Dental Biomaterials Lecture 5
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Questions and Answers

What property of dental gold alloys allows for reduced heating during the casting process?

  • Low thermal conductivity
  • High thermal diffusivity
  • Low specific heat (correct)
  • High specific heat

    • Which statement correctly describes thermal diffusivity?

  • It is the rate at which a material approaches thermal equilibrium. (correct)
  • It describes the thermal stability of a material under stress.
  • It measures how fast a material can hold heat.
  • It quantifies the amount of heat retained by a material.

    • How is the refractive index defined?

  • The frequency of light in a medium
  • The ratio of the velocities of light in two mediums (correct)
  • The absorption coefficient of a material
  • The angle of incidence to angle of refraction ratio

    • What type of reflection occurs when light hits a perfectly smooth surface?

    <p>Specular reflection</p> Signup and view all the answers

    Which of the following properties contributes to high thermal shock in gold or amalgam restorations?

    <p>High thermal diffusivity</p> Signup and view all the answers

    What aspect of light is essential for restorative dentistry to match the appearance of natural teeth?

    <p>Wavelength of light</p> Signup and view all the answers

    In which type of reflection does light get scattered in multiple directions?

    <p>Diffuse reflection</p> Signup and view all the answers

    What causes light to bend when passing from one medium to another?

    <p>Refraction</p> Signup and view all the answers

    What is the primary characteristic of transparent materials?

    <p>They allow light to pass with little distortion.</p> Signup and view all the answers

    Which property of a material blocks the passage of light completely?

    <p>Opacity</p> Signup and view all the answers

    How do fluorescent materials behave when subjected to ultraviolet light?

    <p>They emit light immediately after excitation.</p> Signup and view all the answers

    What is the significance of fluorescence in human teeth?

    <p>It contributes to their brightness and vital appearance.</p> Signup and view all the answers

    What happens to light in a translucent material?

    <p>Some light passes while the rest is scattered or reflected.</p> Signup and view all the answers

    What is the delayed emission of light after excitation called?

    <p>Phosphorescence</p> Signup and view all the answers

    Which color material reflects all colors of light?

    <p>White</p> Signup and view all the answers

    What does the acronym LASER stand for?

    <p>Light Amplification by Stimulated Emission of Radiation</p> Signup and view all the answers

    Which characteristic of laser light refers to all photons having the same wavelength?

    <p>Monochromatic</p> Signup and view all the answers

    What is the primary use of laser in clinical applications?

    <p>Removing soft tissues</p> Signup and view all the answers

    What phenomenon describes that all waves emitted by a laser are parallel?

    <p>Collimated</p> Signup and view all the answers

    In the Munsell color system, which dimension describes the strength or intensity of a color?

    <p>Chroma</p> Signup and view all the answers

    What results from a defect in color sensing receptors in the retina?

    <p>Color blindness</p> Signup and view all the answers

    Which laser type is specifically known for its application in welding high fusing alloys?

    <p>CO2 laser</p> Signup and view all the answers

    Why is it important to perform color matching under various light sources?

    <p>To get accurate color appearance</p> Signup and view all the answers

    What describes the process where light from an object is focused on the retina?

    <p>Refraction</p> Signup and view all the answers

    What is density defined as?

    <p>The mass per unit volume of the material.</p> Signup and view all the answers

    Which property describes the capacity of a material to transfer heat?

    <p>Thermal conductivity</p> Signup and view all the answers

    Why must upper dentures be made of materials with low density?

    <p>To facilitate retention in the mouth.</p> Signup and view all the answers

    What is the co-efficient of thermal conductivity (K) important for in dental procedures?

    <p>Managing heat transfer to protect dental pulp.</p> Signup and view all the answers

    What does the thermal coefficient of expansion (α) measure?

    <p>The change in volume per degree of temperature change.</p> Signup and view all the answers

    Which of the following factors can affect the melting and freezing temperature of dental materials?

    <p>The chemical composition of the material.</p> Signup and view all the answers

    What role does specific heat play in dental materials?

    <p>It indicates how much heat a material can retain.</p> Signup and view all the answers

    What are mass-related properties primarily concerned with?

    <p>Physical phenomena related to mass and volume.</p> Signup and view all the answers

    What phenomenon describes two objects that match in color under one light source but not under another?

    <p>Metamerism</p> Signup and view all the answers

    Which shade guide consists of 26 shades divided into five groups?

    <p>VITA SYSTEM 3D-MASTER</p> Signup and view all the answers

    What is the primary purpose of a dental shade guide?

    <p>To visually determine a color match with natural teeth</p> Signup and view all the answers

    What process is involved in photocolorimetry for shade matching?

    <p>Taking a photograph of matched shades near patient teeth</p> Signup and view all the answers

    Which factor is NOT considered when determining tooth shade using a chair side colorimeter?

    <p>Tooth alignment</p> Signup and view all the answers

    How many tabs does the Chromoscop shade guide contain?

    <p>20 tabs</p> Signup and view all the answers

    What does an isomeric pair signify in color matching?

    <p>Matched colors under all light sources</p> Signup and view all the answers

    Which of the following is NOT a step in the photocolorimetry process?

    <p>Measuring tooth thickness with calipers</p> Signup and view all the answers

    What is the significance of the coefficient of thermal expansion in dental materials?

    <p>It prevents marginal leakage between filling and cavity walls.</p> Signup and view all the answers

    Which of the following best describes the heat of fusion?

    <p>The amount of heat required to convert a solid to a liquid.</p> Signup and view all the answers

    What role does high thermal conductivity in metallic denture base materials play?

    <p>It prevents hot substances from being swallowed.</p> Signup and view all the answers

    Why is matching the thermal expansion coefficient between restorative materials and teeth important?

