Dental Amalgam

Question 1

Filling materials - name direct and indirect and their processes

Answer 1

Direct (eg, amalgam / gold)
- cavity cut (retentive/undercut - helps retain filling)
- directly placed
- flow then set

Indirect (material goes into tooth solid.. its pre made) Pt 2+ visits
- cavity cut (non-retentive) cannot undercut
- impression taken
- material shaped
- cemented into place - may cause loss of tooth tissue

Question 2

Define ‘Amalgam’

Answer 2

Alloy of mercury (Hg) and other metal

Question 3

Define ‘Mercury’

Answer 3

• Element
• Metal
• Extracted from mineral mercury sulphide
• Liquid at standard temperature and pressure

Question 4

Minimarts convention on mercury 2013

Answer 4

Unite nations convention Jan 2013
- Recognises “that mercury is a chemical of global concern owing to its long-range atmospheric transport, its persistence in the environment once anthropogenically introduced, its ability to bio-accumulate in ecosystems and its significant negative effects on human health and the environment.”

“The objective of this Convention is to protect the human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds.”

Question 5

Mercury is toxic - why is it used in dentistry?

Answer 5

Safe in patients - mercury is stable and locked away in solid form and leaches very little mercury

Question 6

Components of amalgam

Answer 6

Liquid; Mercury (Hg) – Normally very pure, triple distilled!

Powder; Metal alloy

= forms amalgam

Question 7

Gamma is used in dental amalgam - Inter metallic compound

Answer 7

Gamma 1 = Ag2H3 (silver mercury amalgam)
Gamma 2 = Sn7Hg (tin mercury amalgam)

Question 8

Mixing dental amalgam

Answer 8

• By hand - toxic skin contact
• Vigorously mixed using a mortar and pestle
• Amalgamator
• Capsulated

Question 9

High copper amalgams - how are they used in dentistry?

Answer 9

Dispersion hardening

Tin and copper and silver = minimisation of formation of gamma 2

Adds subsequent reaction which removes gamma 2

Gamma 1 produced (stable)

Question 10

Which amalgam is susceptible to corrosion?

Answer 10

Gamma 2 (Sn7Hg) susceptible to corrosion

Break down and will crumble away - may leach mercury

Question 11

Properties of amalgam as a filling

Answer 11

• amalgam does not adhere to tooth tissue
• relies on an undercut - mechanical retention of the filling
• not aesthetically pleasing
• conducts heat - sensitivity so may require liner beneath amalgam
• poor tensile strength
• requires second visit - polishing 24hrs later
• long lasting
• creep - melts filling material causing failure of restoration