Dental Materials

Impression Materials Important Notes

1. Classification Of Impression Materials

• Based On Setting Mechanisms
  • Chemical reaction
    • Plaster of Paris — Zinc oxide eugenol
    • Alginate
    • Nonaqueous elastomers
  • Thermally-induced physical reaction
    • Compound wax
    • Agar
• Based On Elasticity
  • Rigid materials
    • Plaster of Paris
    • Zinc oxide eugenol
    • Compound
• Elastic Material
  • Agar
  • Alginate
  • Non-aqueous elastomers

2. Types Of Elastomers

3. Addition Silicone

• Addition Silicone are type II silicone impression materials
• In addition Silicone undergoes an additional type of polymerization terminating in vinyl groups and cross-linked with hydride group
• In addition Silicone has very little residual polymerization
• Thus it is the most dimensionally stable
• Addition Silicone is highly biocompatible
• Addition Silicone Advantages:
  • Dimensionally stable
  • Adequate tear strength
  • Pleasant odor and color
  • Multiple casts can be made from one impression
  • No volatile byproduct
• Addition Silicone Disadvantage
  • Impurities evolve hydrogen gas
  • This hydrogen gas produces pinpoint voids in the stone casts if poured immediately
  • It is prevented by
    • Adding platinum or palladium
    • By delaying the pouring of impression

Read And Learn More: Dental Materials Question and Answers

4. Composition Of polyether Impression Material

5. Impression Techniques

• Multiple Mix technique
  • Two separate mixes are made
  • Heavy body material is placed in the tray
  • Light body is loaded in a syringe
  • Impression is made

• Single Mix
  • Only one mix is made
  • Medium body material is used
  • Part of it is loaded in a tray and part is loaded in a syringe
  • Impression is made

Alginate Impression Material

6. Causes Of The Rough Surface Of Elastomers

• Incomplete polymerization caused by premature removal from the mouth
• The improper ratio of mixing components
• Too rapid polymerization caused by high humidity and high temperature

Impression Materials Long Essay

Question 1. State the properties and uses of rubber-based materials
Answer:

Rubber Based Materials:

Rubber Based Materials Synonyms:

• Rubber impression materials
• Elastomeric impression materials

Rubber Based Materials Properties:

• They are accurate impression material- they excellently reproduce the surface details
• They are dimensionally stable
• Available in various viscosity
• The low viscosity is capable of reproducing even very fine details
• They are generally hydrophobic
• Resilience
• They are flexible with near-complete elastic recovery
• Its coefficient of thermal expansion Is high
• It cannot melt, before melting they pass Into a gaseous state
• They swell In the presence of certain solvents
• They are Insoluble
• They have lower creep resistance
• Tear strength is excellent
• They can be electroplated
• As they don’t adhere well to the Impression tray, tray adhesive is used
• It has a shelf life of about two years
• It may cause dimensional changes due to

1. Curing shrinkage
2. Loss of byproducts
3. Hydrophilic nature
4. Thermal contraction
5. Delayed pouring of cast

Rubber Based Materials Uses:

• In fixed partial dentures for Impressions of prepared teeth
• Impressions of dentulous mouths for removable partial dentures
• Impressions of edentulous mouths for complete dentures
• Polyether Is used for border molding
• For bite registration
• Silicon Is used for making refractory casts

Dental Impression Techniques

Question 2. Advantages and disadvantages of elastomeric Impression material
Answer:

Advantages And Disadvantages Of Elastomeric Impression Material

Question 3. What are elastomers? Write in detail about the types, composition, properties, and manipulation of additional silicone impression material.
Answer:

Elastomers:

• It is a lightly cross-linked impression material that exhibits elastic behavior after setting.
• It refers to a group of rubbery polymers, which are either chemically or physically cross-linked

Addition Silicones:

Addition Silicones Types:

• It is available in four viscosities
• Light bodied
• Medium bodied
• Heavy bodied
• Putty

Addition Silicones Composition:

Addition Silicones Properties:

• Setting time-5-9 minutes
• Mixing time- 45 seconds
• Shelf life 1 to 2 years

Manipulation:

