Dental Amalgam--Dr. Ashman

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Amalgam definition:

From the greek word malagma (meaning poultice or soft mass)

An alloy in which mercury is one of the components, presenting as a soft sivery paste, when freshly prepared, which hardens into a solid mass.

Historical background of amalgam:

used in dentistry for over 175 years
began in Europe in 1820s
used in US since 1830s

While it's use has been controversial at times, due to the perception that mercury can be released, many agencies have confirmed it is not harmful. These agencies include:

WHO
NIH
USPHS
Swedish Medical Research Council

If a patient had 12 amalgam restorations in his/her mouth, the amoutn of metallic mercury released per day would be in the range of _________ micrograms (a very small amount). The World Health Organization has estimated that eating seafood once a week raises urine mercury levels to 5-20 micrograms/L. This is _________ the level of exposure from amalgam.

1.7 micrograms per day

twice the level of amalgam

Which causes more mercury to be released: eating common fish or daily exposure to amalgam restorations?

Eating fish

What are the advantages of amalgam?

*Less than 1% of the population show allergies to it
*Strong, durable, relatively easy to use
*Wear = similar to tooth structure
*Corrosion at margins which resists microleakage at the interface of the tooth w/ the filling
*Molars restored with amalgam were much less likely to require endodontic therapy than molars restored with composite
*REPLACING an amalgam filing results in much less removal of excess tooth structure than removal of a composite
*least time consuming to place
*lowest cost of all "permanent" restorative materials

Why does replacing an amalgam restoration result in less tooth structure compared to a composite restoration replacement?

The amalgam is a different color than tooth structure and it does not bond to the tooth, these both make it easier to take out the least amount of tooth structure when replacing.

What are the disadvantages of amalgam?

*not tooth colored
*does not bond to tooth structure on its own
*contains Hg, which in its elemental form can be dangerous is mishandled
*patient perception is hard to overcome, fewer patients are agreeing to have amalgam fillings
*INITIAL placement of amalgam requires a less conservative preparation.
*Amalgam crowns on endodontically treated teeth can be long lasting

What are some uses of dental amalgam?

*direct, full contour restorations
*build-up of endodontically treated teeth
*most often this restoration serves as a foundation to support a full-coverage crown restoration.
*closing the endodontic access in overdenture abutment teeth
*apical seal for a surgical endodontic therapy

What are the typical constituents of amalgam?

Silver
Tin
Copper
Zinc
Indium
Palladium

Terms on slide #16

Know for exam:
Alloy for dental amalgam
Amalgam
Amalgamation
Creep
Delayed expansion
Dental Amalgam
Dental Amalgam Alloy
Marginal breakdown
Trituration
Condensation

Dental Amalgam Alloy:

Particles of Alloys of:
Ag
Sn
CU
Zn
In
Pd
(may be filings OR spherical)

Dental Amalgam = _____________ + _________.

Dental Amalgam Alloy + Hg (mercury) = dental amalgam

What does "low copper" alloy mean?

Low copper = < 6%

What is the typical composition of a low copper alloy?

Ag (65%)
Sn (29%)
Cu (<6%)
Other (<1%) --most commonly zinc

Who came up with the historical composition of the low copper alloy?

GV Black

What are the steps in formation of the alloy for dental amalgam?

*elemental metals melted together to form an INGOT
*INGOT broken down depending on desired form
*LATHE CUT to form irregular jagged particles
*Atomized to form sperical particles
*Different particle types can be used along or in ADMIXTURE

What are phases in amalgam alloys and set dental amalgams?

Phases are specific alloy combinations of metals found within the bulk of the alloy

Beta phase stoichiometry:

Ag4Sn

Gamma phase stoichiometry:

Ag3Sn

Gamma one phase stoichiometry:

Ag2Hg3

Gamma two phase stoichiometry:

Sn7-8 Hg

Epsilon phase stoichiometry:

Cu3Sn

Eta phase stoichiometry:

Ag-Cu

Eta prime phase stoichiometry:

Cu6Sn5

What are the steps of amalgam alloy formation?

