Dental Amalgam Question And Answers

Dental Amalgam

Question 1. Classify tooth-filling materials. Describe the composition and role of each ingredient of silver amalgam alloy.  
Answer:

Restorative materials: A restorative material is a material that substitutes the missing tooth structure and restores the form and function of the tooth.

Classification of Tooth Filling Materials/Tooth Restorative Materials

1. According to the Nature of Materials:

• Metallic: Dental amalgam, direct filing gold, miracle mix, casting gold, and base metal alloys.
• Non-metallic: Dental cement, composites, and ceramics.

Read And Learn More: Dental Materials Question And Answers

2. According to Life Span:

• Permanent restorative materials: Dental amalgam, direct filing gold, miracle mix, casting gold and base metal alloys, composites, ceramics, and modified glass ionomer cement.
• Semipermanent/intermediate: Life span is weeks to months. Modified zinc oxide eugenol cement, zinc phosphate cement, and zinc polycarboxylate cement.
• Temporary: Life span is days to weeks. Acrylic resins, zinc oxide eugenol cement.

3. According to Placement:

• Anterior restorations: Glass ionomer cement, silicate cement, composites, and ceramics.
• Posterior restorations: Dental amalgam, posterior composites, metal-modified glass ionomer cement, base metal alloys, and metal—ceramics.

Types Of Dental Amalgam

4. According to the Technique:

• Direct restorations: Dental cement, dental amalgam, direct filing gold, composites.
• Indirect restorations: Ceramics, casting gold, and base metal alloys.

5. According to Hardening:

• Acid-base reactions: Dental cement except for resin cement.
• Polymerization: Composites, resin cement, compomers.
• Solidification: Casting gold and base metal alloys, and ceramics.

Composition of Silver Amalgam Alloy:

Role of Each Ingredient of Silver Amalgam Alloy Silver

Silver:

• A major element in the reaction
• Whitens the alloys
• Decreases the creep
• Increases the strength
• Increases the expansion of the setting
• Increases the tarnish resistance

Tin:

• Tin controls the reaction between silver and mercury
• Reduces the strength and hardness
• Reduces the resistance to tarnish and corrosion.

Copper:

• Increases the hardness and strength.
• Increases the setting expansion.

Zinc:

• Zinc acts as “a scavenger or “deoxidizer” during manufacture thus preventing the oxidation of important elements like silver, tin, or copper.
• Zinc causes “delayed expansion” if the amalgam mix is contaminated with moisture during manipulation.

Mercury: Mercury reacts with other metals to form a plastic mass which is conveniently packed into a prepared cavity.

Platinum: Hardens the alloy and increases resistance to corrosion.

Palladium: Hardens and whitens the alloy.

Indium: Indium when added to mercury reduces mercury vapor and improves wetting. It increases the field strength and reduces creep.

Types Of Dental Amalgam

Question 2. Write a short note to get the maximum strength of
the amalgam.
Answer:

The strength of an amalgam is extremely important since the restoration has to withstand the considerable load generated during mastication.

• Insufficient strength leads to the marginal breakdown of restoration or even gross fracture.
• Amalgam has good compressive strength but cannot withstand high tensile or bending stresses. Therefore, the cavity design should be such that the restoration will receive compressive forces and minimize tension or shear force.

Factors Affecting the Strength:

Effect of rate of hardening:  Amalgams do not gain strength as rapidly as might be desired. After 20 minutes, compressive strength may be only 6% of the 1-week strength. ISO specifications stipulate a minimum of 100 MPa at 1 hour and 350 MPa after 24 hours. Since the initial strength of amalgam is low, patients should be cautioned not to bite too hard for at least 8 hours after placement, the time at which at least 70% of its strength is gained.

The 1-hour compressive strength of high-copper single-composition amalgams is exceptionally high (262 MPa), so the chances of accidental fracture is less. Even after 6 months, some amalgams may still be increasing in strength, suggesting that the reactions between the matrix phases and the alloy particles may continue indefinitely.

Effect of trituration: The effect of trituration depends on the type of amalgam alloy, trituration time, and speed of the amalgamator. Both under- and trituration decrease strength in conventional as well as high-copper amalgams. Greater trituration energy leads to improved strength patterns.

Effect of mercury content: Sufficient mercury should be mixed with the alloy to wet each particle of the alloy. Excess mercury in the mix can produce a marked reduction in strength because of the higher γ2 content which is the weakest phase.