1. For The Paste

• Dispense equal length of base and catalyst over a mixing pad
• Incorporate first the catalyst into the base
• Mixing is done by moving the spatula back and forth on the mixing pad
• The process is continued until the mixed paste is uniform in color with no streaks of the base or catalyst

2. For Putty

• An equal number of scoops of each putty is dispensed
• Material is then kneaded with fingers until a uniform color is obtained

Question 4. Classify impression materials and describe in detail about contents, setting, and properties of silicone rubber base impression materials
Answer:

Silicone Rubber Classification:

1. Based On Setting Mechanisms

• Chemical Reaction
  • Plaster of Paris
  • Zinc oxide eugenol
  • Alginate
  • Nonaqueous elastomers
• Thermally-Induced Physical Reaction
  • Compound wax
  • Agar

2. Based On Elasticity

• Rigid Materials
  • Plaster of Paris
  • Zinc oxide eugenol
  • Compound wax
• Elastic Material
  • Agar
  • Alginate
  • Nonaqueous elastomers

Silicon Rubber Based Materials: Silicon rubber-based materials are

1. Condensation silicone
2. Addition silicone

Impression Materials Short Essays

Question 1. What are nonaqueous elastomers and write any one of their compositions?
Answer:

Nonaqueous Elastomers:

Nonaqueous elastomers are

1. Polysulphides
2. Polyether
3. Condensation silicone
4. Addition Silicones

Accuracy Of Impression Materials

Question 2. Ideal requirements of Impression materials
Answer:

Ideal Requirements:

• They should be fluid enough to adapt to oral tissues
• Should be viscous enough to be contained in the tray that is seated in the mouth
• While in the mouth, they should set into a rubbery or rigid solid in a reasonable amount of time
• The set impression should not tear or distort when removed
• The impression made should be dimensionally stable
• Stability should be maintained after the removal of a cast so that a second or third cast can be made
• The material should be biocompatible
• It should be cost-effective
• Should be nontoxic
• Should be acceptable to patients with pleasant odor and color
• Should have an adequate shelf life
• Easy to use with minimum equipment
• Should have adequate strength
• Should be compatible with the die and cast materials
• Should be able to be electroplated

Question 3. Polysulphides
Answer:

Polysulphides

Polysulphides were the first elastomeric impression material to be introduced

Polysulphides Advantages:

• Long working time
• High tear resistance
• Margins easily seen
• Cheaper
• Excellent surface reproduction
• Good flexibility
• Good shelf life
• Can be electroplated

Polysulphides Disadvantages:

• Unpleasant odor and color
• Messy to work
• Extremely viscous and sticky
• Exhibit pseudo plasticity
• High shrinkage occurs
• Hydrophobic

Polysulphides Composition:

• Base
  • Liquid polysulfide polymer
  • Inert fillers
• Reactor
  • Lead dioxide
  • Dibutyl phthalate
  • Sulfur
  • Other substances like magnesium stearate and deodorants

Advantages And Disadvantages Of Impression Materials

Question 4. Elastomers
Answer:

Elastomers

• A lightly cross-linked impression material that exhibits elastic behavior after setting is called elastomer
• They contain large molecules with weak Interaction between them
• They are liquid polymers that can be converted to solid rubber at room temperature

Elastomers Types:

1. According to Chemistry

• Polysulphides
• Condensation silicone
• Addition silicone
• Polyether

2. According to Viscosity

• Light body
• Medium body
• Heavy body
• Very heavy body

3. According to Elasticity

• Type 1
• Type 2
• Type 3

4. According to Wettability

• Hydrophilic
• Hydrophobic

Elastomers Uses:

• In fixed partial dentures for impressions of prepared teeth
• Impressions of dentulous mouths for removable partial dentures
• Impressions of edentulous mouths for complete dentures
• Polyether is used for border molding
• For bite registration
• Silicon is used for making refractory casts

Question 5. Reline technique for elastomeric impression
Answer:

Reline Technique For Elastomeric Impression

• Reline technique is also called the two-stage putty wash technique
• It is used to minimize the effect of Polymerisation shrinkage

Elastomeric Impression Technique:

