L12 Dental Silver Amalgams 2

Question 1

Describe the manipulation of amalgam (characteristics)?

Answer 1

Ease of manipulation

Question 2

What is the marginal adaptation of amalgam like (material characteristics)?

Answer 2

Acceptable marginal adaptation (how well it locks to the surfaces of tooth):
Will shrink slightly (not as much as composite). If shrink exceeds bond strength then you can form gaps causing invasion of bacteria.
Lock and key mechanical retention of cavity, so less conservative

Question 3

Describe the technique sensitivity of amalgam (characteristics)?

Answer 3

Technique insensitivity
Far less technique sensitive than composites

Question 4

Describe the sealing nature of amalgam (characteristics)?

Answer 4

Self-sealing? Textbooks say corrosion products fill gaps at the interface (older amalgams). But obvs don’t want corrosion products in the mouth.

Question 5

Describe the biocompatibility of amalgam (characteristics)?

Answer 5

Not biocompatible - ambiguous. Toxic but if placed correctly there should be no health concerns unless they are allergic.

Question 6

Describe the wear resistance of amalgam (characteristics)?

Answer 6

Good fracture toughness and is wear resistant
Metallic, so strong

Question 7

Describe the cost of amalgam (characteristics)?

Answer 7

Cheaper to place. Not the cost of materials, the time to place - might take 4x longer to place a resin composite.

Question 8

Describe the caries risk with amalgams (characteristics)

Answer 8

Silver amalgams are cariostatic. Bacteria don’t like the amalgam surface unlike in resin composite.

Question 9

Ideal range of mercury content by weight

Answer 9

44-48%

Question 10

What happens if >55% weight of mercury?

Answer 10

Decreased strength, increased corrosion, increased creep, therefore:
Poor condensation techniques and delay between trituration and condensation

Question 11

Is it elemental or residual Hg in mercury?

Answer 11

Residual, NOT free elemental Hg so will not be released to cause negative effect.

Question 12

Where is the highest residual Hg and why?

Answer 12

Highest residual Hg at surface and margins due to the process of condensation
Condensation squashes the particles together to squeeze and make it a smaller volume. Should never have excess that rises to the top.

Question 13

What are the particle types of amalgam?

Answer 13

Spherical, lathe, or admix

Question 14

What does surface area of particles affect?

Answer 14

Surface area affects wettability. Spherical only - don’t need as much mercury

Question 15

Are amalgams fast setting materials?

Answer 15

No, takes more than 24hrs to reach 100% of mechanical properties, due to the precipitation of the different phases it takes a while.

Question 16

Do spherical or lathe cut amalgams set faster?

Answer 16

Spherical alloys set faster since require less Hg

Question 17

Is set amalgam brittle?

Answer 17

Set amalgam exhibits brittle failure:
- intermetallic alloy
- can snap if in thin section, especially without support
- tensile strength less than compressive strength
- weak in think sections
- unsupported edges fracture easily

Question 18

What is creep?

Answer 18

Time dependent response of a solid to stress

Question 19

How does creep change with melting point in amalgam?

Answer 19

Creep increases as melting point is reached

Question 20

Which phases result in creep?

Answer 20

Phases containing Hg in rich concentrations result in creep

Question 21

What is the consequence of creep in amalgam?

Answer 21

Amalgam flows over marginal ridge and thins
Thin sections fracture easily
Marginal deterioration = ‘ditching’

Question 22

Which phase decreases corrosion resistance?

Answer 22

y2 phase decreases corrosion resistance

Question 23

which phase is the most electronegative and what does this mean?

Answer 23

y2 phase is more electronegative than y and y1
It acts as an anode in solution and slowly dissolves

Question 24

In what way is the corrosion reaction insidious?

Answer 24

Aggressive unstopping reaction
Free Hg allows further reaction with y to produce more y1 and y2

Question 25

What is the corrosion reaction?

Answer 25

Sn7Hg (y2) + oral fluids —> tin salts + free Hg

Question 26

What is the dimensional change of amalgams?

Answer 26

Small contraction in the first 30mins as mercury diffuses into alloy particles
Expansion as crystallisation starts

Question 27

What is net contraction in modern amalgams?

Answer 27

Slight contraction, might be enough to form gaps

Question 28

How are gaps in amalgam usually formed?

Answer 28

Gaps are mainly formed due to placement processing and condensation pressure

Question 29

What factors affect micro leakage?

Answer 29

2-20micrometre gap
Affected by poor condensation technique
Corrosion by-products - mercury will be at the sealing edge
Differences in TEC - amalgam is more similar to teeth than resin composites
Type of particle

Question 30

How does type of particle affect micro leakage?

Answer 30

Spherical exhibit increases in micro leakage - more technique sensitive and harder to condense?
Lathe cut exhibit better marginal adaptation

Question 31

What are operator variable?

Answer 31

Trituration
Condensing
Carving/polishing

Question 32

What is trituration?

Answer 32

To coat each particle with Hg. Thorough amalgamation ensured. Use recommended times.

Question 33

How does condensation affect amalgams?

Answer 33

Better condensation achieves better marginal adaptation. Eliminates voids. Removes excess Hg. Spherical alloys more difficult to condense.

Question 34

What does carving/polishing do?

Answer 34

A function of particle morphology
Polishing increases hardness and decreases porosity (might form airborne particles)

Question 35

What are the problems with amalgam?

Answer 35

Lack of aesthetics
Non-adhesive - so less conservative
Lack of strength and toughness (last long in mouth)
Susceptible to corrosion
Lack of biocompatibility (most risk during placement or removal)

Question 36

What are the environmental hazards with amalgam?

Answer 36

Natural emission
Human activity - methyl Hg accumulation in food chain, chlor-alkali production

Question 37

How much amalgam is used in dent?

Answer 37

0.05-0.27%

Question 38

How do we minimise/eliminate environmental Hg release?

Answer 38

Excess amalgam must be stored appropriately
Units with filters and/or separators

Question 39

Environmental concerns around the disposal of amalgam. Where is excess amalgam found?

Answer 39

Major amalgam particles - surplus in trituration capsules and carved surplus
Minor amalgam particles - produced during carving, polishing (sucked up and transported via vacuum)
Lost or extracted teeth (solid waste)