Materials in Dentistry - Lecture 2
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Questions and Answers

What defines a polymer?

  • A material made of large molecules formed from repeating units called monomers (correct)
  • A simple molecule that cannot be broken down further
  • A synthetic material composed entirely of metals
  • A material formed from small molecules connected by ionic bonds

Which type of bond is primarily responsible for the structure of polymers?

  • Hydrogen bonds between chains
  • Ionic bonds within the polymer chain
  • Van der Waals forces between molecules
  • Covalent bonds between monomers (correct)

Which of the following is NOT a dental application of polymers?

  • Cements
  • Composite filling materials
  • Metal implants (correct)
  • Impression materials

What is the characteristic of polar bonds in polymers?

<p>They contribute to low strength and high water sorption (D)</p> Signup and view all the answers

What describes a random copolymer?

<p>Monomers mixed in a relatively random manner along the polymer chain (C)</p> Signup and view all the answers

Which polymer is derived from methyl methacrylate?

<p>Poly-methyl methacrylate (PMMA) (D)</p> Signup and view all the answers

What advantage do polymers offer over metals in dental materials?

<p>Lightweight and flexibility (B)</p> Signup and view all the answers

Which of these is an example of a net advantage of using composite materials?

<p>They provide superior aesthetic results (D)</p> Signup and view all the answers

What characterizes a graft copolymer?

<p>It consists of a main chain with one or more side chains of another monomer attached. (B)</p> Signup and view all the answers

Which effect is NOT associated with extensive cross-linking in polymers?

<p>Increased ductility (A)</p> Signup and view all the answers

How does the molecular weight (M.W) of a polymer affect its properties?

<p>Higher M.W results in a higher melting range and increased stiffness. (A)</p> Signup and view all the answers

What is the clinical significance of polymerization?

<p>Incomplete polymerization can lead to irritation of soft tissues. (D)</p> Signup and view all the answers

Which type of polymerization results in low shrinkage?

<p>Addition polymerization (A)</p> Signup and view all the answers

What is a common characteristic of linear copolymers?

<p>They consist of monomers connected in a sequential manner. (A)</p> Signup and view all the answers

Which of the following is a characteristic of cross-linked polymers?

<p>They exhibit a three-dimensional network structure. (D)</p> Signup and view all the answers

What does condensation polymerization create as a by-product?

<p>A smaller molecule such as water or alcohol (B)</p> Signup and view all the answers

What initiator is used in the polymerization process to generate free radicals?

<p>Benzoyl peroxide (D)</p> Signup and view all the answers

What is a key characteristic of thermoplastic polymers?

<p>They can be reshaped upon heating. (D)</p> Signup and view all the answers

Which factor is NOT associated with the polymerization process?

<p>Volume expansion (D)</p> Signup and view all the answers

What causes the inhibition of polymerization?

<p>Presence of impurities in the monomer (A)</p> Signup and view all the answers

During which step of the polymerization reaction does the chain reaction theoretically continue until all monomers are converted to polymers?

<p>Propagation (C)</p> Signup and view all the answers

What is a common example of a thermoplastic polymer?

<p>Non-cross linked PMMA (D)</p> Signup and view all the answers

What is the significance of adding inhibitors to monomers during storage?

<p>To prevent polymerization and extend shelf life (C)</p> Signup and view all the answers

What effect does polymerization typically have on the temperature of the reaction environment?

<p>It generates heat as the reaction is exothermic. (A)</p> Signup and view all the answers

Which advantage is primarily associated with brittle materials?

<p>High compressive strength (D)</p> Signup and view all the answers

What is a characteristic disadvantage of ionic materials?

<p>Low impact strength (A)</p> Signup and view all the answers

Which material feature primarily contributes to creep behavior?

<p>Covalent microstructure (B)</p> Signup and view all the answers

Which of the following is NOT an advantage of composite polymers?

<p>Polymerization shrinkage (B)</p> Signup and view all the answers

What is a common disadvantage of materials with a crystalline microstructure?

<p>Creep and sag (A)</p> Signup and view all the answers

Which feature is a disadvantage associated with the various components of composite polymers?

<p>Tendency to discoloration (B)</p> Signup and view all the answers

Which of the following is a property of metalic materials in composite polymers?

<p>Strong and stiff (C)</p> Signup and view all the answers

What is a primary factor that limits the performance of brittle materials?

<p>Susceptibility to micro-cracks (C)</p> Signup and view all the answers

What type of bonding primarily holds the chains in thermosetting polymers?