• The thick putty material is made using a stock tray
• Results in preliminary impression
• Spacing is provided by either
  • Cutting away some of the tray putties or
  • Using a thin polyethylene sheet between putty and prepared tooth
• The mix of thin consistency wash material is placed into putty
• Putty wash and tray are seated into the mouth
• The final impression is made

Classification Of Impression Materials

Question 6. Condensation silicon
Answer:

Condensation Silicon

Condensation silicone is one of the silicone impression material

Condensation Silicon Composition:

1. Base

• Polymethyl siloxane
• Colloidal silica
• Color pigments

2. Accelerator

• Orthoethyl silicate
• Stannous octoate

Condensation Silicon Advantages:

• Putty for custom trays
• Clean and pleasant
• Good working time
• Easily seen margins
• Pleasant color and odor
• Can be electroplated

Condensation Silicon Disadvantages:

• Curing shrinkage
• Less shelf life
• Hydrophobic

Impression Materials Short Question And Answers

Question 1. Rubber-based impression material
Answer:

Rubber-Based Impression Material

• It is a lightly cross-linked impression material that exhibits elastic behavior after setting.
• It refers to a group of rubbery polymers, which are either chemically or physically cross-linked

Rubber-Based Impression Material Uses:

• In fixed partial dentures for impressions of prepared teeth
• Impressions of dentulous mouths for removable partial dentures
• Impressions of edentulous mouths for complete dentures
• Polyether is used for border molding
• For bite registration
• Silicon is used for making refractory casts

Properties Of Dental Impression Materials

Question 2. Addition silicone
Answer:

In addition, silicone is the most widely used impression material

Addition Silicone Advantages:

• Pleasant odor and color
• Excellent surface reproduction
• Dimensionally stable
• Good tear strength
• Can be electroplated

Addition Silicone Disadvantages:

• Cause allergic reactions
• Hydrophobic
• Less flexible
• Extra spacing is required in impression trays

Question 3. Cross-linking
Answer:

Cross-linking

The joining of polymer chains to form a three-dimensional network structure is called cross-linking

Question 4. Polyether
Answer:

Polyether

• Polyether was introduced in Germany
• It has good mechanical properties and dimensional stability

Polyether Advantages:

• Fast setting
• Clean
• AutomLx dispense
• Easily seen margins
• Good stability
• Hydrophilic
• Can be electroplated

Polyether Disadvantages:

• Cause allergic reactions
• Heat decreases the setting time

Properties Of Dental Impression Materials

Question 5. Tray adhesives.
Answer:

Tray Adhesives

• Tray adhesives are tacky liquids that are applied with a brush
• They are used to obtain the most accurate impression possible by adhering impression material to the tray
• Tray Adhesives is advisable to use tray adhesive on all trays before making an impression
  Each elastomer has a specific adhesive

Tray Adhesives Method Of Application:

• Apply a thin layer of tray adhesive to the tray using the applicator brush
• Allow to dry for at least 3 minutes
• Load the tray with impression material
• Make an impression

Question 6. Multiple mix impression technique of elastomers.
Answer:

Multiple Mix Impression Techniques Of Elastomers

• Two separate mixes are made
• Heavy body material is placed in the tray
• Light body is loaded in a syringe
• Impression is made

Mechanical Properties Important Notes

1. Stress

• Stress is force per unit area perpendicular to the force direction
• Stress Types:
  • Tensile stress
  • Shear stress
  • Compressive stress

2. Strain

• Strain is the change in length per unit length of an object subjected to stress
• Strain Types:
  • Elastic strain
  • Plastic strain

Read And Learn More: Dental Materials Question and Answers

3. Hardness

• Hardness is resistance to abrasion and indentation
• Hardness tests
  • Macro hardness test – Brinell and Rockwell
  • Micro hardness tests – Knoop and Vickers test

4. Compressive, Tensile, and Shear Stress

5. Ductility

• It is the ability of a metal to be drawn into wire under tensile load without rupture
• It can be measured by percent elongation and cold blend test

6. Malleability

It is the ability of a material to sustain permanent deformation without fracture under compression.