Effect of condensation:  Higher condensation pressure results in higher compressive strength (only for lathe-cut alloys). A good condensation technique will minimize porosity and remove excess mercury from lathe-cut amalgams. However, spherical amalgams condensed with lighter pressures produce adequate strength.

Effect of porosity:  Voids and porosities present in hardened amalgam are weak areas in restoration and cause a reduction in strength.

Effect of cavity design: The cavity should be designed to reduce tensile stresses. Amalgam has strength in bulk, therefore, the cavity should have adequate depth and width.

Effect of particle size: The smaller is the diameter of the original particle, the greater is the strength. Effect of temperature: Amalgam loses 15% of its strength when the temperature is elevated from room temperature to mouth temperature and loses 50% of strength when the temperature is elevated to 60°C.

Question 3. Write a short note on delayed expansion.
Or
Write a brief on delayed expansion.
Or
Write a short note on delayed expansion in silver amalgam.
Or
Answer briefly on the delayed expansion of silver alloy.
Answer:

Delayed expansion is observed in the case of zinc-containing low-copper or high-copper amalgam.

• If a zinc-containing low-copper or high-copper amalgam is contaminated by moisture during trituration or condensation a large expansion can take place. It usually starts after 3–5 days and may continue for months, reaching values greater than
• 400 mm (4%) this is known as delayed expansion or secondary expansion.

H₂O + Zn → ZnO + H₂ (gas)

• This hydrogen gas does not combine with the amalgam but collects within the restoration creating extreme internal pressure and expansion of the mass.
• This causes protrusion of the restoration out of the cavity, increased creep, increased microleakage, pitted surfaces and corrosion. Dental pain, recurrence of caries, and fracture of the restoration are also seen.

Types Of Dental Amalgam

Complications of Delayed Expansion:

• It leads to protrusion of the entire restoration out of the cavity.
• It increases the microleakage space around the restoration.
• It leads to the perforation in the restoration.
• It causes increased flow and creep
• It causes pain due to the pressure exerted by the expanding amalgam.

Question 4. Write a short note on high-copper amalgam.
Or
Write a short note on the high-copper alloy.
Or
Write a short note on high-copper amalgam alloy.
Or
Describe briefly the high-copper silver amalgam.
Or
For setting reaction of high-copper amalgam
Or
Classify dental amalgams and describe high-copper amalgams.
Answer:

High-copper alloys contain more than 6% copper. They are preferred because of their improved mechanical properties, resistance to corrosion, and better marginal integrity because the weakest γ₂ phase is eliminated in high-copper amalgam.

Types of  High-copper amalgam.

1. Admixed alloy powder:
2. Single composition alloy powder.

1. Admixed Alloy Powder:

• They are made by mixing one part silver-copper eutectic alloy (high-copper spherical particles) with two parts silver tin alloy (low-copper lathe-cut particles).
• Amalgam made from admixed powder is stronger than amalgam made from lathe-cut low-copper powder, because of the silver-copper particles which act as filers in the amalgam matrix, hence strengthening the amalgam.
• In its setting reaction, the weakest g2 phase is eliminated by η phase

Composition:

Silver    –   69%

Tin        –   17%

Copper –   13%

Zinc      –      1%

Setting Reaction (Amalgamation):

When the alloy is mixed with mercury, mercury begins to dissolve the outer portion of the particles. Silver from the silver-copper eutectic alloy particles and both silver and tin from the silver-tin alloy particles enter the mercury. The tin dissolved in the mercury reacts with the copper of the silver-copper particles and forms the Cu₆Sn₅(η or Eta).

The η crystals form around the unreacted silver-copper particle. At the same time, γ₁ phase is also formed. As in the low-copper alloys γ₁ surrounds everything forming the matrix. γ₂ is also formed at the same time but is later replaced by η. Thus in admixed alloy the undesirable γ₂ phase is greatly reduced.

Ag₃Sn  +  Ag-Cu  +  Hg Ag₂ Hg₃  +  Cu₆Sn₅  +  Ag₃Sn unreacted  +  Ag-Cu unreacted
(b+g)     (eutectic)    (γ₁) (η)  (b+g)    (eutectic)

Microstructure:

The microstructure of set high-copper admixed amalgam consists of core particles of unreacted γ phase and unreacted Ag–Cu eutectic which is surrounded by the halo of η phase. The core particles are embedded in a matrix of γ₁. Here the γ₂ phase is eliminated and replaced by a stronger η phase.

