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14 Amalgam

14 Amalgam
Academic year: 2021/2022
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chapter 14 Dental amalgam ( 1 Lecture. )

. .. .

.... 1 Lecture.

Contents of lecture

1- Dental Amalgam

1- Definition

2- Uses

3- Packing :

4- composition :

5- Classification according to:

  1. particle shape:
  2. Copper content
  3. Zinc content

6, reaction

  1. Low Cu.
  2. High Cu: ‘’admixed & Unicom, ‘’

7- properties

8- Advantages

9- Disadvantages :

10- Manipulation

11- Is amalgam is safe restoration ??

.

. 2- Galloy

1- History

2- Composition

3- Handling characteristics:

4- Properties :

5- Evaluation

.

3- Amalgam Bonded

1- Definition

2- Advantages

3- resin bonding system

.B ...

A, Amalgam after carving.

B, after final finishing.

Class 1

Class 2

Microstructures of the set amalgams of (A) low-copper, lathe-cut & (B) high-copper, admix and (C) the high-copper, unicompositional types. scans of the elements through colored filters; à blue for Ag & red for Cu & green for Sn. The à blue/black matrix phase is A2Hg3 (γ1) present in all amalgams à green colored Sn7-8Hg (γ2) phase is only present in the low-Cu alloy A. à tangerine colored Cu6Sn5 (η′) phase is minimal in A but substantial in B and C. In alloy B, the source of increased Cu is in the spherical Ag-Cu eutectic phase where η′ surrounds this spherical particle. In alloy C, the source of the increased Cu is in the additional Cu3Sn added to spherical Ag 3 Sn particle and Cu6Sn5 (ηʹ) are present around this spherical particle.

Class 5 ( posterior )

Amalgam restorations from a low-Cu lathe cut alloy (left) and a high-copper admix alloy (right) after 3 years of clinical service

3mmar

Ch 14 : Dental Amalgam

chapter 14 Dental amalgam ( 1 Lecture. )

1- Dental Amalgam

1- definitions : 1. Amalgam: alloy of mercury and any other metal.

2. Dental amalgam : alloy of mercury and silver-tin.

‘’ Ag-Sn + Hg — Dental Amalgam ‘’.

2- Uses : 1 - Class I, II and Class V (posterior) restorations.

2 - Buccal pits.
3 - Core build-up.
4 - Filling of apices of roots after apicectomies.

3- Packing : 1 - Powder & liquid.

2 - Tablets & liquid.
3 - Capsule.
à à capsule is preferred as its provide:
1. Optimum proportion.
2. Easy manipulation.
3. No contamination.
4. Less hazard.

4- General Composition : powder & Liquid.

1- Powder

1) Essential Elements ‘’ Silver & Tin & Copper ‘’

####### element % advantages disadvantages

Silver
‘’Ag’’
65 wt %
1 - Essential for amalgamation process.
2 - increase the strength & setting expansion.
3 - decrease the flow of amalgam.
Tin
‘’Sn’’
29 wt %
1 - Essential for amalgamation process.
2 - decrease the expansion
1 - decrease the strength.
2 - increase the flow
3 - slow the setting

‘’weakest link amongst the alloy ‘’

Copper
‘’Cu’’
6 wt %
1 - increase the strength, hardness.
2 - decrease the flow , creep (eliminates y 2 )
3 - quick the setting
2) Elements may or may not be present ‘’ Zinc & Indium & Palladium ‘’

####### element % advantages disadvantages

Zinc
‘’Zn’’
( less than 0 wt%

or

more than 0,01 wt%

and

not exceeding 1 wt%)
1 - acts as a scavenger

( prevents oxidation of other elements during manufacturing the alloy )

2 - quick the setting

( Helps amalgamation reaction with Hg )

3 - increase the fluidity, workability
& decrease the brittleness.
1 - It causes delayed expansion
in the presence of moisture

due to formation of

####### zinc-oxide & Hydrogen , cause pain

So

####### Amalgam with zinc free is preferred

####### in cases of difficult isolation

####### as class V & Paedodontics.

Palladium reduces tarnish and corrosion.
Indium reduces mercury vapor from restoration.
chapter 14 Dental amalgam ( 1 Lecture. )

2 - according to Copper content

Low copper amalgam

####### (conventional or traditional)

High copper amalgam

####### Admixed Single composition (Unicomposition)

  • It has < 6 wt% Cu
  • It can be lath-cut or spherical
    • 9 %- 20 % Cu
    • has Ag-Cu spherical particles and
lath-cut conventional particles.
  • 13 - 30 % Cu.
  • mainly composed of Ag & Cu & Sn
spherical particles.