    <p>To avoid marginal percolation and its consequences.</p> Signup and view all the answers

    What is the specific heat of a substance?

    <p>The heat required to increase the temperature of 1 gram by 1°C.</p> Signup and view all the answers

    What phenomenon results from the breakage of the marginal seal between a filling and cavity wall?

    <p>Marginal percolation</p> Signup and view all the answers

    Which of the following factors is important in determining the melting temperature of metals in dental casting?

    <p>The melting and freezing temperature.</p> Signup and view all the answers

    What can ensure proper bonding in ceramo-metallic restorations?

    <p>Matching the thermal expansion coefficients.</p> Signup and view all the answers

    Study Notes

    Dental Biomaterials Lecture 5: Physical Properties of Dental Materials

    • Physical properties are based on laws of physics (mass, heat, light, electricity, energy, force, and other physical phenomena).
    • Mechanical properties are a subgroup of physical properties that deal with force.
    • This chapter provides a brief introduction to physical properties, preparing for a more detailed discussion later, where these properties describe specific dental material characteristics.

    I - Mass-related Properties

    • Density: Mass per unit volume of a material.
      • Units: gm/cm³ and pound/in³
      • Clinical importance:
        • Upper dentures require low density for retention.
        • Low-density molten alloys in casting require higher pressure to fill the mold cavity.

    II - Thermal Properties

    • Thermal Conductivity: Material's ability to transfer heat.

      • Low conductivity materials transfer heat slowly.
      • High conductivity materials transfer heat rapidly.

    • Coefficient of thermal conductivity (K): Amount of heat transported in one second across a unit cube when one face is hotter than the other.

    • Thermal Coefficient of expansion (α): Change in length per unit length for a 1°C change in temperature.

      • Clinical significance:
        • Close matching of thermal expansion coefficient between tooth and restorative materials prevents marginal leakage (bacteria, fluids, ions seeping between the restoration and tooth). This avoids discoloration, recurrent caries, and hypersensitivity.

    • Melting and freezing temperature: Temperature at which a material melts (liquid) or solidifies (solid).

      • Important in casting metals and alloys: choosing the correct melting machine and type of investment materials.

    • Heat of Fusion: Amount of heat needed to convert 1 gram of a substance from solid to liquid.

    • Specific Heat: Amount of energy needed to raise the temperature of 1 gram of substance by 1°C.

      • Metals have low specific heat, while non-metals have high specific heat.
      • Clinical importance: Dental gold alloys have low specific heat, meaning prolonged heating during casting is unnecessary.

    • Thermal diffusivity: Rate at which a material changes from non-uniform temperature to thermal equilibrium (uniform temperature).

      • Gold or amalgam restorations have high thermal diffusivity, potentially causing high thermal shock due to high thermal conductivity and low specific heat.

    III - Optical Properties

    • Optics: Science of studying light, sight, and vision (color).

      • Restorative dentistry aims to restore teeth's color and appearance; therefore, understanding light and color science is essential.

    • Nature of Light: Light is a beam of photons. Color is the wavelength of light.

    • Production of Light:

      • Thermal: e.g., the sun, hot metal
      • Electrical: Passing electric current through inert gases like neon
      • Chemical: Fluorescence and phosphorescence

    • Interaction of light and matter:

      • Reflection: Specular (smooth surfaces) reflect light in a single direction, while diffuse (rough surfaces) reflect light in multiple directions. The restoration should have a highly smooth and polished surface for specular reflection.

    • Refraction: Change in light direction when entering a different medium. Refractive index is the ratio of light velocity in vacuum to light velocity in the medium. Matching the refractive indices of the dispersed and matrix phases is important.

    • Scattering: Light is redirected and weakened when passing through a medium with obstructions (inclusions, etc.).

    • Transparency: Material allowing light to pass through without significant distortion (e.g., glass).

    • Translucency: Material letting some light pass and scattering or reflecting the rest (e.g., tooth enamel, porcelain).

    • Opacity: Material that prevents light from passing through (e.g., amalgam or composite).

    • Luminescence: Emission of light from a material due to excitation by other energy types (e.g., UV).

      • immediate emission: fluorescence
      • delayed emission: phosphorescence
      • Clinical importance: Natural teeth emit fluorescent light under UV irradiation.

    • Color:

      • The human eye, with specialized cells (cones), perceives light in three dimensions (hue, value, and chroma, using the Munsell color system) which describes color perceived.
      • Important to match color to adjacent teeth
      • Light source and color appearance: color matching should be done under similar lighting conditions to avoid metamerism.

    • Shade color matching: Used to determine the color of natural teeth, aiding restoration replication.

      • Common methods: dental shade guides (VITA Classical, Chromoscop, and 3D-Master), photocolorimetry, chair-side colorimeters.

    Laser

    • Light Amplification by Stimulated Emission of Radiation (LASER)
    • Production: An element or compound ("medium," solid, liquid, or gas), excited by high energy, produces special light.
    • Laser light characteristics:
      • Monochromatic: all photons have the same wavelength .
      • Coherent: all waves are in phase (same speed).
      • Collimated: all waves are parallel.
      • Named according to the medium: CO2 laser, argon laser, diode laser.
    • Clinical applications: surgery for soft tissue removal/regeneration, ulcer healing, coagulation, curing composites, endodontics, fissure fillings. Laboratory applications: welding alloys, sintering ceramics.

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    Dental Biomaterials Lecture 5 PDF

    Description

    Explore the physical properties of dental materials focusing on mass, thermal properties, and their clinical significance. This quiz introduces fundamental concepts essential for understanding how these properties influence dental practices. Prepare for a deeper dive into material characteristics in subsequent lectures.

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