Amalgam restorations Material science

what is amalgam

Direct, metallic restorative material

what is meant by a direct restoration

fabricated in patient mouth
No need for lab

what teeth is amalgam usually used on, why?

posterior teeth
Amalgam is metallic \= non-aesthetic

examples of direct restorations

Amalgam
Composite resins
Glass ionomer
Resin modified glass ionomer
Intermediate restorative materials (IRM)
Direct gold fillings

indirect restorations

restorations constructed in lab (extra-orally) over a cast by dental technicians

examples of indirect restorations

Porcelain
Gold alloy
Cobalt chromium alloy
Polymers

is there a difference between amalgam and dental amalgam?

yes

amalgam is a mixture of

Any metal or alloy + Hg mercury

dental amalgam is a mixture of

Silver-tin alloy + Hg mercury

dental amalgam alloy is made of

silver-tin alloy

main phase of dental amalgam alloy is called

gamma (Ag3Sn) Silver-tin

alloys present in dental amalgam

Silver Ag
Tin Sn
Copper Cu
Zinc Zn
Lead Pb
Indium In

liquid composition of dental amalgam

mercury

elements necessary for amalgamation reaction

Ag
Sn
Hg

elements that increase setting time

Hg mercury

elements that decrease setting time

Ag silver
Sn tin

elements that increase setting expansion

Ag silver
Cu copper
Hg mercury

elements that decrease setting expansion

Sn tin

elements that increase strength of amalgam

Ag silver
Cu copper
In & Pd Indium and lead

elements that decrease strength of amalgam

Hg mercury
Sn tin

elements that increase corrosion resistance

Ag silver
Cu copper
In & Pd Indium and lead

elements that decrease corrosion resistance

Hg mercury
Sn tin

elements that increase creep

Hg mercury
Sn tin

elements that decrease creep

Ag silver
Cu copper

what is creep

permanent change in shape with time

what will happen if more Hg is used. than necessary

undesired due to decreased strength, decreased corrosion resistance and increased creep

Role of zinc in amalgam

-Scavenger in manufacturing to produce clean, sound castings
-Increase plasticity (easily shaped)
-Reduced brittleness

brittle materials are strong under \___ and weak under \___

strong under compression, weak under tension

Classification of dental amalgam according to:

-Particles shape
-Particle size
-Copper content
-Zinc content

types of dental amalgam (Particles shape)

Lath cut (irregular)
Spherical
Admixed (mix of both)

types of dental amalgam (particles size)

Micro-cut
Fine-cut
Coarse-cut

micro-cut alloy

fine-cut alloy

10-30 um
perfect

coarse-cut alloy

\>30 um
rough final surface

types of dental amalgam (Copper content)

Low copper
High copper

Low copper dental amalgam

high copper dental amalgam

13-30% copper

subtypes of high copper dental amalgam

Admixed
Unicompositional

types of dental amalgam (Zinc content)

Zinc containing
Zinc free

zinc containing amalgam

\> or equal to 0.01% Zn

zinc free amalgam

< 0.01 % Zn

is Zinc always present in amalgam?

yes (even in zinc free) but in very little amounts

what is amalgamation reaction

reaction between Hg and alloy (Ag3Sn) when mixed

amalgamation reaction also called

setting reaction

amalgamation reaction is

chemical : irreversible

what is the microstructure of a material

structure inside material only seen under microscope

Cu copper content in low copper amalgam

less than 6%

particle shape of low copper amalgam

lath-cut or spherical

main phase of low copper amalgam

Gamma (silver tin)

stages of amalgamation reaction

1- Wetting
2- Diffusion
3- Surface reaction

core of amalgam restoration

always unset and unreacted gamma because setting reaction only happens on surface

amalgamation reaction reactants (low copper)

Powder (silver tin) + liquid (mercury)

amalgamation reaction products (low copper)

Matrix (Y1+Y2) + Unreacted particles (Y)

y1 (gamma 1)

Silver mercury (Ag2Hg3)

y2 (gamma 2)

