Questions and Answers
Which of the following are mass-related properties?
What is density?
Mass per unit volume of a material.
What is specific gravity?
The ratio of the density of a material to the density of water at 4°C.
Thermal conductivity is the same as thermal diffusivity.
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What is the heat of fusion?
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What is thermal diffusivity?
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The change in length per unit length of the material for a 1°C change in temperature is called the linear coefficient of thermal expansion (______).
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What is the definition of light?
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Which of the following describes refraction?
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Fluorescence and phosphorescence are the same phenomenon.
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Which parameters can the eye distinguish differences in color?
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Match the types of optical interaction with their definitions:
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What is metamerism in color matching?
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Study Notes
Physical Properties Overview
- Properties that are not related to force application, including mass-related, thermal, electrical, less specific, and optical properties.
Mass-Related Properties
- Density: Mass per unit volume; measured in gm/cm³ or lb/in³.
- Specific Gravity: Ratio of material density to water density at 4°C; numerically equal to density (no units). Important in dentistry for materials used in complete dentures and casting.
Thermal Properties
- Melting and Freezing Temperature: Critical for determining melting machine in dental restorations.
- Heat of Fusion: Heat required to convert 1 gm of solid to liquid at melting temperature; important during metal casting (100°C above melting point).
- Latent Heat of Fusion: Heat released when a liquid solidifies.
- Thermal Conductivity: Heat transfer rate through a material; significant for metallic dental materials.
- Specific Heat: Quantity of heat needed to raise temperature of 1 gm of a substance by 1°C; metals have low specific heat, affecting casting procedures.
- Thermal Diffusivity: Rate of temperature change in a material; relevant for preventing thermal shock to dental pulp.
- Coefficient of Thermal Expansion (α): Linear expansion per degree of temperature change; critical for matching materials to prevent marginal leakage and related issues in dentistry.
Less Specific Properties
- Water Sorption: Amount of water absorbed by materials; affects acrylic resin denture bases and hydrocolloid impression materials.
- Fluidity, Viscosity, and Plasticity: Fluidity refers to liquid flow tendency, viscosity indicates flow resistance, and plasticity denotes deformation ability of solids.
Optical Properties
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Interaction of Light with Matter:
- Reflection: Light reflects off surfaces; smooth surfaces create specular reflection, while rough surfaces scatter light diffusely.
- Refraction: Change in light direction at material boundaries; matching refractive indices is essential for aesthetic restorations.
- Scattering: Redirection of light due to inclusions; affects opacifiers in resins and air bubbles.
- Transmission: Differentiates materials as transparent, translucent, or opaque based on light passage.
- Luminescence: Emission of light; critical in mimicking natural tooth appearance using fluorescing agents.
- Dispersion: Separation of light into spectrum of colors using prisms.
Color Parameters
- Hue: The actual color.
- Chroma: Intensity or saturation of the color.
- Value: Lightness or darkness of the color; highest significance in dental aesthetics for vitality representation.
Shade Selection Factors
- Source of Light: Different lighting conditions affect color perception; color matching is best under multiple light sources.
- Surrounding Colors: Nearby colors influence the perception of an object's color.
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Object Characteristics:
- Translucency: Affects perceived lightness or darkness.
- Surface Texture: Smooth surfaces reflect more light, appearing brighter.
- Scattering Centers: Inclusions can lower value (darker appearance).
- Thickness: Increased thickness can raise opacity and lower value.
- Observer Factors: Individual color perception varies due to response differences, color vision deficiencies, and color fatigue.
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Description
This quiz covers various physical properties relating to materials, including mass-related properties like density and specific gravity. It also explores thermal and electrical properties along with less specific attributes such as fluidity and viscosity. Test your knowledge on how these properties affect material behavior in different applications.
