Dept of Restorative Dentistry, Almajmaah University, Zilfi KSA

classification

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 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

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 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 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

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

Burnishing Pre-carve Post-carve Combined removes excess mercury improves margin adaptation Post-carve 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

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 2 Dispersalloy, Caulk 3Tytin, Kerr

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