2. Single Composition Alloy

Unlike admixed alloy powders, each particle of the alloy powder has the same composition. Therefore, they are called single composition or uncompositional alloys.

Composition

Silver  –   40 – 60%

Tin      –   20 – 30%

Copper –  13 – 30%

Zinc      –     0 – 4%

Indium or Palladium – Small amounts

Setting Reaction (Amalgamation):

• Though each particle has the same composition, silver, tin, and copper present exist in various phases within the particle. Thus each particle contains Ag₃Sn (γ), AgSn (β), and Cu₃Sn (ε). When triturated, silver and tin from the particle dissolve in mercury forming the γ₁ (Ag₂ Hg) crystal matrix that binds together the partially dissolved alloy particles.
• At this stage, very little copper dissolves. Later, a layer of η (Cu₆Sn₅ ) crystals is formed at the surface of alloy particles. Some η (Cu₆Sn₅) crystals also form in the matrix.

Ag-Sn-Cu  +  Hg  → Cu₆Sn₅  +  Ag₂ Hg₃ +  Ag-Sn-Cu
(γ + β + ε)                  (γ₁)         (unreacted)

Microstructure:

• The difference between the elimination of γ₂ phase in an admixed and uni compositional alloy is that in the admixed type the γ₂ forms around the silver, and tin particles and is eliminated around the silver-copper particles.
• In the uni-compositional type, the particles at the beginning of the reaction function like silver tin particles of the admixed type and later the same particles function like the silver-copper particles of the admixed type, eliminating γ₂ phase.

Set amalgam consists of core particles of unreacted γ, β, and ε phases which are surrounded by a mesh of rod-shaped η phase. The core particles and η phase are embedded in a matrix of γ₁.

Question 5. Write a short note on the role of zinc in casting gold alloys and silver amalgam alloys.
Answer:

In casting gold alloy and silver amalgam alloy zinc acts as a scavenger or deoxidizer during manufacture.

• The metals absorb gases like oxygen and get oxidized and oxidation of important elements like silver, copper, tin, and gold would seriously affect the properties of the alloy.
• Zinc prevents this oxidization by itself forming zinc oxide. This then flows on the surface and it can be removed easily. Hence, it is called the “deoxidizer”.

Question 6. Write a short note on the zinc-free alloy.
Or
Write a short note on zinc-free amalgam alloy.
Answer:

Alloys that consist of less than 0.01% of zinc are known as zinc-free alloys:

• Zinc-free amalgam alloys are less plastic and are less workable.
• Zinc-free alloys are used in cases where there is difficulty in moisture control.
• It is used in cases of retrograde filings, subgingival restorations, etc.
• Zinc-free alloys do not show delayed expansion when contaminated with moisture.
• Zinc-free alloys are more susceptible to oxidation.

Question 7. Write a short note on the composition of silver amalgam
alloy.
Answer:

Following is the composition of silver amalgam alloy:

Composition of Different Types of Single Compositional  Silver Amalgam Alloys:

• Ternary alloy in spherical and spheroidal form
  • Silver — 60%
  • Tin — 25%
  • Copper — 15%
•  Quaternary alloy in spheroidal form
  • Silver — 59%
  • Copper — 13%
  • Tin — 24%
  • Indium —  4%.

Question 8. Write a short note on aging of amalgam alloy.
Answer:

Ageing is the process by which the shelf-life of a product is improved. A freshly cut alloy reacts very rapidly with mercury. This is because of the relief of stress in particles produced during the cutting of the ingot.

To reduce the stresses the aging should be done:

• The stresses should be reduced by the following methods:
• The alloys, and filings are stored at room temperature for a few months and reactivity reduces.
• By boiling the filings for 30 minutes in water,, the reactivity of the ingot decreases.
• By treating it with acid due to which reactivity of the ingot decreases.
• The above three methods are the process of aging by which the shelf-life of a product is increased or improved.

Question 9. Write a short note on the alloy mercury ratio.
Answer:

• In earlier days, when amalgam was triturated manually, excess mercury had to be used in order to achieve smooth and plastic amalgam. This excess mercury was removed from an amalgam by:
• Use a squeeze cloth to squeeze out the excess mercury.
• Increasing dryness technique: During condensation of each increment, a mercury-rich soft layer comes to the surface. This is removed by condensing excess amalgam and carving of the excess.
• Eames’ technique or minimal mercury technique: The best method of reducing mercury content is to reduce the original mercury/alloy ratio. In 1959,

Restorative Composites

Dr Wilmer Eames recommended a 1:1 ratio of mercury: alloy.

