Dental Materials

Dental Polymers Important Notes

1. Types Of Polymerization

• Condensation polymerization
  • Involves combining two dissimilar molecules into a third entirely different product
  • Ex: phenol and formaldehyde to form Bakelite
• Addition polymerization
  • When similar molecules are combined the reaction is called an addition reaction
  • In it, the monomer is repeated many times to form a polymer
  • No by-products are formed
  • Example: polymethylmethacrylate

2. Stages Of Polymerization

• Initiation
• Propagation
• Termination
• Chain transfer

3. Copolymerization

• Resin formed by two or more chemically different monomers is called copolymer
• The process of formation is called copolymerization

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Dental Polymers Long Essays

Question 1. Describe polymerization mechanisms. Add a note on stages in addition to polymerization.
Answer:

Polymerization:

• It is the chemical reaction in which monomers of low molecular weight are converted into chains of polymers with a high molecular weight
• Monomer + Monomer + Monomer+ → Polymer
• These monomers are connected by bonds
• It is a repetitive intermolecular reaction

Polymerization Types:

1. Condensation polymerization

• It is divided into two groups
  • Those in which polymerization occurs along with the repeated elimination of small molecules
  • Those in which functional groups like amide, and ester are repeated

2. Addition polymerization

• In this type of polymerization, monomers are repeated and every time one molecule is added the chain continues
• There is no change in chemical composition and no by-products are formed

Inhibition of Polymerization: Polymerization is inhibited by

Polymer And Monomer In Dentistry

1. Impurities

• Any impurity in the monomer that can react with free radicals inhibits or retards the polymerization
• It occurs during storage
• Example: The addition of a small amount of hydro-quinone inhibits polymerization

2. Oxygen It reacts rapidly with free radicals and retards polymerization

Polymers Used In Dentistry

Stages of Addition Polymerization: There are four stages of addition polymerization

1. Induction

• It is the time during which the molecules of the initiator become activated
• It is the activation of free radicals which in turn initiate growing polymer chains
• Thus, this stage is controlled by activation and initiation
• Any impurities present increase the length of the induction period
• It is useful for dental resins
• These resins are activated by heat, chemicals, and light

• Example: Amine acts as an activator and benzoyl peroxide as an initiator for dental resins

2. Propagation

• It is a stage of polymerization during which polymer chains continue to grow to high molecular weights
• It is accompanied by the liberation of heat. Thus it is an exothermic reaction
• The growth of the polymer chain stops if the reactive center is destroyed by the termination reaction

3. Chain Transfer

• During this stage, the growing end of a chain is transferred to another molecule and initiates further chain growth
• Here the active state is transferred from active radical to inactive molecule

Polymerization In Dentistry 

4. Termination It occurs through two processes

• Direct coupling of two free radical end chains
  • The two molecules combine and become deactivated by the formation of a covalent bond

• Exchange of hydrogen atom
  • The hydrogen atom is transferred from one growing chain to another
  • A double bond is produced between them

Dental Polymers Short Question And Answers

Question 1. Copolymerization
Answer:

Copolymerization

• It is the process of polymerization where two or more chemically different monomers combine to form polymers called copolymers.
• There are three different types of copolymers

Polymer And Monomer In Dentistry

1. Random type
2. Graft type
3. Block type

Importance of Copolymerisation: It is used to improve the physical properties of resins

Physical Properties Of Dental Materials Important Notes

1. Tarnish

• Tarnish is the surface discoloration
• Occurs due to
  • Formation of calculus, plaque on the surface of the metal
  • Formation of oxides, sulfides, chlorides
    • Tarnish is the forerunner of corrosion

2. Corrosion

• Corrosion is the actual deterioration of the metal by a reaction with its environment
• Corrosion Types
  • Dry Or chemical corrosion
    • In it, the metal reacts to form oxides, chlorides, and sulfides in the absence of electrolytes
  • Wet Or electrochemical corrosion
    • It requires the presence of water or other fluid as an electrolyte
    • It has 3 types-crevice corrosion, stress, corrosion, and galvanic corrosion

3. Passivation

• Chromium, aluminum, and titanium form strong adherent oxide films on their surface to protect from corrosion
• This is called passivation

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4. Creep

• Creep is defined as time-dependent plastic deformation or strain of material under static load
• Creep Types
  • Static creep
  • Dynamic creep

5. Flow

• Flow is deformation under a small static load
• Flow describes the behavior of amorphous materials such as waxes

6. Metamerism

• Objects that appear to be color-matched under one type of light may appear very different under another light source
• This phenomenon is known as metamerism
• Different light sources used in dental procedures are
  • Daylight
  • Incandescent lamps
  • Fluorescent lamps

7. Coefficient Of Thermal Expansion

The linear coefficient of thermal expansion of some materials concerning tooth enamel are:

Physical Properties Of Dental Materials

Physical Properties Of Dental Materials Long Essays

Question 1. What are Tarnish and Corrosion? What are the causes for it? How to avoid it?
Answer:

1. Tarnish:

Tarnish Definition:

• Tarnish is surface discoloration on a metal or a slight loss or alteration of the surface finish or luster
• It is often the forerunner of corrosion

Tarnish Causes: In the oral cavity

The presence of the following on the surface of restorations

1. Deposits
   • Hard deposits like calculus or
   • Soft deposits like plaque or mucin
2. Stains produced by
   • Presence of pigment-producing bacteria
   • Use of drugs containing iron or mercury
   • Adsorbed food debris
3. A thin film of oxides, sulfides, or chlorides.

Protection Against Tarnish: It can be protected by the following measures

1. Maintaining good oral hygiene
2. Minimizing the intake of tea, coffee, or tobacco that produces stains

2. Corrosion:

Corrosion Definition: It is a process in which the deterioration of a metal is caused by a reaction with its environment

Corrosion Causes: Corrosion occurs due to

1. Water, oxygen, chloride ions, sulfides
2. Various acids such as phosphoric, acetic, and lactic acid

Corrosion Types:

1. Aqueous or Electrolytic or wet corrosion

Its subtypes are

• Galvanic corrosion
• Heterogeneous composition corrosion
• Stress corrosion
• Concentration cell corrosion

2. Dry or chemical corrosion

Protection against corrosion:

It can be protected by the following measures

1. Passivation:

• The process of formation of a strong oxide layer on its surface by metal is called Passivation
• This strong film protects the metal from corrosion
• Examples: Chromium, titanium, and aluminum are passive metals

2. Increasing noble metal content

• Gold, platinum, and palladium are examples of noble metals
• It is suggested that dental alloys must contain at least 50% of these metals
• As these metals are EMF-positive they resist corrosion better than any other metal

3. Polishing

• Well-polished restorations remove surface roughness
• This reduces the chances of concentration cell corrosion

4. Avoiding dissimilar metal restorations

• Dissimilar metals cause Galvanic corrosion
• Thus it should be avoided

Mechanical Properties Of Dental Materials

Physical Properties Of Dental Materials Short Essays

Question 1. Types of corrosion.
Answer:

Types Of Corrosion

1. Dry Corrosion Of Chemical Corrosion:

Corrosion is a non-aqueous corrosion in which the metal reacts to form oxides and sulfides in the absence of electrolytes.

Corrosion Example:

• Formation of Ag₂S in dental restorations containing silver
• Oxidation of alloy particles in dental amalgam.

2. Electrolytic or EIectrochemical Or Wet corrosion:

• It requires the presence of electrolytes
• This electrolyte supplies the ions needed at the cathode and carries away the corrosion products at the anode
• The anode undergoes an oxidation reaction with the production of free electrons
• The reduction reaction occurs at the cathode by accepting electrons from the anode
• The production of electrons should be balanced by the consumption of electrons
• During a reaction, metal with the lower electrode potential becomes the anode
• Its subtypes are

1. Galvanic Corrosion
   • It occurs due to adjacent dissimilar metal restorations
   • Example: Presence of amalgam occlusal restoration with opposing gold inlay
   • Between these two dissimilar metals, saliva acts as an electrolyte producing short-circuit
   • As a result, the patient experiences pain
   • It can be minimized by painting varnish on the surface of the amalgam restoration.
2. Heterogeneous Composition Corrosion
   • It occurs within the structure of the restoration
   • Examples: Eutectic alloys and peritectic alloys
   • Impurities in any alloy enhance corrosion
3. Stress Corrosion
   • A metal is called to be stressed when it undergoes cold working
   • If stressed and unstressed metals are contacted the stressed metals get corroded
   • The stressed metal acts as an anode while unstressed metal is a Cathode
4. Concentration Cell Corrosion Or Crevice Corrosion.
   • It occurs due to variations in the composition of the given electrolyte

Types Of Corrosion Example:

• Differences in the composition of saliva
  • The presence of food debris in between the teeth alters the composition of the saliva
  • Due to this corrosion occurs under the layer of food debris
  • It can be prevented by maintaining good oral hygiene
• Differences in oxygen concentration
  • Due to the presence of pits, the oxygen concentration of the restorations differ
  • The region at the bottom of the pit has a lower oxygen concentration
  • This region behaves as an anode while the alloy surface around the pit becomes a cathode and corrosion results

Physical Properties Of Dental Materials Short Question And Answers

Question 1. Difference between tarnish and corrosion.
Answer:

Difference Between Tarnish And Corrosion

Properties Of Dental Composites

Question 2. Creep and flow.
Answer:

1. Creep Definition:

Creep is defined as time-dependent plastic deformation or strain of material under static load or constant stress near its melting point

Creep Types:

1. Static creep: It is a time-dependent deformation produced in a completely set solid subjected to constant stress.
2. Dynamic creep: Produced when the applied stress is fluctuating

Creep May Cause

• Deformation of dental restorations like an amalgam
• Improper fit of fixed partial dentures

Creep Flow: It is used to describe the rheology of amorphous substances like waxes

Question 3. Hue, value, and chroma
Answer:

Hue, Value, And Chroma: Hue, value, and chroma are the three dimensions of the color

1. Hue
   • It describes the dominant color of an object
   • Example: red, blue, or green
2. Value
   • It is the relative lightness or darkness of the color
   • It is independent of hue
3. Chroma
   • It represents the degree of saturation of a particular color
   • It is always associated with value and hue
   • The higher the chroma, the more intense the color

Hue, Value, And Chroma Measurement:

• The color is determined by the Munsell system
• It consists of a cylinder that shows the three dimensions of color

1. Hue- Changes occur in a circumferential direction
2. Value- Increases towards the top and decreases towards the bottom
3. Chroma- It increases along the radius from an axis

Corrosion Resistance In Dental Materials

Question 4. Metamerism
Answer:

Metamerism Objects that appear to be color-matched under one type of light may appear very different under another light source.

• This phenomenon is known as Metamerism
• To overcome metamerism, it is recommended that the color-matching procedures should be carried out under two or more different light sources out of which one should be daylight
• The light sources used should be the same in the clinic as well as in the laboratory
• The different sources used in dental procedures are Daylight, incandescent lamps, and fluorescent lamps

Question 5. Coefficient of thermal expansion.
Answer:

Coefficient Of Thermal Expansion Definition: The change in length per unit of the original length of a material when its temperature is raised by lk is known as the coefficient of thermal expansion.

Coefficient of thermal expansion Significance:

• It is important in dental applications to produce cast restorations that fit and maintain the seal at a restoration margin.
• It Influences the procedures Involving wax patterns, casting metals, and crowns, placing amalgam and composite resin restorations, and preparing metal-ceramic crowns and bridges.

Question 6. Thermal conductivity.
Answer:

Thermal Conductivity Synonym: Coefficient of thermal conductivity

Thermal Conductivity Definition:

• It is the quantity of heat in calories per second that passes through a specimen 1 cm thick having a cross-sectional area of 1 cm2 when the temperature difference between the surfaces perpendicular to the heat flow of the specimen is 1 degree K.
• In general thermal conductivities increase in the following order:
  • polymers< ceramics < metals

Thermal Conductivity Significance:

• Materials having high thermal conductivity are called conductors and those with low conductivity are insulators.
• The higher the thermal conductivity, the greater the ability of the substance to transmit thermal energy
• Increased thermal conductivity induces greater pulpal sensitivity

Thermal Conductivity Value:

Thermal conductivity is measured as watt per meter per second per degree Kelvin.

