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.
The net total dimensional change contraction after….. considered
final values.
24hours
The low copper content alloys have the greatest change (…….).
The least dimensional changes occur with high copper alloy (………)
-19.7 µm/cm
-1.9 µm/cm
Excessive delayed expansion may also take place if
zinc-containing amalgam are contaminated with water or saliva
Amalgam is stronger in….. and weaker in…….
compressive , tension
Dental amalgam should be supported by base with high module of elasticity , why ?
to minimize deformation and
transverse failure by minimizing tensile stresses
Creep is
Permanent deformation under static load (time dependent plastic
deformation) Below The Elastic Limit
Effect of excessive creep
- Occlusal overhangs lead to marginal breakdown (Ditching) this can produce secondary carries.
- Can cause gingival overhangs lead to gingival inflammation.
- Flattening of contact point and loss of proper contact .
- Increase marginal corrosion due to ditching.
The HIGHEST Creep value ……
The LEAST Creep percent….
the lathe-cut low copper
alloys 6.3%.
unicompositional high
copper alloys. 0.05 -0.09%.
Tarnish and Corrosion
Tarnish is surface discoloration while Corrosion is destruction of a
metal by chemical or electro-chemical reaction.
The rate of failure of amalgam restorations by processes of tarnish
and corrosion can be reduced by using…
a carful finishing and polishing.
Corrosion of amalgam may lead to
Increase porosity
Reduced marginal integrity
Loss of strength
Metallic products lead to a metallic taste in the mouth.
Low Copper Content Alloys has… Resistance To….
While High Copper Alloy…. Resistance To…..
Low , Corrosion
Higher, Corrosion
Reduction of corrosion is achieved by
a. Low mercury alloy ratio to reduce the reaction products especially γ2 phase
b. High copper amalgam alloys to be free of γ2 phase
c. Finishing and polishing of amalgam
as amalgam is a metallic restoration,
the cavity must be lined by an…….. base to prevent ……
insulating , thermal irritation to the pulp
mixing of two ingredients by a process known as
TRITURATION
Trituration is
the process by which mercury is allowed to react with the alloy powder.
Mechanical trituration is By the use of….
amalgamator or amalgamizer
amalgamator, trituration time varies between….
5-20 seconds
Advantages of mechanical trituration
- A uniform and reproducible mix.
- A shorter trituration time can be used.
- A greater alloy/mercury ratio can be used.
1-Fine cut Produce …
2-Coarse cut Produce …
3-Lathe cut produce ….
4-Spherical particles produce…
1- a smother surface during carving
2- amalgam with inferior properties and rough surface
3- Need high condensation pressure, required more mercury
4-
a) Fast setting.
b) Higher early strength.
c) Superior strength properties.
d) Produce a smoother surface during carving
Delayed Excessive expansion:
Occurs due to…. And later on cause
moisture contamination of Zinc Containing amalgam during Triturationor Condensation , which starts 3-5 days after insertion this will causes :
Postoperative pain
Blistering ,open later forming rough surface
Tarnish and corrosion.
high copper alloy are selected rather low copper conventional alloys in order to have a restoration with …
- No gamma two phase.
- Higher early strength.
- Low creep value.
Galvanism phenomena
When two metallic restoration with different degree of electronegativity are present in the oral cavity with an electrically conducting medium (saliva)
Gallium Alloy Restorative Materials
Mercury-Free Restorative Materials
4 - META
( Methacryloxy Ethyl Trimellitic Anhydride)
Can chemically bond to tooth structure.
Fluoride Releasing Amalgam
fluoride released from amalgams
Amalgam Tattoo
soft tissue discoloration due to amalgam which are most common
pigmentation of oral cavity due to accidental subgingival condensation
of amalgam.
