AMALGAM: Properties and Applications

AMALGAM
Presented by,
Swapnika.G.
(1 MDS)
Conservative Dentistry and Endodontics

CONTENTS
• Introduction
• History
• Classification
• Indications & contraindications
• Advantages and Disadvantages
• Composition of amalgam
• Amalgamation reactions
• Properties of amalgam
• Manipulation of amalgam
• Mercury toxicity & various health
hazards
• Recent advances
• Conclusion
• References

INTRODUCTION
• Dental amalgam is an alloy made by mixing mercury with a silver tin
alloy to which varying amount of copper and small amount of zinc
has been added.
• According to Skinner’s, amalgam is a special type of alloy in which
one of its constituent is mercury.
Phillips RW, Anusavice KJ, Shen C, Rawls HR. Phillips' science of dental materials. Elsevier/Saunders; 2013.
Roberson T, Heymann HO, Swift Jr EJ. Sturdevant's art and science of operative dentistry. Elsevier Health Sciences; 2006 Apr 13.

HISTORY
• Amalgam was 1st used by Chinese. There is a mention of silver mercury paste by Sukung
(659AD)
in the Chinese medical literature.
• 1826, M.Traveau is credited with advocating the first
form of amalgam paste , in France.
• 1833, Crawcour brothers introduced amalgam to US.
• 1895, To overcome expansion problems G.V. Black
developed a formula for modern amalgam alloy 67%
silver, 27% tin, 5% copper, 1% zinc.

• 1946 - Skinner, added copper to the amalgam alloy composition in a
small amount. This served to increase strength and decrease flow.
• 1962 - A spherical particle dental alloy was introduced, by Demaree
and Taylor.
• The work of Innes and Youdeis (1963) has led to the development of
of high copper alloys.
• 1973 - first single composition spherical alloy named Tytin (Kerr) a
ternary system (silver/tin/copper) was discovered by Kamal Asgar of
the University of Michigan.
Skinner EW, Phillips RW. Skinner ́s science of dental materials 8 Ed. WB Saunders Company; 1982.

AMALGAM WARS
• In 1845, American Society of Dental Surgeons condemned the use of all filling
material other than gold as toxic, thereby igniting "first amalgam war’.
• In mid 1920's a German dentist, Professor A. Stock started the so called "second
amalgam war".
• "Third Amalgam War” began in 1980 primarily through the seminars and
writings of Dr.Huggins, a practicing dentist in Colorado.

CLASSIFICATION (MARZOUK)
• I. According to number of alloy metals
1. Binary alloys (Silver-Tin)
2. Ternary alloys (Silver-Tin-Copper)
3. Quaternary alloys (Silver-Tin-Copper-Indium).
• II. According to Presence of zinc
1. Zinc containing (more than 0.01%).
2. Non zinc containing (less than 0.01%).
Marzouk MA, Simonton AL, Gross RD. Operative dentistry: modern theory and practice. Ishiyaku EuroAmerica, Incorporated; 1985.

• III. According to the shape of the powdered particles
1. Spherical shape (smooth surfaced spheres)
2. Lathe cut (Irregular ranging from spindles to shavings)
3. Combination of spherical and lathe cut (admixed)
• IV. According to Powder particle size
1. Micro cut
2. Fine cut
3. Coarse cut
• V. According to copper content of powder
1. Low copper content alloy - Less than 4%
2. High copper content alloy - more than 10%
• VI. According to addition of Nobel metals
Platinum, Gold, Pallidum

INDICATIONS OF AMALGAM
• Occlusal Factors
• Isolation Factors
• Operator Ability and Commitment Factors.
CLINICAL INDICATIONS
• Moderate to large Class I and II restorations.
• Temporary caries-control restorations
• Foundations
• Cuspal restorations
• Heavy occlusal contacts.

CONTRA INDICATIONS OF AMALGAM
• Anterior teeth where esthetics is a prime concern.
• Esthetically prominent areas of posterior teeth.
• Small cavity designs.

