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