Amalgam

Question 1

name the classifications of amalgam

Answer 1

composition - traditional, copper enriched

particle type - lathe cute, spherical

Question 2

what is the composition of powder in traditional amalgam

Answer 2

silver tin, copper, zinc - 50% powder

Question 3

what is the powder mixed with

Answer 3

mercury liquid

Question 4

what is the setting reaction in traditional amalgam

Answer 4

AgSn + Hg - gamma, gamma 1, gamma 2

Question 5

what makes up gamma and what is its properties

Answer 5

AgSn - in product, it is the unreacted particles, this improves the mechanical properties and is corrosion resistant

Question 6

what makes up gamma 1 and what is its properties

Answer 6

AgHg - corrosion resistant

Question 7

what makes up gamma 2 and what is its properties

Answer 7

SnHg - weak and corrosive

Question 8

what reduces the mechanical properties

Answer 8

gamma 2 and the fact it takes a while to set, not good early strength with traditional amalgam
insufficient mixing and condensing

Question 9

what is creep

Answer 9

when low level stresses cause a change over time, can result in amalgam protruding above cavity, these are then vulnerable to fracture and can result in microleakage

Question 10

what are the thermal properties of amalgam

Answer 10

high thermal conductivity - deep cavities require a liner

thermal expansion is greater than that of the tooth but not as bad as composite

Question 11

what is corrosion

Answer 11

when the material disperses and breaks down, reduces marginal integrity

Question 12

what is the advantage of using spherical particles over lathe cut

Answer 12

easier to condense and pack into cavity, improves tensile strength and early compressive strength

Question 13

what are copper enriched amalgams

Answer 13

improving the traditional amalgam by introducing copper to reduce the gamma 2, forms Ag-Sn-Cu which is stronger and corrosion resistant compared to HgSn

Question 14

how can copper enriched amalgams be made

Answer 14

either dispersed or single composition formulas

Question 15

what is dispersion modified copper enriched amalgam

Answer 15

when the traditional amalgam is produced, however, gamma 2 is then mixed with silver copper. copper binds to the Hg, removing the SnHg, gamma 2

Question 16

what is single composition amalgam

Answer 16

when copper is added initially and no gamma 2 is produced

Question 17

what is the advantages of copper enriched amalgam

Answer 17

greater earlier tensile strength, less creep, better corrosion resistant, better marginal integrity

Question 18

what are the indications for amalgam

Answer 18

large posterior restoration required

Question 19

when would amalgam not be used

Answer 19

small occlusal cavities or where aesthetics are important

Question 20

what are some advantages of using amalgam over composite

Answer 20

good mechanical properties, cheaper (mostly as can be placed quicker so less operator time), durable

Question 21

what are some disadvantages of amalgam

Answer 21

high thermal conductivity, requires a liner placed, poor aesthetics, may cause toxicity, corrosion, does not bond to tooth (marginal integrity), creep is an issue

Question 22

name the two factors to consider when designing a cavity for amalgam

Answer 22

retention and resistance

Question 23

what is retention is cavity design

Answer 23

as amalgam does not bond to tooth surface, it must be mechanically held in place. create undercuts - larger at the bottom than it is at the top. normally done when removing caries as the disease spreads further in dentine than it does in enamel

Question 24

what is resistance in cavity design

Answer 24

preventing deformation of the material due to masticatory forces. cavity floor should be parallel to occlusal surface and the axial walls should be perpendicular to cavity floor. this reduces the chances of amalgam moving over time and ensures it is packed down to the gingival floor

Question 25

what are the two cavity designs for inter-proximal caries and what one is better for amalgam

Answer 25

self-retentive box and proximo-occlusal preparation, the latter is preferable for amalgam due to the increased retention

Question 26

what affect does moisture contamination have on amalgam

Answer 26

increases corrosion and porosity so reduces mechanical strength and increases creep, important but not as crucial as in composite

Question 27

what affect does condensing have on amalgam

Answer 27

amalgam must be pressed well into cavity using a pluger. in doing so, expels any unmixed mercury to the top of the filling. also ensures that the amalgam is fitted well against the matrix band and to the axial walls as well as other layers

Question 28

why is it important to over fill amalgam

Answer 28

allows operator to carve the amalgam to gain occlusal anatomy, as well as removing any unmixed mercury at the top of the filling

Question 29

what is the affect of inadequate condensing of amalgam

Answer 29

lack of expulsion of mercury, lack of adaptation to tooth tissue, other layers and matrix band. results in reduced mechanical properties

Question 30

how can mercury be absorbed

Answer 30

inhaled via lungs, absorbed in skin, through GI tract, through gingiva and mucosa

Question 31

what are the detrimental affects of mercury toxicity

Answer 31

congenital birth defects, neurological, affects kidneys, immunosuppression

Question 32

what is the future of amalgam

Answer 32

by 2032 - no mining for new mercury, therefore need to work with prevention to reduce need for large posterior cavities. in mean time, amalgam must be separated from water, must be encapsulated and must be collected from waste management establishment