ADVANTAGES
• Ease of use
• High compressive strength
• Excellent wear resistance
• Favorable long-term clinical research results
• Lower cost than for composite restorations

DISADVANTAGES
• Noninsulating
• Nonesthetic
• Less conservative (more removal of tooth structure during tooth preparation)
• Weakens tooth structure
• More technique sensitive if bonded
• More difficult tooth preparation
• Initial marginal leakage

COMPOSITION OF AMALGAM
Composition of some typical commercial amalgam alloys
Spherical alloy Lathe- cut alloy Admix alloy

ROLE OF INDIVIDUAL COMPONENTS
Silver:
Hardness and edge strength
Strength
Tarnishing
Creep
Setting time
Corrosion

Tin:
• Larger contraction
Mercury (pure form):
• Activates reaction
• Spherical alloys— less Hg.
• Admixed alloys— more Hg.
Corrosion
Plasticity
Setting time
Expansion
Rate of reaction

Copper:
Zinc:
Scavenger
Marginal failure.
Indium/Palladium:
Plasticity
Resistance to deformation.
Hardness
Strength
Setting Expansion
Flow

AMALGAMATION REACTION
Mahler DB, Adey JD, Van Eysden J: Quantitative microprobe analysisof amalgam. J Dent Res 54:218–226, 1975.

Schematic drawings that
illustrate the development
sequence of the amalgam
microstructure when lathe-
cut low-copper alloy
particles are mixed with
mercury. A, Dissolution of
silver and tin into
mercury. B, Precipitation of
γ1 crystals in the
mercury. C, Consumption of
the remaining mercury by
growth of γ1 and
γ2 grains. D, The final set
amalgam.

PROPERTIES
Creep
Strength
Dimensional
Stability
Corrosion
Resistance
Flexural
Strength
Elastic
Modulus
Powers JM, Sakaguchi RL, Craig RG. Craig's restorative dental materials/edited by Ronald L. Sakaguchi, John M. Powers. Philadelphia, PA:
Elsevier/Mosby,; 2012.
According to ADA
specification No: 1 for
amalgam

Bullard RH, et al: Effect of coefficient of thermal expansion on microleakage, J Am Dent Assoc 116:871-874, 1988.
Vrijhoef MM, Letzel H: Creep versus marginal fracture of amalgam restorations, J Oral Rehabil 13:299-303, 1986.
Coefficient of thermal expansion-2.5 times greater than tooth
-closer to composite
Compressive strength- similar to tooth
Tensile strength - low
Amalgam- bulk fracture
High fracture toughness
Brittle and low edge strength
High-
copper
amalgams
All
amalgam
s

Compressive Strengths of Low-Copper and
High Copper Amalgam
Amalgam Compressive Strength
(MPa)
1 h 7 day
Low copper 145 343
Admix 137 431
Single
Composition
262 510
STRENGTH
Product Tensile strength
(Mpa)
15min 7 days
LOW COPPER
ALLOYS
a) Lathe cut
b) spherical
3.2 51
4.7 55
HIGH COPPER
ALLOYS
a) Admixed
b) Unicompositional
3.0 43
8.5 56
Tensile Strengths of Low-Copper and
High Copper Amalgam

DIMENSIONAL CHANGES
• When mercury is combined with amalgam it undergoes three distinct
dimensional changes.
• Stage -1: Initial contraction
• Stage -2: Expansion
• Stage -3: Limited delayed contraction.
Modulus of elasticity: 62 Gpa (max)
Knoop’s Hardness Number: 110 kg/mm2

MOISTURE CONTAMINATION
• Certain zinc containing low copper or high copper amalgam alloys
which get contaminated by moisture during trituration or condensation
results in delayed expansion or secondary expansion.
• Occur 3-5 days after insertion and continues for months reaching the
values greater than 400µm/cm (4%).
• Zinc reacts with water, forming zinc oxide and hydrogen gases.
• Main source od contamination— saliva.

CREEP
• Time dependent plastic deformation.
• It is determined by placing a cylinder of set amalgam (4mm diameter 6mm long)
under a 36MPa compressive stress.
• Higher creep — greater degree of marginal deterioration.
Mahler DB, Van Eysden J: Dynamic creep of dental amalgam. J Dent Res 48:501–508, 1969.

CORROSION RESISTANCE
Excessive corrosion can lead to:
• Increased porosity.
• Reduced marginal integrity.
• Loss of strength.
• Release of metallic products in to the
oral environment.
Phases in decreasing order of corrosion resistance
Ag2Hg3 > Ag3Sn > Ag-Cu > Cu3Sn > Cu6Sn5 > Sn7-8Hg.