3 - according to Zinc content

Zinc containing amalgam Zinc free amalgam
has > 0 wt% Zn has < 0 wt% Zn

6- Amalgamation reaction :

Low Cu Ag 3 Sn (y) + Hg ----------> Ag 3 Sn (y) + Ag 2 Hg 3 (y 1 ) + Sn 7 Hg (y 2 ).
High Cu
admixed Ag 3 Sn (y) + Ag - Cu + Hg -------> y + Ag-Cu + Ag 2 Hg 3 (y 1 ) + Cu 6 Sn 3 (η)
Unicompositional Ag 3 Sn (y) + Cu 3 Sn (ε) + Hg ----> y + (ε) + y 1 + Cu 6 Sn 3 (η)
NB1: present in low copper amalgam
à Ag 3 Sn (y): 27 % - 35 %, strongest
à Ag 2 Hg 3 (y 1 ): 54 %- 56 %, strong , formed firstly
à Sn 7 Hg (y 2 ): 11 %- 13 %, weakest and most corrodible phase , formed later.
à y 1 & y 2 act as a matrix to hold the unreacted amalgam alloy ( y ) together.
NB1: à Copper presents in the form, of Ag-Cu eutectic or Cu 3 Sn (ε )form.
à Copper eliminates y 2 (within few hours) or prevents its formation entirely

development sequence of amalgam microstructure when lathe-cut low-copper alloy particles are mixed with mercury A, Dissolution of silver and tin into mercury. B, Precipitation of γ 1 crystals in the mercury. C, Consumption of the remaining mercury by growth of γ 1 and γ 2 grains. D, the final set amalgam

####### Schematic representation

####### of setting reaction and

####### microstructure of admixed

####### amalgam

chapter 14 Dental amalgam ( 1 Lecture. )

7- Properties :

1) Physical P.

1) CTE - value : amalgam has higher CTE three times than that of tooth

  • effect : 1. microleakage with contraction.
2. pressure or even crack with expansion.

2) Thermal

Diffusivity

&

Conductivity

  • value : amalgam has high thermal diffusivity, conductivity
  • effect : Pain ( thermal shock )
  • Protection : it require a base or liner under it
à Varnish in super-facial cavity.
à base in moderate cavities as zinc phosphate or glass inmoer.
à liner ‘’ Ca(OH) 2 ‘’ and base ‘’ zinc-phosphate ‘’ in deep cavities.
2) Mechanical P.

1) Strength à it’s brittle : - strong In compression than In tension .

  • 1h compressive strength should be > 80 MPa.
à at day 1; Tensile strength is about 1/8 of the compressive strength.
à more y In the set amalgam Increases strength but not on expense of matrix.
à high-Cu uni-compositional amalgam has the highest early-compressive strength
and the lathe-cut amalgam has the lowest.

2) Stiffness modulus of elasticity is relatively high .

3) Time-dependant P.

1) Creep - Definition : deformation of material subjected to constant stress below its Y.

  • Value : less 3% , expressed as expansion.
  • Cause : repeated chewing forces specially in presence of y 2.
  • Occurance : high-copper uni-compositional amalgam the lowest creep values while
low copper amalgam associated with y 2 has higher creep rates.
  • Result : Creep is correlated with marginal breakdown (ditching) of the filling Dimensional change of 3 amalgam products over a 24-hour period. A, high-Cu admixed amalgam (Dispersalloy). B, high-Cu single composition amalgam (Tytin). C, lathe-cut low-Cu amalgam (Fine-Cut).

####### Delayed

####### Expansion:

this expansion usually starts 3 to 5 days after Placement and may continue for months, reaching values greater than 400 μm/cm (4%).

chapter 14 Dental amalgam ( 1 Lecture. )

8- Advantages : 9- Diasadvantages :

1 - high compressive strength.
2 - acceptable marginal adaptation which
improves on aging through self-sealing
with corrosion products.
3 - good wear resistance.
4 - low cost.
5 - easy manipulation.
6 - technique insensitivity.
1 - low tensile strength ‘’brittle’’.
2 - Tarnish, long term corrosion.
3 - Galvanic response potential exists.
4 - Local allergic potential.
5 - high thermal diffusivity, conductivity.
6 - Poor aesthetic qualities.
7 - Concern about possible mercury toxicity.
8 - some destruction of sound tooth structure
to obtain macro-mechanical retention

‘’resistance, retention form cavity design’’

as its lack of adhesion to tooth structure.

