Amalgam Flashcards
Define amalgam and dental amalgam
Amalgam : mixture of any metal or alloy with mercury.
Dental amalgam : an alloy of mercury with silver ,tin ,copper and zinc + A direct posterior filling
One of the main features of Tin in dental amalgam
It Increase amalgamation at room temperature
One of the main features of Copper in dental amalgam is
If more than 6% it increases resistance to tarnish and corrosion by elimination of δ2 phase.
One of the main features of zinc in dental amalgam is
act as deoxidizing agent ( scavenger) during melting and fusion of the alloy
* Zinc cause severe delayed expansion, if zinc containing amalgam
contaminated with saliva
Indications of dental amalgam
- For filling posterior teeth (moderate to large class I and class II restorations).
- Class V restoration which not esthetically critical.
- Post & Core build up.
- For cusp rebuilding in conjunction with retentive pins.
- Retrograde root canal filling.
Contraindications of dental amalgam
Can not be used when the esthetic is required
Advantages and disadvantage of dental amalgam
Advantages
1. long serviceability
2. Easy to insert and Not technique-
sensitive.
3. Adequate resistance to fracture
and wear.
4. Marginal leakage decreases with
time.
5. Low cost
6. Minimal leakage due to sealing by
corrosion products.
Disadvantages
1.Non esthetic (Metallic color).
2.Subject to corrosion and galvanic
action.
3.Does not bond chemically to tooth
structure.
4.Less conservative (more removal of
tooth structure during cavity
preparation).
According to the copper content of the amalgam alloy :
- Low copper amalgam: less than 6% copper.
- High-copper amalgam : more than 6% copper.
a) Admix alloy .
b) Uni-compositional alloy .
Setting reaction of low copper amalgam
Ŷ (Ag3Sn + Hg) > Ŷ 1 (Ag2Hg3 )+ Ŷ 2 (Sn8Hg )+unreacted Ý ( Ag3Sn + voids)
One of the main properties of low copper amalgam
Gamma 2 phase is weakest and more corrodible phase.
Types of high copper amalgam
- High copper admixed amalgam(dispersed types)
- High copper uni-compositional amalgam
The reaction of admixed alloy
Amalgamation Reaction (during mixing)
Solid State Reaction during Hardening (Elimination of (Ý2)
Properties of High copper amalgam (admixed)
The absent of Sn8Hg(δ2)
1. More corrosion resistance.
2. Higher compressive strength.
3. Less creep.
Drawback of High copper amalgam (admixed)
- Mixture of two different phase (AgSn )and(Ag- Cu) sedimentation of one type in the bottom of container which affect the distribution of alloy.
- Surface oxidation of silver-copper during storage,
affect reactivity.
Setting reaction of High copper uni-compositional amalgam
Ag 3Sn (Ý) + Cu3Sn (ε) + Hg Cu6Sn5 (η) + Ag2Hg3 (Ý1) + unreacted Ag 3Sn (Ý)
According to zinc percentage :
- Alloy contain more than 0.01% zinc containing alloy.
- Alloy contain less than 0.01% zinc free alloy.
Spherical particles compared to lathe cut
• Have lower surface area/volume
• Less mercury to obtain a homogenous mix( lower Hg/Alloy ratio)
• Smoother surface during carving
• Amalgam alloy with superior strength properties
Dimensional changes during setting
A-Initial contraction in the first 20 minutes
B) Then expansion will take place, the dimensions constant after 6-8 hours.