Presented by--

Hemam Shankar Singh

An amalgam is a special type of alloy that contains mercury as one of its constituents.

1. As permanent filling material for

Class I and class II cavities, and

Class V cavities where esthetics is not important

2. In combination with retentive pins to restore a crown

3. For making dies

4. In retrograde root canal fillings

5. As a core material

1. Silver

2. Tin

3. Copper

4. Zinc

5. Platinum

6. Palladium

7. Indium

1. Based on copper content--low copper alloys

-high copper alloys2. Based on zinc content

-zinc containing (more than 0.01% Zn)-zinc free (less than 0.01% Zn)

3. Based on shape of the alloy particle-lathe cut alloys-spherical alloys-spheroidal alloys

4. Based on number of alloyed metals-binary-ternary-quaternary

5. Based on size of alloy -microcut-macrocut

low copper high copper

lathe-cut lathe-cut spherical sphericalor spherical 2/3 1/3

Admixed unicomposition

Silver 63-73% 40-70% 40-65% 40-60%Tin 26-29% 26-30% 0-30% 22-30%Copper 2-5% 2-30% 20-40% 13-30%Zinc 0-2% 0-2% 0 0-40%

Composition

Silver: major element in the reaction

whitens the alloy

Decrease the creep

Increase the strength

Increase the expansion on setting

Increase the tarnish resistance in the resulting amalgam

Tin: Controls the reaction between silver and mercury

Reduces strength and hardness

Reduces the resistance to tarnish and corrosion

Copper: Increases hardness and strength

Increases setting expansion

Zinc: Acts as a scavenger or deoxidizer

It causes delayed expansion

Platinum Hardens the alloy and increases resistance to

corrosion

Palladium: Hardens and whitens the alloy

Indium: When added reduces mercury vapor and improves

wetting

1. Microleakage

Dental amalgam has the ability of self sealing to microleakage

This may be caused by corrosion products that form in the interface between the tooth and the restoration, sealing the interface and thereby preventing microleakage

The space between the alloy and the tooth permits microleakage of electrolyte, and a classic concentration cell (crevice corrosion) process results.

The common corrosion products found with traditional amalgam alloys are oxides and chlorides of tin

2. Dimensional stability• According to ADA Specification No. 1 amalgam can neither

contract nor expand more than 20µm/cm at 37ºC between 5 minutes to 24hrs.

• Severe contraction can lead to microleakage and to secondary caries

• Excessive expansion can produce pressure on the pulp and postoperative sensitivity

Moisture contamination moisture contamination during

manipulation causes delayed expansion due to reaction between water and zinc present in the amalgam alloy

this expansion starts after 3-5 days, reaching values greater than 400µm (4%)

DIM

EN

SIO

NA

L C

HA

NG

E I

N µ

m/

cm

3. Strengthi. Effect of trituration

undertrituration or overtrituration decreases the strength for both low and high copper amalgams as it affects the reaction between the matrix phase and the alloy particles

ii. Effect of mercury contentsufficient Hg should be mixed with the alloy to wet each particle

of the alloy

increase in mercury content above approximately 54-55% markedly reduced the strength

low mercury content may result in a rough, pitted surface that may lead to corrosion

iii. Effect of condensation» lathe-cut alloygreater the condensation pressure, higher the compressive

strength

higher condensation pressure are required to minimized porosity and to express mercury from lathe-cut amalgam

» spherical alloycondensation with light pressure produces adequate

strength

iv. Effect of porosity• Voids and porosity are possible factors influencing the

compressive strength of hardened amalgam

• It is related to number of factors including plasticity of the mix amalgam

• Plasticity decreases over time from the end of trituration

• Undertrituration also decreases plasticity

• Decrease plasticity causes greater porosity resulting in lower strength of the amalgam

TABLE: comparison of compressive strength of low-copper and high-copper amalgams

compressive tensile

strength (Mpa) strength—24hr

Amalgam 1hr 7Day (Mpa)

Low copper 145 343 60

Admixed 137 431 48

Single composition 262 510 64

4. Creep

creep rate has been found to correlate with marginal breakdown

of traditional low-copper amalgams, i.e. higher the creep greater the degree of marginal deterioration

different alloy have different creep value as shown below

TABLE: comparison of creep of low-copper and high-copper amalgams

Amalgam creep (%)

low copper 2.0

admixed 0.4

single composition 0.13

A B

1. Mercury : alloy ratio

2. Trituration

3. Condensation

4. Carving and finishing

Mercury : alloy ratio Up until the early 1960s it was necessary to use an amount of

mercury considerably in excess of that desirable in the final restoration to achieve smooth, plastic amalgam mixes.

because of deleterious effects of an excessive mercury content procedures were employed to reduce the amount of mercury left in the restoration to an acceptable level.

So, in 1959 a new technique was introduced known as minimal mercury technique , or Eames technique in recognition of the dentist who developed the concept.

According to Eames technique mercury should be 50% by weight or in 1:1 ratio.

Figure: Hardening data (BHN= Brinell hardness number) for two alloys (A and B ) mixed at low, medium, and high settings. Broken lines at 1.0 and 4.5 represent working and carving consistency, respectively.

Under triturated mix of amalgam. Such a mix are grainy and has low strength and low resistance to tarnish.

Aims

To adapt it to the cavity wall

Remove excess Hg

Reduce voids

Proper condensation increases the strength and decreases the creep of the amalgam.

Failure to use a matrix can result in a poorly condensed and weak restoration.

Mixed materials is packed in increments.

Condensation is started at the centre, and the condenser point is stepped sequentially towards the cavity walls

Carving and burnishing is done to reproduce the tooth anatomy and to get a smooth surface respectively

Carving should not be started until the amalgam is hard enough to offer resistance to carving instrument

A scrapping or ringing sound should be heard when it is carved

Polishing is also required as it minimizes corrosion and prevents adherence of plaque

Final polishing should be delayed at least 24hrs after condensation

Mercury is absorbed through skin, lungs or GIT, most commonly by lungs i.e. vapor phase

Penetration into the tooth from the restoration

The threshold limit value of mercury in the air is 0.05mg of Hg/m³ of air, this is the vapor level to which the average worker can be safely exposed for 8hrs a day and 5days per week

Increase in exposure causes toxicity which may associate with signs and symptoms

The lowest level of total blood Hg at which the earliest nonspecific symptoms occur is 35ng/mL

Weakness, fatigue, anorexia, weight loss, insomnia, irritability, shyness, dizziness, and tremors in the extremities are the recognizable symptoms of chronic Hg poisoning

Mercury should be kept in an unbreakable container that are tightly sealed

Spills and leak should be cleaned up immediately by approved methods

Water spray and high-volume evacuation should be used when removing an old amalgam restoration or finishing a new one

Glasses and disposable face mask should be worn to reduce hazards associated with flying particles and the inhalation of amalgam dust

Amalgamators that completely enclose the arms and amalgam capsule during trituration should be used

Since mercury vaporizes at room temperature, operatories should be well ventilated to minimize the mercury level in the air

Use of gloves is a must

1. Reasonably easy to insert

2. Not overly technique sensitive

3. Maintains anatomic form well

4. Has adequate resistance to fracture

5. After a period of time prevents marginal leakage

6. Have reasonably long service life

7. Cheaper than other alternative posterior restorative material like cast gold alloys

1. Color does not match tooth structure

2. More brittle and can fracture if incorrectly placed

3. They are subject to corrosion and galvanic shock

4. Show marginal breakdown

5. Do not bond to tooth structure

6. Risk of Hg toxicity