Dental Biomaterials I - Lecture 5 Quiz

Dental Biomaterials I - Lecture 5: Physical Properties of Dental Materials

• Physical properties are based on laws of physics (mass, heat, light, electricity, energy, force, and other physical phenomena).
• Mechanical properties are a subgroup of physical properties, dealing with force.
• This chapter provides background and preparation for later discussions on how these properties determine characteristics of dental materials.

Mass-Related Properties: Density

• Density is the mass per unit volume of a material.
• Units are gm/cm³ and pound/in³.
• Clinical importance:
  • Upper dentures need low density for retention.
  • Low-density molten alloys need higher pressure during casting to fill molds.

Thermal Properties

• Thermal Conductivity: Ability of a material to transfer heat. Lower conductivity means slower heat transfer.
• Coefficient of Thermal Conductivity (k): Amount of heat transported per second across a unit cube when one face is hotter.
• Thermal Coefficient of Expansion (α): Change in length per unit length for a 1°C change in temperature.
• Melting and Freezing Temperatures: Temperatures at which a material changes from solid to liquid or vice-versa. Critical for casting procedures.
• 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 needed to raise the temperature of 1 gram of a substance by 1°C. Metals have low specific heat, while non-metals have high specific heat.
• Thermal Diffusivity: Rate at which a material converts from non-uniform to uniform temperature. -Important for: -Gold or amalgam restorations: These may cause thermal shock due to their high thermal diffusivity, high thermal conductivity, and low specific heat.

Optical Properties

• Optics: Science of studying light, sight, vision (including color).
• Importance: Restorative dentistry seeks to restore tooth color/appearance. Knowledge of light & color is essential.
• Nature of Light: Light is a beam of photons, color is determined by wavelength of light.
• Production of Light:
  • Thermal (e.g., sun, hot metal)
  • Electrical (e.g., passing electric current through an inert gas)
  • Chemical (fluorescence, phosphorescence)
• Interaction of Light and Matter
  • Reflection (specular and diffuse): Specular reflection occurs on smooth surfaces (e.g., mirrors) where the angle of incidence equals the angle of reflection. Diffuse reflection occurs on rough surfaces, scattering light in all directions. Smooth surfaces are important for restorations to reflect light and appear natural.
  • Refraction: Change in the direction of light as it enters a different medium. Important for the matching of refractive indices of restorative materials & tooth structures.
  • Scattering: Redirection of light rays by inclusions (e.g., air bubbles) in a material. In composites, scattering centers (opacifiers) cause light to emerge in all directions, leading to opaque or semi-opaque materials.
• Properties of Materials Related to Light Transmission/Absorption:
  • Transparency: Allows light to pass through without significant distortion (e.g., glass).
  • Translucency: Allows some light to pass through, scattering or reflecting the rest (e.g., tooth enamel).
  • Opacity: Prevents light from passing through (e.g., amalgam).
• Luminescence (Fluorescence and Phosphorescence): Emitting light in response to stimulation. Fluorescent emit light immediately after stimulation, while phosphorescent light continues after stimulation ceases.
• Importance in Dentistry:
  • Teeth fluoresce under UV light.
  • Restorative materials used in dentistry may be formulated with fluorescent agents to create a more natural appearance.

Laser

• Light Amplification by Stimulated Emission of Radiation (LASER)
• Production of laser light: Solid, liquid, or gas medium excited by high energy to produce special light.
• Characteristics: Monochromatic (single wavelength), Coherent (waves in-phase), Collimated (parallel beams).

Clinical Application of Laser

• Surgery: Removal of soft tissue, Tissue regeneration, ulcer healing, blood coagulation.
• Dentistry: Removal of initial carious lesions, curing composite, endodontics, filling pits & fissures.
• Laboratory:* Welding of high-melting alloys, sintering of ceramics

Color

• Color perception: Object visibility depends on reflecting light. Light is reflected, focused on retina (converted to nerve impulses), transmitted to brain.
• Cone cells (retina): Responsible for color vision.
• Color Definitions:
  • Hue (dominant wavelength): Name of color.
  • Chroma (spectral purity): Saturation/intensity of a color.
  • Value (Luminous reflectance): Lightness or darkness of a color.
• Color Matching:
  • Color match ideal done under multiple light sources
  • Metamerism: Change in color match when observed under different light sources.
  • Isomeric colors: Match under all light sources.

Shade Color Matching

• Used to determine natural tooth color for restorations.
• Shade guides: Standard color standards mimicking dental structures.
• Used to visually match restorations to natural teeth.
• Popular tools like Vitapan 3D-Master and Chromascop.
• Photocolorimetry and chair-side colorimeters facilitate accurate color matching.