Types of Corrosion:
1) Galvanic corrosion:
2) Crevice Corrosion:
3) Stress Corrosion:

MANIPULATION OF DENTAL AMALGAM
PROPORTIONING OF ALLOY MERCURY RATIO:
Eames technique/ No- squeeze cloth technique:
• This technique revolutionized the procedure in
constructing an amalgam restoration by use of
minimal amounts of mercury in the original mix.
• The mercury content of the lathe-cut alloy is about
50% by weight and that for spherical alloys is 42% by
weight.
Eames WB: Preparation and condensation of amalgam with a low mercury/alloy ratio. J Am Dent Assoc 58:78–83, 1959.

TRITURATION
• Process of mixing the amalgam alloy particles with mercury.
Mechanical amalgamators are available in the following speeds:
• Low speed: 32-3400 cpm.
• Medium speed: 37-3800 cpm.
• High speed: 40-4400 cpm.
• Spherical/irregular low-copper alloys – triturated at low speed
• High copper alloys – high speed
• Time of trituration – 3-30 seconds. Variations in 2-3 seconds leads to over or under
trituration.

• Over-trituration( HOT MIX):
Alloy will be hot, hard to remove from the capsule, shiny
and soft.
More fluid consistency and appears flattened.
• Under-trituration( GRAINY MIX):
Alloy will be dry, dull and crumbly; will crumble if dropped
from approx 30 cm.
Low strength and poor resistance to corrosion.
• Normal Mix:
Round and smooth shiny appearance separates in a single
mass from the capsule.

MULLING
• Continuation of trituration
• 2 ways - rubbed between the 1st finger and thumb- 2 to 5
seconds
- pestle free capsule for 2 to 3 seconds
MATRICING

CONDENSATION
• Refers to the incremental placement of the
amalgam into the prepared cavity and
compression of each increment into the others.
• Amalgam should be condensed into the cavity
within 3 min after trituration.

• Average condensation pressures were 3.7+/-1.3 MPa for the small and 2.2+/-
0.9 MPa for the large instrument.
• The total working time required to fill a cavity was on average 131 s;
the amalgam was effectively condensed for 44 s.
Recommended Condensation pressure= 10 to 20 MPa
Lussi A. Brimner M. Portmann P. Burgin W: Condensation pressure during amalgam placement in patients. Ew J Oral Sei 1995;
103: 388-393. Miinksgaard. 1995.

BURNISHING
First Burnish (Pre-carve Burnish):
• Carried out using a large burnisher for 15
seconds
• Use light force and move from the center of
the restoration outwards to the margins.

CARVING
• Using remaining enamel as a guide, carve gently
from enamel towards the center and recreate the
lost anatomy of the tooth.
• A scarping or "ringing" (amalgam crying) should
he heard.

Final Burnish (Post carve burnishing):
• Use a large burnisher at a low load and burnish outwards towards the margins.
• Improves smoothness
Clinical behavior of amalgam restorations found that pre-carved burnishing
improved the marginal integrity of lathe-cut alloys coupled with post-carved
burnishing, it was suggested as a viable substitute for conventional polishing.
If temp raises above 60C, causes release of mercury accelerates corrosion & fracture at
margins.
May KN, Wilder AD, Leinfelder KF: Burnished amalgam restorations: A two-year clinical evaluation. J Prosthet Dent 49:193–197,
1983.

FINISHING & POLISHING
• Finishing can be defined as the process, which continues the carving
objectives, removes flash and overhangs and corrects minimal enamel
underhangs.
• Polishing is the process which creates a corrosion resistant layer by
removing scratches and irregularities from the surface.

BIO-COMPATIBILITY –MERCURY TOXICITY
Mercury is available in 3 forms:
• Elemental mercury (liquid or vapor).
• Inorganic compounds.
• Organic compounds.
Estimated daily intake of mercury:
Source g Hg
vapour
g
inorganic
Hg
g methyl
Hg
Atmospher
e
0.12 0.038 0.034
Drinking
Water
--- 0.05 ---
Food &
Fish
0.94 --- 3.76
Food &
Non-Fish
--- 20.00 ---

CONCENTRATIONS OF MERCURY
• Clarkson TW (1997) – Lowest dose of mercury that elicits a toxic reaction – 3to7 g/kg body
weight.
• Mercury release has been quantified for a number of procedures:
Trituration: 1-2g
Placement of amalgam restoration: 6-8 g.
Dry polishing: 44 g.
Wet polishing: 2-4 g.
Amalgam removal under water spray & high velocity suction: 15-20 g
• Skare I et al (1990) – urine mercury level peak at 2.54 g/L 4 days after placing amalgam
restorations, return to zero after 7 days.

