Denture Base Materials - Part 1

Introduction

• Focus on denture base materials in four parts.
• Topics Covered:
  • Introduction
  • Classification
  • Synthetic resins (classification, ideal requirements, uses)
  • Polymers (nature, structure, polymerization process, copolymers, plasticizers)

Historical Denture Base Materials

1. Vulcanite:

• Contains 32% sulfur and metallic oxides.
• Advantages: Non-toxic, non-irritant, excellent mechanical properties.
• Disadvantages: Absorbs saliva, bacterial proliferation, unpleasant taste/odor, poor aesthetics, dimensional changes.

2. Nitrocellulose:

• Disadvantages: Dimensionally unstable, unpleasant taste, warpage, poor fit, water absorption, poor color stability.

3. Phenol Formaldehyde:

• Disadvantages: Easy discoloration, unaesthetic, difficult to repair.

4. Porcelain:

• Disadvantages: Difficult to fabricate, easy to break.

Classification of Denture Base Materials

1. Metallic: Cobalt chromium, gold, aluminum, stainless steel.
2. Non-Metallic: Acrylic resins, vinyl resins.
3. Temporary Materials: Self-cure/cold-cure resins, shellac base plate, base plate wax.
4. Permanent Materials: Heat cure, metallic denture-based materials.

Synthetic Resins

• Influence: Modern living greatly influenced by synthetic plastics.
• Types: Fibrous/rubber-like, hard/resinous.
• Molecular Weight: High molecular weight polymers.
• Classification:
  • Thermoplastic: Softened under heat/pressure, no chemical change, soluble in organic solvents (e.g., polymethyl methacrylate).
  • Thermoset: Chemical reaction, insoluble in organic solvents (e.g., cross-linked polymethyl methacrylate).

Ideal Requirements of Dental Resins

• Tasteless, odorless, non-toxic, non-irritant.
• Aesthetically good.
• Dimensionally stable, adequate strength, resilience, abrasion resistance.
• Insoluble, impermeable to liquids.
• Lightweight, high thermal conductivity, radioopaque.
• Easy to fabricate and repair.

Uses of Resins

• Making dentures, artificial teeth, restorative material.
• Cements, space maintainers, crown and bridge facings.
• Maxillofacial prosthesis, temporary crowns, root canal filling material.
• Athletic mouth protectors, impression trays.

Polymers

• Definition: Structure made up of numerous monomer units (poly = many, mer = simplest structural unit).
• Examples: Polymethyl methacrylate (PMMA) derived from methyl methacrylate.
• Degree of Polymerization: Total number of mer units in a polymer; higher molecular weight = higher degree of polymerization.
• Molecular Weight Distribution: Ideally narrow distribution for useful polymers.
• Structures:
  • Linear Polymers: Homopolymer, random copolymer, block copolymer.
  • Branched Polymers: Homopolymer, random copolymer, graft copolymer.
  • Cross-Linked Polymers: Two types of monomers in main chain connected by single type.

Polymerization Process

• Definition: Series of chain reactions forming polymers from monomers.
• Types: Condensation (elimination of small molecules) and addition (no byproducts).

Chemical Stages of Polymerization

1. Induction: Initiation phase; energy transferred to monomer molecules.
2. Propagation: Chain reaction continues, molecules added to chain.
3. Termination: Ends chain reaction (direct coupling or hydrogen exchange).
4. Chain Transfer: Further termination mechanism.

Inhibition of Polymerization

• Factors: Impurities, hydroquinone (added to prevent polymerization during storage), oxygen.

Copolymers

• Definition: Polymer formed from different types of monomers.
• Types: Random copolymer, graft copolymer, block copolymer.
• Applications: Improved physical properties, increased flexibility, strength, and adhesive properties.

Cross-Linking

• Definition: Chemical bonds/bridges between linear polymers.
• Applications: Increases strength, solubility, decreases water absorption, increases resistance to crazing.

Plasticizers

• Purpose: Reduce brittleness, increase solubility, reduce strength.
• Types: External (penetrate macromolecules) and internal (integral part of polymer).

Conclusion

• Part 1 covers basics of denture base materials.
• Future parts will cover heat, chemical, and light-activated denture base resins in detail.
• Encouragement to subscribe for more content.