What do you understand by the words abrasive and polishing agents? How and what are the agents used in polishing in gold restorations?
Answer:

Agents used in Polishing Gold Restorations: Gold is relatively a soft material. Therefore, it requires a different approach than that used for other metals used in dentistry. Slow-speed handpiece should be used in finishing and polishing gold alloy.

polishing technique for gold dental restorations

The technique consists of the following steps:

• Contour with carbide burs, heatless stone, or green stone (silicate carbide).
• Finishing with pink stone (aluminum oxide) or medium grade abrasive impregnated rubber wheels and points (brown and green).
• The final finish is done by applying fine abrasive-impregnated rubber wheels, cups, and points.
• Polishing is done by applying tripoli or rouge with rag or leather wheels.

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Write a short note on abrasive and polishing units.
Answer:

Following are the Abrasive and Polishing Units:

• Finishing burs: Burs are made of stainless steel or tungsten carbide. 12–40 fluted carbide burs are usually recommended for finishing depending upon the restorative material. Plain burs are also used before final polishing.
• Diamond instruments and pastes: It is considered a super abrasive because it is the hardest material known and is capable of abrading almost any other material. It is available commercially in the form of bonded abrasive rotary instruments, metal-backed abrasive strips, and polishing pastes.
• Finishing diamonds of medium-fie grit contain diamond particles of 840 µm in diameter. They should always be used with a light force and copious water spray to preserve the very fie diamond coatings. Diamond polishing pastes are also available with particle sizes ranging from 2 to 5 µm. Diamond abrasives are preferably used on ceramic and composite materials.
• Brushes: Brushes can be used either alone or in combination with abrasive particles. Most of the brushes have synthetic bristles, others may have wired bristles for polishing cast restorations.
• Cloth: Cloth carried on a metal wheel may be used for final polishing with/without a polishing medium.
• Felt: Felt is used to attain luster for the metallic restorations usually with a polishing agent. It is available in different shapes of wheels, cones, and cylinders.
• Rotary rubber instruments:
  • Rubber-ended rotary tools are commonly used for polishing procedures.
  • They can be obtained in various shapes of cups, wheels, cones, etc., and are commonly used with other abrasives or polishing pastes.
• Coated discs and strips:
  • The abrasive particles such as sand, cute, garnet, boron carbide, silicon carbide, etc. are held onto a flexible heavy-weight paper or Mylar strips with a suitable adhesive material.
  • The discs may be attached to a mandrel for rotary finishing. Abrasive strips are used by hand in a back-and-forth motion, especially for finishing proximal areas.

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Write a short note on medicated dentifrices.
Answer:

Medicated Dentifrices: Certain medications are added to the toothpastes and toothpowders so as to empower them with prophylactic/ therapeutic activity against specific dental conditions.

These are:

• Fluoride: Sodium monofluorophosphate or sodium fluoride or caries prevention. Most toothpastes contain a fluoride.
• Antiseptics: Chlorhexidine, triclosan, or benzalkonium chloride for prevention and treatment of dental plaque. A copolymer is often included with triclosan to prolong its substantivity.
• Desensitizing agents: Potassium nitrate or strontium chloride are mostly added to treat dentine sensitivity.
• Bleaching agents: Carbamide peroxide is the most common bleaching agent added to stain-removing dentifrices

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Write a short note on rouge.
Answer:

Rouge is an iron oxide inline form. Moss scale: 5–6.

• It is blended with various soft binders into a cake or bar form.
• When impregnated in cloth it is called crocus cloth.
• It is used to polish high-noble metal alloys
• Rouge is contraindicated for polishing stainless steel and cobalt-chromium alloys as iron contaminates the surface and facilitates corrosion.
• It is used as a colouring agent in impression compounds.
• Rouge is mixed with chloroform and is used as antireflux.

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Write a short note on agents for pulp protection.
Answer:

Agents for pulp protection are:

• Varnish
• Sealer
• Liner
• Base.

Varnish:  Varnish or Cavity varnish is a solution of one or more resins in a volatile solvent which when applied onto the cavity walls, evaporates leaving a thin resin film that serves as a barrier between the restoration and dentinal tubules.