Corrosion Resistance In Dental Materials

Question 7. Electrolytic corrosion
Answer:

Electrolytic Corrosion

• It requires the presence of electrolytes
• This electrolyte supplies the ions needed at the cathode and carries away the corrosion products at the anode
• The anode undergoes an oxidation reaction with the production of free electrons
• The reduction reaction occurs at the cathode by accepting electrons from the anode
• The production of electrons should be balanced by the consumption of electrons
• During a reaction, metal with the lower electrode potential becomes the anode

Its Subtypes Are:

1. Galvanic corrosion
2. Stress corrosion
3. Concentration cell corrosion
4. Heterogeneous surface composition corrosion

Structure Of Matter And Principle Of Adhesion Important Notes

1. Contact Angle

• It is an angle formed by the adhesive with the adherent at their interface
• The less the contact angle the more the wettability and spreadability

2. Wetting 

• To produce adhesion the liquid must flow easily over the entire surface and adhere to the solid
• This feature is known as wetting

Read And Learn More: Dental Materials Question and Answers

3. Surface Tension/ Surface Energy

• Wetting and adhesion are directly related to the surface energy of adhesives
• The surface energy of many restorative materials is higher when compared to that of tooth

4. Space Lattice

• Space Lattice can be defined as any arrangement of atoms in space in which every atom is situated similarly to every other atom.
• Space Lattice may be the result of primary or secondary bonds
• There are 14 possible types

Structure Of Matter In Dentistry

Structure Of Matter And Principle Of Adhesion Short Question And Answers

Question 1. Space lattice?
Answer:

Space Lattice Synonym: Crystal structure

Synonym Definition:

• A space lattice can be defined as any arrangement of atoms in space such that every atom is situated similarly to every other atom.
• It may be the result of primary or secondary bonds.

Space Lattice Types: The type of space lattice is defined by the length of each of the three unit cell edges and the angles between the edges

There are 14 possible lattice types or forms

1. Simple cubic space lattice
   • It is the most commonly used form
   • In it, the position of atoms is located at the points of intersection of three sets of parallel planes called crystal planes
   • Other types are
2. Body-centered cubic
3. Face-centered cubic
4. Rhombohedral
5. Orthorhombic
6. Monoclinic
7. Triclinic
8. Tetragonal
9. Simple hexagonal
10. Closed packed hexagonal
11. Rhombic

Adhesive Bonding In Dental Materials

Question 2. Mechanical bonding.
Answer:

Mechanical Bonding: Attachment between the two substances is achieved by mechanical bonding or retention

Mechanical Bonding Applications

1. Non-dental applications

• Mechanical bonding is achieved by the use of screws, bolts, or undercuts

2. Dental applications

1. It is involved in the penetration of the adhesive into the microscopic irregularities in the surface of the substrate
2. Micromechanical bonding is a type of mechanical bonding that is used in dentistry
3. This type is used for

• Retention of a cast restoration
  • Mechanical bonding of the cementing agent improves retention of the casting over the tooth surface
• Resin restorative material
  • Resins are not capable of adhering to the tooth surface
  • Thus before its insertion, the enamel Is treated with phosphoric add called the acid etched technique
• By this minute pores are produced over the enamel surface into which resin flows and provides retention

Question 3. Contact angle?
Answer:

Contact Angle Definition:

The angle formed at the interface of the adhesive and adherend is known as the contact angle.

Contact Angle Significance:

• Contact angle determines the extent to which an adhesive wets the surface of an adherend.
• If the adhesive forces are stronger than cohesive, no angle is formed
• If the adhesive remains as a drop and doesn’t spread, the contact angle will be higher
• The smaller the contact angle between an adhesive and an adherend, the better the ability of the adhesive to flow
• It is used to measure wettability.

Dental Adhesion Mechanisms

Question 4. Surface Tension?
Answer:

Surface Tension Definition: The increase in energy on the surface per unit area is referred to as surface tension.

Surface Tension Synonym:

Surface energy

Surface Tension Reason:

The Energy at the surface of a solid is greater than in its interior because

1. Inside a lattice

• All the atoms are equally attracted to each other
• The interatomic distance arc equal
• Energy is minimal.

2. But at the surface of the lattice

• Atoms are not equally attracted in all directions
• There is only force from the inside of the lattice pulling the outermost atoms inwards.
• This creates tension on the outer surface.

Question 5. Wetting agent?
Answer:

Wetting Agent Definition:

A wetting agent is a surface-active substance that reduces the surface tension of a liquid to promote wetting or adhesion.

Wetting Agent Synonym: It is also called a surfactant.

Wetting Agent Significance:

• To improve the wettability of the set Impression material by gypsum-water mixture, a wetting agent is added.
• It ensures the good surface quality of the gypsum model

Factors Affecting Adhesion In Dentistry

Question 6. Adhesion
Answer:

Adhesion Definition:

• A molecular or atomic attraction between two contacting surfaces promoted by the Interfacial force of attraction between molecules or atoms of two different species is called adhesion.
• The material that is used to cause bonding is known as adhesive and the material to which it adheres is called the adherend.

Adhesion Types: Adhesion may occur by chemical or mechanical adhesion or both.

Adhesion Applications:

1. Restorative procedures

• Incomplete adhesion of restorative materials to the tooth structure results in leakage of the material 1 causing secondary caries

2. Prosthodontic procedures

• Retention of dentures occurs due to adhesion between dentures and saliva and between saliva and soft tissue

3. Periodontal aspects

• Plaque and calculus adhere to the tooth structure

Question 7. Interatomic bonds.
Answer:

Interatomic Bonds The interatomic bonds are classified into primary and secondary bonds

Primary Bonds: They are chemical In nature

Primary Bonds Types:

1. Ionic Bonds: It is a simple bond that occurs due to the mutual attraction of positive and negative charges
2. Covalent Bonds: In covalent bonding, two valence electrons are shared by adjacent atoms
3. Metallic Bond: It is the primary bond occurring between metal atoms

Secondary Bonds

1. Hydrogen Bonds: Occurs in water molecules between an oxygen atom and two hydrogen atoms
2. Van der Walls forces
   • It is due to the formation of a dipole
   • These are weak forces

Adhesive Bonding In Dental Materials

Question 8. Chemical adhesion
Answer:

Chemical Adhesion

• A molecular or atomic attraction between two contacting surfaces promoted by the interfacial force of attraction between molecules or atoms of two different species is called adhesion.
• Types of adhesion – mechanical and chemical
• Chemical adhesion occurs due to primary and secondary bonds

1. Primary Bonds

• Ionic bonds
• Covalent bonds
• Metallic bonds

2. Secondary Bonds

• Hydrogen bonds
• Van der Walls forces

Dental Amalgam Important Notes

1. Composition of amalgam

Mercury In Dental Amalgam

2. Classification of amalgam

• Based on copper content
• Low copper alloys contain less than 6% copper
• High copper alloys contain between 13-and 30% copper
• Based on zinc content
• Zinc-containing alloys
• Zinc-free alloys
• Based on the shape of the alloy particle
• Lathe-cut alloys
• Spherical alloys
• Based on the number of alloyed metals
• Binary alloys
• Tertiary alloys
• Quaternary alloys
• Based on the size of the alloy
• Microcut
• Macrocut

Dental Amalgam Composition Questions and Answers

3. Phases of amalgam

4. Setting reaction

• For low copper alloys
  Ag₃Sn + Hg → Ag₂Hg₃ + Sn₈Hg + Ag₃Sn (unreacted)
• For high copper admixed alloys
  γ + Ag-Cu + Hg → γ₁ + Cu₆Sn₅ + (γ + Ag-Cu) unreacted
• For high copper single composition alloys Ag-Sn-Cu + Hg → γ₁ + η + unreacted alloy particles (γ)

Dental Amalgam Composition Questions and Answers

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5. Lathe cut and spherical alloys

6. Eames’ technique

• It states the minimum mercury alloy ratio
• It should be 1:1
• The mercury content of the finished restoration should be approximately 50 wt%. For spherical alloys, it should be approximately 42 wt%

7. High copper alloys are superior to low copper alloys because:

• Higher resistance to tarnish, corrosion
• Lower creep
• High strength
• Elimination of SnHg phase

Alternatives to dental amalgam 

8. Delayed expansion

• Occurs when zinc-containing alloys are contaminated with moisture during trituration or condensation
• Expansion reaches upto 400 pm/cm
• It occurs 3-4 days after insertion of amalgam
• It is due to the formation and accumulation of hydrogen gas in the restoration leading to pain, sensitivity, and proper sion of the restoration

Composition Of Dental Amalgam

9. Creep

• It is defined as the time-dependent plastic deformation
• The higher the creep, the greater the marginal deterioration
• Values:
• Low copper – 0.8-8%
• High copper – 0.4-0.1%

Components Of Dental Amalgam

10. Tarnish and corrosion products

• Tarnish product – Ag₂S
• Corrosion product
• Low copper – SnO, Sn-O-Cl
• High copper – SnO, Sn-O-Cl, CuO

Alternatives to dental amalgam 

Dental Amalgam Long Essays

Question 1. Discuss the type, properties, and uses of dental amalgam alloys. Add a note on high copper alloys.
Answer:

Dental Amalgam:

Dental amalgam is an alloy of mercury, silver, copper, and tin which may also contain palladium, zinc, and other elements to improve handling characteristics and clinical performance.

Dental Amalgam alloys Types:

• Based on copper content
• Low copper alloys- contain less than 6% copper
• High copper alloys- contain between 13-30% copper
• Based on zinc content
• Zinc containing alloys
• Zinc free alloys
• Based on the shape of the alloy particle
• Lathe cut alloys
• Spherical alloys
• Spherical alloys
• Based on the number of alloyed metals
• Binary alloys
• Tertiary alloys
• Quaternary alloys
• Based on size of the alloy
• Microcut
• Macrocut

Dental amalgam composition 

Dental Amalgam alloys Properties:

• Dimensional stability
  • Amalgam may expand or contract depending on its manipulation
  • Severe contraction can lead to microleakage, plaque accumulation, and secondary caries
  • Excessive expansion can produce pressure on the pulp and postoperative sensitivity
  • It can also lead to the protrusion of restorations
• Effect of moisture contamination
  • If a zinc-containing low copper or high copper amalgam is contaminated by moisture during trituration or condensation, a large expansion results
  • It usually starts after 3-5 days and may continue for months
  • This is called delayed expansion
  • Strength
  • It lacks of strength to resist masticatory forces and thus fractures
• Creep
  • It is a slow progressive permanent deformation of set amalgam that occurs under constant stress
  • Higher the creep magnitude the greater the degree of marginal deterioration
  • Tarnish and corrosion
  • Amalgam restorations often tarnish and corrode the oral environment
• Retention
  • Amalgam does not adhere to tooth structure
  • Retention is by mechanical locking
  • Microleakage
  • Amalgam is a self-sealing restoration
  • They are capable of sealing against, microleakage

Dental Amalgam Uses

Dental Amalgam alloys Use:

• As permanent restorative material for
• Class 1 and class 2 cavities
• Class 5 cavities
• In combination with retentive pins to restore a crown
• For making dies
• In retrograde root canal filling materials
• As a core material

Dental amalgam composition 

High Copper Alloys:

• Contains 13-30%, weight copper
• They are preferred because of
• Improved properties
• Resistance to corrosion
• Better marginal integrity
• Improved performance in clinical trials

Copper Alloys Types:

• Admixed alloys 0 Regular type
• Unicomposition alloy
• Single composition alloy

Copper Alloys Composition:

Dental amalgam properties 

Copper Alloys Setting reaction:

1. Admixed alloy

2. Single composition

Copper Alloys Advantages:

• Set fasts
• Low residual mercury
• Low creep
• Faster finishing
• High strength
• Low condensation pressure

Copper Alloys Disadvantages:

• Less working time
• Condensation pressure is not sufficient

Dental Amalgam Questions And Answers

Question 2. State various merits and demerits of dental amalgams
Answer:

Dental Amalgam:

Dental amalgam is an alloy of mercury, silver, copper, and tin which may also contain palladium, zinc, and other elements to improve handling characteristics and clinical performance.