7. Modulus of elasticity

• The stress/ strain ratio within the proportional limit is called the elastic modulus or Young’s modulus
• It measures the relative rigidity or stiffness of the material

8. Resilience

• It is the amount of energy absorbed by a structure when it is stressed to the proportional limit
• The elastic area of the stress-strain graph gives resilience
• It is measured by R
  • R= P²/2E
  • R = resilience
  • P = proportional limit
  • E = modulus of elasticity

9. Proportional limit

• It is the maximum stress at which stress is proportional to strain and above which plastic deformation occurs
• It represents the maximum stress above which stress is no longer proportional to strain

10. Poisson’s ratio

Poisson’s ratio = Lateral strain/ Axial strain.

Mechanical Properties Of Dental Materials

Mechanical Properties Short Essays

Question 1. Define stress and strain. Name types of stresses and strains. How are these two properties important in the study of dental materials?
Answer:

Stress And Strain

Importance Of Stress And Strain:

• Stress and strain are related to the force applied
• Stress is the displacing force in a given area while strain is the change in dimension
• In the oral cavity, many complex forces exist which tend to deform the material of the restorations
• Thus, it is important to know about the stress and strain of the material to interpret how the material will behave under the effect of such forces

Question 2. Stress and strain relation.
Answer:

Stress And Strain Relation

For each material, there is a stress-strain proportional relationship establishing a stress-strain curve

• As shown in a curve, stress is directly proportional to strain up to point P called the proportional limit, and elastic deformation occurs
• At this point, the object will withstand the forces applied without permanent deformation
• It determines the elasticity of a material
• When the applied load exceeds this point, irreversible deformation occurs resulting in plastic deformation
• After this point, stress is no longer proportional to strain
• The area under the elastic portion of the curve represents resilience
• This indicates the amount of energy required to deform the material to its proportional limit
• The area under the elastic and plastic portion of the curve indicates the toughness of a material.

Types Of Dental Materials And Their Properties

Question 3. Types of stresses
Answer:

Types of Stresses Are:

1. Tensile Stress:

Tensile Stress is the ratio of tensile force to the original cross-sectional area perpendicular to the direction of the applied force

Tensile Stress Direction Offered:

The two forces acting are directed away from each other in the same straight line

Tensile Stress Effect:

The load tends to stretch or elongate a body

2. Shear Stress:

Shear Stress is the ratio of force to the original cross-sectional area parallel to the direction of the force applied

Shear Stress Direction of Forces:

The two forces are directed parallel to each other

Shear Stress Effect:

Shear Stress resists sliding one portion of a body over another

3. Compressive Stress:

Compressive Stress is the ratio of compressive force to cross-sectional area perpendicular to the axis of applied force

Compressive Stress Direction of Forces:

The forces are directed toward each other in the same line

Compressive Stress Effect:

The load tends to shorten a body

Question 4. Hardness (or) Hardness tests
Answer:

Hardness Definition:

Hardness is the resistance of a material to plastic deformation measured under an indentation load

Factors Affecting Hardness:

• The following factors influence the hardness of a material:
• Strength
• Proportional limit
• Ductility
• Malleability

Hardness Tests:

• Microhardness Tests:
  • Knoop hardness test
  • Vickers hardness test
• Macrohardness Tests:
  • Brinell Hardness test
  • Rockwell hardness test

Stress And Strain In Dental Materials

Question 5. Ductility and malleability
Answer:

1. Ductility Definition:

It is the ability of a material to withstand large permanent deformation under a tensile load before it fractures

Ductility Factors Affecting It

• Ductility is dependent on tensile strength
• Ductility decreases as the temperature raises

Ductility Measurements: Ductility is measured by three methods

• By measuring the percentage elongation after fracture
  • It is a common method
  • The initial length of the wire is measured before the fracture
  • This is compared with that of an increase in length after fracture
• Measuring reduction in cross-sectional area of fractured ends

The percentage of decrease in the cross-sectional area of the fractured end is calculated and compared to that of the cross-sectional area before the fracture

•  Cold bend test
  • The material is clamped in a vise and bent around a mandrel of a specified radius
  • The number of bends to fracture is counted

2. Malleability Definition:

Malleability is the ability of a material to sustain permanent deformation without fracture under compression

Malleability Importance: Metals according to their ductility and malleability are

1. First is gold- It is the most ductile and malleable
2. Second is silver
3. Third in ductility is platinum and in malleability is copper

• The ductility is assessed by the stress-strain curve
• After fracture, the stress reduces to zero.