• This method decreases the mercury content to 43% for high-copper as well as single compositional alloys and 55% for lathe-cut low-copper alloys. The excellence of clinical restoration placed by this technique depends on proper manipulation including proportioning of mercury and alloy, trituration, and condensation.
• In the finished amalgam restoration, the mercury content should be approximately 50%, but for spherical alloys, it is relatively less, i.e. 42%. In preproportioned capsules, the mercury/alloy ratio is determined by the manufacturer and is usually less than 50%.
• Low mercury/alloy ratios are not easy to triturate manually. In order to benefit from a low mercury/alloy ratio a high-speed mechanical triturator (amalgamator) is absolutely essential.

Question 10. Write a short note on the amalgamation reaction of low copper alloy.
Answer:

• Low-copper alloy is a type of silver amalgam alloy.
• Low-copper alloy contains less than 6% of copper.

Amalgamation (Setting Reaction):

• When alloy powder and mercury are triturated, the silver and tin in the outer portion of the particle dissolve into the mercury.
• At the same time, mercury diffuses into the alloy particles and starts reacting with the silver and tin present in it, forming silver-mercury and tin-mercury compounds.
• Silver-tin compound is known as the gamma phase (γ).
• The silver-mercury compound is known as the gamma one (γ₁) phase and the tin-mercury as the gamma two (γ₂) phase.

A simple reaction is:

Ag₃Sn + Hg →  Ag₂ Hg₃ +  Sn₈Hg  + Ag₃Sn unreacted

(γ)                               (γ₁)      (γ₂)                 (γ)

The alloy particles do not react completely with mercury. About 27% of the original Ag₃Sn remains as unreacted particles.

Microstructure:

Set amalgam consists of unreacted core particles, i.e. γ surrounded by a matrix of the reaction products γ₁  and  γ₂

Question 11. Enumerate the tooth-colored restorative materials and Discuss the silver amalgam.
Answer:

Tooth-colored restorative materials are:

• Composite resin
• Glass ionomer cement
• Acrylic resin
• Porcelain
• Silicate cement.

Restorative Composites

Question 12. Describe briefly the advantages and disadvantages of silver amalgam
Answer:

Advantages of Silver Amalgam:

• Reasonably easy to insert.
• Not overly technique-sensitive.
• Maintains anatomic form well.
• Has adequate resistance to fracture.
• After a period of time prevents marginal leakage.
• Have a reasonably long service life.
• Cheaper than other alternative posterior restorative materials like gold alloys.
• Wears well and causes minimal wear of natural teeth.

Disadvantages of Silver Amalgam:

• The color does not match the tooth structure.
• They are more brittle and can fracture if incorrectly placed.
• They are subject to corrosion and galvanic shock.
• Corrosion products may stain teeth over time.
• They eventually show marginal breakdown.
• They do not bond to the tooth structure.
• Risk of mercury toxicity.
• Requires removal of some healthy tooth structures for cavity designing.
• Galvanic action: Contact with other metals may cause occasional, minute electrical flow.
• Temporary sensitivity to hot and cold because it is a metal.

Question 13. Write a short note on the polishing of dental amalgam restorations.
Answer:

Polishing leads to the removal of scratches and irregularities from the surface of restoration leaving a smooth, highly glazed surface that is corrosion-resistant.

• Polishing can be done by using descending-grade abrasives such as rubber-mounted stone or rubber cups.
• Final finishing is always done with a polishing agent such as precipitated chalk, tin, or zinc oxide to obtain a metallic luster.
• It should be carried out with very light pressure since heavy pressure causes spur-like overhangs at the margins which fracture during mastication, and result in microleakage.
• It should be kept in mind throughout the polishing procedures that over-abrasion can cause a loss of anatomy or contact and contour.

Polishing should be done 24 hours after condensation:

• Wet polishing is done when a wet abrasive powder is made into a paste for polishing.
• Dry polishing should not be done because it increases the temperature above 60°C resulting in corrosion and fracture at the margins.
• High-copper single compositional alloys due to their high strength can be polished at the same appointment, once the material gains sufficient strength.

Restorative Composites

Question 14. Write a short note on the uses of dental amalgam alloy.
Answer:

• Uses of Dental Amalgam Alloy: Moderate to large Class I preparation.
• Class II preparation in which there is:
  • Heavy occlusion
  • Extension on the root surface.
• In Class V preparations where esthetics is not required.
• For the preparation of dyes.
• As core build-up material.
• As retrograde filling material.
• Class III preparations where isolation is difficult.
• Used as a post-endodontic restoration.
• The fractured tooth cusp is restored with the help of amalgam.

