Materials Quiz 7 (same day)

Silver paste announced in

1826

Dental amalgam consists of

Mercury metal + Amalgam alloy

3 classifications of amalgam alloy powder

Lathe-cut (Low copper)
Admixed (high copper)
Spherical (high copper)

Solubility of amalgam alloy in mercury

Cu - 1 atom
Ag - 10 atoms
Sn - 170 atoms

Gamma phases and composition

Gamma: Ag₃Sn
Gamma1: Ag₂Hg₃
Gamma 2: Sn₇Hg

3 major alloys for dental amalgam

Ag, Sn, Cu (Silver, Tin, Copper)

Properties of the alloys for dental amalgams

Silver - Strength, setting reaction & expansion

Tin - Amalgamation, reduced expansion

Copper - strength, hardness, setting reaction

Zinc - Amalgamation, O2 & H2O remover

Mercury - Amalgamation

What is the creep, compressive strength tests and dimensional change ADA specifications of dental amalgam

Creep: < 1 %
Compressive Strength: 1 hr > 80 MPa | 24 hr > 300 MPa
Dimensional change: -0.15 to +0.20

Amalgam waste handling

Scrap amalgam stored under water, glycerin or tightly capped jar that is completely filled with liquid to minimize gas space

Facts about mercury

naturally occuring
½ of Hg released comes from human activity
<1 % from dentistry but causes up to 45% mercury in water

Biggest exposure of mercury?

Methylmercury (most toxic) from fish

Having ___ amalgam surfaces may increase brain mercury concentration by about ___ micrograms/kgs

25, 10

Mercury exposure symptoms

Kidney inflammation, swollen gums, pronounced tremor and nervous system disturbances

Use of amalgam is contraindicated/ not recommended when:

In proximal or occlusal contact to dissimilar metal restorations
Renal deficiency, allergies to it, endo, children or pregnant

Summary of amalgam

one of most common, safe, used widely, strong, lasting and low-cost

Amalgam is ____ in compression and _____ in tensile

strong, weak
No chemical bonding properties, only mechanical

Lathe-cut vs Spherical

Lathe- more surface area needs more mercury 1.2/1
Spherical - Less surface area less mercury 0.8/1

T/F Elemental mercury is toxic when swallowed

False

Mercury is toxic when spills and inhaled

Yes, 80% by lungs, acute toxicity is rare (easy to die)