10- Manipulation : 1- Selection of the alloy and mercury.

2- Proportion of the alloy to mercury.
3- Trituration ‘’Mixing’’.
4- carrying amalgam and Cavity design.
5- Condensation.
6- Carving and burnishing.
7- Finishing and Polishing
1- Selection of the alloy and mercury

1

Shape of alloy
Spherical alloy require less condensation, less Hg, has higher strength
however its more difficult to contour, has shorter working time.

2

Size of particles Fine particles ‘’medium’’ produce smoother surface during carving , finishing

3

Copper content
High copper amalgam is selected because a restoration has no y 2 thus become
1 - has better mechanical properties
2 - more resistant to tarnish, corrosion.

4

Zinc content
à zinc containing amalgam acts as scavenger, increase the workability.
à zinc-free amalgam is recommended where moisture control is difficult.

5

Selection of Hg It should be pure ‘’highly distilled & free from arsenic content ‘’.
6 Form supply 1 - Powder. 2 - Tablets. 3 - Capsule.
2- Proportion of the alloy to mercury
à ratio can be adjusted using a mechanical dispenser (in case of powder or tablets ) or using capsule.
à every 1% increase in residual Hg above 60% will cause 1% decrease in compressive strength of filling
à In the past; Hg-alloy ratio was 3 : 1 or 8 : 5 and thus Squeezing was required to remove excess Hg
à In I 960 , Eames technique (ratio is 1:1 ) was developed , thus there is no squeeze-cloth technique.
à now; Hg : alloy ratio was 1:1 or even less depending on particle shape , size and type of alloy.

( Ex: ‘’ 54% Hg with lath-cut conventional alloy ‘’ & ‘’ 45% Hg with high-cupper alloy’’ & ‘’ 40% Hg with Spherical alloy’’ )

chapter 14 Dental amalgam ( 1 Lecture. )

####### 8

3- Trituration ‘’Mixing’’
Def.
Its process of mixing of Hg , alloy particles to
produce a coherent , plastic , homogenous mass of
condensable amalgam.

Under mix & Normal mix & over mix

Purpose
rub the film of oxides off the surface of alloy particles
to expose it’s clean surface to mercury
methods
Old technique
‘’manual’’
by hand mixing using
mortar and pestle, then mulling.
Currently
‘’mechanical’’
by amalgamator.
result
1 Normal mix
appear shiny, homogenous, coherent ‘’ separate as a single mass ’’.
2 Under-mix appear dull , crumbly , too soft.

3

Over-mix appear soupy , stick to the inside of capsule, instruments, set fast.

####### Under-mix

####### dull, crumbly, too soft.

####### Normal mix

####### shiny, homogenous, coherent

####### Over-mix

####### soupy, stick

4- carrying amalgam & Cavity design
à amalgam is dispensed into the isolated cavity using amalgam carrier.
à cavity should be filled in increments.
à Undercut is required to retain amalgam.
à cavity should has sufficient depth particularly isthmus part.

Class I preparation Insertion of amalgam by carrier Condensation of amalgam

chapter 14 Dental amalgam ( 1 Lecture. )

####### 10

11- Amalgam safety (Is dental amalgam is safe restoration ?? ) :

à it’s controversial as its safe restoration despite the toxicity of Hg.
à Hg can get access to the body through the skin, ingestion, lung.
à the most dangerous form of Hg in dental clinic is Hg vapor ( organic Hg ).
Good Mercury Hygiene in Dental Clinics
1 - Premeasured capsules should be used.
2 - Hg should be contained in stoppered bottles.
3 - a gloves should be worn ( No touch technique should be used ).
4 - A mask should be worn during working with amalgam.
5 - Amalgam scrap should be stored under water in a closed container.
6 - Spills of Hg should be avoided.
7 - Dental office shouldn’t be carpeted. (No effective way for removing liquid mercury from carpeting).
8 - Use high evacuation system when finishing or removing amalgam.
9 - Working in a well-ventilated spaces with fresh air exchange.

2- Gallium alloy ( Galloy )

history

à It was suggested as early as 1928 in Germany & Under development in Japan since 1956,
à The first commercial alloy was introduced in Tokyo in 1990
and called gallium alloy GF and then Gallium alloy GFII.
à The more recent alloy was introduced in Australia in 1995 and called Galloy.

composition

powder Ag (50%), Sn (25%), Cu (15%) and Pd (9%) and traces (0%), all by weight.
liquid Gallium (62%), indium (25%), tin (13 %) and traces 0%.