Mechanical Properties Short Question And Answers

Question 1. Name types of strength. Discuss the importance of strength in the study of dental materials
Answer:

Strength Definition:

Strength is the stress necessary to cause either fracture or a specified amount of plastic deformation.

Strength Types:

1. Tensile Strength Or Ultimate Tensile Strength: It is the maximal stress the structure will withstand before the rupture
2. Shear Strength: It is the maximal shear stress at the point of fracture of a test specimen
3. Compressive Strength: It is the compressive stress within a compression test specimen at the point of fracture
4. Flexural Strength: It is the force per unit area at the point of fracture of a test specimen subjected to flexural loading
5. Impact Strength: It is the energy required to fracture a material under an impact force

Importance Of Strength:

• Strength describes the types of deformation that can occur
• It measures the interatomic forces over the stressed structure
• Shear strength is used to study the interface between two materials
• Transverse strength is used to test denture base resins and long-span bridges

Question 2. Modulus of elasticity
Answer:

Modulus Of Elasticity Synonyms:

• Young’s modulus
• Elastic modulus

Modulus Of Elasticity Definition:

Modulus Of Elasticity is the relative stiffness or rigidity of material within the elastic range.

Modulus Of Elasticity Measurement:

• It is the ratio of stress to strain and is described as E.
• E= Stress / Strain

Modulus Of Elasticity Importance:

• It indicates that the less the strain, the greater will be the stiffness
• Elastic modulus has a constant value
• It is not affected by the amount of plastic and elastic stress that is induced in the material
• It is independent of the ductility of the material
• By determining Young’s modulus of enamel and dentin, it describes that

1. Enamel is stiffer and more brittle
2. Dentin is more flexible and tougher

Modulus Of Elasticity Unit:

Ciiganewtons per square meter ( GN/ m²)

Elasticity Of Dental Materials

Question 3. Proportional limit
Answer:

Proportional Limit Definition:

Proportional Limit is the maximum stress at which stress is proportional to strain and above which plastic deformation occurs

Proportional Limit Importance:

• The proportional Limit is the greatest elastic stress possible in accordance with Hooke’s law
• Proportional Limit represents the maximum stress above which stress is no longer proportional to strain

Question 4. Resilience
Answer:

Resilience Definition: Resilience is a relative amount of elastic energy’ absorbed within a unit volume of a structure when it is stressed to its proportional limit.

Resilience Measurement: It is measured in terms of the modulus of resilience, R.

• R = P²/2E where,
• R- Modulus of resilience
• P- Proportional limit
• E- Modulus of elasticity
• Resilience can be illustrated by the stress-strain curve
• The area bounded by the elastic region is a measure of resilience

Question 5. Elastic limit
Answer:

Elastic Limit Definition:

Elastic Limit is defined as the greatest stress to which a material can be subjected such that it returns to its original dimensions when the force is released

Elastic Limit Importance:

• Elastic Limit describes the elastic behavior of the material
• Elastic Limit can measure any type of stress

Mechanical Testing Of Dental Materials

Question 6. Poisson’s Ratio
Answer:

Poisson’s Ratio

• When a tensile force is applied along one axis to produce elongation, compressive strain is produced at right angles proportionately.
• It is related to the nature and symmetry of the interatomic bonding forces
• For an ideal isotropic material of constant volume, the ratio is 0.5
• Poisson’s ratio = Lateral strain / Axial strain

Question 6. Strain hardening
Answer:

Strain Hardening Synonyms:

• Cold working
• Work hardening

Strain Hardening Features:

• The process of plastically deforming a metal usually at room temperature is called cold-working
• When a metal is stressed beyond its proportional limit, the hardness, and strength of the metal increase but the ductility decreases
• Repeated plastic deformation of the metal leads to the brittleness of the wire and it will fracture
• In the stress-strain curve, as the elastic modulus remains constant, the plastic deformation part of the curve would be decreased.

Question 7. Define: Elasticity and stiffness
Answer:

Elasticity: Elasticity is the tendency of solid materials to return to their original shape after being deformed.