Question 15. Defie dental amalgam. State the classification of the alloy. Describe the setting reaction of amalgam.
Or
What is dental amalgam? Classify dental amalgam.
Or
Write a short note on dental amalgam alloys.
Answer:

Dental amalgam is an alloy made by mixing mercury with silver–tin alloy to which varying amounts of copper and a small amount of zinc are added.

Classification of Dental Amalgam (Adapted from Marzouk, 1997): Amalgam alloy can be classified as:

 According to the content:

• Copper amalgam
• Silver amalgam
• Preamalgamated alloys
• Amalgam with noble metals

 According to the number of alloy metals:

• Binary alloys (silver–tin)
• Ternary alloys (silver–tin–copper)
•  Quaternary alloys (silver—tin—copper—indium)

According to whether the powder consists of unmixed or admixed alloys:

• Admixed/dispersion or blended alloys
• Single compositional/uni-compositional alloys

According to the shape of the powdered particles:

• Spherical shape (smooth-surfaced spheres)
• Lathe-cut (irregular, ranging from spindles to shavings)
• Combination of spherical and lathe-cut (admixed)

According to the powder’s particle size:

• Microcut
• Finecut
• Coarsecut

According to the copper content of powder:

• Low-copper content alloy: Less than 6%
• High-copper content alloy: 6% to 30%

According to the addition of noble metals:

• Platinum
• Gold
• Palladium

According to the presence of zinc:

• Zinc containing (more than 0.01%)
• Non-zinc-containing (less than 0.01%)

Restorative Composites

Question 16. Define and classify silver amalgam alloy. 
Answer:

Silver amalgam alloy is an alloy that is made by mixing mercury with silver tin alloy to which varying amounts of copper and a small amount of zinc are added.

Question 17. Write a short note on the importance of condensation of silver amalgam.
Answer:

Condensation is a process by which the mix is compacted into a prepared cavity to attain a dense mass.

Following is the importance of condensation of silver amalgam:

• It helps in the development of a continuous matrix.
• It helps in the removal of excess mercury and minimizes porosity.
• It helps in the proper adaptation of silver amalgam to all parts of cavity walls and margins, thereby increasing retention and minimizing microleakage.
• Helps in the better adaptation of incremental layers of amalgam.
• Proper condensation increases the strength of silver amalgam by bringing the strongest phases of amalgam close together.
• It decreases the creep of silver amalgam.

Question 18. Name posterior restorative materials. Write in detail about the classification of  Manipulation 
Answer:

Posterior restorative materials are:

• Silver amalgam
• Cast metal restorations
• Type IX GIC and metal-modified GIC
• Composites
• Compomers
• Gold alloy
• Dental ceramics.

Classification of Manipulation:

The steps in manipulation are as follows:

• Proportioning: By weight or by volume.
• Triturating: Manual or mechanical.
• Dispensing: Transfer into the prepared cavity.
• Condensing: Packing with condensers, pluggers, and burnishers.
• Carving: Using amalgam carvers.
• Polishing: Burs, abrasives, and polishing agents.

The preparation and manipulation of the amalgam alloy at the time of placement is crucial in determining amalgam strength, marginal adaptation, degree of porosity, surface smoothness, and the nature of surface constituents.

Proportioning (Dispensing of Alloy):

Alloy mercury ratio by Eames technique (minimal mercury technique): In silver amalgam, the alloy mercury ratio is important. Excess mercury results in greater expansion after setting. The ideal ratio for alloy mercury is 1:l by the Eames technique and the ideal condensation pressure is about 3 to 4 lbs.

This is achieved by using a squeeze cloth and removing the excess mercury. High condensation pressure will squeeze out the excess mercury.

• The Mercury alloy ratio signifies the parts by weight of mercury and of the alloy.
• The recommended ratio is about 40% of mercury is preferred Volumetric proportioning is better than arbitrary dispensing.
• Pre-weighed capsules give accurate proportioning
• Disposable capsules with pre-weighed alloy and mercury are available. To prevent reaction a thin separator is present. This is perforated before mixing. It is expensive but is an accurate method of proportioning.

Restorative Composites

Trituration of Dispensing of Alloy: Triturating is the mixing of silver amalgam by the agitation of the alloy particles and mercury.

