Composition, properties of amalgam

1. DENTAL AMALGAM
Material aspect

2. OBJECTIVES
 Introduction
 Compositions and functions of each element
 Classifications
 Setting reactions
 Clinical significance of each phases
 Manipulation and types of mixes
 Properties of Amalgam

3. INTRODUCTION
 Amalgam technically means an alloy of mercury with any other
metal. It is an alloy made by mixing mercury with a silver-tin dental
amalgam alloy.

4.  ADA specification : No.1 (amalgam alloy)
 ADA specification : No.6 (mercury)

5. CLASSIFICATIONS
 Based on copper content
1. Low copper alloy
2. High copper alloy
3. High copper admixed alloy
4. High copper unicompositional alloy

6.  Based on particle shape
1. Lathe cut alloy
2. Spherical alloy
3. Admixed alloy
 Based on size of alloy particle
1. Microcut
2. Macrocut

7.  Based on zinc content
1. Zinc containing alloys
2. Zinc free alloys
 Based on number of alloyed particle
1. Binary alloys
2. Ternary alloys
3. Quaternary alloys

8. COMPOSITION
Constituents Low copper
%
Admixed % Unicompositi
onal %
Silver 63-70 69 40-60
Tin 26-29 17 22-30
Copper 2-5 13 13-30
Zinc 0-2 1

9. FUNCTIONS OF ELEMENTS
 Silver
1. Major component of alloy
2. Whitens the alloy
3. Increase strength
 Copper
1. Increases strength
2. Resists tarnish and corrosion
3. Reduces creep

10.  Tin
1. Reduces strength and hardness
2. Increases setting time
 Zinc
1. To prevent oxidation of the other alloy constituents
2. Responsible for delayed expansion

11. SETTING REACTIONS
 Alloy particle + mercury = Amalgam+ non reacted particle

12. LOW COPPER AMALGAM
 Ag Sn + Hg = AgHg +SnHg + unreacted AgSn
1. AgSn >>> gamma phase
2. AgHg >>> gamma 1 phase
3. SnHg >>> gamma 2 phase

13. HIGH COPPER ADMIXED
 PHASE 1:
AgSn + AgCu + Hg = AgHg + SnHg + AgSn + AgCu
1. AgSn >>> gamma phase
2. AgHg >>> gamma 1 phase
3. SnHg >>> gamma 2 phase

14.  Phase 2
SnHg + AgCu =CuSn + AgHg +AgCu
1. SnHg >>> Gamma 2 phase
2. CuSn >>> Etta phase
3. AgHg >>> Gamma1 phase

15. HIGH COPPER
UNICOMPOSITIONAL
ALLOYS
 AgCuSn +Hg = AgHg +CuSn +unreacted AgCuSn
1. AgHg >>> Gamma 1 phase
2. CuSn >>> Etta phase

16. SIGNIFICANCE OF EACH
PHASES
 The Gamma 1 is somewhat strong and corrosion resistant but it is
also brittle . Its makes up approximately half of the amalgam and is
the matrix phase that holds the dental amalgam together .

17.  The Gamma phase is typically the strongest and most corrosion
resistant phase .it s approximately one quarter of the volume of a
dental amalgam .
 The Gamma 2 phase is the weakest and the most corrosion prone
. Its makes up approximately one teeth of the material and is the
weakest part of the dental amalgam .

18. MANIPULATION
The process of mixing alloy and mercury is called trituration .
It can be either ;
Hand trituration (mortar and pestle )
mechanical trituration ( amalgamators )

19. TYPES OF MIXES
 NORMAL MIX
Warm
Homogenous
Shiny in appearance

20.  OVERTRITURATED MIX
Soupy consistency
difficult to handle
 UNDERTRITURATED MIX
Grainy , dull in appearance
Low strength and poor resistance to corrosion due to rough
surface

22. PROPERTIES
 Compressive Strength : Admixed alloy has strength of 430MPa after 7 days.
 Tensile strength : 50MPa after 24hrs
 Increased mercury leads to increased expansion, creep and corrosion.
 Zinc on contamination with water causes delayed expansion.
 Creep is a time dependent plastic deformation that is common in amalgam.
 Corrosion is less in high copper amalgam .
 Non aesthetic hence used as posterior restorative material.
 Easily condensable, finishable and polishable.

23. THANK
YOU