Dental Amalgam Merits:

• Easy to insert
• Not technique sensitive
• Maintain anatomic form well
• Have adequate resistance to fracture
• Prevent marginal leakage after some time
• Have a reasonably long shelf life

Dental amalgam properties 

Dental Amalgam Demerits:

• The color does not match the tooth color
• More brittle
• Less tough than desirable
• Subject to corrosion and galvanic action
• Show marginal breakdown
• Do not bond to tooth structure

Dental Materials Question And Answers

Question 3.  Give the composition of dental amalgam alloys and write in detail about the manipulation and properties of high copper dental amalgam
Answer:

Amalgam alloys Composition:

• Mercury
• It is added to the alloy
• Platinum
• Hardens the alloy
• Increases resistance to corrosion
• Palladium
• Hardens and whitens the alloy
• Indium
• Reduces mercury vapor and improves wetting

Amalgam alloys Manipulation:

1. Selection of materials

• Alloy selection
  • For therapeutic purposes- high resistance amalgam is selected
  • For strength- high copper alloys are selected
  • If moisture control is difficult- non-zinc-containing alloys are selected
• Mercury: alloy ratio
  • To achieve smooth and plastic amalgam an amount of mercury in excess is desirable
  • But because of the harmful effects of excess mercury, it is necessary to reduce the amount of mercury
  • One of the methods for it is to reduce the original mercury/alloy ratio
  • This is called the Eames technique e Sufficient mercury must be present in the mix and it should be as low enough so that mercury content is acceptable during condensation
  • Ratio is 1:1

2. Amalgam alloys Trituration

• Objective
  • To wet all the surfaces of the alloy particles with mercury
  • The film should be rubbed off to obtain a clean surface of alloy for mercury
• Manual mixing
  • A glass mortar with a roughened inner surface and a pestle with a round end are used for mixing
  • It depends on
  • Number of rotations
  • Speed of rotations
  • Pressure placed on pestle
• Amalgam alloys Mechanical mixing

Dental Amalgam Components 

3. Amalgam alloys  Mulling

• It is a continuation of trituration
• It causes the mix to cohere so that it can be readily removed from the capsule
• Achieved by vigorously rubbing between first finger and thumb for 2-5 sec

4. Amalgam alloys Condensation

• Amalgam is placed in a prepared cavity and condensed using suitable condensers
• Aims
• To compact alloy into a prepared cavity
• To remove any excess mercury in each increment
• Reduces voids

Dental Materials Question And Answers

5. Amalgam alloys Carving and finishing

• Carved to reproduce proper tooth anatomy
• Smoothen through burnishing with a ball burnisher
• Final smoothening can be achieved by rubbing with a moist cotton pellet
• Polishing minimizes corrosion and prevents adherence to plaque
• It is delayed for 24 hours
• Wet polishing is desirable

Dental Amalgam Components 

Amalgam alloys Properties:

• Dimensional stability
  • Amalgam may expand or contract depending on its manipulation
  • Severe contraction can lead to microleakage, plaque accumulation, and secondary caries
  • Excessive expansion can produce pressure on the pulp and postoperative sensitivity
  • It can also lead to the protrusion of restorations
• Effect of moisture contamination
  • If a zinc-containing low copper or high copper amalgam is contaminated by moisture during trituration or condensation, a large expansion results
  • It usually starts after 3-5 days and may continue for months
  • This is called delayed expansion
• Amalgam alloys Strength
  • It lacks of strength to resist masticatory forces and thus fractures
  • Creep
  • It is a slow progressive permanent deformation of set amalgam that occurs under constant stress
  • Higher the creep magnitude the greater the degree of marginal deterioration
• Tarnish and corrosion
  • Amalgam restorations often tarnish and corrode the oral environment
  • Retention
  • Amalgam does not adhere to tooth structure » Retention is by mechanical locking
  • Microleakage
  • Amalgam is a self-sealing restoration
  • They are capable of sealing against, microleakage

Advantages And Disadvantages Of Dental Amalgam

Question 4. Write in brief about the setting reaction of both low and high copper amalgam alloy. What are the phases formed during the reaction with a note on factors affecting its strength?
Answer:

Setting Reactions:

1. Low Copper Amalgam Alloys:

Uses Of Dental Amalgam 

2. High Copper Amalgam:

Admixed alloy

3. Single composition:

Amalgam Factors Affecting Strength:

• Effect of trituration

Under-triturated and over-triturated both decrease strength in both low and high-copper alloys

• Effect of mercury
  • Sufficient mercury should be mixed with an alloy
  • Any excess mercury left in the restoration decreases the strength
  • For both low and high copper amalgam, if mercury content increases more than 54%, strength decreases
• Effect of condensation
  • For lathe-cut alloys- greater condensation pressure, higher compressive strength
  • For spherical alloys- lighter condensation pressure produces adequate strength
• Effect of porosity
  • If porosities are greater, strength is lower
  • Effect of amalgam hardening rate
  • Amalgam does not gain strength rapidly

Types Of Dental Amalgam

Question 5. Write the composition, properties, advantages, and disadvantages of amalgam alloys. Add a note on the classification of amalgam alloys.
Answer:

Dental amalgam:

Dental amalgam is an alloy of mercury, silver, copper, and tin which may also contain palladium, zinc, and other elements to improve handling characteristics and clinical performance

Amalgam alloys Properties:

• Dimensional stability
• Amalgam may expand or contract depending on its manipulation
• Severe contraction can lead to microleakage, plaque accumulation, and secondary caries
• Excessive expansion can produce pressure on pulp and postoperative sensitivity
• It can also lead to protrusion of restoration
• Effect of moisture contamination
• If a zinc-containing low copper or high copper amalgam is contaminated by moisture during trituration or condensation, a large expansion results
• It usually starts after 3-5 days and may continue for months
• This is called delayed expansion
• Strength

Dental Amalgam Composition

• It lacks the strength to resist masticatory forces and thus fractures
• Creep
• It is a slow progressive permanent deformation of set amalgam that occurs under constant stress
• Higher the creep magnitude the greater the degree of marginal deterioration
• Tarnish and corrosion
• Amalgam restorations often tarnish and corrode the oral environment
• Retention
• Amalgam does not adhere to tooth structure
• Retention is by mechanical locking
• Microleakage
• Amalgam is a self-sealing restoration
• They are capable of sealing against microleakage

Amalgam alloys Advantages:

• Easy to insert
• Not technique sensitive
• Maintain anatomic form well
• Have adequate resistance to fracture
• Prevent marginal leakage after some time
• Have a reasonably long shelf life

Amalgam alloys: Disadvantages:

• Color does not match with tooth color
• More brittle
• Less tough than desirable
• Object to corrosion and galvanic action
• Show marginal breakdown
• Do not bond to tooth structure

Uses Of Dental Amalgam 

Amalgam alloys Classification:

1. Based on copper content

• Low copper alloys contain less than 6% copper
• High copper alloys contain between 13-30% copper

2. Based on zinc content

• Zinc containing alloys
• Zinc free alloys

3. Based on the shape of alloy particles

• Lathe cut alloys
• Spherical alloys

4. Based on the number of alloy metals

• Binary alloys
• Tertiary alloys
• Quaternary alloys

5. Based on size of alloys

• Microcut
• Macrocut

Components Of Dental Amalgam

Setting Reaction Of Dental Amalgam

Dental Amalgam Short Essays

Question 1. Trituration
Answer:

Trituration Objective:

• To wet all the surfaces of the alloy particles with mercury
• The film should be rubbed off to obtain a clean surface of alloy for mercury

Trituration Types:

• Trituration Manual mixing
  • A glass mortar with a roughened inner surface and a pestle with a round end are used for mixing
  • It depends on
  • Number of rotations
  • Speed of rotations
  • Pressure placed on pestle

Trituration Advantages of Mechanical Mixing:

• Shorter mixing time
• More standardized procedure
• Requires less mercury

Dental Amalgam Setting Reaction 

Question 2. Spherical amalgam alloys
Answer:

Spherical amalgam alloys

• Spherical amalgam alloy is prepared by the atomization process
• The liquid alloy is sprayed under high pressure of inert gas through a fine crack into a large chamber

Spherical amalgam alloys Features:

• Particles are small
• Manufactured by atomization process
• More plastic
• Need wedged matrix to establish proximal contour
• Require less mercury
• Particle size is- 5-40 pm

Spherical amalgam alloys Reactions:

• When triturated with mercury, silver, and tin dissolve in mercury
• γ₁ crystals grow forming a matrix that binds together the partially dissolved alloy particles

Spherical amalgam alloys Composition:

Dental Amalgam Toxicity

Question 3. Amalgam capsule
Answer:

Amalgam capsule

• A capsule serves as a mortar
• A cylindrical metal or plastic piston of a smaller diameter than the capsule is inserted into the capsule and this serves as a pestle
• Alloy powder and mercury are separated by a membrane in it
• Before use the membrane is ruptured by compressing capsule and then placed in an amalgamator

Amalgam capsule Advantages:

• Consistent proportioning
• Low mercury/alloy ratio
• Physical handling is not required

Amalgam capsule Disadvantages:

• Mercury and alloy may leak
• Expensive
• Mercury hazards

Dental Amalgam Setting Reaction 

Question 4. Delayed expansion of amalgam
Answer:

Delayed expansion of amalgam

• If a zinc-containing low copper or high copper amalgam is contaminated by moisture during trituration or condensation a large expansion results
• It usually starts after 3-5 days and may continue for months
• This is called delayed 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
  • Increased creep
  • Increased microleakage
  • Pitted surfaces and corrosion
  • Dental pain
  • Recurrence of caries
  • Fracture of restoration

Dental Amalgam Uses

Question 5. Eames technique
Answer:

Eames technique

• To achieve smooth and plastic amalgam an amount of mercury in excess is desirable
• But because of the harmful effects of excess mercury, it is necessary to reduce the amount of mercury
• One of the methods for it is to reduce the original mercury or alloy ratio
• This is called the Eames technique
• Sufficient mercury must be present in the mix and it should be as low enough so that mercury content is acceptable during condensation
• Ratio is 1:1

Dental Amalgam Short Question And Answers

Question 1. High copper alloy
Answer:

High copper alloy

• Contains 13-30%, weight copper
• They are preferred because of
• Improved properties
• Resistance to corrosion
• Better marginal integrity
• Improved performance in clinical trials

High copper alloy Types:

• Admixed alloys
• Regular type
• Unicomposition alloy
• Single composition alloy

High copper alloy Advantages:

• Set fasts
• Low residual mercury
• Low creep
• Faster finishing
• High strength
• Low condensation pressure

High copper alloy Disadvantages:

• Less working time
• Condensation pressure is not sufficient

Dental Amalgam Setting Reaction 

Question 2. Creep in amalgam
Answer:

Creep in amalgam

• It is a slow progressive permanent deformation of set amalgam that occurs under constant stress
• Higher the creep magnitude the greater the degree of marginal deterioration
• According to ADA’s specification, no 1 creep should be below 3%

Creep in amalgam Creep Values:

Creep in amalgam Factors Affecting Creep:

• Microstructure
• Manipulation

Question 3. Amalgam bond
Answer:

Amalgam bond

• Recently bonding agents like M-R-X type coupling agents have achieved success
• One system uses 4-methacryloxyethyl trimellitate anhydride
• Amalgam bonding agents have a place as an adjuvant to conventional retentive means if properly employed

Amalgam bond Mechanism Of Bonding:

• Bonding is mechanical
• Produced by condensing plastic amalgam mass into a plastic resin layer
• This produces macroretentive areas within the resin

Mercury In Dental Amalgam

Question 4. Gamma 2 phase in silver amalgam
Answer:

Gamma 2 phase in silver amalgam

The formula of γ₂ is Sn₈Hg

Gamma 2 phase in silver amalgam Importance:

• Weakest phase
• Decreases tarnish and corrosion resistance
• Increases creep

Dental Materials Question And Answers

Question 5. Mercury hygiene
Answer:

Mercury hygiene

• Follow aseptic technique
• Should have proper knowledge about mercury disposal and storage
• Use of proper ventilation
• Check mercury levels periodically
• Avoid carpet or floor covering
• Storage of mercury in a closed container in an isolated area
• Use of pre-capsulated alloy
• Use of amalgamators
• Polishing along with coolant
• Avoid direct contact with skin
• Use of evacuators
• Disposal in a closed plastic container
• Clean spilled mercury
• Remove protective clothing before leaving the operating area

Dental Amalgam Setting Reaction 

Question 6. Advantages of high copper amalgam
Answer:

Advantages of high copper amalgam

• Set fasts
• Low residual mercury
• Low creep
• Faster finishing
• High strength
• Low condensation pressure

Dental Implants Short Essays

Question 1. Dental implant materials
Answer:

Dental implant materials

Read And Learn More: Dental Materials Question and Answers

Dental Implants Short Question And Answers

Question 1. Passivation.
Answer:

Passivation

1. Certain metals readily form a strong adherent oxide film on their surface, which protects them from corrosion. Such a metal is said to be passive.
2. Since this oxide film is passive to oxidation, its formation is called passivation. E.g. Chromium, titanium & aluminium.
3. If more than 12% chromium is added to iron or cobalt, we get stainless steel or cobalt-chromium alloys, which are lightly corrosion-resistant and suitable for dental use.

