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