Handling characteristics

1 - Gallium amalgams are more difficult to handle
(because of their sticky nature).
2 - they have sensitive technique.
3 - In most other respects, they are similar to spherical amalgam.

properties

1 - Comparable compressive strength, creep with silver amalgam.
2 - Lower corrosion resistance.
3 - Moisture contamination causes severe expansion
(sometimes causes cracking of the tooth).

Evaluation

####### à Gallium amalgam can be successfully used in simple cavities.

####### à Sealing the restoration before, after placement is mandatory to prevent excessive expansion.

####### à Handling properties need to be modified.

####### à More in-vivo studies are required before market distribution

3- Amalgam Bonding

definition Using resin bonding technology, amalgam is micromechanically bonded to Dentin, enamel

####### advantages

1 - Amalgam retention...
2 - Tooth reinforcement.
3 - Reducing microleakage and post-operative sensitivity.

####### Resin

####### bonding

####### system

à Amalgam bond resin-based adhesive is one of the first to find successes in the market.
à After application of etchant, primer. the mixed amalgam is condensed into the adhesive.
à The resulting bond is almost half of that of composites
chapter 14 Dental amalgam ( 1 Lecture. )

Classification of Tooth Preparations according to

1- Black’s classification

à Class I : - involving all pit-and-fissure
  • These include preparations

####### 1- Occlusal surfaces of premolars and molars.

####### 2- Occlusal 2/3 of the facial & lingual surfaces of molars.

####### 3- Palatal pits of maxillary incisors

à Class II: - involving the proximal surfaces of posterior teeth.
à Class III: - involving the proximal surfaces of anterior teeth
that do not include the incisal angle.
à Class IV: - involving the proximal surfaces of anterior teeth
that include the incisal edge.
à Class V: - involving the gingival third of the facial or lingual surfaces
of all teeth.
à Class VI: - Preparation on the incisal edges of anterior teeth or
the occlusal cusp tips of posterior teeth.
---------------------------------------------------------------

2- Number of involve surfaces

à Simple : if only one tooth surface is involved.
à Compound : if two surfaces are involved.
à Complex : If a preparation involves three or more surfaces.
--------------------------------------------------------------

Note : isthmus

  • it’s the junction bt occlusal and proximal cavities.
  • it’s should be wide ( 1 mm minimum )
to prevent fracture of restoration
chapter 14 Dental amalgam ( 1 Lecture. )

####### 13

####### 18- Creep of dental amalgam is decreased by the use of .......

a- high copper unicompositional dental amalgam alloy b- low mercury/alloy
c- a & b d- none of the above

####### 19- The viscous portion in dental amalgam is represented by ........

a- Ag2 Hg3 (γ1) and Sn8 Hg (γ2) phases b- Ag3Sn (γ) and Cu6Sn5 (η) phases
c- Ag2 Hg3 (γ1) and Ag3Sn (γ) d- None of the above.

####### 20- The elastic portion in dental amalgam is represented by ........

a- Ag2 Hg3 (γ1) and Sn8 Hg (γ2) phases b- Ag3Sn (γ) and Cu6Sn5 (η) phases
c- Ag2 Hg3 (γ1) and Ag3Sn (γ) d- None of the above
21- Dental amalgam alloy is ......... a- intermetallic alloy. b- Eutectic alloy.
c- Solid solution. d- None of the above.
22- amalgam is characterized to be .... a- Brittle b- Viscoelastic c- Metallic d- All of the above

####### 23- Dental amalgam bonded to tooth structure by ....... retention

a- Chemical b- Mechanical c- a &b d- None of the above.

####### 24- Reduction of corrosion in dental amalgam is achieved by .....

a- The use of low mercury alloy ratio to reduce the reaction products especially γ2 phase
b- The use of high copper amalgam alloys to be free of y2 phase
c- Finishing and polishing of amalgam restoration to produce smooth surface.
d- All of the above

####### 25- In low copper amalgam the ............ represent the matrix

a- Ag2 Hg3 (γ1) phase b- Sn8 Hg (γ2) phase c- Ag3Sn (γ) phase d- a & b

####### 26- In high copper amalgam the .......... represent the matrix

a- Sn8 Hg (γ2) phase b- Ag2 Hg3 (γ1) phase c- Ag3Sn (γ) phase d- None of the above

####### 27- The strongest phase in dental amalgam is ........