Cost Of Dental Implants

Finishing And Polishing Materials Important Notes

1. Polishing Agents

2. Rake Angle

• It is the angle between the rake face and the radial line
• Positive Rake Angle – The radial line is ahead of the rake face
• Negative Rake Angle – The rake face is ahead of the radial line
• Zero Rake Angle – The rake face and radial line coincide

Finishing And Polishing Materials Long Essays

Question 1. Enumerate materials and methods while polishing chromium-cobalt alloys and acrylic resin.
Answer:

Polishing:

Polishing is a process of providing lustre or gloss on a material surface

Polishing Agents Used:

• Natural
• Arkansas stone, chalk, corundum, diamond, emery, garnet, pumice, quartz, sand, tripoli, zirconium silicate
• Manufactured or synthetic agents
• Silicon carbide, aluminium oxide, synthetic diamond, rouge, tin oxide

Read And Learn More: Dental Materials Question and Answers

Polishing of Cobalt-Chromium Alloys:

• Electrolytic polishing is done
• It is an electrochemical process
• The alloy to be polished is made anode of an electrolytic cell
• Current is passed
• Some of the anode is dissolved leaving a bright surface

Polishing of Cobalt-Chromium Alloys Advantages:

• Very little material is removed
• The Fit of the denture remains unaltered

Polishing For Acrylic Resin:

• Acrylic resin is a relatively soft materials
• Contour with tungsten carbide bur and sandpaper
• This leaves large scratches
• Remove scratches using a rubber point
• Apply pumice over the canvas buff wheel
• Preliminary polishing is done
• Clean the work
• Apply Tripoli or a mixture of chalk and alcohol with a rag wheel
• Hold the work firmly without excessive pressure
• Repeat this over the entire surface till the surface is bright and well-polished
• Clean the work

Dental Finishing And Polishing Materials

Question 2. State various abrasives used in dentistry
(or)
What are the different types of abrasives and polishing agents?
Answer:

Abrasive And Polishing Agents:

Question 3. Classify dental burs. State their functions
Answer:

Dental Burs:

Dental Burs is defined as a rotary cutting instrument with cutting heads of various shapes and two or more sharp-edged blades, used as a rotary grinder.

Dental Burs Classification:

• According to their mode of attachment to the handpiece
  • Latch type
  • Friction grip type
• According to their composition
  • Stainless steel
  • Tungsten carbide
  • Combination
• According to their motion
  • Right bur-revolves clockwise
  • Left bur- revolves anticlockwise
• According to the length of their head
  • Long
  • Short
  • Regular
• According to their use
  • Cutting burs
  • For finishing and polishing

• According to their shapes
  • Round
  • Pear shaped
  • Inverted cone
  • Wheel shaped
  • Tapering fissure
  • Straight fissure

Dental Burs Functions:

Finishing And Polishing In Dentistry

Question 4. What are the rake angle and clearance angle?
Answer:

Rake Angle Definition:

Rake Angle is the angle between the rake face and the radial line

Positive Rake Angle:

When the radial line leads the face so that the rake angle is on the inside of the radial line, the rake angle is said to be positive

Zero Rake Angle:

• Where the radial line and the face contour correspond the rake angle is zero
• In such an instance, the bur tooth is said to have zero radial rake angle

Negative Rake Angle:

If the face is beyond or leading the radial line in reference to the direction of rotation, the angle formed between the face and the radial line is called the negative rake angle

Clearance Angle:

The angle between the back of the tooth and the work is known as the clearance angle.

Finishing And Polishing Materials Short Essays

Question 1. Describe the action of abrasives and state the requirements of abrasive materials
Answer:

The Action Of Abrasives:

• The action of abrasive is essentially a cutting action
• An abrasive tool has many abrasive points that are not arranged in an ordered pattern
• Thus innumerable random scratches are produced
• Each tiny particles present a sharp edge that cuts through the surface similar to a chisel
• A shaving is formed which crushes to a fine powder
• This powder clogs the abrasive tool and thus frequent cleaning is required

Abrasives Requirements:

• Abrasives Shape
  • It should be irregular in shape
  • Round smooth surfaces are poor abrasives
  • While irregular and jagged particles are more effective
• Abrasives Hardness
  • Abrasive should be harder than the work it abrades

• Abrasives Strength
  • It possesses a high-impact strength
  • The abrasive particle should fracture rather than dull out
  • Fracture of an abrasive is also helpful in shedding the debris accumulated from the work
  • They are most effective when used on brittle tooth enamel
• Abrasives Attrition Resistance:
  • They should have attrition resistance

Question 2. Define abrasive and polishing agents. Give examples of each.
Answer:

Abrasive Agent:

• A hard substance used for grinding, finishing or polishing a less hard substance is called abrasive agent
• Examples- emery, diamond, rouge, etc.

Polishing Agent:

• It is an agent used in the process of providing lustre or gloss on the material surface
• Example- polishing cakes, pumice, etc.

Dental Polishing Techniques

Question 3. Dental bur design
Answer:

Dental Bur Design

• The design of the bur includes the following a Blade or cutting-edge
• It is in contact with the horizontal line or face
• Tooth Face
  • The sides of the tooth ahead of the cutting edge in the direction of the rotation is the tooth face
• The Back Of The Tooth
  • The opposite of the bur tooth is the back of the tooth
• Rake Angle
  • It is the angle between the rake face and the radial line
• Positive Rake Angle
  • When the radial line leads the face so that the rake angle is on the inside of the radial line, the rake angle is said to be positive
• Zero Rake Angle
  • Where the radial line and the face contour correspond the rake angle is zero
  • In such an instance, the bur tooth is said to have zero radial rake angle
• Negative Rake Angle
  • If the face is beyond or leading the radial line in reference to the direction of rotation, the angle formed between the face and the radial line is called the negative rake angle
• Clearance Angle
  • The angle between the back of the tooth and the work is known as the clearance angle
  • The clearance angle of most burs is straight and clearly defined
• Tooth Angle
  • It is the measurement between the face and the back
• Flute Or Chip Space
  • It is the space between successive teeth
  • The number of teeth in a bur is 6 or 8
  • Dental burs provide a negative rake angle

Question 4. Polishing of metals
Answer:

Polishing of Amalgam:

Polishing of Gold Alloys:

Question 5. Factors affecting cutting efficiency of dental burs.
Answer:

1. Dental Burs Reduced Use Of Crosscuts

• Crosscuts are provided at low speed to increase cutting efficiency
• Crosscuts used at high speed produce unduly rough surfaces

2. Dental Burs Extended Heads On Fissure Burs

• Extended head length of burs is used

3. Dental Burs Rounding Of Sharp Tip Angles

• • Sharp tip results in
  • High-stress concentration
  • Increases the tendency for the tooth to fracture
• Rounded Corners Result In
  • Lower stresses in restored teeth
  • Enhances strength of tooth
  • Preserves vital dentin
  • Facilitates adaptation of restorative material

4. Dental Burs Rake angle

A negative rake angle minimizes fracture of the cutting-edge

5. Dental Burs Edge Angle

Increased edge angle reinforces the cutting edge

6. Dental Burs Clearance Angle

• Eliminates rubbing friction of the clearance face
• Provides a stop to prevent the bur edge from digging into the tooth structure
• Provides adequate flute space

Abrasive Materials In Dentistry 

Finishing And Polishing Materials Short Question And Answers

Question 1. Abrasives used in dentistry
Answer:

Abrasives Used In Dentistry

• Natural
• Arkansas stone, chalk, corundum, diamond, emery, garnet, pumice, quartz, sand, tripoli, zirconium silicate
• Manufactured or synthetic agents
• Silicon carbide, aluminium oxide, synthetic diamond, rouge, tin oxide

Question 2. Dentrifices
Answer:

Dentrifices

• Popularly known as toothpaste, these are agents used with a toothbrush to cleanse and polish natural teeth.
• They should have maximum cleansing efficiency the minimum tooth abrasion.

Dentrifices Functions:

• Assist the toothbrush to mechanically remove stains, debris and soft deposits from the tooth.
• To impart a polished surface to the tooth.
• They help to reduce care and maintain healthy gingiva. Improve aesthetics and reduce mouth odours.

Question 3. Pumice
Answer:

Pumice

• Pumice is a type of abrasive
• Pumice is a highly siliceous material of volcanic origin and is used as an abrasive or polishing agent depending upon the particle size.
• Its use ranges from smoothening dentures to polishing teeth in the mouth.
• Flour of pumice extremely fine-grained derivated used for polishing enamel

Question 4. Diamond abrasive
Answer:

Diamond Abrasive

1. The hardest and most effective abrasive for tooth enamel is composed of diamond chips
2. The chips are impregnated in a binder or plated onto a metal shank to form the diamond stones and discs, which are very popular in the dental profession

Dental Finishing And Polishing Procedures

Question 5. Bonded abrasives
Answer:

Bonded Abrasives

• Bonded abrasives consist of abrasive particles incorporated through a binder to form grinding tools such as points, wheels, separating discs, coated thin discs, and a wide variety of other abrasive shapes.
• Particles are bonded by four general methods.

1. Sintering
2. Vitreous bonding (glass or ceramic).
3. Resinous bonding (usually phenolic resins).
4. Rubber bonding (latex-based silicone-based rubber).
5. Because most of the rubber wheels, cups, and points contain latex, a known allergen, all residues must be removed from the polished surface

Question 6. Rouge
Answer:

Rouge

• It is a type of abrasive agent used in dentistry.
• Rouge is a fine red powder composed of iron oxide.
• Is used in a cake form.
• It may be impregnated on paper or cloth known as ‘crocus cloth’.
• It is an excellent polishing agent for gold and Nobel metal alloys. But is likely to be dirty to handle.

Casting Investments And Procedures Important Notes

1. Sprue’s Former

• Provides a channel through which molten alloy can reach the mold after the wax has been eliminated
• Its diameter should be the same as the thickest area of the wax pattern
• It should be attached to the thickest portion of wax to prevent distortion
• Its length should be such that there is a 6 mm of distance from the casting ring to the end of the mold cavity
• It should be spread at a 45° angle to the proximal area

2. Die Materials

3. Casting Defects

Dimensional errors in casting

Surface Irregularities

Read And Learn More: Dental Materials Question and Answers

Porosity

Incomplete Casting

4. Dental Investments

Dental Casting Materials

Casting Investments And Procedures Long Essays

Question 1. What are the types of investments? Describe the composition, properties, and manipulation of gypsum-bonded investments.
Answer:

Types Of Investment Materials:

• Gypsum bonded investments- for casting gold alloys
• Phosphate bonded investments- for metal ceramic and cobalt-chromium alloys
• Silica bonded investments- used in the casting of base metal alloy partial dentures

Gypsum Bonded Investments:

Gypsum Bonded Investments Composition:

Gypsum Bonded Investments Properties:

• Thermal properties
• When gypsum is heated at high temperatures, it shrinks and fractures
• When heated quartz changes its crystalline form
• Expansion
• Expansion aids in enlarging the mold to compensate for the casting shrinkage
• Strength
• The compressive strength for inlay investment should not be less than 2.5 MPa
• Porosity
• The more gypsum crystals the less the porosity
• Fineness
• The finer the investment the smaller will be the surface irregularities on the casting
• Storage
• Investment should be stored in airtight and moisture-proof containers

Gypsum Bonded Investments Manipulation:

• The proper water-powder ratio is determined
• Water is measured by graduated cylinder and powder by weighing balance
• Place a measured volume of water in a parabolic, smooth bowl first
• Add preweighed powder gradually to it
• Allow settling for 30 sec to minimize air entrapment
• The mix is stirred vigorously
• Periodically wiping inside of the bowl with the spatula is done to ensure the wetting of all of the powder and breaking up of the lumps
• Continue mixing until a uniform smooth mix is obtained
• Vibrate the mix using a mechanical vibrator or by repeated tapping against the bench

Types Of Casting Investments In Dentistry

Question 2. Classify investment materials. Discuss the role of thermal expansion.
Answer:

Types Of Investment Materials:

• Gypsum bonded investments- for casting gold alloys
• Phosphate bonded investments- for metal ceramic and cobalt-chromium alloys
• Silica bonded investments- used in the casting of base metal alloy partial dentures

Role of Thermal Expansion:

• Thermal expansion is achieved by placing the mold in a furnace at a temperature not more than 700° C
• Factors affecting it are
• Amount and type of silica present
• Contraction of gypsum is counterbalanced when quartz content is increased to 75% o Method used for casting shrinkage compensation
• Hygroscopic expansion- 0.5-0.6%
• Normal expansion-1-2% o Water/powder ratio
• More water less expansion
• Modifiers
• The small amount of sodium, potassium, and lithium chloride eliminates contraction and increases expansion

Question 3. Write in detail about casting defects.
(or)
Enumerate common causes of casting failures and what precautions you will take to avoid the same.
Answer:

Casting defects:

Question 4. Discuss various steps in the casting procedures of an inlay and add a note on shrinkage porosity.
Answer:

Steps In Casting Procedures:

• Tooth preparation
• The tooth is prepared by the dentist with the proper reduction from all the aspects
• Impression
• The impression is made using elastomeric impression materials
• Die preparation
• Die is prepared using die stone or the impression is electroformed
• Wax pattern fabrication
• Die lubricant is applied
• Then the wax pattern is fabricated over it using inlay type II wax
• Attachment of sprue former
• Length l/8th- l/4th inch away from the open end of •ring
• Width equal to the thickest part of the wax pattern
• Ring liner placement
• The ring liner is placed inside the casting ring e It should be short at one end o the Functions
• Allows for mold expansion
• It reduces heat loss
• Permits easy removal of the investment after casting
• Investing
  • Apply wetting agent over the wax pattern
  • Seat the casting ring in the crucible former
  • Mix the investment and vibrate
  • Apply some investment over the wax pattern
  • Gradually then fill the remaining investment
• Burn out
  • It is carried out
  • To eliminate the wax
  • To expand the mold
  • The ring is placed in a burnout furnace and heated gradually at 400°C for 20 min
• Casting
  • It is a process by which molten metal is introduced into the investment mold
  • Alloys can be melted by
  • Blow torch
  • Electrical induction
  • The ring is transferred from the furnace to the casting machine
  • In it, the alloy is melted and forced into the mold
• Recovery
• Investment is removed and the casting is recovered
• Sandblasting
• Done to clean the remaining investment from the surface
• Pickling
• Surface oxides are removed by pickling in 50% hydrochloric acid
• Polishing
• Minimal polishing is required