Types of Dispensing of Alloy:

• Manual trituration: It is done by using a mortar and pestle.
• Mechanical trituration: Here the capsule is compared to the mortar and the pellet in the capsule is compared to the pestle.

Condensation of Dispensing of Alloy: Condensation is a process by which the mix is compacted into a prepared cavity to attain a dense mass.

Types of Condensation:

There are three types of condensation:

1. Manual condensation
2. Mechanical condensation
3. Ultrasonic condensation.

1. Manual Condensation:

• As trituration is completed the mix material should be packed in increments.
• As material is inserted inside the cavity it is condensed immediately with sufficient pressure.
• Condensation should start from the center to the periphery.
• As the mixture gets condensed some mercury-rich material rises to the surface.
• Some of this mercury should be removed to reduce fial mercury content and improve mechanical properties.
• As these days the working time of amalgam is short, condensation should be done rapidly.
• After proper condensation surface of the restoration becomes shiny.

2. Mechanical Condensation: Mechanical condensers provide a vibration or impact type of force to pack amalgam mix. Less effort is needed than for hand condensation.

3. Ultrasonic Condensation: They produce local heating of amalgam leading to the release of mercury. Proper isolation measures should be taken during condensation. This method is not recommended.

Carving and Burnishing:

Amalgam is overfilled in the cavity so mercury rich surface layer is trimmed away. Carving strokes should proceed from the amalgam surface to the tooth surface. A scraping or ringing sound should be heard while carving:

• Burnishing is done by a ball burnisher using a light stroke from the amalgam surface to the tooth surface.
• Final smoothening is done by rubbing the surface with a moist cotton pellet.
• It improves the marginal adaptation of amalgam.

Dental Amalgam Separator

Polishing of Dispensing of Alloy: It minimizes corrosion and adhesion of plaque. Polishing is delayed for 24 hours after condensation. Wet polish should be used. Polishing should be done with gentle pressure.

Question  19. How and why high-copper amalgam alloy is better than conventional amalgam alloys.
Answer:

Reasons Why High-copper Amalgam Alloy is Better than Conventional Amalgam Alloys:

• In high-copper amalgam alloys, less mercury is required for amalgamation, while more mercury is required for amalgamation in conventional amalgam alloys.
• So hazardous nature and ill effects of mercury are reduced in high-copper amalgam alloy.
• In high-copper amalgam, alloy creep is less, i.e. < 1%, while in conventional amalgam alloy creep is more, i.e. 1–8%.
• In high-copper amalgam alloy tensile strength is high, i.e. 64 MPa, while in conventional amalgam alloy tensile strength is low, i.e. 60 MPa.
• In high-copper amalgam alloy compressive strength is high, i.e. 250–500 MPa while in conventional amalgam alloy, compressive strength is low, i.e. 150-350 MPa.
• In high-copper amalgam alloy dimensional changes are less, i.e. 1–9 µm/cm, while in conventional amalgam alloy dimensional changes are more, i.e. 10–20 µm/cm.
• In a high-copper amalgam alloy setting reaction is fast so burnishing can be done on the same day, while in conventional amalgam alloy settling reaction is slow so early burnishing and finishing is not recommended.
• High-copper amalgam alloys are resistant to corrosion and have better marginal integrity, while conventional amalgam alloys are not resistant to corrosion and have inferior marginal integrity.

Question 20. Describe high-copper silver amalgam alloys And their Advantages.
Or
Describe high-copper amalgam.
Answer:

High-copper alloys are of two types, i.e.

• Admixed alloy
• Single composition alloy.

Advantages of High-copper Silver Amalgam Alloys:

• In high-copper amalgam alloy, less mercury is required for amalgamation. So hazardous nature and ill effects of mercury are reduced in high-copper amalgam alloy.
• In high-copper amalgam alloy creep is less, i.e. <1% In high-copper amalgam alloy tensile strength is high, i.e. 64 MPa
• In high-copper amalgam alloy compressive strength is high, i.e. 250–500 MPa
• In high-copper amalgam alloy dimensional changes are less, i.e. 1–9 µm/cm.
• In a high-copper amalgam alloy setting reaction is fast so burnishing can be done on the same day
• High-copper amalgam alloys are resistant to corrosion and have better marginal integrity.

Question 21. Write a short note on trituration.
Answer:

Trituration is done to wet all the surfaces of alloy particles with mercury.

