amalgam

Question 1

what is amalgam

Answer 1

an alloy formed by the reaction of mercury (liquid) and a powder consisting of metals (commonly silver tin and copper)

Question 2

function of silver and tin in amalgam (gamma phase)

Answer 2

reacts with mercury in liquid to form amalgam

Question 3

function of copper in amalgams

Answer 3

increases strength and hardness

Question 4

zinc and amalgams

Answer 4

not contained in modern amalgams
interactions between zinc and water from blood or saliva could cause hydrogen bubbles to form in amalgam that would cause expansion
this could add downward pressure and therefore pain or push upwards and make the restoration proud

Question 5

why might mercury be added to the powder component of amalgam as well as the liquid

Answer 5

to accelerate the setting time

Question 6

how are lathe cut particles of amalgam achieved

Answer 6

by filing solid ingots (blocks) of amalgam

particles vary in size and are irregular in shape

Question 7

how are spherical amalgam particles achieved

Answer 7

by spraying molten amalgam in an inert atmosphere

particles vary in size but are spherical in shape

Question 8

gamma phase

Answer 8

tin and silver powder
good strength and corrosion resistance
present on both sides of equation
powder of tin and silver on left and also unreacted powder left over on right

Question 9

gamma 1 phase

Answer 9

silver and mercury
holds gamma and gamma 2 phase together by wrapping around them
good corrosion resistance

Question 10

gamma 2 phase

Answer 10

tin and mercury

weakest phase - low strength and lacks corrosion resistance

Question 11

what phase contributes most to amalgams strength

Answer 11

gamma phase

Question 12

what are the advantages of using spherical particles

Answer 12

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

Question 13

amalgam condensation

Answer 13

compacting/compressing each increment into the cavity

Question 14

name 3 factors that decrease amalgam strength

Answer 14

undermixing
too little condensation pressure
slow rate of packing
corrosion (over time)

Question 15

discuss amalgams thermal properties

Answer 15

amalgam has a high conductivity and diffusivity which isnt good
it also has a thermal expansion co efficient which is much greater than that of a tooth
for this reason deep cavities may need a lining to protect the pulp

Question 16

how much copper must be in amalgams for them to be classed as cooper enriched

Answer 16

6%

Question 17

what are copper enriched amalgams also referred to as

Answer 17

non gamma 2 phase amalgams

Question 18

what are the two types of copper enriched amalgams

Answer 18

dispersion modified
single composition
(setting reactions are different)

Question 19

what is the powder compromised of in single composition copper enriched amalgams

Answer 19

copper tin and silver

Question 20

describe the setting reaction of single composition copper enriched amalgams

Answer 20

powder (Sn, Ag, Cu) and liquid (mercury) to powder (Sn, Ag, Cu) and gamma 1 ( Ag, Hg) and CuSn
gamma 1 phase holds the other two components together

Question 21

how does the dispersion modified copper enriched amalgam setting reaction differ from that of traditional amalgams

Answer 21

the inital step is the same - production of gamma, gamma 1 and gamma 2 phases
after several days however the gamma 2 phase interacts with AgCu to form gamma 1 phase and CuSn

Question 22

benefits of cu enriched amalgams compared to conventional

Answer 22

greater strength
less creep
higher corrosion resistance
increased durability of margins

Question 23

amalgam tattoo

Answer 23

traumatic implantation of amalgam into soft tissues leaving behind a grey discolouration

Question 24

why is amalgam still used

Answer 24

long lasting and good long term performance
durable
radiopaque
cheap (time = money, quick to place)

Question 25

what are 3 disadvantages to amalgam

Answer 25

poor aesthetics
poor thermal qualities
may require extra destruction of sound tooth to create a retentive cavity
possibility of mercury toxicity

Question 26

lichenoid lesions

Answer 26

whiteish markings on ssoft tissues (resembles lichen planus)
possible cause = hypersensitivity to amalgam

Question 27

galvanic response

Answer 27

‘battery effect’

electric current between 2 disimilar metals. e.g amalgam and gold

Question 28

retention form

Answer 28

features of a cavity that prevent loss of restoration in any direction

Question 29

resistance form

Answer 29

features of a cavity that prevent the loss of material due to distortion or fracture by masticatory forces

Question 30

what are the 2 options when preparing an inter proximal cavity for an amalgam restoration

Answer 30

self retentive box - undercut areas along axial walls

proximo occlusal - take out fissures as well as proximal caries to achieve retention

Question 31

why does dentine need to be sealed with a lining etc before amalgam is placed

Answer 31

due to amalgams ability to transfer heat readily

Question 32

trituration

Answer 32

mixing to form amalgam

Question 33

minimata convention

Answer 33

global treaty to protect human health and environment from the adverse effects of mercury