Shrinkage Porosity:

Shrinkage Porosity Types:

• Localized shrinkage porosity
  • Occurs when the cooling is incorrect
  • The sprue freezes before the rest of the casting
  • It results in large irregular voids near the sprue casting junction
• Suck back porosity
  • It is an external void seen inside of a crown opposite the sprue
  • A hot spot is created by the hot metal impinging on the mold wall near the sprue
  • The hot spot causes this region to freeze last
  • Since the sprue has already solidified no more molten material is available and the resulting shrinkage causes a peculiar type of shrinkage called suck-back porosity
• Microporosity
  • These are fine irregular voids within the casting
  • Seen when the casting freezes too rapidly

Casting Investments And Procedures Short Essays

Question 1. Ideal requisites of investment materials
Answer:

Ideal Requisites Of Investment Materials

• The investment mold must expand to compensate for the alloy shrinkage
• The powder should have a fine particle size
• Easy manipulation
• Suitable setting time
• Should have smooth consistency when mixed
• At high temperatures, the material should not decompose
• The material should be porous enough
• Must have adequate strength at room temperature to permit handling
• Should have enough strength at higher temperatures to withstand the impact force of the molten metal
• Casting temperature should not be critical
• After casting it should break easily from the surface of the metal
• It should be economical

Dental Casting Procedure Steps

Question 2. Phosphate bonded investments
Answer:

Phosphate Bonded Investments

Phosphate Bonded Investments is the most widely used investment material

Phosphate Bonded Investments Use:

• For casting
• High-fusing noble metal alloys
• Metal ceramic alloy
• Base metal alloy

Phosphate Bonded Investments Classification:

• Type 1- for inlays, crowns, and other fixed restorations
• Type 2- for partial dentures

Phosphate Bonded Investments Composition:

Powder:

• Liquid
• It is in the form of silica sol in water which gives high thermal expansion

Phosphate Bonded Investments Properties:

• Expansion
• Sources of expansion arc:
• Wax pattern expansion
• Setting expansion
• Thermal expansion
• Strength
• Wet strength ranges from 4-10 MPa
• Thermal reactions
• It undergoes thermochemical reactions
• Flow
• Have low flow
• So it can be poured easily into the mold
• Surface smoothness
• Newer investments have improved surface smoothness

Question 3. Hygroscopic expansion
Answer:

Hygroscopic Expansion

• Expansion that occurs in water is called hygroscopic expansion
• It is a physical expansion
• When expansion begins, externally available water is drawn into pores forming a setting mass
• It maintains a continuous aqueous phase in which crystal growth takes place freely

Hygroscopic eExpansion Importance:

Use to expand some gypsum bonded investments

Hygroscopic Expansion Factors Affecting it:

• Mixing method
• Mechanical mixing decreases setting expansion
• Water powder ratio

• Modifiers- accelerators and retarders
• Reduces setting expansion

Gypsum Bonded Investment Materials

Question 4. Die materials
(or)
Ideal requisites of dye material and mention different types of dye materials
Answer:

A positive replica of a prepared tooth or teeth in a suitable hard substance on which inlays, crowns, and other restoration are made is called a die.

Types Of Die Materials:

• Gypsum products
• Type 4 dental stone
• Type 5 dental stone, high strength, high expansion
• Type 5, dental stone, lignosulfonates
• Metal and metal-coated dies
• Electroformed
• Sprayed metals
• Amalgam
• Polymers
• Metal or inorganic-filled resins
• Epoxy
• Cement
• Silicophosphate
• Polyacrylic acid-bonded cement
• Refractory materials

Die Materials Ideal Requirements:

• Dimensionally stable
• Have good abrasion resistance
• Have smooth surface
• Reproduce surface details accurately
• Biocompatible
• Non-injurious
• Color should contrast with wax, porcelain, and alloys
• Easy and quick to fabricate
• Inexpensive

Question 5. Electroformed dies
Answer:

Electroformed Dies Advantages:

• Dimensional accurate
• Hard, abrasion resistant
• Imparts a smooth surface
• Cheap
• Better marginal definition
• Does not absorb oil or water
• Prevent cuspal wear

Electroformed Dies Disadvantages:

• Difficult to trim
• Silver bath- a health hazard
• Not compatible with impression material
• Color contrast is not good
• Poor adaptation to wax
• The pattern tends to lift from margins

Phosphate Bonded Investments

Question 6. Casting shrinkage
Answer:

Casting Shrinkage

Question 7. Back pressure porosity
Answer:

Back Pressure Porosity

• This is caused by inadequate venting of the mold
• If the bulk of the investment is too great the escape of air becomes difficult causing increased pressure in the mold
• The gold will solidify before the mold is completely filled resulting in a porous casting with rounded short margins
• Avoided by
• Using adequate casting forces
• Use of investment of adequate porosity
• Place the pattern not more than 6-8 mm from the end of the ring

Question 8. Sprue former
Answer:

Sprue Former

• A sprue former is made of wax. Plastic or metal
• Thickness is in proportion to the wax pattern

Sprue Former Functions:

• To form a mount for the wax pattern
• To create a channel for the elimination of wax during burnout
• Forms channel for entry of metal which compensates for alloy shrinkage during solidification

Dental Casting Defects And Causes

Question 9. Types and uses of casting machines
Answer:

Casting Machines Types:

Casting Machines Steps:

Casting Investments And Procedures Short Question And Answers

Question 1. Sprue
Answer:

Sprue

Sprue provides a channel so that molten metal flows into mold space after the wax pattern has been eliminated

Sprue Types:

• Wax
• Plastic
• Metal

Sprue Functions:

• Provides a channel for the flow of molten alloy
• Provides reservoir to compensate for shrinkage
• Provides a channel for wax elimination

Sprue Requirements:

• Diameter: greater than the thickest part of the wax pattern
• Attachment- to the thickest part of the wax pattern
• Sprue length- such that end of the wax pattern is l/8th to l/4th inch away from the open end of the casting ring
• Direction- 45° to the bulkiest portion of wax
• Reservoir- to compensate for shrinkage

Dental Investment Materials Properties

Question 2. Divestment
Answer:

Divestment

• The combination of die material and investing medium is called divestment
• A gypsum-bonded investment is mixed with colloidal silica liquid
• The die with the wax pattern is invested in divestment
• The setting expansion is 0.9%
• Thermal expansion is 0.6% when heated to 677°C
• Divestment phosphate is a phosphate-bonded investment that is used in the same manner as divestment
• It is suitable for use with high-fusing alloys

Question 3. Hygroscopic expansion
Answer:

Hygroscopic Expansion

• Expansion that occurs in water is called hygroscopic expansion
• It is a physical expansion
• When expansion begins, externally available water is drawn into pores forming a setting mass
• It maintains a continuous aqueous phase in which crystal growth takes place freely

Hygroscopic expansion Importance:

Use to expand some gypsum bonded investments

Question 4. Types of investment materials
Answer:

Types of investment materials

• Gypsum bonded investments- for casting gold alloys
• Phosphate bonded investments- for metal ceramic and cobalt-chromium alloys
• Silica bonded investments- used in the casting of base metal alloy partial dentures

Question 5. Porosities
Answer:

Porosities Types:

• Caused by solidification shrinkage
• Localized shrinkage porosity
• Suck back porosity
• Microporosity
• Caused by gas
• Pinhole porosity
• Gas inclusion
• Subsurface porosity
• Caused by air entrapment
• Backpressure porosity

Porosities Prevention:

• Use of correct sprue thickness
• Correct placement of sprue
• Use of reservoir
• Use of adequate casting forces
• Use of porous investment and proper vents
• Place pattern -8 mm away from the end of the ring

Common Casting Errors In Dentistry

Question 6. Casting defects
Answer:

Casting Defects

• Distortion
• Surface roughness
• Porosity
• Caused by solidification shrinkage
• Localized shrinkage porosity
• Suck back porosity
• Microporosity
• Caused by gas
• Pinhole porosity
• Gas inclusion
• Subsurface porosity
• Caused by air entrapment
• Back pressure porosity
• Incomplete casting
• Contamination of casting due to oxidation

Question 7. Pickling
Answer:

Pickling

• The surface oxides from the casting are removed when necessary by pickling in 50% HC1
• HC1 is heated with the casting in it
• It is usually done for gold alloys
• It is not a routine procedure
• Performed only when indicated

Question 8. Die materials
Answer:

Die materials

A positive replica of a prepared tooth or teeth in a suitable hard substance on which inlays, crowns, and other restoration are made is called die

Types of Die Materials:

• Gypsum products
• Type 4 dental stone
• Type 5 dental stone, high strength, high expansion
• Type 5, dental stone, lignosulfonates
• Metal and metal-coated dies
• Electroformed
• Sprayed metals
• Amalgam
• Polymers
• Metal or inorganic-filled resins
• Epoxy
• Cement
• Silicophosphate
• Polyacrylic acid-bonded cement
• Refractory materials

Dental Casting Techniques MCQs

Question 9. Casting ring liners and their functions
Answer:

Casting Ring Liners Types:

• Fibrous ceramic aluminous silicate
• Cellulose
• Ceramic cellulose combination

Casting Ring Liners Functions:

• Allows for mold expansion
• It reduces heat loss
• Permits easy removal of the investment after casting

Question 10. Reservoir
Answer:

Reservoir

• The reservoir is a piece of wax attached to the sprue former approximately 1 mm from the pattern
• Reservoir can be used as an added precaution
• Reservoir is used to prevent localized shrinkage porosity

Question 11. Suck back porosity
Answer:

Suck Back Porosity

• It is an external void seen inside of a crown opposite the sprue
• A hot spot is created by the hot metal impinging on the mold wall near the sprue
• The hot spot causes this region to freeze last
• Since the sprue has already solidified no more molten material is available and the resulting shrinkage causes a peculiar type of shrinkage called suck-back porosity

Question 12. Epoxy resin dies
Answer:

Epoxy Resin Dies

Epoxy resin dies are most effective with rubber-based impression materials

Epoxy Resin Dies Advantages:

• Tougher
• Effective with rubber-based impression materials

Epoxy Resin Dies Disadvantages:

• Slight shrinkage
• Viscous
• The setting takes up to 24 hours

Question 13. Localized shrinkage porosity.
Answer:

Localized Shrinkage Porosity

• It occurs when the cooling is incorrect
• The sprue freezes before the rest of the casting
• It results in large irregular voids near the sprue casting junction

Localized Shrinkage Porosity Prevention:

• Sprue should be directed at 45 degrees to the wax pattern
• The reservoir should be placed

Lost Wax Casting In Dentistry

Question 14. Advantages of gypsum bonded investment.
Answer:

Advantages Of Gypsum Bonded Investment

• It can produce an expansion that is sufficient for com- sensation for the shrinkage
• Made up of fine particles which results in a smooth surface of the casting
• Easy to mix and handle
• Setting time can be controlled
• The set material is porous which helps to prevent the formation of backpressure during casting
• The strength of the set material is sufficient to withstand forces generated by the metal during casting

Dental Waxes Important Notes

1. Classification of Waxes

2. Composition of Wax Paraffin

3. Technique

Dental Wax Materials

4. Types Of Waxes And Their Uses

5. Components of Base Plate Wax

• Paraffin – 75%
• Bee’s wax-12%
• Added colors

Read And Learn More: Dental Materials Question and Answers

Dental Waxes Long Essays

Question 1. Describe the composition, properties, and manipulation of inlay wax.
Answer:

Inlay Wax:

Inlay Wax Composition:

Inlay Wax Properties:

1. Inlay Wax Flow

• Ideally, type I inlay wax should exhibit marked plasticity or flow at a temperature slightly above the mouth temperature
• At 45 degrees C- both types should have a flow between 70-90%
• At 37 degrees C- the type should not flow more than 1%
• At 30 degrees C- type 2 should not flow more than 1%

2. Inlay Wax Thermal Properties

• Thermal conductivity is very low
• They have a high coefficient of thermal expansion
• It has a linear expansion of 0.7% with an increase in temperature of 20 degrees C

3. Inlay Wax Distortion

• It is the most serious problem
• Occurs during the forming and removal of the pattern from the mouth or die
• Occurs due to
  • Thermal changes
  • Relaxation of stress due to
  • Contraction on cooling
  • Occluded gas bubble

