Amalgam

Question 1

what type of material is amalgam?

Answer 1

an alloy

Question 2

how can amalgam be classified?

Answer 2

by its:

• composition
• particle shape & size

Question 3

what are the different compositions of amalgam?

Answer 3

• traditional

- copper enriched

Question 4

what materials is amalgam composed of?

Answer 4

• Ag (silver)
• Sn (tin)
• Cu (copper)
• Zn (zinc)
• Hg (mercury)

Question 5

what makes up the powder aspect of amalgam?

Answer 5

• silver-tin (Ag3Sn)
• copper
• zinc
• mercury in powder

Question 6

what is the liquid aspect of amalgam composed of?

Answer 6

Hg (mercury)

Question 7

what is the function of the silver-tin compound found in amalgam?

Answer 7

it reacts with the Hg liquid to form amalgam

Question 8

what is the function of copper in the makeup of amalgam?

Answer 8

increases strength and hardness of material

Question 9

how can the mercury found in amalgam be described?

Answer 9

very pure (triple distilled)

Question 10

what are the different particle types that amalgam can be composed of?

Answer 10

• Iathe cut

- Spherical, spheroidal

Question 11

what is the setting reaction of amalgam?

Answer 11

Ag3Sn + Hg —> Ag3Sn + Ag2Hg3 + Sn7Hg9

Question 12

what is the gamma phase of the amalgam setting reaction?

Answer 12

Ag3Sn

Question 13

what is the gamma 2 phase of the amalgam setting reaction?

Answer 13

Ag2Hg3

Question 14

what is the gamma-2 phase of the amalgam setting reaction?

Answer 14

Sn7Hg9 (tin-mercury)

Question 15

what are the characteristics of the gamma phase of the amalgam setting reaction?

Answer 15

• good strength

- good corrosion resistance

Question 16

what are the characteristics of the gamma-1 phase of the amalgam setting reaction?

Answer 16

• good corrosion resistance

Question 17

what are the characteristics of the gamma-2 phase of amalgam?

Answer 17

• weak and poor corrosion resistance

Question 18

what is the average tensile strength of amalgam?

Answer 18

60MPa

Question 19

what amalgam phase has the highest tensile strength?

Answer 19

gamma phase

Question 20

what amalgam phase has the lowest tensile strength?

Answer 20

gamma-2 phase

Question 21

why is zinc not commonly used in amalgams anymore?

Answer 21

• zinc can interact with saliva/blood
• bubbles of H2 formed within amalgam
• pressure buildup causes expansion
  (downward pressure causes pulpal pain, upwards pressure causes restoration to sit proud of surface)

Question 22

what handling factors may affect the properties of amalgam?

Answer 22

• proportioning and titration
• condensation/how well it is packed into cavity
• carving and polishing

Question 23

what are the amalgam properties dependant on?

Answer 23

• handling factors
• cavity design
• affected by corrosion

Question 24

what type of amalgam particles are better? why is this?

Answer 24

spherical particles

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

Question 25

what type of cavities are amalgam restorations particularly suited to? why is this?

Answer 25

- cavities in posterior teeth | - high abrasion resistance

Question 26

what factors may decrease the strength of an amalgam restoration?

Answer 26

- undermining - low condensation pressure (when packing into cavity) - slow rate of packing - corrosion

Question 27

why is creep a problem in amalgam restorations?

Answer 27

affects marginal integrity & can contribute to microleakage

Question 28

what is creep?

Answer 28

when a material experiences: - low level stress levels (below elastic limit stress) which are applied repeatedly over a prolonged time period - causes material to flow resulting in permanent deformation

Question 29

how might ditching occur in amalgam restorations?

Answer 29

- low magnitude forces are applied to amalgam repeatedly - amalgam flows and changes shape - amalgam sitting proud of tooth surface - prone to fracture, resulting in ditched margins

Question 30

what is the thermal expansion of amalgam? is this good or bad?

Answer 30

x3 of tooth | - not ideal & may lead to margin gaps

Question 31

what is the thermal conductivity of amalgam? is this good or bad?

Answer 31

- high which is bad | - may need to use a liner in deep cavities

Question 32

what is the thermal diffusivity of amalgam? what does this mean for the material?

Answer 32

- high - when a transient thermal stimuli is applied amalgams temperature rises quickly - can damage the pulp

Question 33

what are the bonding properties of amalgam?

Answer 33

- does not bond to tooth | - needs mechanical retention from undercuts

Question 34

what type of cavity prep requires removal of MORE tooth surface, composite or amalgam?

Answer 34

amalgam!

Question 35

what type of amalgam particles require less force when packing into the cavity?

Answer 35

spherical particles

Question 36

what amalgam phase is most likely to experience corrosion?

Answer 36

gamma-2 phase

Question 37

how can corrosion be reduced in amalgam materials?

Answer 37

- enrich with copper - polish margins - avoid galvanic cells

Question 38

what is copper enriched amalgam?

Answer 38

amalgam with: - non gamma 2 phase - high copper (copper>6%)

Question 39

what are the two types of copper enriched amalgam materials?

Answer 39

- dispersion modified (original) | - single composition types

Question 40

what does an increased copper content provide amalgam?

Answer 40

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

Question 41

what is the setting reaction of single composition copper enriched amalgam?

Answer 41

AgSnCu + Hg —> AgSnCu + Ag2Hg3 + Cu6Sn5

Question 42

what type of amalgam (both original and copper enriched) has the highest compressive strength?

Answer 42

Cu single composition

Question 43

what material has a higher compressive strength, amalgam or composite?

Answer 43

amalgam

Question 44

how does the elastic modulus of amalgam compare to that of enamel?

Answer 44

- lower elastic modulus | - amalgam is less rigid than enamel

Question 45

what are the advances of amalgam as a restorative material?

Answer 45

- strong - hard - durable - radiopaque - use friendly

Question 46

what are some disadvantages of amalgam as a restorative material?

Answer 46

- corrosion - leakage (does not bond) - poor aesthetics - mercury (perceived toxicity, environmental)

Question 47

what can be done to an amalgam cavity prep to avoid ditching?

Answer 47

- ensure the CSMA is between 90-120 degrees - if the CSMA is less than this then there is an insufficient bulk of amalgam which would make it more susceptible to fracture - if it is more there are undermined enamel margins also making it more susceptible to fracture