OK, I've tried googling, and I still don't have an answer...

HOW does the amalgam process work?
I know it invovles mercury (although some don't..) and it basically
allows metal to be molded into your teeth.. essentially making the metal
act like epoxy resin (ie fluid for a "setting up" period, then hard
forevermore.).

Can someone please explain the theory about how it works?

Thanks,
Des
Brisbane
OZ

From:
http://www.brooks.af.mil/dis/DMNOTES/amalgam.pdf

DENTAL AMALGAM

Historical Composition

G.V. Black believed that amalgam should consist of:

67% silver, 27% tin, 5% copper, and 1% zinc

Low-Copper (Traditional, Conventional) Amalgam

Composition:

Silver 60%

Tin 29%

Copper 6%

Zinc 2%

General Setting Reaction:

Ag Sn + Hg ---- Ag Sn + Ag Hg + Sn Hg 3 3 2 3 8

silver-tin mercury silver-tin silver-mercury tin-mercury

gamma gamma gamma 1 gamma 2

When low-copper amalgam is triturated, mercury diffuses into

the silver-tin particles and silver and tin dissolve, to a

very limited extent, into the mercury. As this occurs, the

particles become smaller. Because the solubility of both

silver and tin in mercury is limited (0.035 and 0.6 weight

percent respectively) and because silver is much less soluble

in mercury than is tin, silver precipitates out first as

silver-mercury (gamma 1) followed by tin in the form of tinmercury

(gamma 2).

The set amalgam consists of core gamma particles surrounded by

a matrix of gamma 1 and gamma 2.

High-Copper (New-Generation, Gamma-2 Free) Amalgam

Composition:

Silver 40% to 70%

Tin 12% to 30%

Copper 12% to 30%

Indium 0% to 4%

Zinc 0% to 1%

Palladium 0.5%

High-copper amalgam was developed in 1962 by the addition of

silver-copper eutectic particles to traditional silver-tin

lathe-cut particles in an attempt to dispersion strengthen or

dispersion harden the alloy. Although clinical tests showed 1

that these new alloys had better physical properties, the

improvement was not due to dispersion hardening (because the

silver-copper eutectic particles were too large and too far

apart to impede dislocation movement) but rather were the

result of formation of Cu Sn , the eta phase. The fact that 6 5

tin had a greater affinity for copper than for mercury meant

that the gamma-2 phase was reduced or eliminated. This

resulted in the dramatic improvement in physical properties.

It is important to note that high-copper alloys must contain

at least 12% copper to eliminate the gamma-2 phase. Compared

to their low-copper amalgam counterparts, high-copper alloys

exhibit the following physical properties: greater strength,

less tarnish and corrosion, and less creep. Overall, they are

also less sensitive to handling variables and produce better

long-term clinical results.

Purposes of Constituents in Amalgam

Silver -- increases strength and expansion

Tin -- decrease strength and expansion and lengthens the

setting time.

Copper -- increases strength, reduces tarnish and

corrosion, and reduces creep and, therefore, marginal

deterioration. Copper accomplishes these effects by tying up

tin, preventing the formation of gamma 2, the weakest, most

tarnish- and corrosion-prone phase, and the phase with the

highest creep values. In addition, it reduces creep by tying

up tin and forming copper-tin (Cu Sn ), the eta phase, whose 6 5

crystals interlock to prevent slippage and dislocations at the

grain boundaries of gamma-1 particles which is a major cause

of creep in amalgam. Is added at the expense of the silver.

Copper is insoluble in mercury.

Zinc -- is added for the benefit of the manufacturer

because it prevents oxidation of the other metals in the alloy

during the manufacturing process; in so doing, it keeps the

alloy from turning dark. Zinc accomplishes this by combining

readily with oxygen to form zinc oxide. An alloy with 0.01%

zinc is "zinc-free" while an alloy with 0.01% zinc is "zinccontaining".

If a low-copper, zinc-containing alloy is

moisture contaminated, it will result in surface blistering,

internal corrosion, and a delayed expansion of up to 4% by

volume beginning 3 to 5 days after the contamination and

continuing for up to six months. This can lead to a reduction

in strength of up to 24%. Although, moisture contamination 2

of zinc-containing high-copper amalgams has not been shown to

cause delayed expansion, moisture contamination of all types 3,4

of amalgam should be avoided because it can cause a reduction

in strength. Research has found that high-copper amalgam

alloys that contain zinc in a 1% concentration exhibit lower

rates of margin fracture than do zinc-free alloys. This is 5

believed to be due to zinc's behavior as a sacrificial anode

which delays corrosion of tin in the Cu Sn phase.

--


Don Thompson

Ex ROMAD


"Des Bromilow" wrote in message
...
OK, I've tried googling, and I still don't have an answer...

HOW does the amalgam process work?
I know it invovles mercury (although some don't..) and it basically
allows metal to be molded into your teeth.. essentially making the metal
act like epoxy resin (ie fluid for a "setting up" period, then hard
forevermore.).

Can someone please explain the theory about how it works?

Thanks,
Des
Brisbane
OZ

ask at sci.med.dentistry .


"Des Bromilow" wrote in message
...
OK, I've tried googling, and I still don't have an answer...

HOW does the amalgam process work?
I know it invovles mercury (although some don't..) and it basically
allows metal to be molded into your teeth.. essentially making the metal
act like epoxy resin (ie fluid for a "setting up" period, then hard
forevermore.).

Can someone please explain the theory about how it works?

Thanks,
Des
Brisbane
OZ

Thanks!!!!
So basically the metal is dissolved in the mercury,

Yes. I was going to answer "they break a barrier in the capsule separating the
mixed powdered metals and the mercury, and then they shake it until it's well
mixed." I guess you're a little farther along than that....



Yours,

Doug Goncz, Replikon Research, Seven Corners, VA
Unpublished work Copyright 2003 Doug Goncz
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