Tin mercury (Sn7-8Hg)

microstructure of low copper amalgam

Matrix of y1 and y2 Holding unreacted core of y

strength of y, y1 and y2

y\> y1\> y2

corrosion resistance of y, y1 and y2

y1\> y\> y2

what alloy is the weakest and most corrosive in low copper amalgam

y2 (tin mercury)

low copper amalgam is also called

gamma 2 containing amalgam

disadvantages of low copper amalgam

Low strength
Low corrosion resistance
High creep
Low marginal integrity

copper content of admixed high copper dental amalgam

30%

particle shape in admixed high Cu dental amalgam

lath-cut (y) and spherical (Ag-Cu)

phases in admixed high copper dental amalgam

y (2/3) \= lathcut
Ag-Cu (1/3) \= spherical

difference between high and low copper dental amalgam (phase wise)

y2 removed in high Cu dental amalgam by adding more copper instead

amalgamation reaction of admixed high copper dental amalgam (Reactants)

Powder: y (Ag3Sn) + Ag-Cu
Liquid: Hg

amalgamation reaction of admixed high copper dental amalgam (Products)

Matrix: y1 (Ag2Hg3)
Unreacted particles: y (Ag3Sn). and Ag-Cu
+ Cu6Sn5 (n)

what phase does high copper amalgam have instead of y2

n phase (Cu6Sn5)

n phase compared to y2

n is stronger and more corrosion resistant

microstructure of admixed high copper dental amalgam

matrix: y1 Holding unreacted core of y and Ag-Cu
n (copper tin) is a helix around Ag-Cu

corrosion resistance of y, y1, Ag-Cu and n

y1\> y\> Ag-Cu\> n

disadvantages of admixed high copper dental amalgam

-Sedimentation of one type of powder at bottom
-Surface oxidation of Ag-Cu (silver copper) during storage \= slows down amalgamation reaction

Copper content of unicompositional high copper dental amalgam

13-30%

particle shape of unicompositional high copper dental amalgam

all spherical

phases in unicompositional high copper dental amalgam

y and ε

ε in unicompositional high Cu dental amalgam is

Cu3Sn (Copper tin)
Also called Epsilon

amalgamation reaction of unicompositional high Cu dental amalgam (Reactants)

Powder: y (Ag3Sn) + ε (Cu3Sn)
Liquid: Hg

amalgamation reaction of unicompositional high Cu dental amalgam (Products)

Matrix: y1 (Ag2Hg3)
Unreacted particles: y and ε
+ n (Cu6Sn5)

microstructure of unicompositional high Cu dental amalgam

matrix of y1 holding unreacted y+ε that are surrounded by n

corrosion resistance of y, y1, n, ε and Ag-Cu

y1\> y\> Ag-Cu\> ε\> n

amalgamation is a \___ reaction

surface reaction (has core of unreacted particles)

what forms the matrix in amalgamation reaction

reaction products

completion of amalgamation reaction

days to weeks (specially with low copper amalgam)

advantages of high copper dental amalgam

y2 free
High early strength
High corrosion resistance
Low creep
Improved marginal integrity

properties of dental amalgam

Dimensional changes
Creep
Strength
Corrosion
Biological properties

dimensional changes in dental amalgam

Initial contraction followed by expansion, then dimensions become stable
Net change:
-expansion
-contraction
-Delayed expansion

when does delayed expansion of amalgam happen

moisture-contamination with zinc-containing type

creep happens due to

viscoelastic nature of amalgam

creep leads to

Gingival overhang
Marginal ditching

strength of dental amalgam

Brittle w/ low edge strength
Max strength after 7 days

how to maximize strength of amalgam

Adequate cavity depth (1.5-2mm)
Stiff base under restoration
High copper amalgam
Cavosurface angle 90 or more

corrosion of amalgam

disintegration of metal by reaction with its environment

corrosion of amalgam causes

Porosity
Strength
Metallic taste

benefit of corrosion in amalgam

seals margins (only self-sealing material)

Biological properties of amalgam

Source of Hg exposure
Hg toxicity
Risk of allergy and neural disorders

sources of Hg exposure

Direct contact
Amalgamator
Removal of old restoration

who is at higher risk of Hg exposure and toxicity

dental staff more at risk than patients

which is more hazardous: Hg vapor or liquid

vapor

Hg hygiene in dental office

Avoid baseboard heaters
Avoid carpeting
Proper ventilation
Regular monitoring of Hg vapor level

Hg hygiene technique

check amalgamator regularly
Avoid ultrasonic condensor
Use water and suction when removing old amalgam
store Hg in cool space
Store amalgam scrap in capped jars containing water w/ X-ray filter