*metallic elements smelted together to form an alloy
*molten alloy poured into ingots to cool (because of rapid cooling conditions from the as-cast state, an ingot of a silver-tin alloy contains nonhomogenous grains of varying composition)
*ingot goes to an oven for 24 hours at a temperature which produces an equilibrium phase relationship. (this temperature is just below the SOLIDUS temperature--the temp at which the last liquid solidifies)
*Cooling--Rapid cooling = high beta phase Ag4Sn, while slow cooling produces a maximum amount of gamma phase Ag3Sn
*Ingot is milled into rough, irregular shards OR atomized into roughly spherical nodules

Atomization of alloy to form spherical particles:

*Involves melting stock metal by induction heating and then allowing it to floow at a controlled rate through an atomizing nozzle.
*Metal is struck by high speed, preheated inert gas that disintegrates the stream of metal into fine droplets, which form into spheres as they descend through chamber.
*Most of the heavy droplets will be collected in this way but many smaller will be carried over in the gas flow and deposited into a 2nd chamber

What happens when mercury is added to the dental amalgam lathe-cut low copper alloys?

Amalgamation
*mercury comes in, starts to mix in with fragment. Tin and Silver in the outer portion start to dissolve into the mercury, while Hg is dissolving into the alloy particles. Silver is slower to dissolve, creating a crystal that gets bigger and bigger while consuming the mercury. The amalgam will begin to harden at this point. (working time is defined by these parameters)

Amalgamation occurs when:

mercury contacts the surface of the silver-tin alloy particles

Which is more soluble in mercury, Silver (Ag) or Tin (Sn)?

Tin is much more soluble:
Ag = .035
Sn = .600

Since Tin is much more soluble in Hg than Silver, the _________ particles precipitates first, then the ___________ precipitates later.

Gamma 1 phase first
Gamma 2 phase later

When the solubility in mercury is exceeded, ____________ of two binary metallic compounds precipitate into the mercury. These are the ________________ (____ phase) and __________________ (______ phase).

crystals of two binary metallic compounds

body centered cubic Ag2Hg3 (gamma 1 phase)
hexagonal Sn7-8Hg (gamma 2 phase)

Which phase precipitates first w/ low copper alloys?

gamma 1 phase
(because tin is much more soluble than silver, in mercury)

**these gamma 1 phase precipitates are cubic, body centric(Ag2Hg3)

Which phase precipitates second w/ low copper alloys?

gamma 2 phase

**these gamma 2 phase precipitates are hexagonal (Sn7-8Hg)

What are the 4 steps of amalgamation of low copper alloy (very basic description):

1-dissolution of silver and tin into mercury
2-precipitation of gamma 1 crystals in the mercury
3-consumption of the remaining mercury by growth of gamma 1 and gamma 2 grains
4-final amalgam set (reaction stops because there is no more Hg to react with the tin)

Immediately after trituration, what two parts coexist to give a plastic consistency to the mix?

powdered alloy and liquid Hg

As ________________ grows, free Hg liquid is consumed and the amalgam hardens.

gamma 1 and gamma 2 crystals

The usual mixture of 1 part Hg and 1 part alloy powder produces insufficient Hg to ________________________.

dissolve all the alloy powder, so there are unconsumed alloy particles in the set amalgam.

If there are unconsumed alloy particles in the set amalgam, what does this mean as far as excess Hg contributing to possible Hg toxicity to the patient?

All the Hg is tied up because it is bound to Sn or Ag--this prevents problems in patients concerning toxicity.

In 1963, Innes and Youdelis added what to the low copper alloy particles.

sperical particles of AgCu alloy.

**this was the first change in formulation since GV Black.

The sperical particles of AgCu alloy mixed with lathe-cut particles are called __________.

admixed alloys

(slivers w/o much copper and spheres w/ copper)

Which amalgam is stronger, low copper or high copper alone or mixed? Why?

Admixed (both types of particles) is a stronger amalgam because there is LESS MATRIX GAMMA 2 AND MORE STRONG FILLERS (such as AgCu/AgSn in the set amalgam.

**For composites, too--less matrix more strong fillers makes the material stronger overall.

Which alloys are particularly resistant to marginal breakdown?

Admixed high copper RESISTANT TO MARGINAL BREAKDOWN.

Which alloy are we using at Roseman?

DISPERSALLOY

_____________ + ______________ = admixed high copper alloy.

Lathe cut + spherical high copper = admixed

What phases are created with admixed high copper alloy?