Objectives of Trituration:

• To remove the oxide layer.
• For pulverizing pellets into particles that can be easily wetted by mercury.
• To decrease the particle size as it increases the surface area of each alloy particle which leads to fast and complete amalgamation.
• To keep γ₁ and γ₂ matrix crystals as minimum as possible and to evenly distribute them throughout the mix for consistent amalgamation achieving adequate strength.
• To provide good amalgamation and to achieve a workable mix of amalgam in a short time this increases the working time for insertion, condensation, and carving of restoration.

Trituration is done by:

• Manual mixing
• Mechanical mixing.

Manual Mixing: In this glass mortar and pestle is used. Mortar has an inner surface that is roughened for increasing friction between amalgam and glass surface. Pestle is a glass rod with a round end.

During manual mixing operator should take the following precautions:

• Mortar should be rested on a firm base.
• Uniform pressure should be applied. A trituration pressure of 2 to 3 psi is needed for proper mixing.
• Time should be well controlled.
• The surface texture of the mortar and pestle is rough.

Dental Amalgam Separator

Mechanical Mixing:

• They are more commonly used to triturate amalgam alloys with mercury.
• Disposable capsules serve as mortar. Some capsules have cylindrical metal or plastic pieces in the capsule which serve as pestle. A capsule is inserted between the arms on top of the machines.
• When switched on the arms holding the capsule oscillate at high speed triturating the amalgam. Most amalgamators have hood that covers the arms holding the capsule in order to confine mercury spray and prevent accidents.
• Amalgamators have an automatic timer and speed control device. Its speed ranges from 3,200 to 4,400 cycles per minute.
• High-copper alloys require higher mixing speeds

Advantages of Mechanical Trituration:

• A uniform and reproducible mix is attained.
• The time required for trituration becomes much less.
• Contamination of the atmosphere by mercury is reduced.
• Alloy: Mercury ratio is good as it is proportioned by the manufacturer.

Question 22. Write a short note on mercury toxicity.
Answer:

Mercury is toxic to vital creatures:

• Free mercury should neither be sprayed nor exposed to the environment.
• Mercury hazards can occur during trituration, condensation, and finishing of restoration.
• Mercury vapors can be inhaled.
• Contact of skin to mercury should be avoided as it is absorbed by the skin.
• Mercury should not get in the sink as it reacts with the metal. It also reacts with gold.
• For mercury toxicity dental surgeons and dental assistants are at high-risk.

Mercury toxicity occurs when there is sudden exposure to high levels of mercury especially from elemental mercury or organic mercury. It results in immediate and severe symptoms requiring urgent medical attention. Toxic levels of mercury are measured in micrograms.

Levels of Mercury Toxicity (In Urine)

• At the level of 4 µg: This level is attributed as the upper limit in urine when extensive restoration of amalgam is present in the patient’s mouth.
• At levels 0 to 25 µg: No known health hazards are detected.
• At level 25 to 100 µg: Decreased response on tests done for brain conduction. The decreased response is related to verbal skills.
• At levels 100 to 500 µg: Mild to moderate effects can be seen:
  • Irritability
  • Depression
  • Nervous system disturbances, i.e. memory loss.
• At level 500 to 1,000 µg: Pronounced symptoms:
  • Inflammation of kidney
  • Tremors and pronounced nervous system disturbances
  • Swollen gums.
  • At 2000 mg: Joint pain develops
  • At 4000 mg: Hearing loss and death.

Question 23. Write a short note on the Amalgam tattoo.
Answer:

It is also known as localized argyrosis.

• Amalgam tatto is an intraoral pigmentation.
• It is characterized by the deposit of restorative debris composed of a mixture of silver, mercury, tin, zinc, and copper in subepithelial connective tissue

Causes of Amalgam tattoo:

• It results during condensation in abraded gingiva during amalgam restoration.
• It enters lacerated mucosa by rotatory instruments at the time of removal of old amalgam filing.
• During a tooth extraction, the broken pieces of amalgam may enter in the socket or below the periosteum leading to an amalgam tattoo.
• Amalgam particles may enter surgical cuts during root canal treatment with retrograde amalgam filing.

Clinical Features Amalgam tattoo:

• Most common sites are gingiva and alveolar mucosa.
• Occur at any age and females are more commonly affected.
• Appears as a flat macule or sometimes slightly raised lesions with margins being well defied and diffused.
• The color of pigmentation is blue-black and may gradually increase in size.

Treatment: Surgical excision should be done.

