Dental amalgam: composition, properties and clinical uses

Dental amalgam

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education
www.indiandentalacademy.com


Contents
1. Introduction
2. History
3. Advantages and disadvantages
4. Classification
5. composition
6. Purpose of each ingredient
7. Manufacturing of alloy
8. Setting reaction
9. Properties
10. Gallium alloys

1. Manipulation
2. Failures
3. Amalgam bonding
4. Combi-restorations
5. Conclusion
6. references


Introduction
► Amalgam : alloy that contains mercury as one of
its constituent

► Amalgam: derived from greek word
malagma= emollient
malassein= soften

► Alloy : latin word
alligare= to combine


History
► 1STform of amalgam developed by
M.Taveau( 1826) in Paris.
► Crawcour brothers(1833) introduced it in
dental profession . Called Royal Mineral
Succedaneum .
► Amalgam War: 1840-1850
► Dr.G.V.Black(1896):
► ADA Specification 1 in 1929

Advantages
► Durable
► High compressive
strength
► Insoluble in the fluids of
mouth
► Adaptability to walls of
preparation
► Least time consuming to
place
► Ability to corrode-
decreased microleakage
► Ability to take polish


Disadvantages
► Not tooth colored
► Does not bond to tooth structure
► Lack of edge strength
► High conductivity
► Mercury toxicity


Classification

► No of alloys:
1. Binary alloys– silver and tin
2. Ternary: silver , tin and copper
3. Quarternary: silver ,tin, copper, indium

► Powder particle size:
1. Micro cut
2. Fine cut
3. Coarse cut


► Based on copper content
1. Low copper: <6%Cu
2. High copper: >6% Cu
admixed: 28%
single composition- 13-30%


► Shape of powdered particle
1. Irregular: spindles, shavings
2. Spherical
3. Spheroidal
Based on zinc:
1. Zinc containing alloy: > 0.01% Zn
2. Zinc free: < .01% Zn


Based on addition of noble
metals
1st generation: 3 parts silver+1 part tin
peritectic
► 2nd generation: copper is added upto 4%
► 3rd generation : silver copper eutectic alloy +
original alloy
► 4th generation : alloying of copper to silver and
tin upto 29%
► 5th generation : silver, copper ,tin, indium
► 6th generation: alloying palladium 10%,
silver62%, copper 28%--- eutectic lathecut
blended into 1st gen in ratio of 1:2

Composition

► Conventional low copper alloy

Silver: 68-72%
Tin: 25-27%
Copper: 2-6%
Zinc: 0-3%


Admixed alloy

►Mixture of lathe cut low copper alloy
and spherical alloy
►Silver: 60-69%
►Tin: 17-25%
►Copper: 9-20%
►zinc: 0-1%

Single composition
Each particle has same composition

► silver:40-60%
► Tin: 22-30%
► Copper: 13-30%
► Indium: 0-5%
► Palladium: 0-1%


Functions of each ingredients
► Silver:
1. Increases strength
2. Increase setting expansion
3. Decreases flow
4. Improves color
5. Setting time decreased
6. Resist tarnish and corrosion

Tin
► Advantages:
1. Decreases expansion
2. Helps in amalgamation

► Disadvantages:
1. Decreases strength
2. Setting will be slow
3. Increases flow
4. Tarnish and corrosion


copper
► Advantages:
1. Increases strength and hardness
2. Decreases flow
3. Setting will be quick

► Disadvantages:
1. Increases expansion
2. Can be tarnished
3. Brittleness


Zinc

► Advantages:
1. Scavenger/ de-oxidiser
2. Helps in workability
3. Quickens the setting time
4. Increases ultimate strength

► Disadvantages:
1. Increases expansion in presence of moisture
2. Diminishes edge strength


Mercury

► Advantages:
1. Gives plasticity and softness
2. Binds the particles together
3. Essential for setting reaction and
hardening