• Maximum allowable level of mercury in blood is 3 g/L
• The Occupational Safety & Health Administration (OSHA) has set a TLV of
0.05 mg/m3 as the maximum amount of mercury vapor allowed in the
work place.
• Average Daily dose of mercury from dental amalgam for patients with
more than 12 restored surfaces has been estimated at up to 3 g.

• An urticarial rash may be followed by dermatitis.
• Long-term response — oral lichen planus or lichenoid reactions
AMALGAM TATOO:
• Scraps of amalgam may fall into open surgical or extraction wounds.
• Excess amalgam may be left in the tissues following sealing the apex of a
root canal with a retrograde amalgam.
• Pieces of amalgam may be forced into the mucosa.
SENSITIVITY TO AMALGAM RESTORATIONS

SOURCES OF MERCURY EXPOSURE IN DENTAL
OFFICE

DENTAL MERCURY HYGIENE
Well ventilated
Precapsulated alloy
use
Proper alloy: mercury ratio
Amalgamator
Non- absorbent floor coverings
Spilled mercury
No vaccum cleaner
Skin- soap and water
Urine analysis
Professional clothing

SCRAP AMALGAM DISPOSAL
• In a tightly closed container.
• Under radiographic fixer solution.
• Dispose mercury contaminated items in
sealed bags.
• Do not dispose mercury contaminated items
in medical waste containers or bags or
along with the waste that will be
incinerated.

RECENT ADVANCES
RESIN COATED AMALGAM:
• Mertz-fairhurst and others evaluated bonded and sealed composite restorations
placed directly over frank cavitated lesions extending into dentin versus sealed
conservative amalgam restorations and conventional unsealed amalgam
restorations.
• The results indicate that both types of sealed restorations exhibited superior
clinical performance and longevity compared with unsealed amalgam restorations
over a period of 10 years.
Mertz-Fairhurst EJ, Curtis JW, Jr, Ergle JW, Rueggeberg RA, Adair SM. Ultraconservative and cariostatic sealed restorations: Results at year
10. J Am Dent Assoc. 1998;129:55–66. [PubMed] [Google Scholar]

• The studies concluded that a fluoride containing amalgam may release fluoride
for several weeks after insertion of the material in mouth.
BONDED AMALGAM:
• The bond strengths recorded in studies have varied, approximately 12–15 Mpa.
• Using a spherical amalgam— mean bond strength of 27 Mpa.
• Bond strengths achieved with admixed alloys tend to be slightly lower than
those with spherical alloys.
FLUORIDATED AMALGAM:
Summitt JB, Burgess JO, Osborne JW, Berry TG, Robbins JW. Two year evaluation of amalgambond plus and pin-retained
amalgam restorations (abstract 1529) J Dent Res. 1998;77:297.

CONSOLIDATED SILVER ALLOY SYSTEM:
• It uses a fluoroboric acid solution to keep the surface of the silver alloy particles
clean.
• The alloy, in a spherical form, is condensed into a prepared cavity in a manner similar
to that for placing compacted gold.
GALLIUM – AN ALTERNATIVE TO AMALGAM:
• It was found that mixing gallium with either nickel or copper and tin
produced a pliable mass that could be condensed into a prepared
cavity, which, after setting, had physical properties suitable for a
restorative material.
Some physical properties of gallium-copper-tin alloys.CAUL HJ, SMITH DL, SWEENEY WT J Am Dent Assoc. 1956 Dec;
53(6):677-85.

AMALGAM ALTERNATIVES:
• Composites
• Glass- ionomer
• Cast gold alloys
AMALGAM SUBSTITUTES: equal or better properties than
amalgam
• Gallium alloys
• Cast alloys
• Mercury free direct filling alloy (ADA – NIST patented)

CLINICAL STUDIES
Opdam, N. J. M., Bronkhorst, E. M., Loomans, B. A. C., & Huysmans, M.-C. D. N. J. M. (2010). 12-year Survival of Composite vs.
Amalgam Restorations. Journal of Dental Research, 89(10), 1063–1067.
This retrospective study shows that large composite restorations had a higher survival in the combined
population and in the low-risk group, and three-surface amalgams exhibited better survival in high-risk
patients.