a- Ag3Sn (γ) phase b- Sn8 Hg (γ2) phase c- Ag2 Hg3 (γ1) phase d- None of the above

####### 28- The most corroidable phase in dental amalgam is .......

a- Ag3Sn (γ) phase b- Sn8 Hg (γ2) phase c- Ag2 Hg3 (γ1) phase d- Cu6Sn5 (η) phase

####### 29- The weakest phase in dental amalgam is .........

a- Ag3Sn (γ) phase b- Sn8 Hg (γ2) phase c- Ag2 Hg3 (γ1) phase d- Cu6Sn5 (η) phase

####### 30- The net total dimensional change in dental amalgam is ...........

a- Expansion b- Contraction c- No dimensional change d- None of the above

####### 31- Marginal adaptation and seal of dental amalgam can be obtained by .....

a- Good condensation b- corrosion products at amalgam tooth interface
c- Application of amalgam bonded system d- all of the above
-----------------------------------------------------------------------------

True or false

1- amalgam use at stress bearing areas.
2. Spherical particles require less mercury than typical lath-cut.
3. Delayed expansion does not occur in zinc free amalgam restorations.
4. Usually spherical amalgam particles are subjected to heat treatment
to relief stresses induced during preparation.
5. Dental amalgam is an alloy containing mercury and any other metal.
6. Dental amalgam is indicated for class V anterior restorations.
7. Spherical particles need large condenser tips during condensation.
8. to protect the underlying dentine from thermal conductivity of amalgam its indicated to
insert liner , base in deep cavity and base in moderate cavity , liner or varnish in shallow cavity.
chapter 14 Dental amalgam ( 1 Lecture. )

####### 14

9. ( Sn 2 Hg) is weakest , most corrodible phase in amalgam.
10. the advantages of burnishing is homogenicity of microstructure of surface layer result in strong margins.
11. Conventional amalgam has lower strength than high Cu amalgam.
-----------------------------------------------------------------------------

Give reason

Q 1 : avoid contamination of saliva especially in case of zinc containing amalgam.
answer:
Q 2 : In children, zinc free dental amalgam should be used rather than zinc containing amalgam.
answer: due to in children it is so difficult to have good isolation during condensation of dental amalgam
Q 3 : during cavity preparation for amalgam we have to maximize the compressive force than tensile force.
answer:
Q 4. corrosion of amalgam is a benefit.
answer: due to it is seal the marginal gap which result from contraction dental amalgam after setting
(self sealing property)
Q 5. Dental amalgam always corrodes
answer: as it is heterogeneous structure ( always contain more than one phase)
Q 6. In dental amalgam spherical , spheroidal powders should be exposed to homogenization process.
answer: to eliminate the cored structure , allow even distribution of Ag3Sn (γ ).
Q 7 : Aging or annealing is not necessary for spherical , spheroidal powders in dental amalgam.
answer: due to no cold working occur so, no internal stresses occurs.
Q 8 : Delayed [secondary] expansion of zinc containing dental amalgam.
answer: due to moisture contamination of dental amalgam during trituration or condensation
which cause release of H2 gas.
Q 9 : High-copper alloys have become the material of choice in dental amalgam.
answer: due to elimination of Sn8Hg (γ2) phase, which is the weakest , most corroidable phase.
Q 10 : to obtain better properties of amalgam; minimum amount of Hg should always be mixed with powder.
answer: due to increase the amount of mercury (Hg) leads to
1- increase the amount of Ag2Hg3 (γ1) + Sn8Hg (γ2) phases
2- decrease the amount of Ag3Sn (γ) phase So, it decrease strength and
increase creep , corrosion of dental amalgam.
Q 11 : creep of dental amalgam
answer: due to visco-elastic nature of material : - the viscous portion Ag2Hg3 (γ1) , Sn8Hg (γ2).
  • the elastic portion Ag3Sn (γ) , Cu6Sn5 (η).
Q 12 : creep is very high in conventional low copper amalgam.
answer: as it is contain the viscous portion Ag2Hg3 (γ1) , Sn8Hg (γ2)
while in high copper amalgam the creep is more less as it doesn’t contain Sn8Hg (γ2).
Q 13 : Nano-amalgam is not present as nanocomposite and other dental materials.
answer: as the nano-particles amalgam will produce a very large surface area and this will
require an extensive amount of mercury results a friable , weak amalgam
-----------------------------------------------------------------------
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14 Amalgam

Course: Dental Amalgam

University: Helwan University

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. 3mmar’s Dental material 0106 39 700 30 mahmoud_3mmar@yahoo.com
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