lathe cutting 2nd heat treatment
2) alloy ageing:
* heat the alloy at 100C for 1 hour
* it removes residual stress introduced during cutting

Question 14

Classification of amalgam according to number of alloy metals?

Answer 14

1) Binary alloys: silver-tin
2) ternary alloys: silver-tin-copper
3) quaternary alloys: silver-tin-copper-indium

Question 15

Classification of amalgam to whether the powder consists of unmixed or admixed alloys?

Answer 15

Certain amalgam powders are only made up of one alloy. Other have one or more alloys or metals physically added to the basic alloy. Eg adding copper to binary silver tin alloy

Question 16

Classification of amalgam according to shape of powdered particles?

Answer 16

1) spherical shaped (smooth surfaced spheres)
2) lathe cut (irregular spindles)
3) admixed (combination of lathe cut and spherical)

Question 17

Classification of amalgam according to powder particle size?

Answer 17

1) micro cut
2) fine cut
3) coarse cut

Question 18

Classification of amalgam according to copper content of powder?

Answer 18

1) low copper content (1-6%)

2) high copper content (more than 6%)

Question 19

Where amalgam is used?

Answer 19

1) class 1 and class 2 cavities
2) cuspal restorations (with pins usually)
3) cavities in posterior teeth, used in combination with composite resins
4) as a die material
5) class 3 in unaesthetic areas
Class 5 lesions in non aesthetic areas

Question 20

Where amalgam should not be used?

Answer 20

1) anterior teeth where aesthetics is of primary concern

2) prominent areas of posterior teeth

Question 21

What are the advantages of amalgam used in dentistry?

Answer 21

1) easy to use, easy to manipulate
2) relatively inexpensive
3) excellent wear resistance
4) Restoration is completed within one sitting
5) good compressive strength
6) sealing ability improves with age by formation of corrosion products at tooth amalgam interface
7) bonded amalgam has less micro leakage

Question 22

Disadvantages of amalgam?

Answer 22

1) non aesthetic appearance
2) tarnish and corrosion
3) metallic taste and galvanic shock
4) Discolouration of tooth structure
5) lack of chemical and mechanical adhesion to tooth structure
6) mercury toxicity
7) promotes plaque adhesion