Sealer: It is used to seal dentinal tubules and to treat dentin hypersensitivity. An adhesive sealer is commonly used under indirect restorations. For the application of sealer, a cotton tip applicator is used to apply sealer on all areas of exposed Denton.

Liner:  Liner or Cavity liners are cement coatings of minimal thickness that are applied to the prepared cavity when the remaining dentin thickness is adequate.

Base:  Base or cavity base is a layer of cement placed beneath a permanent restoration to encourage recovery of the injured pulp and to protect it against numerous types of insults to which it may be subjected.

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Write a short note on the biocompatibility test.
Or
Write in brief on biocompatibility tests for dental materials.
Answer:

Evaluation of biocompatibility of dental materials is a complex and comprehensive area due to unwanted tissue reactions that occur in many types.

• Individual test methods are usually adequate only to describe a single aspect of certain types of unwanted reactions.
• Following are the biocompatibility tests: These tests are carried out at three levels one after another. If the material is successful in the first test then only the second test is carried out and likewise. If successful in the second test then the subsequent tests are carried out.

Group I: Initial or Primary Tests:

• Genotoxicity test: In this test, the effect of the material on the genes is carried out.
• Cytotoxic assays: By these tests, the effect of the material or its leachable products is studied on the metabolic functions of the test cell system.
• Cell plating and growth tests: These tests are done to determine if the material interferes with cell functions by releasing some component of the material into the medium. In this a small piece of sterile material is placed in the cells of tissue culture dishes then the cells are plated at a particular density within the cells in tissue culture medium for l to 3 days. Biologically inert materials like siloxane polymer or Teflon are used as negative controls.
• Mutagenesis assays: These assays are done in vitro to identify materials and chemicals that are capable of producing cancer.

Group II: Intermediate or Secondary Tests: After screening by initial tests of the materials developed for a specific use, the successful materials are tested generally on experimental animals, i.e. guinea pigs, rodents, and hamsters.

• Systemic toxicity test: In this, the product is evaluated for its potency to create systemic toxicity.  For this oral median lethal dose (LD50) test is done in which a test sample is daily administered to rats for l4 days. If half or more than half of the animals survive it is considered that the product has passed the test.
• Inhalation toxicity test: This test is done on guinea pigs, rats, rabbits, or hamsters in exposure to aerosol preparations and the material is sprayed for l0 times around the head and chest of the animals for 30 seconds at half an hour intervals.
• If any animal dies within 3 minutes the product is considered very toxic. If none of the animals dies in four days the product is considered safe.
• Mucous membrane irritation test: In this, the product is applied directly to the oral mucous membrane or abraded skin continuously for several weeks in 10 animals. The histological examinations are done along with controls, if there is no irritation or histological changes the product is considered safe.
• Skin irritation toxicity and sensitization tests (maximization test).
• Implantation tests: Done for the materials that will contact subcutaneous tissues and bone.

Group III: Human Trials: If the material has passed primary and secondary tests, it is ready for trial in humans where: Reactions and performance under clinical conditions are studied.

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Write a short note on cytotoxicity.
Answer:

Cytotoxicity is defined as the cascade of molecular events that interfere with macromolecular synthesis, causing unequivocal cellular, functional, and structural damage. Cytotoxic screening can be done in vivo or in vitro.

In vitro, tests are conducted on cultured cells like mouse L–929 fibroblasts and human Hela cells. There are many in vitro tests. For example, Agar overlay technique; Agar is spread over a layer of culture cells in a culture plate. The test material is then placed on it and incubated. A toxic material will show a clear zone of dead cells.

Advantages of Cytotoxicity:

• Screening a large number of samples quickly and inexpensively
• Quantifying results
• Greater sensitivity to toxic material than usage tests
• Testing for specific functions of cell metabolism.

Disadvantages of Cytotoxicity:

• Limitation of testing to only one cell type at a time
• Dissimilarity of test cells and host cells
• Lack of inflammatory and other tissue protective mechanisms in tissue culture.

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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.

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Question 1. 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 2. 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.

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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.

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