► Disadvantages:
1. Mercury toxicity

Selenium: Improves the biocompatability of
amalgam (Sato and Kumei-1982)

► Indium: Decreases the mercury vapour
released during mastication( Dowell and Youdelis
1992)

► Platinum: Hardens alloy and corrosion resistant

► Palladium: Hardens and whitens alloy

Manufacturing of alloy

Lathecut:

Ingot: 20-25 cm long and 3-8 cm diameter

Homogenised anneal of ingot: oven 400C for 6-8 hrs

Ballmilling : to reduce size

particle treatment with acids to improve the
reactivity

Aging process towww.indiandentalacademy.com life
improve shelf

Spherical alloy

► Atomised: liquid alloy
into a closed chamber
filled with inert gas

► Size: 2-43 microns
► Acid treatment


Setting reaction

► Amalgamation occurs when Hg contacts Ag-Sn
► Low copper alloys:
► Ag3Sn + Hg ---Ag2Hg3 +Sn8Hg+Ag3Sn

Microstructure:
► Unreacted particles surrounded by matrix of
gamma1 and gamma2,
► Voids


High copper admixed

► 1part silver-copper eutectic alloy + 2 parts silver tin
alloy
► Ag3Sn +Ag-cu+ Hg ---Ag2Hg3
+Sn8Hg +Ag3Sn + Agcu
►Later,
►Sn8Hg +Ag-Cu- Cu6Sn5+ Ag2Hg3

►Gamma2 is eliminated
►Core :Ag3Sn and Ag-cu surrounded by a halo of Cu6Sn5(n)

Single composition
► Ag3Sn + Cu3Sn+ HgCu6Sn5 +Ag2Hg3
► Core: Ag3Sn and Ag-Cu
► Matrix: Ag2Hg3
► Cu6Sn5 is present in gamma1 matrix rather
than as halo around Ag-Cu


Dimensional changes
► ADA specification1:
-15Micron to + 20
microns at 37c between
5 min and 24hrs after
beginning of trituration

► Theory of dim.change:
1. Initial contraction
2. Expansion
3. Delayed contraction


► Severe contraction:
1. Microleakeage
2. Plaque accumulation
3. Secondary caries

► Excessive expansion
1. Pressure on pulp
2. Post op sensitivity
3. Protrusion of restoration

Factors affecting dimensional
change
► Constituents: more gamma- more exp
tin– less exp
► Mercury: more ->expansion high
► Particle size: smaller size-> more
contraction
► Trituration:
more energy, longer time-
contraction
► Condensation: more forces  contraction
► Particle shape: irregular expansion

Creep
► Creep: time dependent plastic strain of
material under static load or constant
stress
► ADA specification : 3% or less
► Low copper alloys: 0.8% to 8%
► High copper alloys: 0.1%
► Factors: 1. influence of microstructures
2. manipulative variables
► High creep: more marginal detoriation


Compressive strength
► Satisfactory compressive strength: 310 MPa
► After 7 days , comp strength of high copper
alloys is more than low copper alloys
► After 1hr, single composition alloy strength
is double that of other alloys
► Amalgam is weak in tension


Factors affecting strength
► Trituration: more energy more strength
► Mercury: weakest phase
► Condensation: more forcemore strength
► Porosity: decreases strength
► Particle shape: regular and smooth  strong
► Particle size: smaller diameter greater strength
► Corrosion: decreases strength
► Gamma2 2nd weakest phase


Rate of attaining strength
► Accelerated strength:

1. Decreased particle size.
2. More trituration energy
3. More condensation energy
4. Smooth and regular particles
5. Homogenisation heat treatment
6. Minimum mercury in the mix

Tarnish and corrosion
► Tarnish: surface discoloration on metal or
even slight loss or alteration of the surface
finish or luster.
► Corrosion: actual detoriation of ametal by
reaction with its environment
► Active corrosion: interface between tooth
and restoration crevice corrosion
► selfsealing


