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Questions and Answers
What is the definition of density in the context of dental materials?
What is the definition of density in the context of dental materials?
How does low thermal conductivity affect a material in dental applications?
How does low thermal conductivity affect a material in dental applications?
Which of the following is NOT a thermal property mentioned in relation to dental materials?
Which of the following is NOT a thermal property mentioned in relation to dental materials?
What is the significance of the coefficient of thermal conductivity (K) in dental materials?
What is the significance of the coefficient of thermal conductivity (K) in dental materials?
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Which physical property is directly related to the retention of upper dentures?
Which physical property is directly related to the retention of upper dentures?
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What is the primary significance of the coefficient of thermal expansion in dentistry?
What is the primary significance of the coefficient of thermal expansion in dentistry?
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What occurs as a result of breakage of the marginal seal between a filling and the cavity wall?
What occurs as a result of breakage of the marginal seal between a filling and the cavity wall?
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Which of the following correctly defines the heat of fusion?
Which of the following correctly defines the heat of fusion?
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In the context of denture base materials, what is a benefit of high thermal conductivity?
In the context of denture base materials, what is a benefit of high thermal conductivity?
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Why is the melting temperature important in dental casting?
Why is the melting temperature important in dental casting?
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Study Notes
Dental Biomaterials Lecture 5: Physical Properties of Dental Materials
- Physical properties are based on the laws of physics; describing mass, heat, light, electricity, energy, force, and other physical phenomena.
- Mechanical properties are a subgroup of physical properties dealing with force.
- This course chapter briefly describes physical properties as a background for later detailed discussions in which these properties are used to describe the characteristics of specific dental materials.
Mass-Related Properties
- Density: Is the mass per unit volume of the material. Units are gm/cm³ and pound/in³.
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Clinical Importance:
- Upper dentures should be made of materials with low density for retention.
- Molten alloys with low density require higher pressure during casting to fill the mold cavity.
Thermal Properties
- Thermal Conductivity: The ability of a material to transfer heat. Heat transfer occurs at a slower rate in materials with low thermal conductivity than those with high thermal conductivity.
- Coefficient of Thermal Conductivity (K): The amount of heat transported in one second across a unit cube when one face is hotter than the other.
- Thermal Coefficient of Expansion (α): The change in length per unit length of a material for a 1°C change in temperature. Changes in temperature lead to changes in interatomic distance.
- Melting and Freezing Temperature: The temperature at which a material melts (liquid state) or freezes (solid state). In casting, melting temperature of metals and alloys is crucial to determine the melting machine and select the investment materials.
- Heat of Fusion: The amount of heat required to convert 1 gram of a substance from the solid state to a liquid state. Measured in joules or calories.
- Specific Heat: The amount of heat in calories used to increase 1 gram of substance by 1°C. Metals have lower specific heat compared to non-metals.
- Thermal Diffusivity: The rate by which a material transitions from non-uniform temperature to thermal equilibrium (uniform temperature).
Optical Properties
- Optics: The science of studying light, sight (how well the eyes capture images), and vision (how the brain processes the information coming from the eyes, including color).
- Restorative dentistry aims to restore color and appearance of natural teeth; therefore, knowledge of light and color principles is necessary.
- Nature of Light: Light is a beam of photons, and color is the wavelength of light.
- Production of Light: Light is produced thermally (e.g., the sun, hot metal), electrically (e.g., passing electric current through an inert gas), and chemically (e.g., fluorescence, phosphorescence).
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Interaction of Light and Matter:
- Reflection: The change in the direction of light rays when they encounter a surface. Smooth surfaces cause specular reflection; rough surfaces cause diffuse reflection.
- Refraction: The change in direction of light beams (bending) as they enter a different medium.
- Scattering: The redirection of light rays passing through a medium due to obstructions (inclusions), which results in attenuation.
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Properties of Materials in Relation to Light Transmission and Absorption:
- Transparency: The ability of a material to allow the passage of light where little distortion occurs (e.g., glass).
- Translucency: The ability of a material to allow passage of some light, with scattering or reflection of the rest. (e.g., tooth enamel, porcelain, composite, pigmented acrylic resin).
- Opacity: The property of a material to prevent light passage; objects cannot be seen through them. (e.g., opaque materials absorb light, with some reflected back).
- Luminescence (Fluorescence and Phosphorescence): Occurs when the emitted light wavelength is longer than the exciting light's wavelength. Includes immediate emission (fluorescence) and delayed emission (phosphorescence).
- Importance in Dentistry: Sound human teeth emit fluorescent light when excited by ultraviolet radiation (365 nm). Fluorescence contributes to the brightness and vital appearance of teeth. Restorative materials and dental porcelains are formulated with fluorescing agents.
- Laser: Light Amplification by Stimulated Emission of Radiation. Lasers are produced when an element or compound (solid, liquid, or gas) is excited by high energy to produce specific light.
- Clinical Applications of Laser: Used in surgery, removal of initial carious lesions, curing composite materials, endodontics, filling pits and fissures, and laboratory applications: welding and sintering ceramics.
Color in Dentistry
- Color Definition: Color perception is described using three dimensions (hue, chroma, and value) in the Munsell color system.
- Clinical Significance: A restoration with the correct hue but too high a value will appear too bright, while a restoration with correct hue and too low value will appear dead or dull.
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Light Source and Color Appearance: Color matching should be done under multiple color sources and under the same lighting conditions.
- Metamerism: The change in color matching between objects under different light sources.
- Two objects that match under one source of light but do not match under other sources are called a metameric pair.
- Two objects that color match under all light sources are described as isomers.
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Shade Color Matching: Techniques for determining the color of natural teeth to ensure that artificial substitute restorations have similar colors and aesthetics.
- Methods:
- Dental Shade guides (VITA Classical, Chromascop, VITA 3D-Master): sets of standard color standards mimicking natural tooth structures to visually match.
- Photocolorimetry: the clinician or assistant holds matching shade guide teeth next to patient teeth then the photograph is used to measure the color using a computer program.
- Chair side colorimeters: portable devices used to determine tooth shade by directly applying to the patient's tooth.
- Methods:
Evaluation Sheet #6:
- The evaluation sheet contains questions about clinical significance of density, thermal conductivity, coefficient of expansion, melting/freezing temperature, specific heat, and thermal diffusivity.
- What lasers are, how they work, their characteristics and clinical applications.
- Properties of materials related to light transmission and absorption.
- Color dimensions, isomerism, and metamerism.
- Shade color matching and its various methods.
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Description
Explore the physical properties of dental materials in this engaging quiz. This chapter delves into mass-related and thermal properties, providing insight into their clinical implications. Test your knowledge on topics like density and thermal conductivity as they relate to dental practice.