• • Change of shape of wax during molding
  • From manipulation
  • Time and temperature of storage
• A freshly made wax pattern tends to change its shape and size over a period of time
• Upon cooling it contracts and after it attains equilibrium, the pattern attains a state of dimensional stability

Inlay Wax Manipulation:

• Direct Technique
  • Stick wax is softened over a flame
  • It should be rotated until it becomes shiny
  • It is repeated till the wax is warm throughout
  • The wax is then kneaded together and shaped approximately to the form of a prepared cavity
  • It is inserted into the cavity and held under finger pressure
  • Wax should be cooled gradually at mouth temperature
  • Withdraw the wax pattern carefully on the long axis of the preparation
• Indirect Technique
  • Die is lubricated with lubricant containing a wetting agent
  • An inlay pattern is prepared over it by either of the following methods
  • Dipping method
  • Die can be dipped repeatedly into the hot liquid wax
  • Addition method
  • The melted wax may be added in layers or painted on with a brush
  • The prepared cavity is overfilled and the wax is then carved to the proper contour

Properties Of Dental Waxes

Question 2. Classify and give the composition of various types of wax used in dentistry.
Answer:

Classification of Waxes:

1. According to Origin

• Plant origin
• Carnauba wax
• Ouricury
• Candelilla
• Japan wax
• Mineral wax
• Paraffin wax
• Microcrystalline
• Barnsdahl
• Ceresin
• Insect
• Beeswax
• Animal
• Spermaceti

2. According to Use

• Pattern waxes
• Inlay casting
• RPD casting
• Baseplate
• Processing waxes
• Boxing wax
• Utility wax
• Sticky wax
• Impression waxes
• Corrective
• Bite registration

3. ADA classification- based on flow

• Type 1 – inlay casting wax
• Class 1-soft
• Class 2-hard
• Type 2-baseplate wax
• Class 1-soft
• Class 2- hard
• Class 3- extra hard

Composition of Waxes Used in Dentistry:

Question 3. What are the ideal requisites of inlay wax? Write in detail the composition, reasons for wax distortion, and methods to control the same.
Answer:

Ideal Requisites of Inlay Wax: When softened, the wax should be uniform

• Color should contrast with the die materials
• There should be no flakiness or surface roughening
• It should not chip, flake or tear during carving
• During burnout, it should vaporize completely without residue
• The wax pattern should be completely rigid and dimensionally stable at all the times
• Should be plastic slightly above mouth temperature and become rigid when cooled to mouth temperature
• Should have a good flow when heated and set rigidly when cooled

Wax distortion:

Wax distortion Causes:

• If the wax is not at uniform temperature when inserted in the cavity
• Some portions may contract more than other
• If the wax is not held under uniform pressure during cooling
• If fresh wax is melted and added in an area of deficiency, the added wax will introduce stresses during cooling
• During carving some molecules of wax will be disturbed and stresses will result

Wax distortion Prevention:

• After removal avoid touching the wax pattern with the fingers as much as possible to prevent any temperature changes
• Invest the pattern immediately after removal from the mouth or die
• Once investment hardens, there will be no more distortion of the pattern
• Minimal carving and change in temperature
• Store it in the refrigerator if necessary

Inlay Wax Vs Casting Wax

Question 4. Classify waxes used in Dentistry. Describe the composition, manipulation, and uses of Inlay wax.
Answer:

Inlay Wax Classification:

1. According To Origin

• Plant origin
• Carnauba wax
• Ouricry
• Candelilla
• Japan wax
• Animal origin
• Spermaceti
• Insect
• Beeswax
• Mineral origin
• Paraffin wax
• Microcrystalline
• Barnsdahl o Ceresin

2. According to Use

• Pattern waxes
• Inlay casting
• RPD casting
• Base plate
• Processing wax
• Boxing wax
• Utility wax
• Sticky wax
• Impression was a Corrective
• Bite registration

3. ADA Classification – based On Flow

• Type 1 – inlay casting wax
• Class 1 – soft
• Class 2 – hard
• Type 2 – baseplate wax
• Class 1 – soft
• Class 2 – hard
• Class 3 – extra hard

Inlay Wax

Inlay Wax Manipulation

• Direct Technique
  • Stick wax is softened over a flame It should be rotated until it becomes shiny
  • It is repeated till the wax is warm throughout
  • The wax is then kneaded together and shaped approximately to the form of a prepared cavity o It is inserted into the cavity and held under finger pressure
  • Wax should be cooled gradually at mouth temperature
  • Withdraw the wax pattern carefully on the long axis of the preparation
• Indirect Technique
  • Die is lubricated with lubricant containing a wetting agent
  • An inlay pattern is prepared over it by either of the following methods
  • Dipping method – die can be dipped repeatedly into the hot liquid wax
  • Additional method – the melted wax may be added in layers or painted on with a brush
  • The prepared cavity is overfilled and the wax is then carved to the proper contour

Inlay Wax Uses:

• Type 1 – rarely used
• Type 2 – used in direct technique
• Type 3 – used in an indirect technique for inlays, onlays, and full crown

Dental Waxes Short Essays

Question 1. Causes and prevention of wax distortion.
Answer:

Wax Distortion Causes:

• If the wax is not at uniform temperature when inserted in the cavity
• Some portions may contract more than other
• If the wax is not held under uniform pressure during cooling
• If fresh wax is melted and added in an area of deficiency, the added wax will introduce stresses during cooling
• During carving some molecules of wax will be disturbed and stresses will result

Wax Distortion Prevention:

• After removal avoid touching the wax pattern with the fingers as much as possible to prevent any temperature changes
• Invest the pattern immediately after removal from the mouth or die
• Once investment hardens, there will be no more distortion of the pattern
• Minimal carving and change in temperature
• Store it in the refrigerator if necessary

Dental Waxes For Prosthodontics

Question 2. Impression waxes
Answer:

Impression Waxes

• Impression waxes are used to record non-edentulous portions of the mouth
• Generally used in combination with other impression materials

Dental Waxes Short Question And Answers

Question 1. Name types of inlay wax and other waxes used in dentistry.
(or)
Types of wax
Answer:

Types of Inlay Waxes:

Other Waxes Used In Dentistry:

1. Pattern Waxes

• Inlay casting
• RPD casting
• Baseplate

2. Processing Waxes

• Boxing wax
• Utility wax
• Sticky wax

3. Impression Waxes

• Corrective
• Bite registration

Question 2. Baseplate Wax
Answer:

Baseplate Wax

• It is referred to as modeling wax
• They are classified under pattern waxes because they are used in the construction of dentures and appliances made of acrylic and like materials

Baseplate Wax Uses:

• To make occlusal rims
• To form a contour of the denture after teeth are set
• To make patterns for orthodontic appliances and other prostheses

Classification Of Dental Waxes

Question 3. Sticky Wax
Answer:

Sticky Wax

• It is quite tacky when melted
• Becomes firm and brittle when cooled
• It is used to join and temporarily stabilize the components of a bridge before soldering the pieces of the broken denture before the repair

Question 4. Bite registration wax.
Answer:

Bite Registration Wax

• It is the most versatile
• Easy to manipulate
• When softened uniformly it remains soft for adequate working time
• The flow at 37.5°C varies from 2.5% to 22%
• It is susceptible to distortion on removal from the mouth

Bite Registration Wax Uses:

To record the relationship between upper and lower teeth

Bite Registration Wax Composition:

• Beeswax or paraffin or ceresin
• Some may contain aluminum or copper particles

Bite Registration Wax Supplied As:

U-shaped rods or wafers

Bite Registration Wax Procedure:

• The wax is softened in warm water
• The soft wax is placed in the patient’s mouth and asked to bite
• After the wax hardens wax is removed and cooled
• Replaced again in mouth to check
• The cast is poured into indentations formed by teeth and then mounted over an articulator

Question 7. Causes of distortion of inlay wax pattern.
Answer:

Causes Of Distortion Of Inlay Wax Pattern

• If the wax is not at uniform temperature when inserted in the cavity
• Some portions may contract more than other
• If the wax is not held under uniform pressure during cooling
• If fresh wax is melted and added in an area of deficiency, the added wax will introduce stresses during cooling
• During carving, some molecules of wax will be disturbed and stresses will result

Gypsum Products Important Notes

1. Gypsum Types

• Type 1- dental plaster, impression
• Type 2 – Dental plaster, model
• Type 3 – Dental stone/ hydro cal
• Type 4 – dental stone, high strength/ die stone
• Type 5 – dental stone, high strength, and high Expansion

2. Gypsum Terms

• Cast – a replica of the entire arch
• Die – a replica of a single-tooth
• Investment – when plaster is mixed with silica
• Divestment – it is an investment containing die stone

3. Gypsum Manufacture

• Calcination is the process of heating gypsum for the manufacture of plaster
• Types of calcinations

4. Gypsum Setting Reaction

• When the plaster is mixed with water calcium sulfate hemihydrate reacts with the water
• The solution gets supersaturated to form dihydrate
• Reaction is Exothermic
• (CaSO₄)₂. H₂O + 3H₂O → 2CaSO₄.2H₂O + unreacted (CaSO₄)₂ .H₂O + heat
• Hemihydrate + water -> dehydrate + unreacted hemihydrate
• Hemihydrate is four times more soluble than dihydrate

Read And Learn More: Dental Materials Question and Answers

5. Gypsum Setting Time – Factors Affecting It

• Accelerators:
  • It decreases setting time
  • Example: potassium sulfate, NaCl in low concentration, adding a small amount of slurry water in mixing water
• Retarders
  • It increases setting time
  • Examples: acetates, borates, citrate, NaCl in high concentration, colloids like gelatin, glue, agar
• Other factors
  • Calcination process
  • Fineness – Finer particles faster the setting
  • W:P ratio – more water increases setting time
  • Mixing – rapid mixing shorter the setting time
  • Temperature- increase in temperature shorter the setting time

Dental Gypsum Products

6. Gypsum Measurement Of Setting Time

• Initial set measurement
• Loss of gloss test
• Initial Gillimore needle test
• A small needle of 1/4 lb weight and diameter of 1/12” is used
• Final set measurement
• Vicat needle test – The needle used is 300 gm and 1 mm diameter
• Final Gillimore needle test – needle used is of 1 lb weight and 1/24” diameter

7. Gypsum Setting Expansion

• Normal setting Expansion
• Setting Expansion without water immersion
• Hygroscopic setting Expansion
• It is Expansion that occurs in water due to additional crystal growth potential

8. Factors Affecting Setting Expansion

• Factors that increase setting Expansion
  • Less W:P ratio
  • Setting underwater
  • Alpha hemihydrate
  • Finer particles
• Factors that decrease setting Expansion
  • More W:P ratio
  • Beta hemihydrate
  • Use of modifiers

9. Gypsum Wet and dry strength

• Wet/ Green strength
• Strength occurs due to the presence of Excess water than required is called wet strength
• Diy strength
• The strength that occurs when Examplecess of water is dried
• It is 2-4 times more than that of wet strength

Gypsum Products Long Essays

Question 1. What are the various gypsum products used in dentistry? Describe the composition, manipulation, and setting reaction of dental stone.
Answer:

Types of Gypsum Products Used in Dentistry:

• Type 1- Dental plaster, impression
• Type 2- Dental plaster, model
• Type 3- Dental stone
• Type 4- Dental stone, high strength
• Type 5- Dental stone, high strength, high Expansion

Dental Stone:

Dental Stone Composition:

• Alpha hemihydrate
• Coloring agent- 2-3%
• Potassium sulfate
• Borax-retarder

Dental Stone Manipulation:

• The proper water-powder ratio is determined
• Water is measured by graduated cylinder and powder by weighing balance
• Place a measured volume of water in a parabolic, smooth bowl first
• Add preweighed powder gradually to it
• Allow settling for 30 seconds to minimize air entrapment
• The mix is stirred vigorously
• Periodically wiping inside of the bowl with the spatula is done to ensure the wetting of all of the powder and breaking up of the lumps
• Continue mixing until a uniform smooth mix is obtained
• Vibrate the mix using a mechanical vibrator or by repeated tapping against the bench
• Pour it into the impression

Dental Stone Setting Reaction:

• Calcium sulfate hemihydrates react with water
• Dissolution of calcium sulfate hemihydrates
• Formation of a saturated solution of calcium sulfate
• Aggregation of less soluble calcium sulfate dehydrate
• Precipitation of crystals

Types Of Gypsum In Dentistry

Question 2. Write in detail the setting reaction of dental plaster and indicate various uses in dentistry.
Answer:

Dental Plaster Setting Reaction:

