Fundamentals of Materials Science

FUNDAMENTALS OF MATERIALS SCIENCE

Introduction

  • The study of materials science encompasses understanding the properties, behaviors, and applications of various materials. This generally covers physical, chemical, and mechanical properties relevant to various fields, especially in dental materials and engineering.

Challenges in the Oral Environment

  • Hostile Oral Environment:

    • Factors contributing to the degradation of dental materials:

    • Saliva composition

    • pH levels

    • Temperature changes

    • Mechanical forces from chewing

The Goal of Materials Science

  • No Ideal Material Exists!

    • Materials must be chosen considering specific applications, properties, and environmental interactions.

Periodic Table of Elements

  • Structure and Information of Elements:

    • Elements categorized by:

    • Atomic Number

    • Symbol

    • Name

    • Atomic Mass (in g/mol)

    • Electrons per shell

    • State of matter

    • Groups covered include:

    • Alkali metals

    • Alkaline earth metals

    • Transition metals

    • Lanthanides

    • Actinides

Examples of Elements:

  • Hydrogen (H)

    • Atomic Number: 1, Atomic Weight: 1.008, State: Gas

  • Helium (He)

    • Atomic Number: 2, Atomic Weight: 4.0026, State: Gas

  • Iron (Fe)

    • Atomic Number: 26, Atomic Weight: 55.845, State: Solid

Three Properties of Materials

  1. Physical Properties:

    • Include mass, force, light, heat, electricity.

  2. Mechanical Properties:

    • Related to materials' resistance to forces.

  3. Chemical Properties:

    • Include setting reactions and degradation.

  4. Biologic Properties:

    • Effect on living tissue.

Physical Properties of Materials

Density

  • Definition: Amount or mass of a material in a given volume.

    • Depends on the type of atoms present.

    • High-density objects feel heavy.

    • Different states of matter exhibit different densities:

    • Gas (less dense)

    • Liquid

    • Solid (more dense)

Boiling and Melting Points

  • Concept:

    • Atomic bonds between atoms or molecules break down due to thermal energy.

    • High melting points may complicate material workability.

Amalgam Composition

  • Example:

    • Pure silver (melting point 961°C) + mercury (melting point 39°C) forms a workable amalgam.

    • When packed into cavities at body temperature (37°C), the amalgam hardens with volumetric expansion occurring.

Corrosion and Degradation

  • The addition of tin helps control expansion, yet it introduces corrosion issues, highlighted by challenges in the tin-mercury phase that affects longevity.

Other Physical Characteristics Affecting Dentistry

Vapor Pressure

  • Definition: Measure of a liquid's tendency to evaporate at a given temperature.

    • High vapor pressure relates to higher evaporation rates.

    • Evaporation vs. Boiling:

    • Bubbles form when vapor pressure exceeds atmospheric pressure.

    • Important for using solvents in dentistry.

Thermal Conductivity

  • Definition: Amount of heat that passes through a material.

    • Ability of materials to transfer heat influences their use in clinical applications (e.g., dental restorations).

Thermal Conductivity vs. Thermal Diffusivity

  • Thermal Diffusivity: Rate of heat spread within a material.

  • Significance in dental materials for insulation of dental pulps and preventative measures against heat transfer during procedures.

Coefficient of Thermal Expansion and Contraction

  • Definition: Change in volume/length of a material with temperature change.

    • Cooling causes contraction; heating causes expansion.

    • Linked to percolation issues in dentistry, affecting microleakage and potential bacterial penetration between interfaces.

Key Concepts Related to Adhesion and Viscosity

Mechanical Adhesion and Chemical Adhesion

  1. Mechanical Adhesion:

    • Involves physical interlocking of materials.

  2. Chemical Adhesion:

    • Involves chemical bonding at the molecular level.

Viscosity

  • Definition: Ability of a material to flow; high viscosity means high resistance to flow.

  • Changes in viscosity affect functional ability (e.g., dental cements/adhesives).

Wetting and Contact Angle

  • Wetting:

    • Refers to the liquid's ability to maintain contact with solid surfaces.

    • Influences adhesion and bonding effectiveness.

    • Characterized by contact angles:

    • Hydrophilic surfaces: Low contact angles (0°-90°) enhance wetting.

    • Hydrophobic surfaces: High contact angles (>90°) decrease wetting.

Surface Energy and Surface Tension

  1. Surface Energy:

    • Attraction force a material’s surface exerts.

    • High-energy surfaces facilitate adhesion.

  2. Surface Tension:

    • Resistance of liquid to deform or break.

    • Influences spreading and therefore adhesion capabilities.

Mechanical Properties of Materials

Hardness and Toughness

  • Hardness: Resistance to scratching or indentation; measured using tests like Knoop or Durometer.

  • Toughness: Capability of a material to deform without fracturing; relevant for certain dental materials.

Stress and Strain Relationships

  1. Stress: Force per area acting on a material, defined as ( ext{Stress} = rac{ ext{Force}}{ ext{Area}}) and measured in psi or pascals (N/m²).

  2. Strain: Change in length relative to original length, indicating deformation resulting from stress.

Stress-Strain Curve

  • Graphical representation of the relationship between stress and strain. Key features include:

    • Elastic Limit: Point where material deforms elastically.

    • Yield Strength: Point where material begins to deform plastically.

    • Ultimate Strength: Maximum stress a material can withstand before failure.

    • Illustrates important properties like resilience and toughness, relating to maximum deformation before fracturing.

Stress Types in Materials

  1. Compression: Stress that presses or crushes a material.

  2. Tension (Tensile): Stress that stretches a material.

  3. Shear: Sliding forces affecting the material at planes.

  4. Torsion: Twisting actions, relevant for certain types of implants.

  5. Bending: Combination of compressive and tensile forces acting on a material.

Fracture Toughness and Fatigue in Materials

  • Fracture Toughness: Energy required to fracture a material with existing cracks.

  • Fatigue: Results from repetitive stress leading to structural microcrack growth and eventual failure; important in predicting material performance in clinical settings.

Summary of Dental Materials

  • Table comparing various dental materials by their tensile strength, compressive strength, shear strength, elastic modulus, and hardness values reflecting their mechanical properties.

Conclusion

  • The field of materials science is integral to understanding the development and application of materials, particularly in dentistry, where properties such as adhesion, viscosity, and thermal characteristics play crucial roles in performance and patient outcomes.

Questions?

  • Open to discussion and questions regarding materials science and its applications.