Dental Biomaterials Lecture 5

Dental Biomaterials Lecture 5 Notes

• Physical Properties of Dental Materials: This chapter provides background for later discussions, using physical properties to describe dental material characteristics.

• Physical Properties Basis: Based on physics laws describing mass, heat, light, electricity, energy, force, and other physical phenomena.

• Mechanical Properties: A subset of physical properties focusing on force.

• Mass-Related Properties:

  • Density: Mass per unit volume of material. Units are gm/cm³ and pound/in³.
  • Clinical Importance (Density):
    • Upper Denture Retention: Low-density materials are crucial for denture retention.
    • Casting Procedures: Low-density molten alloys require higher pressure during mold filling.

• Thermal Properties:

  • Thermal Conductivity: Material's ability to transfer heat. Lower conductivity materials transfer heat slower; higher conductivity materials transfer faster.
  • Coefficient of Thermal Conductivity (K): Amount of heat transferred per second across a unit cube with one face hotter than the other.
  • Thermal Coefficient of Expansion (α): Change in length per unit length for a 1°C temperature change. Change in temperature results in change in interatomic distance.
  • Clinical Significance (Thermal Coefficient of Expansion): Close matching of the material's expansion coefficient to tooth material is important to avoid marginal leakage and microleakage.
  • Melting and Freezing Temperatures: The temperature at which a material melts into a liquid or freezes into a solid. Critical in casting and investment material selection.
  • Heat of Fusion: Amount of heat needed to convert 1 gram of material from solid to liquid state.
  • Specific Heat: Amount of heat in calories needed to increase the temperature of 1 gram of substance by 1°C. Metals have lower specific heat than nonmetals.
  • Thermal Diffusivity: Rate at which a material transitions from non-uniform to uniform temperature. High thermal conductivity and low specific heat for gold and amalgam restorations can result in higher thermal shock.

• Optical Properties: The science of studying light, sight, vision.

• Optics in Dentistry: Restoring teeth color/appearance. Understanding light and color principles is essential.

• Nature of Light:

  • Light is a beam of photons.
  • Color is determined by the wavelength of light.

• Production of Light:

  • Thermal (e.g., sun, hot metal)
  • Electrical (passing current through an inert gas like neon)
  • Chemical (fluorescence and phosphorescence)

• Interaction of Light and Matter:

  • Reflection:
    • Specular: Light reflects off a smooth surface in one direction (e.g., mirrors).
    • Diffuse: Light reflects off rough surfaces in all directions.
    • Clinical Significance in Dentistry: Material surface smoothness for specular reflection to maintain natural appearance.
  • Refraction: Change in light direction upon entering a medium of differing density. Refractive index is the ratio of the speed of light in a vacuum to its speed in the medium. Materials with matched refractive indices give superior results
  • Scattering: Light redirection or reduction in intensity due to medium obstructions (e.g., opacifiers in composite materials or air bubbles).

• Properties of Materials in Relation to Light Transmission and Absorption:

  • Transparency: Light passes through, objects are clearly visible.
  • Translucency: Light passes through, but is scattered or reflected (objects are seen vaguely).
  • Opacity: Light does not pass through (e.g. solid color).

• Luminescence (Fluorescence and Phosphorescence): Emission occurs when emitted light wavelength is longer than the exciting waves.

• Fluorescence - immediate emission.

• Phosphorescence: delayed emission.

• Importance in Dentistry (Luminescence): Sound teeth exhibit fluorescence, restorative materials may contain fluorescing agents, contributing to tooth brightness and vibrancy.

• Laser: Light Amplification by Stimulated Emission of Radiation. Characteristics include Monochromatic, Coherent, and Collimated; producing a special type of light.

• Clinical Applications (Laser): Surgery, removal of carious lesions, curing composite, endodontics, and filling pits and fissures with hydroxyapatite.

• Laboratory Applications (Laser): Welding of high-melting-point alloys and sintering of ceramics.

• Color: Crucial for aesthetic dentistry. Important to reproduce colors correctly and match adjacent teeth.

• Color Definition and Dimensions: Munsell color system uses hue, chroma, and value to describe color.

• Shade Color Matching:

  • Dental Shade Guides: Standardized color standards mimicking natural teeth for matching restorations to teeth.
  • Methods (Photocolorimetry, Chair-side Colorimeter):
    • Photocolorimetry: Holding shade guide next to teeth and taking a photo. Lab technician measures color via a computer program.
    • Chair-side Colorimeter: Handheld device measuring tooth shade directly.

• Metamerism and Isomeric Pairs:

  • Metamerism: Change in color matching of two objects under different light sources.
  • Isomeric Pair: Color-matched objects under all light sources.

• Summary: The lecture provides crucial information about physical and optical properties, their applications in dentistry, as well as methods for shade color matching and color reproduction.

Explore the physical and mechanical properties of dental materials in Lecture 5 of the Dental Biomaterials course. This lecture focuses on density, thermal conductivities, and their clinical importance in denture retention and casting procedures. Gain insights into how these properties influence the effectiveness of dental materials.