On the Instability of Amalgams

- Abstract

- Introduction

- Micro structure

- Types of dental amalgams

- Formation of droplets...

- Increased mercury emission...

- References

  On the Instability of Amalgams...cont. - Micro structure

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Micro structure.

 

Metallic alloys are seldom homogenous blends of ingredients. If polished and studied under a microscope areas of different compositions can be observed. These are called phases.

Phases in dental amalgam can be classified as

I/ Alloy powder phases
II/ Initial phases
III/ Transformation phases

When a dental amalgam is prepared a metallic alloy powder is mixed with a certain amount of liquid mercury. This mass hardens resulting in a mix of unaffected alloy powder and new, initial phases. The metal is however not in a state of equilibrium (4). Over the time of years a transformation of the initial phases takes place creating new ones. The result is a mix of alloy, initial and transformation phases. The initial phases contain more mercury than the transformation ones giving free mercury as a result.

In the description of the compositions of different phases of amalgam dental researchers almost without exception use a terminology from the field of chemistry. In my opinion this nomenclature gives the false impression that these phases are stable chemical compounds. This is the reason for the unorthodox nomenclature used below.

Alloy phases

These are well-known and there is no dispute over their composition
g-phase (gamma): 3Ag/1Sn - conventional and non-gamma-two amalgams.
e-phase (epsilon): 3Cu/1Sn - non-gamma-two amalgams.

Initial phases

Several investigators have been trying to identify the composition of these phases. A great number of different compositions have been proposed:

g-1 (gamma-one): 2Ag/3Hg, 3Ag/4Hg, 4Ag/5Hg, 5Ag/8Hg, 11Ag/15Hg, 22Ag/29Hg, 22Ag/1Sn/27Hg (4). From recent scientific literature it is obvious that the g-1 phase contains some tin (4, 7, 8).

g-2 (gamma-two): 6Sn/1Hg, 7Sn/1Hg, 8Sn/1Hg (2, 4).

h' (eta-prim): 6Cu/5Sn (4).

What especially catches the eye is the great number of proposed compositions of the g-1 phase. This could be due to the transformation of g-1 to b-1, see below.

Transformation phases

b-1 (beta-one) 0.475Hg/0.45Ag/0.075Sn, 1Ag/1Hg (9, 10).

h' (eta-prim): 6Cu/5Sn (4).

 

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