Questions and Answers
What is the definition of Heat of Fusion?
What happens to the temperature of the solidifying liquid during the liberation of the latent heat of fusion?
Why is it important to heat the molten alloy nearly 100°C above the melting temperature during casting?
Why is prolonged heating unnecessary during casting of dental gold alloys?
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What is the importance of thermal conductivity in dentistry?
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Why is a cement base placed between a large amalgam filling and the tooth?
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What is the formula to calculate thermal diffusivity?
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Which type of denture base has high thermal conductivity?
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What is the unit of density?
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What is the specific gravity of water at 4°C?
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What is the clinical importance of low density in dental materials?
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Why is high density an advantage in casting?
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Which of the following is NOT a thermal property?
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What is the clinical importance of melting temperature in dentistry?
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What is the main reason for avoiding overheating molten metals during casting?
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What are the two main categories of physical properties discussed in the content?
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What is the coefficient of thermal expansion?
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What is the clinical importance of the coefficient of thermal expansion in dentistry?
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Which of the following materials has a higher coefficient of thermal expansion?
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What is marginal percolation?
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What is one of the consequences of marginal percolation?
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What is the clinical importance of water sorption in dentistry?
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What is viscosity?
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Which of the following is NOT a factor that affects the insulating efficiency of a material?
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Study Notes
Physical Properties of Dental Materials
Mass-Related Properties
- Density is the mass per unit volume of a material, measured in gm/cm³
- Specific gravity is the ratio of the density of a material to the density of water at 4°C, with no units
Clinical Importance of Density
Advantages of Low Density
- Retention of upper dentures (e.g., non-metallic denture base materials are lighter than metallic ones)
- Patient comfort due to lighter weight
Advantages of High Density
- Casting (e.g., low-density alloys require more casting forces)
Thermal Properties
Melting and Freezing Temperature
- The temperature at which a material melts or freezes
- Importance in dentistry:
- Determining the melting machine or method
- Avoiding overheating to prevent porosities
- Determining investment material qualities
Heat of Fusion
- The amount of heat required to convert 1 gm of a material from solid to liquid state
- Latent Heat of Fusion: the heat liberated when a material solidifies
- Importance in dentistry:
- During casting, allowing time for the molten alloy to cool before solidification
Specific Heat
- The quantity of heat needed to raise the temperature of 1 gm of a substance by 1°C
- Metals have low specific heat, while non-metals have high specific heat
- Importance in dentistry:
- Dental gold alloys require minimal heating during casting
Thermal Conductivity
- The amount of heat that passes through a body per second
- Importance in dentistry:
- Metallic denture bases and fillings maintain healthy tissue condition
- Thermal insulation is necessary for pulp protection (e.g., cement base between tooth and filling)
Thermal Diffusivity
- The rate of heat diffusion in a body
- Importance in dentistry:
- Insulating efficiency is influenced by diffusivity and thickness
- Thermal shock prevention in amalgam fillings
Coefficient of Thermal Expansion
- The change in length per unit length for a 1°C change in temperature
- Clinical importance in dentistry:
- Marginal percolation and leakage in restorations
- Porcelain-metal bonding in ceramo-metallic restorations
- Matching coefficient of thermal expansion between porcelain and denture base
- Distortion of wax patterns due to high coefficient of expansion
Electrical Properties
- Electrical conductivity and resistivity
Less Specific Properties
Water Sorption
- The amount of water adsorbed on the surface and absorbed into the material
- Clinical importance in dentistry:
- Compensating for polymerization shrinkages in acrylic denture bases
- Dimensional changes in hydrocolloids when immersed in water
Fluidity, Viscosity, and Plasticity
- Fluidity: the tendency of a liquid to flow
- Viscosity: the resistance of a fluid to flow
- Plasticity: related to solids and semi-solids
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Description
This quiz covers the physical properties of dental materials, including mass-related properties, thermal properties, and more. Test your knowledge of density, specific gravity, melting temperature, and other essential concepts.