• A study conducted by Letzel et al concluded that the leading mode of failure of
amalgam restorations was bulk fracture (4.6%), followed by tooth fracture (1.9%),
and marginal ridge fracture (1.3%).
Alcaraz MG, Veitz‐Keenan A, Sahrmann P, Schmidlin PR, Davis D, Iheozor‐Ejiofor Z. Direct composite resin fillings versus amalgam
fillings for permanent or adult posterior teeth. Cochrane database of systematic reviews. 2014(3).

CONCLUSION
There are certain advantages inherent with amalgam such as
technique insensitive, excellent wear resistance, less time consuming,
less expensive which are not present in the newer materials, these
factors will continue to make amalgam the material of choice for
many more years to come.

REFERENCES
• Phillips RW, Anusavice KJ, Shen C, Rawls HR. Phillips' science of dental materials.
Elsevier/Saunders; 2013.
• Roberson T, Heymann HO, Swift Jr EJ. Sturdevant's art and science of operative dentistry. Elsevier
Health Sciences; 2006 Apr 13.
• Skinner EW, Phillips RW. Skinner ́s science of dental materials 8 Ed. WB Saunders Company;
1982.
• Marzouk MA, Simonton AL, Gross RD. Operative dentistry: modern theory and practice. Ishiyaku
EuroAmerica, Incorporated; 1985.
• Powers JM, Sakaguchi RL, Craig RG. Craig's restorative dental materials/edited by Ronald L.
Sakaguchi, John M. Powers. Philadelphia, PA: Elsevier/Mosby; 2012.

• Summitt JB, Burgess JO, Osborne JW, Berry TG, Robbins JW. Two year evaluation of
amalgambond plus and pin-retained amalgam restorations (abstract 1529) J Dent
Res. 1998;77:297.
• Some physical properties of gallium-copper-tin alloys.CAUL HJ, SMITH DL, SWEENEY WT J Am
Dent Assoc. 1956 Dec; 53(6):677-85.
• Fluoride release from a fluoride-containing amalgam in vivo.Skartveit L, Tveit AB, Ekstrand J
Scand J Dent Res. 1985 Oct; 93(5):448-52.
• Eichmiller FC, Giuseppetti AA, Hoffman KM. Acid activation of silver powder for cold-welding
(abstract 110) J Dent Res. 1998;77:119.
• Opdam, N. J. M., Bronkhorst, E. M., Loomans, B. A. C., & Huysmans, M.-C. D. N. J. M. (2010). 12-
year Survival of Composite vs. Amalgam Restorations. Journal of Dental Research, 89(10), 1063–
1067.
• Alcaraz MG, Veitz‐Keenan A, Sahrmann P, Schmidlin PR, Davis D, Iheozor‐Ejiofor Z. Direct
composite resin fillings versus amalgam fillings for permanent or adult posterior teeth.

• Vrijhoef MM, Letzel H: Creep versus marginal fracture of amalgam restorations, J Oral Rehabil
13:299-303, 1986.
• Mertz-Fairhurst EJ, Curtis JW, Jr, Ergle JW, Rueggeberg RA, Adair SM. Ultraconservative and
cariostatic sealed restorations: Results at year 10. J Am Dent Assoc. 1998;129:55–
66. [PubMed] [Google Scholar]
• Bullard RH, et al: Effect of coefficient of thermal expansion on microleakage, J Am Dent Assoc
116:871-874, 1988.
• Eames WB: Preparation and condensation of amalgam with a low mercury/alloy ratio. J Am Dent
Assoc 58:78–83, 1959.
• Lloyd CH, Adamson M: The fracture toughness of amalgam. J Oral Rehab 12:59–68, 1985.
• Clarkson TW. The toxicology of mercury. Critical reviews in clinical laboratory sciences. 1997 Jan
1;34(4):369-403.
• Skare I, Bergström T, Engqvist A, Weiner JA. Mercury exposure of different origins among
dentists and dental nurses. Scandinavian journal of work, environment & health. 1990 Oct

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