amalgam

Question 1

what is dental amalgam?

Answer 1

an alloy formed by the reaction of mercury(l) and silver/tin/copper/other metal powder

Question 2

what are the 2 classifications of amalgam?

Answer 2

traditional

copper enriched

Question 3

what are the functions of silver/tin

Answer 3

gamma phase

reacts with Hg liquid to form amalgam

Question 4

what is the function of copper?

Answer 4

increases strength and hardness

Question 5

what is the function of zinc

Answer 5

scavenger during production
preferentially oxidises and slag formed/removed
-some zinc free

Question 6

what is the function of Hg in powder?

Answer 6

pre-amalgamated alloys react faster

Question 7

describe lathe cut particles

Answer 7

coarse, medium, fine

formed by filing ingots

Question 8

describe spherical particles?

Answer 8

range of particle sizes

formed by spraying molten metal into inert atmosphere

Question 9

what is the simplified setting reaction?

Answer 9

powder + liquid -> unreacted particles + amalgam matrix

Question 10

describe gamma particles

Answer 10

good strength & corrosion resistance

Question 11

describe gamma 1

Answer 11

good corrosion resistance

Question 12

describe gamma 2

Answer 12

weak poor corrosion resistance

Question 13

which gamma has the highest tensile strength?

Answer 13

gamma

Question 14

what are the setting dimensional changes in traditional amalgam?

Answer 14

initial contraction -solution of alloy particles in Hg

expansion - gamma 1 crystalisation

Question 15

what are the setting dimensional changes in modern amalgam?

Answer 15

small contraction

solid solution of Hg in Ag3Sn

Question 16

why does zinc cause expansion?

Answer 16

bubbles of H2 formed within amalgam
pressure build up causes expansion
downward pressure can cause pulpal pain
upward- rest sits proud

Question 17

what affects amalgam properties?

Answer 17

handling factors
-proportioning & trituration
-condensation
-carving & polishing
dependent on cavity design
affected by corrosion

Question 18

what are the advantages of spherical particles?

Answer 18

less Hg required
higher tensile strength
higher early compressive strength
less sensitive to condensation
easier to carve

Question 19

describe the strength of amalgam

Answer 19

early poor

late (>24hrs) ok

Question 20

what factors decrease strength?

Answer 20

undermixing
too high Hg content after condensation
too low condensation pressure
slow rate of packing
-increments dont bond
corrosion

Question 21

describe creep in amalgam

Answer 21

visco-elastic
-results in deformation
high in traditional
affects marginal integrity

Question 22

what is creep?

Answer 22

when a material experiences low-level stress levels which are applied repeatedly
over prolonged time it may flow-permanent deformation

Question 23

what materials does creep affect?

Answer 23

amalgam
alloys
waxes
plastics

Question 24

what happens when amalgam experiences creep?

Answer 24

sits proud of tooth
causes ditched margins
vulnerable to fracture at margins
causes microleakage
leads to secondary caries

Question 25

what is the biocompatibility concern in amalgam?

Answer 25

mercury toxicity

Question 26

what is the thermal expansion?

Answer 26

x3 of tooth

Question 27

what is the thermal conductivity?

Answer 27

high | may need to use liner/varnish in deep cavities

Question 28

what is the thermal diffusivity?

Answer 28

high | when transient thermal stimuli applied amalgams temp rises quickly

Question 29

describe amalgam bonding

Answer 29

doesnt bond to tooth | needs mechanical retention

Question 30

describe the handling/viscosity

Answer 30

mixing, working, setting times ok viscosity -packing into cavity= user friendly

Question 31

describe corrosion

Answer 31

``` gamma 2 most electronegative weakens material at margins may contribute to sealing margins reduced by: -copper enriched -polishing margins -avoiding galvanic cells ```

Question 32

aesthetics?

Answer 32

poor

Question 33

radiopaque?

Answer 33

yes

Question 34

anticariogenic?

Answer 34

no

Question 35

smooth surface?

Answer 35

yes, if well polished, may deteriorate

Question 36

setting shrinkage?

Answer 36

net overall shrinkage

Question 37

what are the 2 types of copper enriched amalgam?

Answer 37

dispersion modified single composition types -introduced to increase uptake by profession -more common

Question 38

what is dispersion modified amalgam?

Answer 38

Ag-Cu spheres + conventional lathe cut alloy

Question 39

what is the benefit of copper?

Answer 39

modification to setting reaction

Question 40

what are the benefits of copper enriched?

Answer 40

higher early strength less creep higher corrosion resistance increased durability of margins

Question 41

what is the thermal expansion rate the same as?

Answer 41

enamel and dentine

Question 42

what is the failure rate lower than?

Answer 42

all composites

Question 43

what are the advantages of amalgam?

Answer 43

``` strong hard durable radiopaque user friendly ```

Question 44

what are the disadvantages of amalgam?

Answer 44

``` corrosion leakage poor aesthetics mercury -perceived toxicity -environmental impact ```

Question 45

which type of amalgam has the least microleakage?

Answer 45

permite