Amalgam Flashcards
WHat are the disadvanatges of amalgam?
poor aesthetics
not adhesive
destructive cavity prep
contains mecrury
What is the composition of amalgam allot powder ?
Silver: 65-74% Tin: 25-28 Copper: 0-6 Zinc: 0-3 Mercury: 0-2
How is amalgam used in clinic?
Two part capsule
1 half has mercury
2nd half has the allow powder
What is the purpose of Zn?
Reacts with water forming ZnO which causes delayed expansion of the amalgam
What is the setting reaction for amalgam?
Ag3sn + Hg = Ag3Sn + Ag2Hg3 + Sn7-8Hg
Which is gamma, gamma 1 and gamma 2?
Gamma: Ag3Sn
Gamma 1: Ag2Hg 3
Gamma 2: Sn 7-8 Hg
Upon setting, does the amalgam contract stay the same or explain?
Initially small contraction followed by expansion as gamma 1 forms
Net overall is small contraction
But not an issue since there is no bond between amalgam and tooth
What is the corrosion resistance for gamma, gamma 1 and gamma 2?
All high Except gamma 3
What is the strength for gamma 1, gamma 2 and gamma?
Gamma high
Gamma 1 and 2 low
To improve the quality of amalgam, what has been done?
Copper has been added and this gets rid of the gamma 2
Reduces chance of galvanic corrosion
What are the proportions in gamma 2?
Silver: 60-70 Tin: 18-30 Copper: 12-30 Zinc: 0-3 Mercury : 0-2
How does the setting reaction work with high copper amalgam?
Gamma 2 phase broken down to produce more gamma 1
Sn7-8Hg + AgCu = Ag2 Hg3 + cu6sn5
What are the two types of allow particles in amalgam?
Lathe cut : irregular and cut with a lathe
and spherical : alloy molten and sprayed through fine nozzle and solidifies into spherical droplets
Choice is based on dentist on preference
What is it called when there spherical and lathed cut alloy is together?
Dispersed phase
T/F amalgam is an inter metallic compound?
T
T/F amalgam is highly ductile
F
It is an alloy that has areas of specific stochiometric ratio which do not flow past each other readily
What are the phases of amalgam production?
Trituratiin: mixing that brings the mercury and allow powder together and mixes them allowing them to begin the amalgamation reaction
Proportioning: choose the ratio of allow to mercury
Condensation: compressing the amalgam into the cavity
Carving and polishing
T/F over trituration is better than under?
T
If amalgam is setting too quickly then need to have a LONGER mix time
Which type of shape of allow powder mixes more easily and needs less trituration?
Spherical
In the Proportioning phase, what is the effect of too much apmercury?
This leads to a weak amalgam
In the Proportioning phase, what is the effect of too little apmercury?
This leads to a porous material
T/F during the condensation phase this reduced the amount to voids present?
T
In the condensation process, what is bought to the surface?
Excess mercury
T/F condensation adapts the amalgam to the cavity?
T
Which type of alloy, spherical or lathe flows more readily and what effect does this have on the condensation?
Spherical
Needs smaller loads by largere condensers
T/F closer marginal adaptation can be harder using spherical alloys?
T
What happens in the carving and polishing phase?
Final contouring and excess mercury to is removed
What does excess mercury result in?
Mere gamma 2 thus more unreacted Hg and a softer material
What type of material is amalgam?
Alloy
T/F the coefficient of thermal expansion is higher that that of an enamel?
T
This can lead to stresses developing in tht tooth and cause enamel to fracture
T/F the coefficient of thermal conductivity is higher that that of an enamel?
T this means heat can be transmitted to the pulp and thus need a liner for deep cavities
T/F amalgam is brittle?
T
This means it tends to fracture at the narrows point at the isthmus leading to bulk fracture
T/F
Amalgam corrodes?
T
What is the consequences of amalgam corrosion?
Good and bad
Good: helps with marginal seal
Bad:corrosion products into body, material becomes rough, loss of contiour, loss of material,
How can ditches in amalgam develop?
Pressure leads to creep/ flow or material which then snap off and form a ditch
What percentage of metals are in the final amalgam?
Mercury: 44-48%
Silver 30-35
Tin 9-15
Copper: 0-15
Maybe small amount of zinc
What’s the purpose of mercury in the alloy power?
Aids mixing
What are the advantages if amalgam bonding agents?
- Adhesion to dental tissues
- Imparts greater strength to that tooth and material structure
- More conservative prep
- Reduced microleaage
- reduces need for pins
- seals dentine
What are the disadvantages of amalgam binding agents?
Time consuming
Cosltly
Difficult to obtain uniform layer of adhesive pooling
Less effective condensation
Adhesive sticks to instruments and can become embedded in amalgam which then weakens it
Lack Of data on how effective
Where can galvanic corrosion occur in amalgam?
Within the amalgam betwen different phases
Between other metal or alloy in mouth
Is galvanic corrosion always bad?
No
Products may create a seal around margin especially shortly after placing the amalgam
T/F amalgam conducts more heat than gold?
F
Gold dose
This is because of the intermetallic compound and not a substitional compound
Which systems does mercury cause damage to?
Nervous Cardiovascular Pulmonary GI Renal
Teratogenic
What forms can mercury come in?
Elemental and methyl
Methyl most toxic
Mecury is a liquid or solid at room temp?
Liquid but very volatile
What is the max amount of mercury allowed per week for an average person and pregnant person?
3.3 micrograms per Kg per week
Preg: 1.6
60kg person = 200 micrograms
Preg: 100 micrograms
How much does a one spill capsule contain of mercury?
400mg Hg
What is the dose of mercury to the lungs and GI tract during normal function?
Lungs: 2micrograms Hg per day
GI: less than 1 microgram per day
In ppl with 8 fillings
Wet amalgam release more of less HH than dry amalgam?
Wet releases less than dry
How much did fecal Hg levels remain high after amalgam removal?
For 60 days after and less than 10% absorbed by GI
What should you use when removing amalgam?
Rubber dam
In which people is Mecury released in?
Brixists
Bleacing
Gum chewer
How much does diet contribute to mercury?
Swordfish : 1 mixrogram Hg per g
Tuna: 0.3 micro Hg per g
Water 1 microgram per L
They contain methyl mercury
What is the link between MS and amalgam?
Slight non stat significant increase of MS in amalgam which means could by chance
Where has amalgam been banned?
Sweden
Norway
What are the stages to finishing amalgam,?
Carve the amalgam
Burnish
Polish 24 hours later to provide a scratch free surface
What does burnishing do?
Crested a better marginal adaptation
