Dental Amalgam

Question 1

What is amalgam?

Answer 1

alloy + mercurary

Question 2

What is dental amalgam?

Answer 2

alloy containing silver, tin and certain elements and mercury

Question 3

What is the reaction of alloy and mercury called?

Answer 3

amalgamation

Question 4

What is the predominant element in alloy?

Answer 4

silver

Question 5

What does silver combine with?

Answer 5

tin, the main reaction

Question 6

Why is mercury added?

Answer 6

increase rate of reaction - pre-amalgamation

Question 7

What does zinc preferentially react with?

Answer 7

oxygen

Question 8

What would you call an alloy with less than 0.01% zinc?

Answer 8

zinc free alloys

Question 9

What percent are zinc containing alloys?

Answer 9

more than or equal to 0.01%

Question 10

When does zinc produce hydrogen gas?

Answer 10

when reacted with water

Question 11

Why is moisture control important (specifically with zinc)?

Answer 11

zinc reacts with water to produce hydrogen gas and excessive delayed expansion

Question 12

Do the majority of alloys have zinc?

Answer 12

no

Question 13

What form of mercury is used and why?

Answer 13

pure form otherwise inferior physical properties result

adversely affect the setting characteristics of the amalgam

Question 14

Is mercury distilled?

Answer 14

yes, 3 times

Question 15

What is the appearance of contaminated mercury?

Answer 15

dull appreance - we know encapsulate

Question 16

What are the 3 phases of amalgamation? (mercury with alloy)

Answer 16

Question 17

What is the unreacted core surrounded by?

Answer 17

amalgam matrix

(gamma 1 silver/mercury and gamma 2 tin/mercury)

Question 18

What depth of the outer layer react with alloy particles?

Answer 18

3-5 um

Question 19

What is gamma 1?

Answer 19

silver

Question 20

What is the gamma 2 phase?

Answer 20

tin-mercury phase

Question 21

What is the most critical phase?

Answer 21

gamma 2 phase

Question 22

What are the features of the gamma 2 phase?

Answer 22

most chemically electrically active component

physical properties inferior to gamma and gamma 1 phases

more prone to corrosion

poor tensile strength

Question 23

What phases are the green, purple and blue in the amalgam?

Answer 23

green = gamma 1 (silver/mercury)
purple = gamma 2 (tin/mercury)
blue = gamma (silver/tin)

Question 24

What is tensile strength?

Answer 24

ability of a material to withstand pulling forces in an axial direction

Question 25

What shape do you test tensile strength on?

Answer 25

cylinder

Question 26

What is creep?

Answer 26

gradual dimensional change under load

Question 27

What phase is more susceptible to creep?

Answer 27

gamma 2

Question 28

What can creep lead to?

Answer 28

ditching

Question 29

What is ditching?

Answer 29

the amalgam has move over time, thinned out at the margin - can chip creates channels called a ditch

Question 30

What is the percent of creep with amalgam?

Answer 30

c6%

Question 31

What does high copper amalgams attempt to eliminate?

Answer 31

gamma 2 phase

Question 32

What percent is high copper amalgams?

Answer 32

above 13% content

Question 33

What is the result of high copper amalgams?

Answer 33

higher mechanical strength properties more rapid set to full strength reduction in creep reduced susceptibility to corrosion

Question 34

What is compressive strength?

Answer 34

ability of a material to withstand axially loaded pushing forces (applied along long axis)

Question 35

What are the setting reactions of high copper dental amalgam?

Answer 35

essentially the same as conventional alloys

Question 36

In high copper amalgam setting reactions, what phase has little to nothing left in the final amalgam?

Answer 36

gamma 2

Question 37

In high copper amalgam, what 2 thing preferentially react?

Answer 37

copper and tin

Question 38

What complex is formed in the high copper amalgam setting reaction?

Answer 38

silver-tin-copper complex little to no gamma 2 left

Question 39

In high copper amalgam, hat surrounds the silver/tin/copper complex?

Answer 39

copper/tin

Question 40

What are the types of high copper amalgam alloy?

Answer 40

dispersed phase ternary alloys

Question 41

Describe the dispersed phase of high copper amalgam alloy?

Answer 41

copper dispersed throughout the alloy alloy particles either contain silver-tin or silver-copper silver content may be kept the same as conventional alloys increased strength

Question 42

Describe ternary alloys (high copper content amalgam alloy)

Answer 42

contain 3 elements usually silver, tin and copper all in one particle compositional

Question 43

What is the effect of eliminating gamma 2 in high copper alloys?

Answer 43

greater microleakage increased postoperative sensitivity increased risk of recurrent caries may be overcome by bonding in situ

Question 44

What is the role of gamma 2 in amalgam?

Answer 44

corrosion product of gamma2 fill the marginal micro gap at cavity interface decrease microleakage

Question 45

What are the 3 types of alloy?

Answer 45

lathe cut spherical admixed

Question 46

What is the lathe cut alloy like?

Answer 46

irregular particles produced - affects reactivity with mercury blend various particle sizes to reduce reactivity

Question 47

What is admixed alloys like?

Answer 47

combination of irregular and spherical particles sometimes called blended