Amalgam Delayed expansion Setting reaction Mercury toxicity

1. Dental Amalgam
Dr Anupam Sharma

2. Dental Amalgam
Amalgam - an alloy of mercury.
Amalgamation – the process of mixing liquid mercury
with one or more metals or alloys to form an amalgam.
Dental Amalgam – an alloy of mercury, silver, copper
and tin which may also contain palladium, zinc and other
elements to improve handling characteristics and clinical
performance.

3. 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
.
Alloy composition (1896 Dr. G.V. Black) –
Silver – 65 wt %
Tin – 29 wt%
Copper – 4 wt%
Zinc – 0.01 wt %
During 1970 Copper – 6 wt % to 30 wt %

4. An annealed ingot of alloy
↓
Milling machine / lathe
↓
Cutting tool
↓
needle-like chips
↓
Ball-milling
↓
Particle treatment by acid
↓
Stress- relieving process ( An annealing cycle at a
moderate temperature usually for several hours at
approximately 100c.
Manufacture of alloy powder –
1. Lathe-cut powder obtained as follows :

5.  Lathe – cut.
 Spherical

6. 2. Atomized powder – atomized powder is
made by melting together the desired elements.
The liquid metal is atomized into fine spherical
droplets of metal. Heat and acid treatment is
given to the particle.

7. Classification of Dental Alloys
I According to the number of metals
Binary alloys – ( Ag – Sn)
Ternary alloys – ( Ag – Sn – Cu)
Quaternary alloys – ( Ag – Sn – Cu – In)
II According to whether the powder consists of
unmixed or admixed alloys.
III According to the shape of particles –
Lathe cut (irregular shape)
Spherical (smooth surface spheres)
Spheroidal (spherical with irregular)

8. IV According to the particle size –
Microcut
Finecut
Coarsecut
V According to the copper content –
Low copper alloy ( <6 wt% Cu)
High copper alloy ( 6 to 30 wt% Cu)
VI According to the zinc content –
Zinc alloy (zinc 0.01 wt %)
Non-zinc alloy (zinc <0.01 wt %)

9. VII According to mercury content –
3 wt % mercury in pellet of alloys –
preamalgamated alloys.
VIII According to the addition of noble metals –
Noble-metal alloys (Palladium, gold,
platinum)

10. The compositional changes in alloy powder
First generation – (Ag - Sn)
Silver-tin peritectic alloy (3:1)
Second generation – (Ag – Sn + Cu – Zn)
Addition of 4% copper and traces of zinc to
gamma phase of basic alloy powder.
Copper decreases plasticity and increases
strength and hardness.
Zinc acts as a deoxidizer.

11. Third generation – (Ag – Cu + Ag – Sn)
Addition of spherical silver copper eutectic
alloy to the original alloy powder.
Fourth generation – (Ag – Sn – Cu)
Alloying of copper to silver and tin in the
percentage upto 29 wt % - ternary alloy.

12. Fifth generation – (Ag – Sn – Cu – In)
Alloying of silver copper tin and indium
together creating quaternary alloy.
Sixth generation –
Alloying of palladium (10 wt %), silver (62 wt
%), copper (28 wt %) to form a eutectic alloy
which is lathe cut and blended into a first,
second or third generation amalgam alloy in a
ratio of 1:2.
(Ag – Cu – Pd + 1st or 2nd or 3rd generation)
1 : 2

13. γ - Ag 3 Sn
γ1 - Ag 2 Hg 3
γ2 - Sn 7-8 Hg
ε - Cu 3 Sn
η - Cu 6 Sn 5
Silver copper eutectic - Ag - Cu
Amalgamation
Metallurgic phases in amalgam

14. Amalgamation for low copper alloys
16.78 Ag 3 Sn + 37 Hg ↔ 12 Ag 2 Hg 3 + Sn 8 Hg + 8.78 Ag 3 Sn
β + γ + Hg ↔ γ 1 + γ 2 + β + γ ( unreacted particles )
Thus a typical low copper amalgam is a composite in which
unreacted particles are embedded in γ 1 & γ 2 phases.