• When the plaster is mixed with water it takes up one and a half molecules of water
• A suspension is formed that is fluid and workable
• Hemihydrates dissolve until it forms a saturated solution
• This solution gets supersaturated to form dehydrate which gets precipitated
• As dehydrate precipitates the solution is no longer saturated with the hemihydrates, so it continues to dissolve
• Dissolution of hemihydrates and precipitation of dehydrate proceeds until no further dehydrate precipitates out of the solution
• The reaction is Exothermic
  (CaSO₄)₂. H₂O + 3H₂O → 2CaSO₄.2H₂O + unreacted (CaSO₄). H₂O + heat
• Hemihydrates + water-> dehydrate + unreacted hemihydrates + heat

Dental plaster Theories:

• Colloidal theory
• It proposes that when mixed with water, plaster enters into the colloidal state through a sol-gel mechanism
• In a sol state, hemihydrates particles are hydrated to form dehydrate, thereby entering into an active state
• As water is consumed, the mass converts to a solid gel
• Hydration theory
• Rehydrated plaster particles join together through hydrogen bonding to the sulfate groups to form a set material
• Dissolution precipitation theory- crystallization theory
• The most widely accepted theory
• According to it, the plaster dissolves and reacts to form gypsum crystals which interlock to form a set solid

Dentistry Uses:

• For making impressions in complete denture and maxillofacial prosthesis
• Bite registration material

Question 3. Classify gypsum products and write in detail about the chemistry and properties of type 2 gypsum products.
Answer:

Gypsum Products Classification:

• Type 1- Dental plaster, impression
• Type 2- Dental plaster, model
• Type 3- Dental stone
• Type 4- Dental stone, high-strength
• Type 4- Dental stone, high strength, high Expansion

Type 2 Gypsum Product- Dental Plaster, Model

Type 2 Gypsum Product Chemistry:

• When the plaster is mixed with water it takes up one and a half molecules of water
• A suspension is formed that is fluid and workable
• Hemihydrates dissolve until it forms a saturated solution
• This solution gets supersaturated to form dehydrate which gets precipitated
• As dehydrate precipitates the solution is no longer saturated with the hemihydrates, so it continues to dissolve
• Dissolution of hemihydrates and precipitation of dehydrate proceeds until no further dehydrate precipitates out of the solution
• The reaction is Exothermic
  (CaS0₄)₂. H₂0 + 3H₂0 → 2CaS0₄.2H₂0 + unreacted (CaS0₄)₂. H₂0 + heat
• Hemihydrates + water → dehydrate + unreacted hemihydrates + heat

Type 2 Gypsum Product Properties:

• Natural white
• Weak
• Compressive strength is low- 9 MPa
• Tensile strength- 0.6 MPa

Properties Of Dental Gypsum

Question 4. Describe in detail the setting reaction and the various factors that affect the dimensional stability of the dental stone.
Answer:

Factors Affecting Dimensional Stability:

• Mixing method
• Mechanical mixing decreases setting Expansion
• Water powder ratio

• Modifiers- accelerators and retarders
• Reduces setting Expansion

Question 5. What are the different methods of manufacturing of gypsum products? Write the setting reaction of gypsum. Mention the uses of gypsum products.
Answer:

Methods of Manufacturing Gypsum Products

• Dry calculations
  • Gypsum is ground and heated in an open kettle or kiln at a temperature of 110-130 degrees C
  • The process is called dry calcination
  • Beta calcium sulfate hemihydrates are formed, which have spongy, irregular large orthorhombic crystal particles
  • CaSO₄.2H₂O → CaSO_{4 1/2}  H₂O
  •  Type 1 and type 2 are formed by this method
• Wet Calculations
  • when gypsum is ground and heated under steam pressure at a temperature of 110-130 degrees C in a closed kettle or kiln or an autoclave the process is called wet calculations
  • Alpha calcium sulfate hemihydrates are formed, which consist of smaller, regularly shaped crystalline particles in the form of rods or prisms
  • Type 3 is formed by this method
  • Microscopically crystals of type 3 are in the form of rods and prisms
• Dehydration By Boiling With Chemicals
  • The gypsum is calcined by boiling it in a 30% calcium chloride solution
  • The chlorides are then washed away or autoclaved in the presence of sodium succinate 0.5%
  • Improved stone is manufactured by this method
  • These particles are denser among all three types
  • After controlled grinding, these powders have an even higher apparent density, and microscopically the particles that are cuboidal in shape yield an even stronger set of material

Gypsum Products Setting Reaction

• When the plaster is mixed with water, it takes up 1 1/2 molecules of water, i.e. it regains its water of crystallization and becomes calcium sulfate dehydrate
• A suspension is formed that is fluid and workable
• Hemihydrates dissolve until it forms a saturated solution
• This solution gets supersaturated to form dehydrate which gets precipitated
• As dehydrate precipitates the solution is no longer saturated with the hemihydrates, so it continues to dissolve
• Dissolution of hemihydrates and precipitation of dehydrate proceeds until no further dehydrate precipitates out of the solution
• The reaction is Exothermic
  (CaSO₄)₂. H₂O + 3H₂O → 2CaSO₄.2H₂O + unreacted (CaSO₄)₂. H₂O + heat
  Hemihydrates + water-> dehydrate + unreacted hemihydrates + heat

Gypsum Products In Dentistry MCQs

Gypsum Products Uses:

• General use
• For preparing statues and in construction work
• Medical use
• For splinting and making plaster casts
• In dentistry
• For making an impression of the mouth and face
• To make molds, casts, and dyes over which dental prostheses and restorations are made
• To mount the casts on articulators
• For bite registration
• As dental investment materials

Question 6. Discuss the plaster of Paris in detail.
Answer:

The Plaster Of Paris

• Type 1 or impression plaster is also known as plaster of Paris
• It was the earliest impression material in dentistry
• Because of its rigidity and nonelastic nature, it often had to be fractured for its removal from undercut areas in the mouth
• The fractured pieces were then reassembled outside and a cast was poured

Plaster Of Paris Uses:

• For making an impression in complete denture and maxillofacial prosthesis
• Bite registration material

Plaster of Paris Properties

• The setting time should be under accurate control
• The dentist must have sufficient time to mix, load the impression tray, carry the loaded tray to the patient’s mouth, and place it in position
• The plaster should harden promptly once in position so that there is minimum discomfort to the patient
• The desirable setting time is 3-5 min
• The setting Expansion should be low for better accuracy
• Both setting time and Expansion are controlled by modifiers
• The plaster should have enough strength to fracture cleanly without crumbling to facilitate its removal from undercut areas

Plaster of Paris Composition:

• Dental plaster
• Potassium sulfate
• Borax- retarder
• Coloring agents- to help the dentist and technician distinguish between the cast material and the impression
• Flavoring agents- to make it more acceptable to the patient
• It may sometimes contain potato starch to make it soluble
• After the cast hardens, the impression and cast are immersed in hot water
• The starch swells and the impression disintegrates, making it easy to separate the cast from the impression
• This is called soluble plaster

Uses Of Gypsum In Dentistry

Question 7. Define calculations. What is the process of calcination?
Answer:

Calculations Definition:

The process of heating gypsum for the manufacture of plaster is known as calcination

Process of Calcination:

• Dry calcinations
  • Gypsum is ground and heated in an open kettle or kiln at a temperature of 110-130 degrees C
  • The process is called dry calcination
  • Beta calcium sulfate hemihydrates are formed, which have spongy, irregular large orthorhombic crystal particles
  • CaSO₄.2H₂O → CaSO_{4 1/2}  H₂O
  • Type 1 and type 2 are formed by this method
• Wet calculations
  • When gypsum is ground and heated under steam pressure at a temperature of 110-130 degrees C in a closed kettle or kiln or an autoclave the process is called wet calculations
  • Alpha calcium sulfate hemihydrates are formed, which consist of smaller, regularly shaped crystalline particles in the form of rods or prisms
  • Type 3 is formed by this method
  • Microscopically crystals of type 3 are in the form of rods and prisms

Question 8. Identify the different gypsum products with reference.
Answer:

The different gypsum products with reference

Question 9. Normal and hygroscopic Expansion
Answer:

Normal And Hygroscopic Expansion

All gypsum products show a linear Expansion during setting, due to the outward thrust of the growing crystals during setting

Normal Setting Expansion:

Setting Expansion without water immersion is called normal setting Expansion

Normal Setting Expansion Importance

• Undesirable in the construction of cast
• Causes change in occlusal relations
• Desirable in case of investment materials

Hygroscopic Expansion:

• Expansion that occurs in water is called hygroscopic Expansion
• It is a physical Expansion
• When Expansion begins, Externally available water is drawn into pores forming a setting mass
• It maintains a continuous aqueous phase in which crystal growth takes place freely

Hygroscopic Expansion Importance:

Use to Expand some gypsum bonded investments

Setting Time Of Gypsum Products

Gypsum Products Short Essays

Question 1. High strength, high Expansion dental stone
Answer:

High Strength, High Expansion Dental Stone

• It is a Type 5 gypsum product
• It is the most recent gypsum product
• It has a high compressive strength
• Improved strength is due to a lower water-powder ratio
• Setting Expansion is increased from 0.1% to 0.3%
• It is to compensate for the shrinkage of base metal alloys

High Strength, High Expansion Dental Stone Uses:

Fabrication of cast crown due to inadequate Expansion

High Strength, High Expansion Dental Stone Contraindication:

In the production of dies of inlays due to unacceptably tight fits.

Question 2. Calcium sulfate hemihydrates
Answer:

Calcium Sulfate Hemihydrates

• The principal constituent of gypsum-based products such
• as dental plasters and stones are calcium sulfate hemihydrate
• The chemical formula is (CaSO₄)_{2 .}H₂O → CaSO_{4 1/2}  H₂O
• Depending on the method of calcination, different forms of hemihydrate can be obtained.
• They are:
• Alpha hemihydrate.
• It is called dental stone
• It consists of smaller, regularly shaped crystalline particles in the form of rods or prisms
• Alpha-modified hemihydrate o Beta hemihydrate
• It is known as dental plaster
• It consists of large, irregularly shaped orthorhombic crystal particles with capillary pores
• Alpha and beta forms differ in crystal size, surface area, and degree of lattice perfection
• Alpha hemihydrate requires much less water when it is mixed than beta hemihydrate
• Beta hemihydrate particles absorb more water because the crystals are more irregular in shape and porous

Question 3. Die stone
Answer:

Die Stone

• Type 4 and Type 5 gypsum products are used as die materials
• Type 4
• Have cuboidal shaped particles g Has reduced surface area
• Minimal setting Expansion
• Have a setting Expansion of 0.1% or less
• Type 5
• Have improved compressive strength e Setting Expansion is 0.3%
• Increased Expansion is used in compensation for the base metal alloy solidification shrinkage

Die Stone Advantages:

• In Expensive
• Easy to use
• Compatible with other impression materials
• Good strength
• Good working time
• Minimal shrinkage
• Have color contrast
• Has smooth surface
• Sets quickly

Die Stone Disadvantages:

• Brittle
• Susceptible to abrasion during the carving of the wax pattern

Classification Of Dental Gypsum

Question 4. Types of gypsum products
Answer:

Types of Gypsum Products Uses:

Question 5. Accelerators and retarders
Answer:

Accelerators And Retarders

Chemicals that decrease setting time are called accelerators while increase setting time are called retarders.

