Dental Materials Science 2 - Resin-Based Composites

General Composition of Resin-Based Composites

  • Resin-based composites (RBC) consist of:
    • Organic resin matrix (main component)
    • Inorganic filler particles (impart strength and wear resistance).

Types of Resin-Based Composite Used in Dentistry

  • Hybrid composite resin
  • Micro-fill composite
  • Flowable composite
  • Bulk-fill composite

Characterization of Resin-Based Composites

  • Resins are characterized by the size and amount of filler which can affect:
    • Mechanical properties
    • Aesthetic properties
    • Handling characteristics.

Key Terminology

  1. Hybrid Composite Resin: Combines both micro-fine and macro-fine filler particles for a balance of strength and aesthetics.
  2. Micro-fill Composite: Small particles for excellent polishability and aesthetics but lower strength.
  3. Flowable Composite: Lower viscosity to flow into cavity preparations but may have lower strength.
  4. Bulk-fill Composite: Designed for placement in thicker sections (4-5mm) with reduced polymerization shrinkage.

Components of Dental Resin-Based Composite

  • Essential components include:
    • Monomers (e.g. Bis-GMA, TEGDMA)
    • Fillers (e.g. silica, barium glass)
    • Coupling agents (to bond filler particles to the resin matrix)
    • Initiators for curing process (e.g. camphorquinone).

Chemical Curing vs. Light Curing

  • Chemically cured composites rely on a chemical reaction typically initiated by an amine or peroxide.
  • Light-cured composites polymerize when exposed to a specific wavelength of blue light.

Understanding Free Radical Polymerization

  • Free radical polymerization is initiated by a photoinitiator that generates free radicals upon light exposure leading to polymer chain growth.
  • Important factors include:
    • Type of photoinitiator used
    • Light intensity and wavelength
    • Thickness of the material layer.

Factors Affecting Polymerization

  • Filling Color: Affects depth of light penetration and eventual polymerization effectiveness.
  • Power of Curing Light: Higher power can enhance polymerization depth and quality.
  • Depth of Cure: The distance between the light source and material can impact curing efficacy.

Clinical Requirements for Resin-Based Composites

  1. Good mechanical properties to withstand occlusal forces.
  2. Proper aesthetics matching the tooth color .
  3. Minimal thermal and chemical sensitivity.
  4. Effective and safe bonding to tooth structures.

Polymerization of Single-Paste (Light Cured) Composite

  • Involves combination of initiation (activation of initiators by light), propagation (chain growth), and termination (ceases growth upon deactivation or combining of radicals).
  • Factors affecting polymerization include material thickness, light exposure time, and curing light characteristics.

Comparison of Types of Resin-Based Composites

  1. Nanocomposite: Superior strength, lower shrinkage, enhanced polishability.
  2. Multipurpose Composite: Versatile; suitable for anterior/posterior use.
  3. Micro-fill Composite: Best for esthetics but has higher shrinkage.
  4. Bulk-fill Composite: Suitable for posterior restoration due to reduced shrinkage; however, shade options may be limited.
  5. Flowable Composite: Easily adaptable for different cavity shapes but may result in higher wear.