Manipulation of dental amalgam
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Transcript Manipulation of dental amalgam
Dept of Restorative Dentistry,
Almajmaah University, Zilfi
KSA
Based on number of alloyed metals
Binary contain silver & tin
Ternary contain silver, tin and copper
Quaternary contain silver, tin, copper
and zinc / indium
Based on particle shape
Lathe cut particle alloys
Spherical particle alloys
Lathe cut
Irregular in shape in the form of shavings
Low Cu ( < 6%)
High Cu
spherical
Smooth spherical shaped particles
low Cu
High Cu
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
Based on Zinc content
Zinc free alloys contain less than 0.01 %
zinc
Zinc containing alloy contain more than
0.01% zinc
Based on method of Adding Cu
Single composition alloys
Admixed alloys
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
Admixed alloys
Physical mixing of lathe- cut and spherical
particles spherical alloys
require more mercury
lathe-cut particles more difficult to wet
Variables
Dimensional change
Strength
Corrosion
Creep
Dimensional Change
Most high-copper amalgams undergo a
net contraction
Contraction leaves marginal gap
initial leakage
○ post-operative sensitivity
reduced with corrosion over time
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
Strength
Develops slowly
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
Corrosion
Reduces strength
Seals margins
low copper
○
6 months
SnO2, SnCl
gamma-2 phase
high copper
○
6 - 24 months
SnO2 , SnCl, CuCl
eta-phase (Cu6Sn5)
Creep
Slow deformation of amalgam placed under a
constant load
Gamma 2 dramatically affects creep rate
Correlates with marginal breakdown
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
Dentist-Controlled Variables
Manipulation
trituration
condensation
burnishing
polishing
Trituration
Mixing time
refer to manufacturer
recommendations
Overtrituration
“hot” mix
○
sticks to capsule
decreases working / setting time
slight increase in setting contraction
Undertrituration
grainy, crumbly mix
Condensation
Forces
lathe-cut 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
Burnishing
Pre-carve
removes excess mercury
Post-carve
improves margin adaptation
improves smoothness
Combined
less leakage
Early Finishing
After initial set
prophy cup with pumice
provides initial smoothness to restorations
recommended for spherical amalgams
Polishing
Increased smoothness
Decreased plaque retention
Decreased corrosion
Alloy Selection
Handling characteristics
Mechanical and physical
properties
Clinical performance
Handling Characteristics
Spherical
advantages
○ easier to condense
around pins
○ hardens rapidly
○ smoother polish
disadvantages
○ difficult to achieve tight contacts
○ higher tendency for overhangs
Handling Characteristics
Admixed
advantages
○ easy to achieve tight contacts
○ good polish
disadvantages
○ hardens slowly
lower early strength
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
Caulk
3Tytin, Kerr
2 Dispersalloy,
Mercury toxicity
Allergy < 1% of treated population
An antigen antibody-reaction
itching
rashes
sneezing
swelling
Difficulty in breathing
Toxicity
Mercury vapor inhalation ( to dentist or
dental assistant)
Type IV hypersensitivity reaction.
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.
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