Dental Materials Quiz

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Questions and Answers

What is the relationship between the size of abrasive particles and the roughness of the finished surface?

The roughness of the finished surface is proportional to the size of abrasive particles.

How does the efficiency of smaller particle abrasives change with force?

The efficiency of smaller particle abrasives increases with force.

What are the factors that can affect finishing pressure?

Greater force leads to more rapid removal of material and deep cuts into the surface.

What is the purpose of lubrication in the polishing process?

<p>Lubrication has a cooling effect, carries away heat and debris, and may obscure the cutting surface.</p> Signup and view all the answers

What are the four types of strengths discussed in the text?

<p>Compressive Strength, Flexural Strength, Fatigue Strength, Fracture Toughness</p> Signup and view all the answers

What is the role of environment in fatigue strength?

<p>It is important to avoid areas of stress concentration, surface defects, and notches to prevent fatigue failure. Dental materials are subjected to many moderate stresses during mastication cycles.</p> Signup and view all the answers

What is the difference between toughness and fracture toughness?

<p>Toughness refers to the ability of a material to absorb energy and delay fracture, while fracture toughness refers to the ability of a material with cracks to resist fracture by absorbing energy.</p> Signup and view all the answers

What is creep and which materials undergo creep?

<p>Creep is the time-dependent deformation of an object subjected to a constant stress. Most materials undergo creep at temperatures close to their melting point, but ceramics and most metals do not undergo creep.</p> Signup and view all the answers

What is the ultimate strength of a material?

<p>The limit of applied force a material can withstand</p> Signup and view all the answers

What is the ultimate tensile strength/stress?

<p>Maximum load in tension (or compression)</p> Signup and view all the answers

What is the fracture strength of a brittle material?

<p>The stress at which a brittle material fractures</p> Signup and view all the answers

Between which two strengths does strain hardening occur?

<p>Between Yield Strength (B) and Ultimate Strength (C)</p> Signup and view all the answers

What happens during necking?

<p>Reduction in cross-sectional area, material can no longer withstand the maximum stress, strain increases, leads to fracture</p> Signup and view all the answers

What is the elastic modulus of a material?

<p>A measure of the rigidity of a material, defined by the ratio of stress to strain (below elastic limit)</p> Signup and view all the answers

What are the various terms used to measure the physical and mechanical properties of dental materials?

<p>The various terms used to measure the physical and mechanical properties of dental materials are: elastic modulus, proportional limit, elastic limit, yield stress, ultimate strength, fracture strength, ductility, resilience, and toughness.</p> Signup and view all the answers

What is the concept of stress and strain?

<p>Stress is the force applied to a material per unit area, while strain is the resulting deformation or change in shape of the material.</p> Signup and view all the answers

What is the clinical significance of the physical and mechanical properties of materials in dentistry?

<p>The physical and mechanical properties of materials in dentistry are important for determining their suitability for specific dental applications, such as dental restorations. These properties can affect the durability, strength, and overall performance of the restorations in the oral cavity.</p> Signup and view all the answers

What are some of the mechanical properties of dental materials?

<p>Some of the mechanical properties of dental materials include: elastic modulus, ductility, resilience, toughness, yield strength, ultimate strength, and fracture strength.</p> Signup and view all the answers

What is the difference between abrasion, finishing, and polishing?

<p>Abrasion refers to the wearing away of a surface by rubbing, cutting, or scraping. Finishing involves contouring to remove excess material and produce a smooth surface, while polishing is the final removal of material to create a smooth, highly reflective surface without scratches.</p> Signup and view all the answers

Why is it important to polish tooth structures and restorations?

<p>Polishing tooth structures and restorations helps to improve aesthetics, minimize trauma to hard and soft tissues, improve tissue health, and increase the longevity of the restorative material.</p> Signup and view all the answers

What factors influence the rate and efficiency of abrasion?

<p>The hardness of the abrasive particles must be greater than the surface being abraded. The shape of the abrasive particles also plays a role, as objects with sharp edges have enhanced cutting efficiency. However, repeated use can dull the instrument and cause debris clogging.</p> Signup and view all the answers

What are some types of abrasives used in dentistry?

<p>Some types of abrasives used in dentistry include diamonds, carbide, emery, aluminum oxide, cuttle, tin oxide, garnet, and pumice.</p> Signup and view all the answers

What is the definition of force?

<p>Force is defined as one body interacting with another, generating force applied through contact of bodies or at a distance. It has three defining characteristics: point of application, magnitude (lbs, kg, N), and line of action.</p> Signup and view all the answers

What is the range of occlusal forces in the posterior region at the mandibular hinge axis?

<p>The range of occlusal forces in the posterior region at the mandibular hinge axis is 400-800 N for 1st and 2nd molars, 300 N for premolars, 200 N for canines, and 150 N for incisors.</p> Signup and view all the answers

What are the predictors of occlusal force?

<p>Facial form and muscle definition are good predictors of occlusal force. High mandibular angle is associated with lower occlusal force, while lower mandibular angle is associated with higher occlusal force.</p> Signup and view all the answers

What is the definition of stress?

