Dental amalgams I

Question 1

properties of dental amalgams

Answer 1

shiny
metal
conducts heat

Question 2

types of amalgam

Answer 2

conventional dental amalgams

high copper content alamgams

Question 3

conventional amalgam constituent

Answer 3

silver III (in the gamma phase)
tin
copper 
zinc
mercury

Question 4

gamma phase

Answer 4

alloy of silver III tin
inermetallic alloy
therefore has an inter metallic phase
silver3tin is the solid part

Question 5

shapes of the powder particles

Answer 5

spherical 
lathe cut (corse or fine grain)

Question 6

influence of the shape and size of the powder particles on amalgam

Answer 6

handling (spherical easier to handle)
setting reactions (fine grain set quicker due to SA)
final properties of the restoration

Question 7

setting reaction of amalgam

Answer 7

alloy and mercury = alloy + silber mercury phase + tin mercury phase
gamma + mercury = gamma + gamma 1 (Silver)+ gamma 2

Question 8

micrograph of amalgam

Answer 8

unreacted gamma (left as islands)
surrounded by gamma1/2 crystals)

Question 9

reasons for replacement of amalgam restroatiosn

Answer 9

primary caries
secondary caries
poor margin
restoration failure
tooth fracture

Question 10

tooth fracture causes

Answer 10

weakened tooth structure
undermined enamel
residual caries

Question 11

recurrent caries causes

Answer 11

contamination
poor matrix techniques(either poor contact point or poorly adapted can lead to proximal overhangs)
poor condensation

Question 12

poor condensation

Answer 12

insufficient mixing of the mercury with the amalgam
leads to porosity and excess silver
reduced amalgam strength

Question 13

poor marginal adaptation

Answer 13

marginal leakage
recurrent caries
corrosion

Question 14

gross amalgam fracture casuses

Answer 14

shallow preparations
non retentive proximal boxes
sharp internal angles

Question 15

shallow preparations of amalgam

Answer 15

amalgam is weak
low tensile strength
if placed in thin sections subject to bending forces

Question 16

non retentive proximal boxes

Answer 16

gaps between teeth
reduce risk by cutting rention grooves
amalgam can fall out due to low tensile strength

Question 17

sharp internal angles

Answer 17

stress concentrations

sharp increases risk of fracture of both tooth and restroation

Question 18

marginal breakdown

Answer 18

incorrect cavosurface angles
delayed expansion
overfilling/underfilling/overcarving
creep and corrosion

Question 19

delayed expansion of amalgam

Answer 19

zinc in amalgam can react with water in saliva
form zinc oxide and hydrogen in the amalgam
amalgam expands as bubbles of hydrogen form
leads to pressure on the pulp
restoration can sit proud

Question 20

creep

Answer 20

when metal moves slowly overtime with load

Question 21

corrosion

Answer 21

electrochemical degresation