<p>Primary covalent bond (B)</p> Signup and view all the answers

How do thermosetting polymers behave upon reheating?

<p>They decompose at high temperatures (B)</p> Signup and view all the answers

Which of the following is a characteristic property of composites?

<p>Ability to control material properties (B)</p> Signup and view all the answers

What is a notable disadvantage of composite materials?

<p>Tendency to discoloration (A)</p> Signup and view all the answers

Which of the following materials is primarily used in making dental crowns and bridges?

<p>Ceramics and glasses (C)</p> Signup and view all the answers

What type of bond is primarily found in feldspar?

<p>Ionic bond (A)</p> Signup and view all the answers

Which of the following is true about thermosetting polymers?

<p>They have high abrasion resistance (C)</p> Signup and view all the answers

What is the primary phase that remains unchanged during the firing process in ceramics?

<p>Crystalline phase (C)</p> Signup and view all the answers

Flashcards

Polymer

A large molecule formed by connecting smaller molecules called monomers through strong covalent bonds.

Monomer

The smallest repeating unit that forms a polymer chain.

Covalent Bonds in Polymers

Strong bonds that hold monomers together within a polymer chain.

Polar Bonds in Polymers

Weak bonds between polymer chains, responsible for properties like low strength and water absorption.

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Co-polymer

A polymer formed by connecting two or more different types of monomers.

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Random Copolymer

Two types of monomers are randomly arranged along the polymer chain.

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Alternating Copolymer

Monomers alternate in a regular pattern within the polymer chain.

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Composite

A type of polymer used to create tooth-colored fillings, sealants, and sometimes as a base in denture fabrication.

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Block Copolymer

A linear copolymer with one or more long uninterrupted sequences of each polymeric species. Imagine it like a chain where different colored beads (monomers) are grouped together in long stretches.

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Graft Copolymer

A branched copolymer with one monomer chain to which one or more side chains of another monomer are attached. Picture a main chain with side branches of a different type.

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Cross-Linked Polymer

Adjacent linear chains are linked together in various positions through strong covalent bonds, forming a 3-dimensional network.

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Polymerization

The process of monomers chemically bonding together to form high molecular weight molecules. Picture the monomers connecting like small pieces forming a big structure.

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Residual Monomer

The amount of monomer that does not fully polymerize, which can cause potential irritation. Think of incomplete baking that leaves some ingredients uncooked.

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Addition Polymerization

Polymerization process where two molecules join together to form a larger molecule without elimination of a smaller molecule. Think of two parts joined together without losing anything.

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Condensation Polymerization

Polymerization process where two molecules join together to form a larger molecule while eliminating a smaller molecule as a by-product. Think of two parts joining together and releasing a small extra bit.

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Effect of Cross-Linking on Polymer Properties

Increased strength, hardness, and glass transition temperature (Tg) are benefits. However, it can also make the material brittle, less soluble, less ductile, and cause a decrease in water sorption. Imagine a material becoming stronger and more rigid, but also less flexible and less absorbent.

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Initiation in Polymerization

A polymerization reaction where the initiator is activated by light, heat, or a chemical activator, which then generates free radicals that attack a double bond of a monomer, starting a chain reaction.

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Propagation in Polymerization

The stage of polymerization where free radicals react with monomers, adding them to the growing polymer chain.

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Termination in Polymerization

The process of stopping the polymerization chain reaction. Occurs when two growing chains meet and combine, or an atom is transferred from one chain to another, resulting in a complete, stable polymer.

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Inhibition of Polymerization

A substance that slows down or prevents polymerization by interfering with the free radical reaction. Examples include hydroquinone and oxygen. Added to monomers for long-term storage.

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Thermoplastic Polymer

A type of polymer that can be repeatedly softened by heating and hardened by cooling. They have linear or branched structures without cross-linking.

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Thermoset Polymer

A type of polymer that does not soften or melt when reheated. They have a strong, rigid structure with cross-linking.

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Exothermic Reaction in Polymerization

The process where heat is released during polymerization due to the breaking of chemical bonds.

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Polymerization Shrinkage

The reduction in volume that occurs as a polymer forms from its monomer components.

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Brittle Material

A material that readily breaks when subjected to tension, showing poor resistance to pulling forces.

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High Compressive Strength

A material with a high ability to withstand compression, like being squeezed or pressed.

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Tensile Strength

The ability of a material to resist being pulled apart, measured by how much force it can withstand before breaking.