Cu6Sn5 (N1 phase)
Ag2Hg3 (Gamma 1 phase)--Mostly
(also Epsilon, Gamma, and Eta)

Which phase is present in low copper BUT NOT in high copper alloy?

NO GAMMA 2 PHASE!

What is the other high copper alloy used?

High Copper Single Composition Alloy

What is Tytin?

From SS White is an EXAMPLE OF SINGLE COMPOSTITION ALLOY.

T/F
High copper single composition alloy is strictly a spherical alloy

True

SPHERICAL ALLOY ONLY

What are the major componenets of single-composition alloys?

Silver (60%)
Copper (13%)
Tin (27%)

Atomized particles of single composition alloy have ________ microstructures, consisting of fine lamellae.

dendritic

T/F
Very little copper is dissolved in alloy particles of a single composition mix.

TRUE

T/F
N crystals found in the meshes of rodlike crystals are much larger than the N crystals found in the reaction particles of admixed amalgams.

TRUE

single composition has larger N particles

What interlocking crystals are believed to improve the amalgam's resistance to deformation in the single composition alloy?

N crystals
(with gamma one crystals)

What is the reaction of single composition alloy?

Ag-Sn-Cu alloy particles + Hg > gamma 1 + N + unconsumed alloy particles

Can the undesirable gamma two phase form in single-composition? Why or why not?

YES

Very true if the atomized powder has not been heat treated or if the powder has been treated too long at too high a temperature.

HOWEVER, most have little to no gamma two.

What does ANSI/ADA Specification No. 1 state about amalgam?

Requires that amalgam neither contract nor expand more than 20 micrometers/centimeter, when measureed at 37C, between 5min-24hrs after the beginning trituration. This specimen size is essentially equivalent to the bulk used in large amalgam restorations.

When does amalgam contraction occur?

From the commencement of trituration for about 20 minutes.

*Contraction continues as long as the gamma1 phase continues to grow*

Why does amalgam contraction occur?

metallic crystals dissolve in the liquid Hg, causing the GAMMA-1 PHASE to continue to grow.

What effect do MANIPULATIONS that shorten setting time/decrease Hg contact do?

FAVOR CONTRACTION

*LONGER TRITURATION TIMES (shorten setting time)
*SMALLER PARTICLE SIZE (increased surface area per unit mass)
*HEAVIER CONDENSATION (greater force squeezes Hg out of the mix)

What is the effect of water contamination during trituration or consensation steps?

EXPANSION of the filling will start between 3-5 days post-op and can continue for months after.

What type of reaction does expansion in amalgam involve?

Electrolytic reaction with water and zinc.

**THEREFORE: NONZINC alloys do NOT experience this expansion.

T/F
Moisture contact with amalgam after it has been condensed causes no expansion.

TRUE

Creep:

TIME-DEPENDENT STRAIN OR DEFORMATION THAT IS PRODUCED BY STRESS.

Why does creep increase susceptibility to marginal breakdowns?

Creep can cause an amalgam restoration to extend out of the cavity preparation.

What causes creep rates to INCREASE?

*Higher Gamma-1 volume fractions

*PRESENCE OF GAMMA 2 PHASE IS ALSO ASSOCIATED WITHI HIGHER CREEP RATES

What causes creep rates to DECREASE?

*Larger Gamma-1 grain sizes

*ABSENCE OF GAMMA-2 PHASE (as w/ single-compostion HIGH COPPER AMALGAMS) may be associated with N rods (which act as barriers to deformation of the gamma-2 phase.

In large part, success of clinical performance of amalgam restorations is due to its tendency to ____________________.

minimize marginal leakage

How does amalgam minimize marginal leakage?

*corrosion products are deposited at the margin

**LOW COPPER amalgams deposit corrosion products at a HIGHER RATE than high copper amalgams.

Amalgam vs. Composite

AMALGAM:
NOT technique sensitive
Greater Longevity
Radioopacity
Appearance easily distinguished from tooth
Marginal gap sealing over time
Greater durability (90% still functional after 10 yrs)

COMPOSITE:
More aesthetic
More expensive
Require more time to place
Requires less removal of healthy tooth structure
Good thermal insulators
No galvanic reaction

What have USDA, FDA, ADA, WHO, USPHS, NIH determined concerning amalgam?