Stiffness:

• Stiffness is the ratio of the force required to create a specified deflection
• Stiffness is the ability of a material to resist bending or stretching
• A stiff material has a high Young’s modulus.

Question 8. Yield strength
Answer:

Yield Strength

• Yield Strength is the stress at which a test specimen exhibits a specific amount of plastic strain.
• Yield strength is greater than the proportional limit
• If it exceeds the masticatory stresses, the restorations may not function any longer.

Question 9. Toughness
Answer:

Toughness

• Toughness is the ability of a material to absorb elastic energy and to deform plastically before fracture
• Toughness increases with increases in strength and ductility
• The greater the strength and the higher the ductility, the greater the toughness
• Tough material is generally strong.

Compressive Strength Of Dental Materials

Question 10. Ductility and malleability
Answer:

Ductility:

• Ductility is the ability of a material to withstand large permanent deformation under a tensile load before it fractures
• Factors affecting it are:
  • It is dependent on tensile strength
  • It decreases as the temperature raises

Malleability:

Malleability is the ability of a material to sustain permanent deformation without fracture under compression.

Biocompatibility Of Dental Materials Short Essays

Question 1. Evaluation of toxicity of dental materials
Answer:

Evaluation Of Toxicity Of Dental Materials

• There are three basic types of tests to evaluate the toxicity of dental materials
• They are as follows:

Biocompatibility Of Dental Materials

Question 2. Biocompatibility of dental materials
Answer:

Biocompatibility Of Dental Materials

• Biocompatibility is the ability of a material to elicit an appropriate biological response in a given application in the body
• It is the interaction between the body and the material
• It is a dynamic interaction
• It depends upon

1. Location of the material
2. Its duration in the body
3. Properties of the material
4. The health of the host
5. Biocompatibility in a young person differs from that in an older individual
6. A biological interface is created when the material is placed in the body
7. Biological tests are

• In vitro tests
• Animal tests
• Usage tests

Read And Learn More: Dental Materials Question and Answers

Dental Materials Clinical Guidelines:

1. Define The Use Of The Material

• First how the material will be used must be considered
• Next, the composition of the material is considered
• Even very small changes in the composition or processing of a material can alter its biocompatibility

2. Define How The Material Has Been Tested

• Which test is to be used must be decided
• The testing conditions must be as relevant as possible

3. Think In Terms Of Risk And Benefit

Though no material is 100% safe, the use of materials in the body requires a risk-benefit analysis

Types Of Biocompatible Dental Materials

Biocompatibility Of Dental Materials Short Question And Answers

Question 1. Toxic effects of materials
Answer:

1. Toxic Effects Of Materials Toxicity

Some of the materials may release substances into the patient’s body in adequate amounts and cause toxicity

2. Toxic Effects Of Materials Inflammation

• It involves the activation of the host’s immune system
• It may result from toxicity or allergy
• It results in edema of the tissue with infiltration of inflammatory cells and other lymphocytic cells

3. Toxic Effects Of Materials Allergy

• Allergic reactions occur when the body treats the material as foreign material
• It involves T and B lymphocytes, monocytes, or macrophages

Biocompatibility In Dentistry

4. Toxic Effects Of Materials Mutagenic Reactions

• It alters the base pair sequences of the DNA in cells
• They are caused by
• Direct interactions between a substance and DNA
• Indirect alterations in cellular processes

5. Toxic Effects Of Materials Local Effects

Local effects occur in the pulp of the tooth, in the periodontium, at the root apex, in buccal mucosa or tongue

6. Toxic Effects Of Materials Systemic Effects

It involves the distribution of materials via simple diffusion or through lymphatics or blood vessels

7. Toxic Effects Of Materials Immunotoxicity

It may result from a material causing either an increase or decrease in cellular function

Biocompatibility Testing Methods In Dentistry

Question 2. Microleakage and its Significance
Answer:

Microleakage And Its Significance

• When the restorative material fails to adhere well to the tooth surface, a microscopic space exists between the restoration and the preparation cavity
• Fluids, microorganisms, and oral debris can penetrate freely along this space
• This phenomenon is called microleakage
• It leads to

1. Secondary caries
2. Stain or discoloration
3. Sensitivity