► Both low and high copper corrosion
products are oxides and chlorides of tin
► In high copper amalgam: corrosion process
is limited,since n (Cu6Sn5) is least
susceptible to corrosion than gamma2
► Gold restoration when placed in contact with
an amalgam,large difference in
EMFcorrosion

Other properties
Effect of moisture contamination:
► Zinc-containing amalgam contaminated by
moisture , a large expansiondelayed
expansion or secondary expansion
► H2O + Zn ZnO2 +H2 (gas)
► This hydrogen gas collects in restoration 
expansion, protrusion , increased creep,
increased microleakage, corrosion, pain.

Marginal adaptation
► Tendency to minimise microleakeage –self
sealing
► Due to corrosion products which seals
restoration
► Low copper alloys–> 2-3 months
► High copper alloys10-12 months
► Problems due to improper adaptation
1. Marginal detoriation
2. Accumulation of debris
3. Recurrent caries
4. Post op sensitivity

Gallium alloy
► Alloy: Liquid:
Silver60%
Tin 25% Gallium 62%
copper 13% Iridium 25%
Palladium 20%
Tin 25%


Gallium alloys
► Puttkammer 1928
► Comp.strength and tensile strength
comparable to amalgam
► Creep—0.09%
► Sets early polishing can be done on same
day
► They expand after mixing, better marginal
seal
► Sticks to walls of capsule.
► More costly.

Copper amalgam
► Copper and mercury
► Antiseptic
► Composion: 70%Hg , 30% copper-  pellet
► Heated in a spoon,then triturated
► Adv: increased hardeness,
not effected by moisture,
no creep
Disadv: discoloration and shrinkage

Manipulation

1. Choice of alloy and mercury
2. Proportioning
3. Trituration
4. Mulling
5. Condensation
6. Burnishing
7. Carving
8. Finishing and polishing

Choice of alloy and mercury
► Selection of alloy depend on:
setting time, particle size and shape,
composition, presence or absence of zinc.
► 90% amalgams placed are high Cu ,admixed
alloys
► Adv: no gamma2,
low creep
high early strength
good corrosion resistance
decreased marginal failure
► Zinc containing and zinc free:

Proportioning of alloy and mercury
► Preferably done by weight rather than volume
► Mode of supply: powder particles, pellet
,disposable capsules, reusable capsules
► Dispensers with preweighed tablets and Hg
containers are available
► NO TOUCH :preweighed capsules are available
with alloy and Hg seperated by membrane.
► Size of mix:400,600,800 +appropriate Hg--- color
coded

Contd
► Reusable capsules :1.friction fit
2. screw type—better
► Disposable capsules should not be reused
► Increasing dryness techique: 52-53% Hg
very plastic mix,
large restorations,
multiple auxillary means of
retention
► Eames technique: 48-50% Hg

Trituration

► Act or rubbing
Objectives:
► Achieve workable mass
► Removes oxides from powder particles
► Pulverize pellets to particles
► Dissolve particles of powder in Hg
► Reduce particle size
► Keep gamma1 matrix crystals minimal and
evenly distribute


Triturators

► 2 types: hand and mechanical
► Hand: mortar and pestle
► Mechanical: amalgamators
► Has plastic or metal capsule, metal or plastic ball
or pestle.
► Hoods.
► 3 basic movements of pestle:
centrifugal
figure 8
straight line


Contd

► Coherence time: minimum mixing time required for an
amlagam to form a single coherent pellet.
► Effective trituration depends on duration and speed of
mixing.
► Duration:
► Speed:
low :3200-3400 cycles/ min
medium:3700-3800 cycles /min
high :4000-4400 cycles/min
► Spherical or irregular low copper: low speed
► High copper alloys: high speed


