1. Dept of Restorative Dentistry, Almajmaah University, Zilfi KSA

2. classification

3. Based on number of alloyed metals
Binary contain silver & tin
Ternary contain silver, tin and copper
Quaternary contain silver, tin, copper and zinc / indium

4. Based on particle shape
Lathe cut particle alloys
Spherical particle alloys

5. Lathe cut Irregular in shape in the form of shavings Low Cu ( < 6%)
High Cu

6. spherical
Smooth spherical shaped particles low Cu High Cu

7. Based on Copper Content
Low-copper alloys
4 to 6% Cu
High-copper alloys
thought that 6% Cu was maximum amount
due to fear of excessive corrosion and expansion
Now contain 9 to 30% Cu
at expense of Ag

8. Based on Zinc content Zinc free alloys contain less than 0.01 % zinc
Zinc containing alloy contain more than 0.01% zinc

9. Based on method of Adding Cu
Single composition alloys
Admixed alloys

10. Single composition Each particle has same composition
Also known as UNICOMPOSITIONAL
Single Composition Lathe-Cut
Single Composition Spherical
require less mercury
smaller surface area easier to wet

11. Admixed alloys
Physical mixing of lathe- cut and spherical particles spherical alloys
require more mercury
lathe-cut particles more difficult to wet

12. Variables
Dimensional change
Strength
Corrosion
Creep

13. Dimensional Change Most high-copper amalgams undergo a net contraction
Contraction leaves marginal gap
initial leakage
post-operative sensitivity
reduced with corrosion over time

14. Dimensional Change Net contraction type of alloy
spherical alloys have more contraction
less mercury
condensation technique
greater condensation = higher contraction
trituration time
overtrituration causes higher contraction

15. Strength Develops slowly Spherical alloys strengthen faster
1 hr: 40 to 60% of maximum
24 hrs: maximum
Spherical alloys strengthen faster
require less mercury
Higher compressive vs. tensile strength
Weak in thin sections
unsupported edges fracture

16. Corrosion Reduces strength Seals margins low copper high copper
                          
                          
Corrosion
Reduces strength
Seals margins
low copper
6 months
SnO2, SnCl
gamma-2 phase
high copper
months
SnO2 , SnCl, CuCl
eta-phase (Cu6Sn5)

17. Creep Slow deformation of amalgam placed under a constant load
Gamma 2 dramatically affects creep rate
Correlates with marginal breakdown

18. Creep High-copper amalgams have creep resistance
prevention of gamma-2 phase
requires >12% Cu total
single composition spherical
eta (Cu6Sn5) embedded in gamma-1 grains
interlock
admixture
eta (Cu6Sn5) around Ag-Cu particles
improves bonding to gamma 1

19. Dentist-Controlled Variables
Manipulation
trituration
condensation
burnishing
polishing

20. Trituration Mixing time Overtrituration Undertrituration
refer to manufacturer recommendations
Overtrituration
“hot” mix
sticks to capsule
decreases working / setting time
slight increase in setting contraction
Undertrituration
grainy, crumbly mix

21. Condensation Forces lathe-cut alloys spherical alloys admixture alloys
small condensers
high force
spherical alloys
large condensers
less sensitive to amount of force
vertical / lateral with vibratory motion
admixture alloys
intermediate handling between lathe-cut and spherical

22. Burnishing Pre-carve Post-carve Combined removes excess mercury
improves margin adaptation
Post-carve
improves smoothness
Combined
less leakage

23. Early Finishing After initial set prophy cup with pumice
provides initial smoothness to restorations
recommended for spherical amalgams

24. Polishing Increased smoothness Decreased plaque retention
Decreased corrosion

25. Alloy Selection Handling characteristics
Mechanical and physical properties
Clinical performance

26. Handling Characteristics
Spherical
advantages
easier to condense
around pins
hardens rapidly
smoother polish
disadvantages
difficult to achieve tight contacts
higher tendency for overhangs

27. Handling Characteristics
Admixed
advantages
easy to achieve tight contacts
good polish
disadvantages
hardens slowly
lower early strength

28. Compressive Strength (MPa)
Amalgam Properties
Compressive Strength (MPa)
% Creep
Tensile Strength
(24 hrs) (MPa)
Amalgam Type
1 hr
7 days
Low Copper1
145
343
2.0 60
Admixture2
137
431
0.4 48
Single Composition3
262
510
0.13 64
1Fine Cut, Caulk Dispersalloy, Caulk 3Tytin, Kerr

29. Mercury toxicity Allergy < 1% of treated population
An antigen antibody-reaction
itching
rashes
sneezing
swelling
Difficulty in breathing

30. Toxicity Mercury vapor inhalation ( to dentist or dental assistant)
Type IV hypersensitivity reaction.

31. Precautions Skin contacted should be washed with soap and water.
Spilled mercury should be cleaned as soon as possible.
Clinic should be well ventilated.
Amalgam scrap and mercury contaminated instruments should not be subjected to heat sterilization.
Vacuum cleaners should not be used.
Ultrasonic amalgam condenser should not be used.

32. Suggested reading Craig’s Restorative Dental Materials
13th edition by Sakaguchi RL and
Powers JM
Philip’s Science of dental materials 11th edition by Kenneth J. Anusavic