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Plastic Deformation

The tendency of a material to deform permanently when subjected to stress, resulting in a change in its shape.

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Composite Material

A type of material that combines two or more distinct substances to achieve improved properties, often with a matrix and a filler.

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What are composites?

Materials that are formed by chemically bonding two or more different materials with distinct properties, resulting in a final material with intermediate characteristics.

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What are thermosetting polymers?

A type of polymer that undergoes a chemical reaction during the molding process to produce a permanent, irreversible shape. It cannot be remelted or reshaped after the initial setting.

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What kind of bond is responsible for the strength of thermosetting polymers?

The type of bond holding together the chains of a thermosetting polymer, formed by sharing electrons between atoms.

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Explain 'Bond' in relation to composites.

The bonding mechanism responsible for holding together the different components of a composite material. The bond type varies depending on the materials being combined.

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Describe the two phases of ceramics and glasses.

The amorphous phase of the material is responsible for translucency (aesthetics) and is capable of softening and flowing during the melting process to form a glass-like matrix. The crystalline phase, typically composed of alumina (Al₂O₃) and zirconia (ZrO₂), retains its structure during firing and provides mechanical strength and crack resistance.

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What type of bonds are prevalent in ceramics and glasses?

The bonds that hold the atoms together in ceramics and glasses. The dominant bond is ionic in feldspar, but covalent bonding is present in silica.

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What are the important characteristics of composites in dentistry?

The properties include moderate hardness, stiffness, and good biocompatibility, making them suitable for dental applications.

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What are the main characteristics of ceramics and glasses in dentistry?

A non-conductive material that resists the flow of heat and electricity. It's also insoluble in most common liquids and resists chemical reactions.

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Study Notes

General Classes of Materials (Lecture 2)

  • The lecture covers Polymers, Composites, and Ceramics
  • The material includes a variety of dental applications for each class

Metallurgy

  • This section discusses the basic properties of metals
  • Includes types of bonds, and applications in dentistry

Polymers

  • Definition: Polymers are large molecules made from smaller molecules called monomers linked together through covalent bonding
  • Types of Bonds:
    • Covalent bonds hold monomers together within the polymer chain
    • Polar/Hydrogen bonds exist between polymer chains
  • Nature/Structure: Polymers can be linear, branched, or cross-linked
    • Polymers are often amorphous or show partial crystallinity degrees
  • Dental Applications:
    • Impression materials (e.g., alginate, elastomers)
    • Composite filling materials
    • Cements (e.g., glass ionomer, zinc polycarboxylate)
    • Acrylic denture base and artificial teeth
    • Soft lining materials
  • Co-polymers: Polymers formed from a mixture of monomers

Composites

  • Definition: Composites are a combination of two or more materials with different properties.
  • Uses: Sealants, veneers, restorations, core buildup, cements, and denture teeth
  • Properties: Intermediate properties
    • Moderate hardness and stiffness
    • Thermal and electrical insulation
    • Formable, and machinable
    • Opaque or translucent

Ceramics

  • Definition: Ceramics are inorganic, non-metallic, solid materials made from metal and non-metal oxides.
  • Properties:
    • High hardness, melting temperature, modulus of elasticity
    • Insulating qualities and chemical inertness
    • Brittle
  • Dental Applications:
    • Crowns, bridges, inlays
    • Onlays, and other restorations

Polymerization

  • Definition: A process where monomers chemically bond together to form polymers.
  • Types:
    • Addition polymerization: Monomers link together with no by-product (free radicals or ionically)
    • Condensation polymerization: Monomers link together with a byproduct (water, alcohol)
    • Rapid in addition polymerization

Thermal Behavior of Polymers

  • Thermoplastic Polymers:
    • Linear or branched structure
    • Reversible, soften with heat, and harden with cooling
  • Thermosetting Polymers:
    • Cross-linked structure
    • Irreversible chemical reaction
    • Do not resoften after curing

Factors Associated with Polymerization

  • Heat Evolution: Polymers release heat during polymerization
  • Shrinkage: Change in volume during polymerization
  • Residual Monomers: Unreacted monomers remain after polymerization.

Inhibition of Polymerization

  • Impurities and oxygen: Prevent polymerization by inhibiting further growth

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General Classes of Materials PDF

Description

This quiz covers various classes of materials used in dentistry, including polymers, composites, and ceramics. It highlights their properties, types of bonds, and specific dental applications such as impression materials and filling materials. Assess your understanding of these materials and their significance in dental practices.

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