Operative I: 6.1 Amalgam (Material Lecture)

What are the components of amalgam?

- liquid mercury

- metal alloy (silver, tin, and copper)

What is the purpose of silver (Ag) in amalgam, and what is the percentage?

- increases the strength and expansion

-2/3 of concentration of the alloy

What is the purpose of tin (Sn) in amalgam?

-controls the reaction between silver and mercury as without tin, the reaction would be too fast

- decrease expansion

What is the purpose of copper (Cu) in amalgam?

- helps increase strength

- reduces creep (warping) which reduces marginal deterioration

- reduces tarnish and corrosion

What is creep in amalgam?

warping, deformation of an amalgam under compressive stress

What are the advantages of amalgam?

-easier to place than composite

- similar wear resistance as tooth structure

- strong under compressive forces and biting

- seals its own margins over time

- realatively long service life

- cost effective

- resin-free therefore no risk of resin allergic reaction

- minimal post-op sensitivy since we don't open dentin tubules

How does amalgam seal its own margins over time?

Tin (Sn) leaches out and reacts with oxygen and chlorine to form a precipitate that seals the open margins (process takes 6-12 months)

What are the disadvantages of amalgam?

- needs bulk

- poor aesthetics

- briddle under tensile forces

- subject to corrosion

- does not support weakened tooth structure

- lack of chemical adhesion to tooth structure

What are the indications for amalgam?

-class 1 and II (composite not great in high occlusal stress)

- class V for non-esthetic areas

- As a core build-up material

- restorations that have heavy occlusal contacts

- areas difficult to isolate

What is compressive strength?

The resistance of a material to breaking under compression. In other words, occlusal load or bite

What is critical to the strength of amalgam?

- proper amalgam condensing

What are the types of corrosion present in amalgams?

- galvanic shock

- crevice corrosion

- stress corrosion

What is galvanic shock?

- when 2 dissimilar (amalgam and gold) metals come in contact

- gives a "shock or zing" sensation

- A positive to negative charge is produced, similar to a battery

What is crevice corrosion?

- an electrochemical reaction that occurs when plaque deposits cover the amalgam surface

- the covered area has a lower oxygen and higher hydrogen ion concentration, making it behave anodically and corrode

- A higher hydrogen ion concentration equates to a lower pH environment which gradually leads to tooth decay

What is stress corrosion?

- regions within the dental amalgam that are under stress have a higher probability of corrosion, thus resulting in stress corrosion

- for occlusal dental amalgams greatest combination of stress and corrosion occurs along the margins due to the grain boundaries of the Hg-Sn interface breaking down

What are factors that effect the strength of amalgam?

- condensation (or condensing)

- trituration (mixing)

- temperature

- effect of porosity

- effect of hardening

What has more pressure exerted on the amalgam: large or small condenser?

small

What controls the size of your isthmus in your amalgam preparation?

It cannot be smaller than your smallest condenser

What happens if you only use a large condenser and not the smaller one first?

Using a large condenser at the beginning will create porosity and weaken the amalgam

What does clumpy amalgam indicate?

not mixed long enough

What does matte shiny amalgam indicate?

proper mix time

What does a super shiny amalagm indicate?

overmixed amalgam

How much strength does the amalgam lose when the temperature is elevated from room temperature to mouth temperature?

15%

How much strength does the amalgam lose when the temperature is elevated by hot coffee or soup?

50%

In regard to temperature, what is important to instruct your patients to do?

Instruct the patient to avoid hot foods or liquids for the day. The amalgam is in its critical state of set for the first 8 hours

What are some causes of porosity?

- improper trituration

- particle shape issues (defective or expired amalgam)

- insertion of too large increments into the cavity

- delayed insertion after trituration

- non-plastic mass of amalgam (alloys powders not immersed)

- not enough force in condensing

What is an amalgam tattoo?

- develops when a piece of amalgam, or dispersed amalgam dust, get trapped in the tissue (usually in an open sore, or constant contact of amalgam to the cheek)

- can be blue, grey or dark

- non-toxic, no treatment intervation needed

Why is amalgam bacteriostatic?

- Amalgam is bacteriostatic as mercury and copper contribute greatly to the antimicrobial effectiveness.

- works against S. Mutans and A. viscous (gingivitis)

Who are the high-risk populations?

- children under 6

- women who are pregant or planing to be

- nursing mothers

- people with neurological impariment or kidney dysfunction

- people who are sensitive to mercury, silver, copper, tin, or zinc

If a woman is pregnant, does the FDA recommend removing the amalgam since they are in the high-risk population?

No. Removing intact amalgam fillings results in unnecessary loss of healthy tooth structure and exposes you to a temporary increase in mecurary vapor released during removal

What are the neurological conditions that lead to a patient being high risk for amalgam?

- Multiple Sclerosis

- Parkinson's disease

- Alzheimer's disease

T/F. There is no scientific documentation of adverse local or systemic effects from dental amalgams.

True

T/F. The daily intake of mercury from air, water, and food exceeds that from dental amalgams.

True

If you use amalgam in your practice, what does the EPA require you to do and have?

- An amalgam separator

- Dry amalgam waste, teeth with amalgam, spent amalgam capsules, contact/non-contact amalgam, and vacuum filters must be disposed of and recycled in a properly labeled container

What type of amalgam does our school use?

Spherical amalgam

When having an amagalm restoration, when does the highest mercury exposure occur?

- During filling placement and removal of the amalgam filling