Trituration energy
► Trituration(work) = motor speed *
time * capsule-pestle action
► Trituration Energy:
1. Speed or no. of unit movements per unit
time
2. Thrust of the movement
3. Weight of the capsule or pestle
4. Difference in size between pestle and
capsule
5. Time www.indiandentalacademy.com

Mulling

► Continuation of trituration
► Provides homogenicity to the mix
► 2 ways:
1. Mix is enveloped in dry piece of rubberdam and
rubbed betweem 1st finger and thumb.
2. After trituration,pestle is removedfrom capsule
and mix is triturated for 2-3 sec.
► This assures cleaning of capsule walls of
remnants of mix and developing a single
coherent mix

Type of mix

Test for correct mix:

Normal mix:

May be warm
Smooth and soft

Overtrituration:
Alloy will be hot
Hard to remove from the
capsule
Shiny wet and soft

Undertrituration
1. Alloy will be dry
2. Will crumble if dropped from
approximately 30cm

condensation
► Continuation of trituration process
► Purpose:
1. Squeezes unreacted Hg out of increments
2. This Hg squeezed to surface binds further
sucessive increments
3. Forces used brings stronger phase together
boosting final strength
4. Adapts plastic mix to the walls of preparation
5. Decreases no. of voids

Condensation
► Should start immediately after trituration
► 3-3 ½ min
► Further condensation causes cracks
► 3 ways: 1. hand condensation
2. mechanical: a. vibratory
b. impact
3. ultrasonic
► Pressure inversely proportional to square of
surface area


Types of condensors
► Shapes:
1. Round
2. Parallelogram
3. Diamond
4. Elliptical
Various contours:
1. Flat
2. Concave
3. angular


Round condensors

► 3 instruments of diameter 15,25,35
► Angle 10 degrees to shaft
► Nibs 7mm long
► 15-25 diameter: compressing amalgam in
small pits
► 35 diameter: final heavy pressure in
occlusal surface of molars


Parallelogram condensors
► 2 pairs
► Smaller: 30*10- 7-10
10* 30-7-10
proximo occlusal in bicuspids and
molars
► Larger: 35* 15- 7-10
15*35-7-10
molars

► Sweeney’s instruments

has sharp angles
condensing amalgam
into angles


condensation
► Face or nib should be flat or smooth
► Atleast 6 pounds should be used
► Amalgam is inserted into cavity in small
increments and condensed with smaller
instruments.
► Minimises voids and adapts to smaller
details
► Near surface, larger consensors are used.

Nonspherical alloys
► Force applied at 45deg
to walls and floor
► Next increment at 90
deg to previous one
► Centre to periphery
condensation
► Excess Hg which
comes to surface is
excavated and
discarded.

Spherical alloys

► Large increments
► Largest condensor that
will fit the cavity, to
prevent lateral escape
of spherical part
► Particles have
tendency to roll over
► Less energy than
nonspherical


Final appearance

Concave amalgam surface should face
condensor indicating proper angulation and
application of forces

Condensed increment should not be
indentented
by further cond. force showing a coherent
mass

Blotting mix
► An overdried amalgam mix is condensed
heavily on the restoration using large
condensors
► Blots excess Hg from critical marginal and
surface area of restoration


Burnishing or surfacing
► Process of rubbing, usually performed to make a surface
shiny
► Light strokes, from amalgam to tooth surface

► Objectives:
1. Dec size and no. of voids on critical areas and margins
2. Brings excess Hg to surface
3. Adapts amalgam to cavosurface anatomy

► Precarve and post carve burnishing


carving
► Anatomical sculpting of amalgam.
► Begins immediately after condensation and precarve
burnishing

► Objectives:
1. Produce restoration with no under hangs
2. Proper physiological contours and contacts
3. Adequate and compatible marginal ridges
4. Physiological embrasures
5. Functional non interfering occlusal anatomy
6. Enhance periodontal health and integrity

