Dental Biomaterials I - Lecture 2: Structure of Matter

Dental Biomaterials I - Lecture 2: Structure of Matter

• Matter: Any substance with mass and occupying space.
• Atom: The fundamental unit of matter, having all the characteristics of an element. Made up of protons, neutrons, and electrons.
  • Protons: Positively charged particles located in the nucleus.
  • Neutrons: Neutral particles found in the nucleus.
  • Electrons: Negatively charged particles orbiting the nucleus.
• Atomic Basis and Properties: There's a direct relationship between the atomic arrangement and a material's properties.
• Interatomic Attraction:
  • Primary Bonds (Chemical Bonds): These hold atoms together in solids.
    • Ionic Bonds: Attraction between oppositely charged ions (metal and nonmetal). Sodium chloride (NaCl) is a classic example.
      • Characteristics: Strong bonds, heat-resistant, insoluble in organic solvents, soluble in ionized solvents (like water, acids, and alkalis), can conduct electricity in solution.
      • Dental Examples: Gypsum, phosphate-based cements.
    • Covalent Bonds: Sharing of electrons between atoms (nonmetal and nonmetal). An example is dihydrogen (H2).
      • Characteristics: Strong, water-insoluble, soluble in organic solvents, electrical and thermal insulators.
      • Dental Examples: Dental resin.
    • Metallic Bonds: Valence electrons are shared freely among atoms (usually metals), forming an electron cloud.
      • Characteristics: Good electrical and thermal conductivity, luster, ductility, and malleability.
      • Dental Examples: Dental amalgam, casting alloys, wrought wires.
  • Secondary Bonds (Physical Bonds): These are weaker attractions.
    • Hydrogen Bonds: Strongest secondary bond, arising from the polar nature of molecules like water.
      • Characteristics: Weak bonds, low melting points, high thermal expansion.
    • Van der Waals Forces: Weaker attractions between temporary dipoles, found in inert gases.
      • Characteristics: Weakest secondary bond, low melting points.

Structure of Solids

• Crystalline Solids: Atoms arranged in a highly ordered, repeating pattern called a space lattice.
  • Characteristics: Definite melting temperatures. Examples: Metals, quartz, diamond.
• Amorphous Solids: Atom arrangement is random and lacks long-range order.
  • Characteristics: No definite melting temperature; gradually softens upon heating, and gradually hardens upon cooling. Examples: Glass, some polymers (e.g., waxes, rubber, dental resins).

Space Lattice

• Space Lattice: The arrangement of atoms in a solid, resulting from primary or secondary bonds.
• Unit Cell: The smallest repeating unit within a space lattice.
• Lattice Types: There are 14 possible types, like cubic (simple, body-centered, face-centered), tetragonal, etc.

Objectives

• Students will be able to describe the relationship between atomic structure and properties of materials
• Compare and contrast different types of chemical bonds (ionic, covalent, metallic) and their roles in dental materials.
• Differentiate between molecules and lattices and provide examples of restorative materials that exhibit each.