THERE IS NO DATA TO COMPEL A CHANGE IN THE CURRENT USE OF DENTAL AMALGAM

T/F
Alloy for Dental Amalgam is the same as Dental Amalgam Alloy

TRUE

Define Amalgamation:

The process of mixing liquid mercury with one or more metals or alloys to form amalgam

Define Creep:

Time-dependent strain or deformation that is produced by a stress. The creep process can cause an amalgam restoration to extend out of the cavity preparation, thereby increasing its susceptibility to marginal breakdown.

Define delayed expansion:

Gradual expansion of a zinc-containing amalgam over weeks to months, which is associated with hyrdrogen gas development caused by contamination of the plastic mass w/ moisture during its manipulation in a cavity preparation.

Define dental amalgam:

An alloy of mercury, silver, and tin which may also contain palladium, zinc, and other elements to improve handling characteristics and clinical performance. The general term amalgam is used as a synonym by the dental profession.

Define dental amalgam alloy:

An alloy of silver, copper, tin, and other elements that is formulated and processed in the form of powder particles or as a compressed pellet. this is also known as alloy for dental alloy for dental amalgam.

Define marginal breakdown:

Gradual fracture of the perimeter or margin of a dental amalgam restoration that leads to the formation of gaps or ditching at the external interfacial region between the amalgam and the tooth.

Define trituration:

Process of grinding powder, especially within a liquid. In dentistry, the term is used to describe the process of mixing the amalgam alloy particles with mercury in an amalgamator.

What is the goal of condensation?

To deliver freshly mixed amalgam alloy to prepared cavity so that the greatest possible density is attained and complete continuity of the Gamma-1 matrix with the remaining alloy particles
If this goal is achieved, strength of amalgam is increased and creep is decreased.

What happens with increased time in the condensation step?

The longer the time between mixing and condensation, the weaker the amalgam.

In addition to amalgam strength, what is the major outcome of condensation?

To bring the mercury rich amalgam to the top of each increment, allowing for each increment layer to bond to each other.

Fine Cut from LD Caulk is an example of:

low copper alloy

Dispersalloy is an example of what type of alloy?

High copper alloy

Historically, why was excess Hg added to the amalgam mix?

Hg was added to the mix to obtain a smooth mass. Excess Hg was then wrung from the mix through a porous cloth or excess was worked to the top of the restoration and then removed.

Why was the addition of excess Hg stopped?

*produced inconsistent results
*unsafe handling of liquid Hg

What do today's prepackaged capsules contain regarding the mercury:alloy ratio?

*Include powdered alloy and just the right amount of Hg to produce approximately 50wt%Hg, (40wt% with high copper alloy).
*This eliminates chance for liquid Hg to escape or evaporate.

Trituration machines are also called:

amalgamators

What are the 4 variable components of amalgam mixing?

*size of mix
*intensity of oscillations
*length of time of the oscillations
*composition of mix

What are the size variables of amalgam mixes?

Small mix = 1 spill
Large mix = 2 spills

2 spills require more mix

What are the various intensities of oscillations regarding amalgam mixing?

3200-3400 (cycles per minute)
3700-3800 (cpm)
4000-4400 (cpm)

How does the composition of mix vary?

Sperical alloys takes less time than lathe-cut alloys

How does overtrituration affect the working time?

Working time of the mix is decreased

(this means either too much TIME or too much INTENSITY

How can you tell if mix is overtriturated?

If it feels hot or hard

What pressure is recommended for condensing amalgams?

15 lb (66.7 N)

Condensation should be the ___________ the alloy can stand within the comfort of the patient.

most

What will happen if a condensor greater than 2mm is used?

It will not permite adequate force to be generated

When should a round faced condensor be use? Rectangular or Triangular faced condensor?

Round: in rounded cavities

Rectangular/Triangular: in angled cavities

Which type of alloy condenses more easily?

Spherical alloys (more than Lathe-cut)

Why is it recommended to overfill a cavity?

This brings Hg to the survace any amalgam that has excess Hg will then be removed as the restoration is carved.

Is minute/fine recreation of all anatomic detail necessary when finishing an amalgam restoration?

No

What will be the result of burnishing and smoothing the amalgam surface?

Desired appearance BUT burnishing slow setting amalgams can compromise the marginal integrity.

What would you use a cotton pellet for?

Rubbing the amalgam surface with a wet cotton pellet is an acceptable method for smoothing the surface.