<p>Stress (S or σ) is the force per unit cross-sectional area acting on a material. It is calculated as Stress = F/A, where F is the applied force and A is the cross-sectional area. The SI unit for stress is Pascal (Pa), which is equivalent to N/m².</p> Signup and view all the answers

What are the properties of dental glass ionomer cements as permanent filling materials?

<p>The properties of dental glass ionomer cements as permanent filling materials include compressive strength, tensile strength, corrosion resistance, and resistance to creep.</p> Signup and view all the answers

Why did the occlusal composite resin restoration show signs of secondary caries in the patient who consumed hot homemade soup and cola with ice?

<p>The occlusal composite resin restoration showed signs of secondary caries because the frequent exposure to hot homemade soup and beverages with ice caused thermal cycling and microleakage, leading to the breakdown of the restoration and the development of caries.</p> Signup and view all the answers

Which type of crown, porcelain fused to metal (PFM) crowns or zirconia crowns, would be better suited for a patient with bruxism and a heavy bite based on just hardness?

<p>Zirconia crowns would be better suited for a patient with bruxism and a heavy bite based on just hardness. Zirconia is known for its high hardness and resistance to wear, making it more suitable for patients with heavy biting forces and a history of bruxism.</p> Signup and view all the answers

What is the shape of the indenter used for a Vickers hardness test?

<p>The shape of the indenter used for a Vickers hardness test is a diamond square pyramid.</p> Signup and view all the answers

Which term describes the ability of a material to absorb energy without permanent deformation?

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

What is the slope of the stress-strain curve in the elastic region called?

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

Which term refers to the maximum stress a material can withstand without permanent deformation?

<p>Yield strength (B)</p> Signup and view all the answers

What is the measure of a material's ability to resist fracture under tensile stress?

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

Which of the following is the main reason for the outstanding clinical performance of amalgam restorations?

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

Why did the occlusal composite resin restoration show signs of secondary caries in the patient who consumed hot homemade soup and cola with ice?

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

Which type of crown, porcelain fused to metal (PFM) crowns or zirconia crowns, would be better suited for a patient with bruxism and a heavy bite based on just hardness?

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

What is the shape of the indenter used for a Vickers hardness test?

<p>Diamond square pyramid (A)</p> Signup and view all the answers

Which region of the stress-strain curve represents reversible strain?

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

What is the highest stress point on the stress-strain curve where stress is linearly proportional to strain?

<p>Proportional limit (D)</p> Signup and view all the answers

What is the force per unit cross-sectional area that is acting on a material called?

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

What is the fractional change in the dimensions caused by the force called?

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

Which of the following factors can lead to distortion or physical changes in a dental restoration due to increased temperature?

<p>Higher speed during finishing (C)</p> Signup and view all the answers

What is the unit of measurement for the size of abrasive particles in dental materials?

<p>Micrometers (µm) (B)</p> Signup and view all the answers

Which of the following is NOT a desired outcome of the polishing process in dentistry?

<p>Reducing corrosion of metal restorations (B)</p> Signup and view all the answers

Which of the following dentifrices is chemically inactive and mechanically cleans teeth?

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

Which of the following is the correct definition of fracture toughness?

<p>The energy required to resist the propagation of an existing crack or flaw (B)</p> Signup and view all the answers

What is the primary cause of the signs of secondary caries in the occlusal composite resin restoration of a patient who consumes hot homemade soup and cola with ice?

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

Which of the following materials is NOT known to undergo creep?

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

What is the correct definition of fatigue strength?

<p>The stress at which a material fails under repeated loading (A)</p> Signup and view all the answers

Which of the following is NOT a type of abrasive used in dentistry?

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

What is the purpose of finishing in dentistry?

<p>To remove excess material and produce a smooth surface (B)</p> Signup and view all the answers

Which abrasive is commonly used to polish metallic restorations and enamel?

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

What is the main difference between finishing and polishing in dentistry?

<p>Finishing involves contouring and removing excess material, while polishing involves the final removal of material to achieve a smooth and reflective surface (C)</p> Signup and view all the answers

Which term characterizes the strength of a material and is defined as the limit of applied force a material can withstand?

<p>Ultimate Strength (B)</p> Signup and view all the answers

What is the measure of the rigidity of a material, defined by the ratio of stress to strain below the elastic limit?

<p>Elastic Modulus (D)</p> Signup and view all the answers

Which term represents the stress at which a brittle material fractures?

<p>Fracture Strength (A)</p> Signup and view all the answers

Between which two strengths does strain hardening (cold working, work hardening) occur?

<p>Yield Strength and Ultimate Strength (C)</p> Signup and view all the answers

What happens during necking?

<p>All of the above (D)</p> Signup and view all the answers

What is the displacement or size of the deformation directly proportional to, according to Hooke's Law?

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

Flashcards

Abrasive particle size

Smaller particles typically result in a smoother surface finish.

Finishing pressure

The force applied during finishing, affected by cut depth and material properties.

