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

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

Answer 9

• good corrosion resistance

Question 10

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

Answer 10

• weak and poor corrosion resistance

Question 11

what amalgam phase has the highest tensile strength?

Answer 11

gamma phase

Question 12

what handling factors may affect the properties of amalgam?

Answer 12

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

Question 13

what are the amalgam properties dependant on?

Answer 13

• handling factors
• cavity design
• affected by corrosion

Question 14

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

Answer 14

Cavities in posterior teeth, due to higher abrasion resistance than materials such as composite.

Question 15

what factors may decrease the strength of an amalgam restoration?

Answer 15

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

Question 16

why is creep a problem in amalgam restorations?

Answer 16

affects marginal integrity & can contribute to microleakage

Question 17

what is creep?

Answer 17

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 18

how might ditching occur in amalgam restorations?

Answer 18

• 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 19

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

Answer 19

x3 of tooth

- not ideal & may lead to margin gaps

Question 20

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

Answer 20

High, which is may lead to sensitivy from heat and cold. A lining could be used to help alliviate this.

Question 21

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

Answer 21

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

Question 22

how can corrosion be reduced in amalgam materials?

Answer 22

• enrich with copper
• polish margins
• avoid galvanic cells

Question 23

what is copper enriched amalgam?

Answer 23

amalgam with:

• non gamma 2 phase
• high copper (copper>6%)

Question 24

what does an increased copper content provide amalgam?

Answer 24

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

Question 25

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

Answer 25

Cu single composition

Question 26

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

Answer 26

amalgam

Question 27

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

Answer 27

• lower elastic modulus

- amalgam is less rigid than enamel

Question 28

what are the advances of amalgam as a restorative material?

Answer 28

• strong
• hard
• durable
• radiopaque
• use friendly

Question 29

what are some disadvantages of amalgam as a restorative material?

Answer 29

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

Question 30

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

Answer 30

• 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