Amalgam Flashcards
describe the composition, setting reaction and influence of particle shape on traditional amalgam
70% silver
25% tin
3% copper
some zinc and some mercury
how does the behaviour of amalgam compare to composite resins
describe the mechanical properties of amalgam
strength
abrasion resistance
creep
describe the mechanical properties of copper enriched enamel
same as traditional but stronger due to presence of copper
describe the thermal properties of traditional enamel
describe the thermal properties of copper enriched amalgam
what are some factors affecting amalgams clinical performance
what is dental amalgam
an alloy formed from the reaction of liquid mercury and silver, tin, copper and other metal powders
why is particle shape of amalgam important to consider
it affects the handling properties like how easy it is to mix and apply as well as the final properties like its strength in restoration
what is the function of the silver and tin powder in amalgam
an intermetallic compound called Ag3Sn, reacts with mercury liquid to form amalgam in the gamma phase
what is the function of copper in the powder of amalgam
increase the strength and hardness of the material
what is the function of zinc in the powder of the amalgam
scavenger during production, preferentially oxidises and slag formed and removed. some zinc is free
what is the function of mercury powder in the amalgam
can allow it to react faster but only found in some traditional amalgams
what is the function of liquid mercury in amalgam
50% of amalgam by weight, is triple distilled and reacts with the metal powders to form amalgam
what are lathe cut particles
coarse, medium and fine particles formed by filing ingots
what are the spherical particle types
range of sizes and are formed by spraying molten metal into an inert atmosphere
what is the setting reaction of amalgam in simple terms
Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9
which section of the amalgam settings action is the amalgam matrix
Ag2Hg3 + Sn7Hg9
describe the gamma 1 phase
this is A2Hg3 ie silver mercury
describe gamma 2 phase
Sn7Hg9 ie tin mercury
what is the gamma phase
this is silver tin, and is found on both sides of the setting reaction as there are some unreacted particles left over
describe the set structure of amalgam
gamma gives good strength and corrosion resistance
gamma 1 gives good corrosion resistance
gamma 2 gives poor strength and low corrosion resistance
function of the voids in amalgam
decrease strength and increase corrosion
what is gamma in the amalgam structure
unreacted silver tin particles
which amalgam component has the greatest tensile strength
gamma silver tin at 170 MPa
what is the tensile strength of gamma 1
30 MPa
what is the tensile strength of gamma 2
20 MPa
what is the tensile strength of amalgam
60 MPa
what is responsible for initial contraction in setting the dimensional changes for traditional amalgam
a solution of alloy particles in mercury
describe the setting dimensional changes observed in traditional amalgam
solution of alloy particles in the mercury causes initial contraction, and then there is gamma 1 crystallisation to create expansion
describe the setting dimensional changes in modern amalgam
small contraction, with a solid solution of mercury in the gamma
is there any clinical sign of the dimensional changes caused by amalgam setting
no, as the expansion and contraction is less than 0.2% of the initial size
summarise zinc and expansion
this is about the interaction of zinc with saliva and blood, which leads to hydrogen bubbles forming the saliva, building pressure and causing expansion. if there is downward pressure than there is pulpal pain, and if there is upward pressure then the restoration will sit proud of the surface
why is it important to use zinc free materials
when zinc reacts with blood this creates hydrogen bubbles within the amalgam and expansion causing pulpal pain and raised restorations
what is the interaction of zinc with saliva and blood
Zn + H2O -> ZnO + H2
what are the properties of amalgam dependent on
handling factors such as proportioning, titration, condensation, carving and polishing
cavity design
corrosion
some products have variations as well
what are the advantages of spherical particles
less mercury required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve
what are the amalgam properties (long list)
strength
rigidity
abrasion resistance
creep
setting shrinkage
thermal expansion
thermal conductivity
corrosion
bond to tooth, microleakage
handling and viscosity
biocompatibility
aesthetics
radiopaque
anticariogenic
smooth surface
describe the strength of amalgam
compressive strength to withstand biting forces
tensile forces as well for the abrasion resistance
early amalgam has a poor strength but over 24 hours sees an increase in strength
describe the abrasion resistance seen in amalgam
high which is suitable for posterior teeth as teeth slide over one another during mastication
too high resistance for deciduous teeth
what are factors that decrease the strength of amalgam
undermixing
too high mercury content after condensation
too low condensation pressure
slow rates of packing, meaning the increments do not bond
corrosion
what does slow rate of packing mean for amalgam and why is it bad
this means you are not applying enough pressure when placing the material or you are taking too long to build up the material which leads to the increments not bonding properly
describe creep in amalgam
amalgam is viso elastic. creep is when a material experiences low level stress levels ie below the elastic limit stress which are applied repeatedly over a prolonged period of time, resulting in flow and permanent deformation
creep affects the marginal integrity of amalgam, and also depends on cavity design and corrosion
which materials experience creep the most
amalgam
alloys
waxes
plastics
list the stages to amalgam creep
amalgam is fitted into the cavity
low magnitude forces are applied repeatedly through biting
amalgam shape sits proud around the margins
not long after, biting forces will break the edges off created divots around the margin
ultimately leads to micro leakage and potential for secondary caries
how much can amalgam thermally expand
three times of the tooth
describe the thermal conductivity of amalgam
high, may need to use liner or varnish in the deeper cavities
describe the thermal conductivity of amalgam
high, so when a transient thermal stimuli is applied like through drinking tea, the amalgam temperature rises quite fast
describe how amalgam bonds
it does not bond to the tooth and requires mechanical retention.