Question 24. Classify silver alloys. (June 2014, 5 Marks)
Or
Write a short note on the classification of silver amalgam.
Answer:

The following are the classifications for silver amalgam:

Classification of Dental Amalgam (Adapted from Marzouk, 1997)

Amalgam alloy can be classified as:

• According to the content
• Copper amalgam
• Silver amalgam
• Preamalgamated alloys
• Amalgam with noble metals

According to the number of alloy metals:

• Binary alloys (silver–tin)
• Ternary alloys (silver–tin–copper)
• Quaternary alloys (silver—tin—copper—indium)

According to whether the powder consists of unmixed or admixed alloys:

• Admixed/dispersion or blended alloys
• Single compositional/uni-compositional alloys

According to the shape of the powdered particles:

• Spherical shape (smooth-surfaced spheres)
• Lathe—cut (irregular, ranging from spindles to shavings)
• Combination of spherical and lathe-cut (admixed)

According to the powder’s particle size:

• Microcut
• Finecut
• Coarsecut

According to the copper content of powder:

• Low-copper content alloy: Less than 6%
• High-copper content alloy: 6% to 30%

According to the addition of noble metals:

• Platinum
• Gold
• Palladium

 According to the presence of zinc:

• Zinc containing (more than 0.01%)
• Non-zinc-containing (less than 0.01%)

Additional classification based on the generations of amalgam:

•  The first-generation amalgam was that of GV Black, i.e. three parts silver and one part tin (peritectic alloy)
•  Second-generation amalgam alloys: Three parts silver, one part tin, 4% copper to decrease the plasticity and to increase the hardness and strength, and 1% zinc which acts as an oxygen scavenger and decreases brittleness
• Third-generation: First-generation + spherical amalgam— copper eutectic alloy
• Fourth-generation: Adding copper up to 29% to original silver and tin powder to form ternary alloy so that tin is bound to copper
• Fifth-generation: Quaternary alloy, i.e. silver, tin, copper, and indium
•  Sixth-generation consists of a eutectic alloy containing silver (62%), copper (28%), and palladium (10%) which is lathe-cut and blended into the first-, second-, or third-generation amalgam in the ratio of 1:2.

Dental Amalgam Separator

Question 25. Explain the physical properties of dental amalgam.
Answer:

ADA specification no. 1 for amalgam alloy lists three physical properties as a measure of the quality of amalgam, i.e. strength, dimensional change, creep, and flow.

Strength: The compressive strength of dental amalgam is strong but it is weak in tension and shear.

Compressive Strength:

• High-copper single compositional alloys have the highest compressive strength of 510 MPa. This value is obtained after 7 days.
• As 1-hour compressive strength is also important due to clinical significance, it is much less than half the final strength.
• Patients should be told not to use hard masticatory forces for 6 to 8 hours after restoration gets done, at this time 70 to 80% of total strength is achieved.
• Compressive strength is the least for the low-copper alloys both in 1 hour duration or 7 days duration.

The following are the compressive strengths of various amalgams:

Tensile Strength:

• Amalgam cannot withstand high tensile or bending stresses and can fracture easily in improperly designed restorations.
• So the cavity should be designed so the restoration will receive minimal tension or shear forces.
• The tensile strength of both the low and high-copper amalgam ranges from 48 MPa to 64 MPa.

Dental Amalgam Separator

Following is the tensile strength of various amalgams:

Dimensional Change:

• As mercury gets combined with the amalgam it undergoes two dimensional changes, i.e. contraction and expansion.
• Excessive contraction can lead to microleakage, sensitivity, and secondary caries, while excessive expansion can produce pressure on the pulp and post-operative sensitivity and protrusion of restoration.
• As per ADA specifications no. 1, amalgam should neither contract nor expand more than 20 µm/cm when measured at 37°C between 5 minutes and 24 hours after the beginning of trituration.
• Expansion is more for low-copper than high-copper alloys.
• Modern amalgam shows net contraction, while old amalgam always shows expansion.

Creep and Flow:

• Creep is defined as time-dependent plastic deformation.
• A creep of dental amalgam is a slow progressive permanent deformation of set amalgam which occurs under static or dynamic loading over a period of time.
• High-copper alloys as compared to conventional silver tin alloys have low creep values.
• It is mainly associated with low-copper amalgam.
• Low creep values lead to marginal deterioration while very high creep values result in the ditching of amalgam restoration.

Various creep values of amalgam are:

Flow refers to the deformation which occurs during the setting of amalgam. The greater is the flow, the greater the chances of restoration failure