15. Amalgamation

16. Amalgamation for admixed high copper alloys
16.78 Ag 3 Sn + Ag Cu (eutectic) + Hg ↔
12 Ag 2 Hg 3 + Cu 6 Sn 5 + 8.78 Ag 3 Sn + Ag-Cu
β + γ + Ag-Cu + Hg ↔ γ 1 + η + β + γ +Ag-Cu
Amalgamation for single composition high copper alloys
β + γ + ε + Hg ↔ γ 1 + η + β + γ + ε

17. Behavior of Amalgam
1 Dimensional changes
During setting amalgam undergoes three distinct
dimensional changes.
Stage I – Initial contraction.
Stage II – Expansion.
Stage III – Limited delayed contraction.
According to ADA specification # 1 for amalgam,
-20 or +20 micron/cm dimensional changes acceptable.

18. Factors affecting the dimensional changes
A. Constituents
B. Mercury
C. Particle size / shape
D. Trituration
E. Condensation
F. Contamination

19. Amalgam
Compressive
strength [MPa]
Tensile
Strength
[MPa]
1 hr 7 days 24 hrs
Low Copper 145 343 60
Admixed 137 431 48
Single
Composition
262 510 64
2 Strength

20. Factors affecting the strength of Amalgam
A Temperature F
Particle size /
shape
B Trituration G
Inter-particle
distance
C Mercury H Dispersion
D Condensation I γ 2 phase
E Porosity J Corrosion

21. Fractured Restoration

22. 3 Creep
Static creep : Deformation produced in a completely
set solid subjected to a constant stress.
Creep value for amalgam
Amalgam Creep value
Low copper 2.0 %
Admix 0.4 %
Single composition 0.13 %

23. Creep

24. Factors affecting creep value of amalgam
A. Trituration
B. Alloy Mercury ratio
C. Condensation
D. Type of alloy

25. Mercuroscopic expansion
Extrusion of the amalgam margins due to creep
is promoted by
electrochemical corrosion, during which
mercury from Sn-Hg re-reacts with Ag-Sn particles
and produces further expansion
Mechanism was originally proposed by Jorgensen

27. Technical considerations
A. Choice of the alloy and mercury
B. Proportioning
C. Trituration
D. Mulling
E. Matricing
F. Condensation
G. Burnishing
H. Carving
I. Finishing and polishing

28.  Amalgamators
 Capsules

30.  Under-triturated
 Properly-triturated

31. After carving After polishing

32. Recent advances
Gallium alloys- AgSn particles in Ga-In
Gallium melts at 28 C
Au mixed with other noble metals to form the restoration
matrix
ADA-NIST- Patented a mercury free direct filling alloy
based on silver coated Ag-Sn particles
Minimize the mercury required for mixing- 15% to 25%
range

33. Mercury management
Mercury has the potential to be hazardous if not
managed properly
Alloying reaction of mercury with Ag-Sn should go to
completion
Contribution of mercury derived from amalgam to the
overall body is relatively low
First amalgam war between dentists using gold foil and
those using dental amalgam
1920- Inferences were made that mercury is not tightly
bound in amalgam

34. 1980- Dr. Hal Huggins condemned amalgam
No basis for claims that amalgam was a significant
health hazard

35. Mercury absorption, transportation,
and excretion in the body

36. Sources of mercury hazards in dental
operatory

37. Mercury
Toxicity

38. Dental Mercury Hygiene Recommendations
Train all personnel
Make personnel aware of the potential sources of
mercury vapor in the dental operatory
Work in well ventilated spaces
Periodically check the dental operatory atmosphere for
mercury vapor. The current limit is 50 microgram per
cubic meter

39. Dental Mercury Hygiene Recommendations
 Work area should facilitate cleanup.
 Floor should be non-absorbent, seamless and
easy to clean.
 Use precapsulated alloy as far as possible.
 Use an amalgamator with completely enclosed arm
 Avoid skin contact with mercury or freshly mixed
amalgam

40. Dental Mercury Hygiene Recommendations
 Properly dispose of precapsulated alloy after use.
 Use high volume suction when finishing and
removing amalgam
 Suction system should have amalgam traps or filters
 Salvage and store all scrap amalgam
 Scrap amalgam should be stored under radiographic
fixer solution

41. Dental Mercury Hygiene Recommendations
 When feasible, recycle amalgam scrap and waste
amalgam
 Dispose of mercury contaminated items in sealed
bags as per regulations
 Clean up mercury spills using trap bottles, tape or
freshly mixed amalgam to pick up droplets, and
commercial clean up kits
 Remove professional clothing before leaving the
work place