Denture Base Polymers Overview

Denture Base Polymers

• Denture bases are the parts of dentures that support and hold artificial teeth.
• They rest on the tissues.
• Functions include supporting and retaining teeth, stress distribution, and improving aesthetics.
• Requirements of denture bases include having strength and durability, satisfactory thermal properties (thermal conductivity and CTE), accuracy and dimensional stability, chemical stability, insolubility and low sorption of oral fluids, absence of taste and odor, biocompatibility, natural appearance and color stability, adhesion to other materials, ease of fabrication, and a moderate cost.
• Denture bases can be classified as metallic or non-metallic. Metallic include cast gold alloys, cast cobalt-chromium, cast titanium and titanium alloys, and swaged stainless steel.
• Advantages of metallic denture bases include high mechanical properties, resistance to scratching, minimal allergy and bacterial/fungal colonization.
• Disadvantages of metallic denture bases include not matching gingival tissues, difficulty in construction/repairs, finishing/polishing, relining, weight, and cost.
• Non-metallic denture bases include heat-cured PMMA, self-cured PMMA and light-cured PMMA.
• Advantages of non-metallic bases include a color that matches gingival tissues, ease of construction, repair, finishing, polishing, relining, lightweight, and cost.
• Disadvantages of non-metallic bases include moderate mechanical properties, susceptibility to scratching, lack of heat transmission, possible allergies, potential for crazing or bleaching, more colonization likelihood.
• Acrylic resins are polymers of methyl methacrylate.
• Types of acrylic resin used in denture bases include heat-cured, self-cured, and light-cured.
  • Heat-cured acrylic is common with low monomer content, and usually supplied in powder and liquid form.
  • Self-cured acrylic uses a chemical activator to initiate polymerization.
  • Light-cured acrylic uses visible blue light as an activator, is supplied in sheets, and is adapted to the cast dentures.
• Acrylic resin teeth are similar to the base resins but are strengthened with cross-linking agents.
• Porcelain teeth are harder, more stain-resistant, and held to the denture by mechanical undercuts.
• Porcelain teeth are rarely used because they wear on opposing teeth and cause bone loss in supporting and opposing alveolar ridges.
• Polymerization is a chemical reaction that forms polymer chains from monomers.
  • Addition polymerization occurs without loss of mass.
  • Condensation polymerization involves the loss of a small molecule like water.
  • Free radical polymerization stages: Initiation, Propagation, and Termination.
• Inhibitiors in polymerization process can prevent monomers from becoming polymers.
• Polymer structure can be linear, branched, or cross-linked; cross-linked polymers are more rigid.
• Polymerization is affected by different chemical factors.

Denture teeth

• Denture teeth come in various shapes, sizes, and shades.
• Teeth shape is chosen to match the patient's natural teeth, often based on previous photos.
• Tooth sizes are determined by the patient's arch size.
• Patients sometimes desire overly bright white teeth and need appropriate color guidance.
• Teeth should have good appearance (similar to natural teeth in shape, color and translucency).
• Teeth should have compatible attachment to denture bases.
• Teeth need to have low density to not increase the overall weight.
• Teeth should be strong and tough to resist fracture.
• Teeth need to withstand mouth abrasions during cleaning.
• Teeth should allow dental grinding for occlusion adjustments.

Denture construction steps

• Flasking: Molding denture
• Wax elimination: Removal of wax used in the mold
• Proportioning, mixing and packing: Mixing resins for base
• Trial closure: Checking fit with the mouth
• Curing: Polymerization process
• Deflasking, finishing & polishing: Final shaping and polishing
• Mixing ratio is typically 3:1 by volume, 2:1 by weight.
• Initial mixing is done in a sealed glass jar to prevent loss of monomer by evaporation.
• Mixing ratio that is too high or too low can result in poor quality dentures.
• Polymerization stages: Sandy, Stringy/sticky, Dough, Rubbery, and Stiff stages
• Curing stages for heat-cured resin involves gradually increasing temperatures above 70 degrees C., where exothermic reaction may result in undesirable boiling.
• Curing times and temperatures can vary based on denture complexity