How long must you wait to polish an amalgam restoration?

24-48 hours

Does polishing the amalgam make it last longer?

NO

Just makes it look better and attracts less plaque

What could happen if you vigorously polish an amalgam?

Could raise the temp of the pulp (above 60C or 140F) which would IRREVERSIBLY DAMAGE PULP

Expansion is caused by:

*insufficient trituration
*insufficient condensation
*MOISTURE CONTAMINATION OF A Zinc containing alloy

What may be the outcome of expansion of anamalgam restoration?

*Often FAILURE (extends beyond margins)
*PAIN (expands and creates stress on the tooth)
*BROKEN TOOTH

How long does it take for expansion to become noticeable to the patient? When does it go away?

Noticeable in 4-5 days

Continues indefinitely

What is the process of expansion?

Moisture reacts with zinc in the alloy and releases H2 gas, which causes mass of the filling to expand

How can expansion be reversed?

Only by replacing the filling w/out moisture contamination

If a patient returns to your office a day after you placed an amalgam restoration due to tooth sensitivity, what is the most likely reason for this?

Restoration too high

Describe the amalgam used by Roseman:

*DISPERSALLOY made by Dentsply

*Dispersed phase admixed amalgam
*Lathe-cut particles
*Eutectic spheres of AgCu spheres
*50% Hg by weight

What is dispersed phase?

*alloy in which the gamma-2 phase is ELIMINATED OR MINIMIZED
*an admixture of lathe-cut AgSn and spherical AgCu alloy particles
*w/ addition of Hg, the Cu and Sn dissociate from Ag and combine with each other, leaving more of the Ag available to combine w/ the Hg which increases the Gamma-1 (Ag2Hg3) and reducing or eliminating the Gamma-2 phase

What are the components of Dispersalloy?

Ag (69.5%)
Sn (17.7%)
Cu (11.8%)
Zn (1.0%)

What are the components of each pre-dosed capsule?

600mg Hg
600mg powdered alloy

Is Dispersalloy susceptible to expansion?

YES!

1% Zn

Performance Data on Dispersalloy:

Compressive strength >300MPa
Dimensional change during hardening -1%- 2%
Working time 3.5 - 4.5 mintues

Direct Gold:

AKA Gold Foil

Not on our current board exams

Which description best describes Dispersalloy?
1. admixed lathe-cut and spherical alloy
2. low copper alloy
3. zinc-free alloy
4. spherical alloy
5. lathe-cut alloy

1. admixed lathe-cut and spherical alloy

What type of mixure is Dispersalloy?

admixed lathe-cut and spherical alloy

If a person had 12 amalgam fillings, what is the amount of Hg released into a person's system?

~1.7 micrograms/day

(less than eating fish 3x a week)

T/F
Creep is minimal in single composition alloys

True

Insertion and/or condensation of amalgam in the presence of moisture can lead to which phenomenon?
1. shrinkage of the filling after it has been inserted
2. expansion of the filling after it has been inserted
3. loss of marginal integrity
patient pain response onset delayed four days or more
1 and 2 only
2 and 3 only
3 and 4 only
1, 2 and 4 only
2, 3 and 4 only

2, 3, and 4 only

What effect does overtrituration have on the amalgam?
1. no effect
2. dry mix
3. wet mix
4. mix sets too fast
5. slows set
1 only
2 and 5 only
3 and 4 only
2 and 4 only
3 and 5 only

2 and 4 only

The amount of Hg released into a person's system who has 12 amalgam fillings is
1. ~1.7μg/day
2. more than would enter the system from eating fish once a week
3. less than would enter the system from eating fish once a week
4. impossible to measure because it is so great
5. both 1 and 3

both 1 and 3

Creep is a phenomenon found in some amalgam fillings.
Creep is minimal in alloys high in gamma
Creep is minimal in alloys high in gamma
Creep is minimal in single composition high copper alloys
Creep is a result of the amalgam shrinking away from the margin
Creep has no serious effect on the longevity of the restoration

Creep is minimal in single composition copper alloys

Amalgam has been used in all the following circumstances :
1. full-contour direct restorations
2. restoration of endodontically treated teeth
3. sealing of the apices of surgically endodontically treated teeth
4. sealing the endodontic access of overdenture abutment teeth
5. all of the above

All of the above

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