Dental Resins and Polymerization Concepts

Dental Resins/Synthetic Resin

• Nonmetallic materials, made by combining organic compounds.
• Can be molded into many shapes.
• Also known as "plastics," categorized as fibrous, rubber-like, resinous, or hard-rigid.
• Composed of polymers, large molecules with high molecular weight, often termed as polymers.

Thermal behavior

• Thermoplastic: Softens under heat, becomes liquid at high temperatures, and can be molded without chemical change. Solvable in organic solvents.
• Thermoset: Undergoes a chemical reaction during molding, permanently changing its composition. Becomes infusible and insoluble after curing.

Polymerization

• Monomer: A single unit molecule.
• Polymer: A molecule formed from many monomer units.
• Free Radical: A molecular fragment with an unpaired electron.
• Cross-linked polymer: A network polymer with high molecular weight, formed by covalent bonds between polymer chains.
• Copolymers: Made from two or more monomers.
• Plasticize: To soften.

Polymerization Process (Acrylic and Rubber-reinforced Acrylic)

• Involves conversion of low molecular weight monomers to high molecular weight polymers.
• The process involves adding monomer to polymer to create a plastic mass that can be packed into a mold.

Denture Base Construction

• Impression Making:
  • Preliminary impression is taken first.
  • Study cast is constructed from the preliminary impression.
  • An individual tray is made for the final impression.
  • Master/working cast is created based on the final impression.
• Construction of Denture Base (DB) Wax Pattern:
  • 1-2 layers of high fusing pink wax are applied to the master cast.
  • Wax is adapted to the master cast and edges are sealed.
• Investing: This process uses a metal flask with four parts: base, lower half, upper half, and cover.
  • The master cast is placed in the lower half of the flask.
  • Powder of Paris (POP) is poured into the lower half and allowed to set.
  • Colorgard, a separating medium, is applied to prevent the union between investing medium and the flask parts.
  • The upper half of the flask is placed on top of the lower half and filled with POP.
  • The filled flask is put in a presser to remove excess POP.
  • Colorgard is also applied before investing.
• Wax Elimination:
  • The flask is placed in boiling water for 5-10 minutes to soften the wax.
  • The upper and lower halves of the flask are separated.
  • The softened wax is removed, and hot water is poured into the mold space to create a clear space.
  • The mold space is cleaned and prepared for packing resin.
• Packing of Resin:
  • Two methods: Dough-molding technique/Compression molding and Injection-molding technique.
  • Dough-molding Technique:
    • Uses polymer and monomer in specific ratios by volume (3-3.5:1) or weight (2-2.5:1).
  • Injection-molding Technique:
    • Uses a vent in the flask to attach an outside injector that pushes soft resin into the mold space.

Trial Closure

• The polyethylene sheet separates the resin from the lower mold surface to prevent sticking.
• Trial closure ensures proper mold filling and eliminates air bubbles.

Curing/Processing

• Heating resin to polymerize it.
• Two methods: Rapid Curing and Slow Curing.
• Rapid Curing
  • Uses a water bath to slowly increase the temperature until boiling.
  • Allows the assembly to remain in the bath for 1-1.5 hours after boiling.
• Slow Curing
  • The ideal curing cycle.
  • The assembly is placed in a water bath at 74°C for 6-8 hours (often overnight).

Denture Cleaners

• Dentures collect deposits like natural teeth: stains, calculus.
• Two common removal methods:
  • Professional repolishing.
  • Soaking or brushing at home.
• Ideal denture cleaner requirements:
  • Nontoxic, easy to remove and leaves no traces.
  • Able to remove organic and inorganic deposits.
  • Harmless to denture materials, eyes, skin, and clothing.
  • Stable in storage.
  • Preferably bactericidal and fungicidal.

This quiz covers the essential concepts of dental resins and synthetic polymers, including their thermal behavior and classification as thermoplastics and thermosets. Additionally, it explores the process of polymerization, focusing on monomers, polymers, free radicals, and copolymers.