some suggest using new bonding systems base on 4-meta to get the bond to the tooth but this is not widely accepted
describe corrosion of amalgam
gamma 2 is the most corrosive
the material weakens through corrosion at the margins particularly
how can amalgam corrosion be reduced
copper enrichment
polishing margins
avoiding galvanic cells
how are the amalgam aesthetics
poor
is amalgam cariogenic
no
what is the amalgam surface like
smooth if polished well, can deteriorate over time
what are the two types of copper enriched amalgam
dispersion modified and single composition
describe dispersion modified copper enriched amalgam
originally, silver-copper spheres and conventional lathe cut alloys were used.
originally it was thought that the spherical particles would act as a strengthening agent, but increased copper content gave beneficial modifications to setting reactions
describe the process of the dispersion modified amalgam setting reaction
first, as a conventional material, gamma + Hg -> gamma, gamma1 and gamma2
second stages takes several days and is a reaction of gamma2 with silver copper to form Cu6Sn5 + gamma1
describe the single composition formula of amalgam
powder is silver, tin and copper
12-30% copper
both spherical and lathe cut particles
what is the setting reaction of single composition amalgam
Ag-Sn-Cu powder + Hg -> Ag-Sn-Cu + y1 _ Cu6Sn5
describe what happens when Ag-Cu spheres were added to the normal lathe cut amalgam particles
a halo forms around the AgCu spheres. the halo consisted of Cu6Sn5. this is dispersion modified copper enriched amalgam with the halo acting as a fourth reaction product
what was the first attempt to introduce copper to amalgam
addition of Ag-Cu spheres to lathe cut enamel particles which formed the halo as a fourth reaction product
what was the second attempt to introduce copper to amalgam
have it within the amalgam powder itself, to eliminate the halo. this is the single composition form of copper enriched amalgam, with the setting reaction producing just three reaction products. better properties than the dispersion modified version
what are the benefits of using copper enriched amalgam
higher early strength
less creep
higher corrosion resistance
increased durability of margins
which amalgam has the most creep
traditional amalgam with lathe cut particles
which amalgam has the lowest creep
copper enriched single composition amalgam
what is permite
the amalgam material used in glasgow
non gamma 2 amalgam with lathe cut and spherical particles
what is the compressive strength of permite after 24 hours
goes from 260MPa to 500 MPa
enamel compressive strength
250MPa
dentine compressive strength
280MPa
hybrid composite compressive strength
300 MPa
amalgam compressive strength
500MPa
enamel tensile strength
35
dentine tensile strength
40-260
hybrid composite tensile strength
50
amalgam tensile strength
60
elastic modulus units
GPa
elastic modulus of enamel
50
elastic modulus of dentine
12
elastic modulus of hybrid composite
14
elastic modulus of amalgam
30
hardness of enamel
350
hardness of dentine
60
hardness of hybrid composite
90
hardness of amalgam
100
advantages of amalgam
strong
hard
durable
radiopaque
user friendly
disadvantages of amalgam
corrosion
leakage
does not bond to tooth
poor aesthetics
mercury has a perceived toxicity and environmental impact should also be considered
how is amalgam classified
according to particle shape and size, and traditional vs non gamma 2