Carving - steps
► Initial carving– discoid carver removes extra
bulk
► Accessible embrasures : sharp explorer or lateral
edge of hollenback carver
► Creating triangular fossa: discoid /cleoid
This coupled with previous procedure will erect
marginal ridges
► Margination: discoid /hollenback removes
marginal flash,
from tooth to amalgam

Contd

► Facial and lingual grooves: hollenback, chisel,
cleoid /discoid
► Cusp ridges and inclined planes: hollenback
placed concurrently on amalgam and adjacent
tooth surface ,lateral movement with intact tooth
as guide
► Anatomic grooves: anatomic burnisher

► Post carve burnishing : light forces
not done in fast setting amalgams

Finishing and polishing
► Finishing: process which continues the carving
objectives, removes flash and overhangs ,
corrects minimal underhangs
Done at placement appointment

Polishing: smoothing the surface to a point of high
gloss or lusture.
Creates corrosion resistant layer by removing
scratches & irregular surface
After 24hrs preferably

objectives
1. Conversion of superficial amalgam into
relatively inert layer galvanically
2. Removal of superficial scratches and
irregularities
3. Minimises concentration cell corrosion


contd
► Gross smoothening: finishing burs
► Polishing agents: Tinoxide, Zincoxide ,PPT chalk
► Polishing convex surfaces like facial ,lingual
proximal: progressive finer disks, abrasive
impregnated cups
► Concave surfaces : Abr impregnated rubber points
► Contact areas and gingival embrasures: linen
polishing strips or dental tape
► Abundance of air-coolant and intermittent contact


Failures of amalgam
► Visual level
1. Marginal fracture
2. Bulk fracture
3. Dimensional change
4. Secondary caries
5. Tooth fracture

► Microstructural level
1. Corrosion and tarnish
2. Stresses

► Pain following restoration

Reasons for failures

► Defective cavity preparation: 56% of failures
► Defective manipulation: 42% failures
► Defective matrix adaptation
► Defective materials


Marginal failures


Defective cavity preparation
► Insufficient occlusal extension
► Under extension of proximal box
► Over extended cavity preparation
► Cavity depth
► Floor
► No butt joint
► Fracture of isthmus
► Sharp axiopulpal line angle
► Incomplete removal of caries
► Hyperemia of pulp
► Additional retentive forms to be in dentin

Defective amalgam manipulation

► Improper condensation
► Incorrect mercury alloy ratio
► Contamination
► Defective finishing and polishing


Post operative pain
► High points
► Delayed expansion
► Inadequate pulp protection
► Continuous leakage around filling


Finishing and polishing
► Overcarving
► Failure to polish
► Temperatures greater than 65c  mercury
is released from amalgam
► Amalgam which have greater tendency for
tarnish and corrosion


Amalgam bonding
► Amalgam is hydrophobic while enamel and
dentin are hydrophilic.
► Wetting agent should have both the
properties
► 4-methyloxy ethyl trimellitic anhydride
► Thick layers of bonding agents(10-50
microns) are applied about 8-10 times
► Amalgam bond, scotch bond MP, All Bond
2, www.indiandentalacademy.com

Bonding interface
► Tag formation
► Chemical binding to the inorganic or org
components of dentin
► Formation of hybrid layer of reinforced
dentin


Advantages

► Dentin sealing
► Resistance and retention form increased
► Improves marginal seal
► Use of retention pins eliminated
► Microleakeage ,recurrent caries,
postoperative sensitivity reduced
► Cavity can be made conservatively
► Cost effective for extensively carious tooth


Limitations
► Technique sensitive
► Bond strength is reduced after some years
► Cost of bonded amalgam is more than
nonbonded


conclusion


References

1. Dr .G.V.Blacks Operative dentistry
2. Operative Dentistry By Mc Gehee
3. Dental materials by Philips
4. Craigs restorative dental materials
5. Dental materials by Soratur
6. Marzouk
7. Charbeneau
8. Restoration of tooth Str: G.J.Mount

Thank you


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