Dental Biomaterials I - Lecture 5 Quiz

Dental Biomaterials I - 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 focused on force.
• This chapter provides foundational knowledge to prepare for more detailed discussions on how these properties describe specific dental materials.

Mass-related Properties: Density

• Density is the mass per unit volume of a material.
• Units include gm/cm³ and pound/in³.
• Low density materials are important for denture retention.
• During casting, low-density alloys require higher pressure to fill mold cavities.

Thermal Properties

• Thermal Conductivity: The material's ability to transfer heat. Heat transfer occurs at a lower rate in materials with low thermal conductivity than those with high thermal conductivity.
• Coefficient of Thermal Conductivity (K): Measures the rate of heat transported across a unit cube when one face is hotter than the other.
• Thermal Coefficient of Expansion (α): Measures the change in length per unit length of a material for a 1°C change in temperature.
• Melting and Freezing Temperatures: Temperatures at which a material changes from solid to liquid or vice-versa. Important in casting alloys and selecting investment materials.
• Heat of Fusion: Amount of heat required to convert 1 gram of a substance from solid to liquid state.
• Specific Heat: Amount of heat in calories used to increase the temperature of 1 gram of a substance by 1°C. Metals have low specific heat, non-metals have high specific heat.
• Thermal Diffusivity: Rate at which a material converts from non-uniform temperature to thermal equilibrium (uniform temperature). High thermal diffusivity in gold/amalgam restorations can lead to thermal shock due to high thermal conductivity and low specific heat.

Optical Properties

• Optics: The science of studying light, sight, vision (including color).
• Restorative dentistry requires knowledge of light/color principles to restore natural tooth color and appearance.
• Nature of Light: Light is a beam of photons. Color is the wavelength of light.
• Production of Light: Light can be produced thermally e.g. sun, hot metal) electrically (e.g. by passing electric current through gas), or chemically (e.g. fluorescence, phosphorescence).
• Interaction of Light and Matter:
  • Reflection:
    • Specular reflection occurs when light bounces off a smooth surface in one direction (e.g., mirrors).
    • Diffuse reflection occurs when light bounces off a rough surface in multiple directions.
  • Refraction: Change in the direction of light beams when they pass into a different medium.
  • Scattering: When light rays passing through a medium are obstructed by inclusions. This results when introducing opacifiers or air bubbles in certain dental materials.
• Transparency, Translucency, Opacity:
  • Transparency: Materials allowing light to pass through without distortion (e.g., glass).
  • Translucency: Materials letting some light pass through but scattering/reflecting the rest (e.g., tooth enamel, porcelain).
  • Opacity: Materials preventing light passage (e.g., most casting materials).
    • Black materials absorb all colors, white materials reflect all colors, and colored materials absorb other colors (except for the color reflected).
• Luminescence: Occurs when the wavelength of the emitted light is longer than the exciting light (e.g., fluorescence, phosphorescence).
  • Fluorescence is immediate emission, while phosphorescence lasts after excitation ceases.
• Clinical Significance of Luminescence: Sound teeth emit fluorescent light when exposed to ultraviolet radiation, this is also used in materials to enhance whiteness.
• Laser: Light Amplification by Stimulated Emission of Radiation.  Lasers are produced by exciting atoms or compounds via high-energy stimulation and have unique properties like monochromatic, incoherent, and collimated light beams. Usage ranges from oral surgery to laboratory work, like welding and sintering applications.
• Clinical Significance of Lasers: Important for oral surgery because of coagulation properties, removal of carious lesions, composite curing, endodontic work and procedures where hydroxyapatite filling materials may be needed.
• Color Matching (Shade Guides): Guides used to match the color of natural teeth, ensuring artificial restorations possess similar color and esthetics. VITA Classical, Chromoscop, and Vitapan 3D Master Shade Guides are discussed in terms of their construction and applications in shade selection. Different methods are available for shade matching: photocolorimetry, and chair-side colorimeters.

Color Definition and Dimensions

• Color perception is categorized into hue, chroma, and value, as described by the Munsell system.
  • Hue: Dominant wavelength (color name).
  • Chroma: Saturation/intensity of a color.
  • Value: Luminous reflectance, or lightness/darkness.