Lubrication in polishing

Reduces friction, prevents heat, and improves surface finish.

Tensile strength

Material's ability to withstand pulling force.

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Yield strength

Point where a material begins permanent deformation under stress.

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Compressive strength

Material's ability to withstand squeezing force.

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Shear strength

Material's ability to resist force causing layers to slide past each other.

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Fatigue strength

Material's ability to withstand repeated stress cycles.

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Toughness

A material's ability to absorb energy without permanent deformation.

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Fracture toughness

Resistance to crack propagation under stress.

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Creep

Gradual deformation under constant stress (high temp).

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Ultimate strength

Maximum stress a material can withstand before failure.

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Ultimate tensile strength (UTS)

Highest stress before 'necking' (thinning).

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Dental polishing

Refines surfaces, improves aesthetics, and reduces plaque.

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Occlusal forces

Forces in the posterior region (200-400N).

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Force

Push or pull on an object.

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Stress

Force per unit area.

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Glass ionomer cement

Dental material with biocompatibility, adhesion, and fluoride release.

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Secondary caries

Caries in restorations due to microleakage (e.g., thermal).

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Vickers hardness test

Hardness test using a diamond indenter.

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Elastic modulus

Slope of linear portion of stress-strain curve (rigidity).

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Fracture toughness

Material's resistance to crack propagation.

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Distortion (dental restorations)

Changes in shape due to temperature differences.

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Abrasion types

Types of abrasives include aluminum oxide and silicon carbide.

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Hooke's Law

Deformation is proportional to load within elastic limit.

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Study Notes

Abrasive Particles and Surface Roughness

  • Smaller abrasive particles typically produce a smoother finished surface due to their ability to refine and polish.
  • Efficiency of smaller abrasives improves with increased force, enhancing their cutting ability but may reduce overall effectiveness at excessive loads.

Finishing Pressure and Lubrication

  • Finishing pressure is influenced by factors such as depth of cut, material properties, and tool interaction.
  • Lubrication in polishing reduces friction, prevents heat buildup, and enhances the surface finish.

Material Strengths

  • Four strengths discussed include tensile strength, yield strength, compressive strength, and shear strength.
  • Environment plays a significant role in fatigue strength, as factors like temperature and humidity can affect material performance.

Toughness and Creep

  • Toughness refers to a material's ability to absorb energy without permanent deformation, while fracture toughness specifically measures its resistance to fracture under stress.
  • Creep is the gradual deformation of materials under constant stress, commonly observed in metals and polymers at high temperatures.

Ultimate Strengths

  • Ultimate strength is the maximum stress a material can withstand before failure.
  • Ultimate tensile strength (UTS) is a specific term for the highest stress a material can endure before necking occurs.

Properties of Dental Materials

  • Various physical and mechanical properties of dental materials include hardness, tensile strength, compressive strength, and fracture toughness.
  • Abrasion, finishing, and polishing are distinct processes; polishing refines surfaces to achieve a shinier finish, while finishing removes material to improve shape and fit.

Importance of Polishing

  • Polishing tooth structures and restorations enhances aesthetics, reduces plaque accumulation, and increases durability.
  • Factors influencing abrasion rate include particle size, hardness of the abrasive, and applied force.

Occlusal Forces and Definitions

  • Occlusal forces in the posterior region at the mandibular hinge axis typically range between 200 to 400 N.
  • Force is described as the push or pull acting on an object, while stress is force per unit area.

Properties of Dental Glass Ionomer Cements

  • Dental glass ionomer cements exhibit properties such as biocompatibility, adhesion to tooth structure, and fluoride release as permanent filling materials.

Restoration Issues

  • Secondary caries in the occlusal composite resin restoration were linked to thermal expansion due to hot beverages, which may have caused microleakage.
  • Zirconia crowns generally have superior hardness compared to porcelain fused to metal (PFM) crowns, making them ideal for patients with bruxism.

Hardness Testing and Stress-Strain Curve

  • The Vickers hardness test employs a diamond-shaped indenter for measuring material hardness.
  • The elastic modulus represents the slope of the linear portion of the stress-strain curve, indicating material rigidity.

Fracture Toughness and Distortion

  • Fracture toughness is defined as the ability of a material to resist crack propagation under stress.
  • Distortions in dental restorations due to temperature changes can stem from differential thermal expansion among materials.

Measurement Units and Effectiveness in Polishing

  • The size of abrasive particles in dental materials is often measured in micrometers.
  • A desired outcome of polishing includes achieving a smooth surface; however, excessive material removal is not beneficial.

Fatigue Strength and Abrasion Types

  • Fatigue strength denotes the maximum stress a material can withstand repeated loading cycles.
  • Types of abrasives used in dentistry include aluminum oxide, silicon carbide, and diamond.

Finishing and Polishing Differences

  • Finishing prepares the surface for polishing, while polishing enhances aesthetic qualities without altering shape.
  • The main property describing material strength is yield strength, defining the limit of applied force it can withstand.

Hooke's Law

  • Hooke's Law states that deformation is directly proportional to the applied load within the elastic limit of a material.

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