Question 6. Die materials
Answer:

Die Materials

A positive replica of a prepared tooth or teeth in a suitable hard substance on which inlays, crowns, and other restoration are made is called a die

Types of Die Materials:

• Gypsum products
• Type 4 dental stone
• Type 5 dental stone, high strength, high Expansion
• Type 5, dental stone, lignosulfonates
• Metal and metal-coated dies
• Electroformed
• Sprayed metals
• Amalgam
• Polymers
• Metal or inorganic-filled resins
• Epoxy
• Cement
• Silicophosphate
• Polyacrylic acid-bonded cement
• Refractory materials

Die Materials Ideal Requirements:

• Dimensionally stable
• Have good abrasion resistance
• Have smooth surface
• Reproduce surface details accurately
• Biocompatible
• Noninjurious
• Color should contrast with wax, porcelain, and alloys
• Easy and quick to fabricate
• In Expensive

Dental Gypsum Setting Reaction

Question 7. Factors controlling the setting time of plaster
Answer:

Factors Controlling The Setting Time Of Plaster

• Manufacturing Process
• If calculations are not complete, gypsum particles remain and the resulting product will set fast
• If soluble anhydrite is in Examplecess, the plaster will set fast
• If natural anhydrite is in Examplecess, plaster sets slow
• Fineness
• The finer the particle size of the hemihydrates, the faster the mix hardens because
• Hemihydrates dissolve fast
• Gypsum nuclei are more
• Crystallization is fast
• Water-powder ratio
• More water, fewer nuclei present per unit volume
• Thus setting time is prolonged
• Mixing
• The longer and more rapidly the plaster is mixed, the shorter the setting time
• Temperature
• On increasing the temperature the rate of the reaction increases slightly and the setting time is shortened
• Modifiers
• Chemical decreasing setting time is called accelerators while that which increases setting time is called retarders

Question 8. Dental stone
Answer:

Dental Stone

Dental Stone is a type 3 gypsum product

Dental Stone Composition:

• Alpha hemihydrate
• Coloring agent – 2-3%
• Potassium sulfate – accelerator
• Borax – retarder

Dental Stone Manipulation:

• The proper water-powder ratio is determined
• Water is measured by graduated cylinder and powder by weighing balance
• Place a measured volume of water in the parabolic, smooth bowl
• Add preweighed powder gradually to it
• Allow settling for 30 seconds to minimize air entrapment
• The mix is stirred vigorously
• Periodically wiping inside the bowl with the spatula is done to ensure the wetting of all of the powder and breaking up of the lumps
• Continue mixing until a smooth uniform mix is obtained
• Vibrate the mix using a mechanical vibrator or by repeated tapping against the bench

Dental Stone Properties:

• Compressive strength – 3000-5000 psi
• Setting Expansion – 0.06-0.12%
• Hardness – 82 RHN

Dental Stone Uses:

• For preparing master casts
• To make molds

Gypsum Products Short Question And Answers

Question 1. Dental stone
Answer:

Dental Stone Composition:

• Alpha hemihydrate
• Coloring agent- 2-3%
• Potassium sulfate
• Borax-retarder

Dental Stone Manipulation:

• The proper water-powder ratio is determined
• Water is measured by graduated cylinder and powder by weighing balance
• Place a measured volume of water in a parabolic, smooth bowl first
• Add preweighed powder gradually to it
• Allow settling for 30 seconds to minimize air entrapment
• The mix is stirred vigorously
• Periodically wiping inside of the bowl with the spatula is done to ensure the wetting of all of the powder and breaking up of the lumps
• Continue mixing until a uniform smooth mix is obtained
• Vibrate the mix using a mechanical vibrator or by repeated tapping against the bench
• Pour it into the impression

Advantages And Disadvantages Of Gypsum

Question 2. Measurement of setting time of dental plaster
Answer:

Dental Plaster Setting Time:

The time that elapses from the beginning of mixing until the material

Dental Plaster Measurement:

• Loss of gloss test
• As the reaction proceeds, some of the Examplecess water is used to form dehydrate
• As a result, the mix loses its gloss
• Exothermic reaction
• As the setting reaction is Exothermic, the temperature rise of the mass is used to measure the setting time
• Initial Gillmore test
• A small Gillmore needle having % lb weight and a diameter of 1/12″ is used
• The mixture is spread out and the needle is lowered onto the surface
• The time at which it no longer leaves an impression is called the initial set
• Vicattest
• A Vicat needle weighing 300 gm and a diameter of 1 mm is used
• The needle with a weighed plunger rod is supported and held just in contact with a mix
• Soon after the gloss is lost, the plunger is released
• The time elapsed until the needle no longer penetrates the bottom of the mix is known as the setting time
• Gillmore test for the final set
• A larger Gillmore having a 1 lb weight and diameter of 1/24″ is used
• The elapsed time at which this needle leaves only a barely perceptible mark on the surface is called the final setting time

Question 3. Hygroscopic Expansion
Answer:

Hygroscopic Expansion

• Expansion that occurs in water is called hygroscopic Expansion
• It is a physical Expansion
• When Expansion begins, Externally available water is drawn into pores forming a setting mass
• It maintains a continuous aqueous phase in which crystal growth takes place freely

Hygroscopic Expansion Importance:

Use to Expand some gypsum bonded investments

Question 4. Setting Expansion
Answer:

Setting Expansion

All gypsum products show a linear Expansion during setting, due to the outward thrust of the growing crystals during setting

1. Normal Setting Expansion:

Setting Expansion without water immersion is called normal setting Expansion

Normal Setting Expansion Importance:

• Undesirable in the construction of cast
• Causes change in occlusal relations
• Desirable in case of investment materials

2. Hygroscopic Expansion:

• Expansion that occurs in water is called hygroscopic Expansion
• It is a physical Expansion
• When Expansion begins, Externally available water is drawn into pores forming a setting mass
• It maintains a continuous aqueous phase in which crystal growth takes place freely

Hygroscopic Expansion Importance:

Use to Expand some gypsum bonded investments

Dental Plaster Vs Dental Stone

Question 5. Impression plaster Or plaster of Paris
Answer:

Impression Plaster Or Plaster Of Paris

• Type 1 or impression plaster is also known as plaster of Paris
• It was the earliest impression material in dentistry
• Because of its rigidity and nonelastic nature, it often had to be fractured for its removal from undercut areas in the mouth
• The fractured pieces were then reassembled outside and a cast was poured

Plaster of Paris Uses:

• For making an impression in complete denture and maxillofacial prosthesis
• Bite registration material

Plaster of Paris Properties:

• The setting time should be under accurate control
• The dentist must have sufficient time to mix, load the impression tray, carry the loaded tray to the patient’s mouth
• and place it in the position
• The plaster should harden promptly once in position so that there is minimum discomfort to the patient
• The desirable setting time is 3-5 min
• The setting Expansion should be low for better accuracy
• Both setting time and Expansion are controlled by modifiers
• The plaster should have enough strength to fracture cleanly without crumbling to facilitate its removal from undercut areas

Question 6. Bite registration paste
Answer:

Bite Registration Paste

• Materials used for recording the occlusal relationship between natural and artificial teeth are
• Impression plaster o Impression compound
• Wax
• Resin
• Metal oxide
• Zinc oxide eugenol paste
• ZOE paste is used often because
• It has a shorter setting time to prevent distortion
• Has more plasticizers to prevent it from sticking to teeth and rims
• Has almost no resistance to closing the mandible
• The record obtained is more rigid, more stable, and more accurate

Question 7. List various gypsum products and write about methods of testing setting time.
Answer:

Types of Gypsum Products Used In Dentistry:

• Type 1- Dental plaster, impression
• Type 2- Dental plaster, model
• Type 3- Dental stone
• Type 4- Dental stone, high strength
• Type 5- Dental stone, high strength, high Expansion

Methods for Measuring Setting Time:

• Loss of gloss test
• Exothermic reaction
• Initial Gillmore test
• Vicattest
• Gillmore test for the final test

Dental Plaster Vs Dental Stone

Question 8. Wet and dry strength
Answer:

Wet And Dry Strength

Wet strength is the strength obtained when the water is Excess of that required for hydration of the hemihydrates

• Dry strength – When excess water in the specimen is driven off by drying, the strength obtained is dry
• It may be two or more times as high as wet strength

Wet And Dry Strength Factors Affecting it:

• Water-powder ration- the greater the ratio- the less the dry strength
• Saturation- increase in mixing time, increases strength
• Modifiers- lowers the strength

Rigid Impression Materials Important Notes

1. Types of ZOE paste

• Type 1 – Hard – sets in 10 minutes
• Type 2 – Soft – sets in 15 minutes

2. Effect of adding water to ZOE paste

• Accelerates setting reaction
• Decreases setting time

3. Composition of ZOE paste

4. Uses of ZOE paste

• Making wash impression of edentulous ridges – most commonly used
• Bite registration
• Post-surgical pack
• Temporary relines
• Root canal filler
• Temporary filling material
• Luting agent

Read And Learn More: Dental Materials Question and Answers

5. Composition of impression compound

Impression Compound In Dentistry

Rigid Impression Materials Long Essays

Question 1. Classify impression materials. Write in detail about the composition, manipulation, and uses of impression compound
Answer:

Impression materials Classification

1. Based on setting mechanisms

• Chemical reaction
  • Plaster of Paris
  • Zinc oxide eugenol
  • Alginate
  • Nonaqueous elastomers
• Thermally-induced physical reaction

1. Compound wax
2. Agar

2. Based on elasticity

• Rigid materials
  • Plaster of Paris
  • Zinc oxide eugenol
  • Compound wax
• Elastic material
  • Agar
  • Alginate
  • Nonaqueous elastomers

Impression Compound:

Impression Compound Composition:

Impression Compound Manipulation:

• Impression compound may be softened over a flame or by immersion in a warm water bath
• It is then removed and usually kneaded with the fingers in order to obtain uniform plasticity
• An oversized tray is selected
• Material is loaded over it and quickly seated onto the tissues to be recorded
• It should be held gently in position until the impression cools below the fusion temperature
• Under no circumstances the impression should be disturbed or removed until it reaches oral temperature

Impression Compound Uses:

• For making a preliminary impression of edentulous ridges
• To make a special tray for the construction of dentures
• For border molding of an acrylic custom tray during the fitting of the tray
• For individual tooth impression
• To check undercuts in inlay preparations

Question 2. Classify impression materials. Write a note on the composition, manipulation, and various uses of zinc oxide eugenol paste
Answer:

Zinc Oxide Eugenol Paste:

Zinc Oxide Eugenol Paste Composition:

Zinc Oxide Eugenol Paste Manipulation:

• Mixing is done on an oil-impervious paper or a glass mixing slab
• The proper proportion of the two pastes is obtained by squeezing two strips of paste of the same length onto the mixing slab
• Two strips of contrasting color are combined with the first stroke of a flexible stainless steel spatula
• Mixing is continued for 1 minute until a uniform color is achieved
• The material is loaded into the tray by swiping on the sides of the tray and then spread in a smooth uniform motion
• It is placed in the mouth till it sets

Zinc Oxide Eugenol Paste Uses:

• As impression material for edentulous ridges
• As surgical dressing
• As bite registration paste
• As temporary filling material
• Root canal filling material
• Cementing medium
• Temporary relining material for dentures

Dental Impression Techniques      

Rigid Impression Materials Short Essays

Question 1. Impression compound
Answer:

Impression compound

Impression compound is a rigid impression material

Impression compound Properties:

• Fusion temperature
  • The temperature below which a definite reduction in plasticity occurs during the heating of the impression compound is called the fusion temperature
  • Impression compound exhibits a fusion temperature range rather than a fixed point
• Thermal properties
  • Thermal conductivity
• It has a very low thermal conductivity
  • Coefficient of thermal expansion
  • It is high due to the presence of resin and wax
• Flow
  • Good flow is desirable while impression making
• Dimensional stability
  • Relaxation of impression compound occurs in a comparatively short period of time
  • To avoid it, the cast is poured immediately
• Detail reproduction
  • Due to low flow and high viscosity, it has less detailed reproduction

Question 2. Zinc oxide eugenol impression paste
Answer:

Zinc oxide eugenol impression paste Properties:

• Dimensional stability
• Slight shrinkage occurs during hardening
• Consistency and flow
• The thick paste can compress the tissues
• Zinc oxide eugenol has a very good flow
• Rigidity and strength
• Resist distortion and fracture when removed from the mouth
• Compressive strength -7 Mpa
• Biological properties
• Causes a burning sensation in the mouth
• Can cause tissue irritation

Types Of Rigid Impression Materials

Rigid Impression Materials Short Question And Answers

Question 1. Impression compound
Answer:

Impression compound

Impression compound is a rigid, reversible impression material

Impression compound Classification:

• According to ADA specification no. 3, dental impression compounds are classified into two types as follows:
• Type 1- Impression compound
• Type 2-Tray compound

Impression compound Applications:

• For making a primary impression
• For individual tooth impression
• Peripheral tracing or border molding
• To check undercuts in inlay preparation

Question 2. Zinc oxide eugenol paste
Answer:

Zinc oxide eugenol paste

Zinc oxide eugenol is a rigid impression material

Zinc oxide eugenol paste Advantages:

• It has a sufficient body so as to make up for any minor under-extensions in the tray itself during impression making
• It has enough working time to complete border molding
• Can be checked in the mouth repeatedly
• Registers accurate surface details
• Does not require any separating media since it does not stick to the cast material
• Minor defects can be corrected locally without discarding a good impression

Zinc oxide eugenol paste Disadvantages:

• It requires a special tray for impression making
• It is sticky in nature and adheres to tissues
• Eugenol can cause a burning sensation and tissue irritation
• It cannot be used for making an impression of title and undercut areas as it is inelastic in nature

Rigid Impression Materials In Dentistry 

Question 3. Noneugenol paste
Answer:

Noneugenol paste

• Noneugenol pastes were developed to overcome the disadvantages of eugenol like
• Burning sensation
• Disagreeable taste
• Chronic gastric irritation

Noneugenol paste Composition

• Base Paste
  • Zinc oxide
  • Gum
  • Lorothiodol- fungicide
• Reactor
  • Coconut fatty acid
  • Rosin- a thickening agent
  • Chlorothymol- bacteriostatic
  • Antibiotics like tetracyclines may be incorporated
• Reaction
  • Zinc oxide reacts with carboxylic acid
  • This reaction is not affected by temperature and humidity

Zinc Oxide Eugenol Impression Material 

Question 4. Mention accelerator for ZOE paste.
Answer:

Mention accelerator for ZOE paste

Accelerators for ZOE paste are

1. Calcium chloride
2. Zinc acetate
3. Primary alcohols
4. Glacial acetic acid