Acrylic Resins in Prosthetic Dentistry

Objectives

• List the important properties of acrylic resins.
• Describe the procedure for heat processing a denture.
• Compare properties of hard and soft lining materials.
• List indications for short- and long-term soft liners.
• Compare chairside vs. laboratory-processed hard liners.
• List indications for using acrylic denture teeth vs. porcelain teeth.
• Use an ultrasonic cleaner for cleaning dentures.
• Educate patients on home care for dentures.
• Inform patients about precautions when cleaning dentures.
• Fabricate custom impression trays for upper and lower arches.
• Fabricate record bases for complete dentures using light-cured material.

Introduction to Acrylic Resins

• Definition: Acrylic resins are synthetic polymers crucial in prosthetics, particularly for removable appliances.
• Uses: Commonly employed in constructing complete/partial dentures, orthodontic retainers, and maxillofacial prostheses.

Properties of Acrylic Resins

• Modifiers: Alter the physical properties:
  • Plasticizers soften acrylic plastics for better pliability.
• General Properties:
  • Polymerization shrinkage.
  • Dimensional change due to water sorption.
  • Strength: Generally low; susceptible to wear.
  • Thermal conductivity: Poor conductor of temperature.

Types of Processing Acrylics

• Chemical-Cured:
  • Softer and more porous.
  • Less color stability.
  • Higher shrinkage risk.
• Heat-Cured:
  • Stronger, less shrinkage.
  • Better wear resistance and color stability.
• Microwave Processing:
  • Short processing time (~5 min).
• Injection Molding:
  • Faster than heat curing, involves injecting material into a mold.
• Light-Cured Resins:
  • Fast, user-friendly but requires a light-curing unit.
• CAD/CAM:
  • Integrates traditional methods and digital systems for improved fit and reduced appointments.

Soft vs. Hard Relining Materials

• Soft Relining Materials:
  • Applied to the tissue-bearing surface of the denture base.
  • Used for short-term (days/weeks) or chronic conditions.
  • Short-term variants called tissue conditioners.
• Hard Relining Materials:
  • Used to improve fit by filling spaces as bone resorbs.
  • Can be done chairside or in a lab:
  • Chairside: Immediate adjustment using an acrylic bur for attractive fit.
  • Laboratory: More durable reline created, fewer staining problems.

Denture Teeth Types

• Acrylic Resin Teeth:
  • Most common, strong bond to acrylic base.
• Composite Resin Teeth:
  • More natural appearance.
• Porcelain Teeth:
  • Hard, brittle, highly wear-resistant.

Maxillofacial Prostheses

• Used to replace facial tissues lost due to various reasons (trauma, disease, etc.).
• Characteristics needed:
  • Match skin color.
  • Tear-resistant, flexible, stain-resistant, attachable with adhesives.

Denture Repair Techniques

• Chemical-Cured Repair Material:
  • Lab-repaired, must be disinfected.
• Light-Cured Repair Material:
  • Uses intense blue light for curing.

Instructions for New Denture Wearers

• Speaking: May require practice.
• Eating: Initial biting force reduced by 20%.
• Fit: Maxillary denture forms seal; mandibular looser.
• Soreness: Areas prone to irritation include bite spots against cheeks.
• Looseness: Expect changes as alveolar bone shrinks over time.
• Regular Checkups: Essential for checking fit and oral health.

Care of Acrylic Resin Dentures

• Home Care:
  • Clean with denture brush twice daily.
  • Avoid dropping; hold over towel/water.
  • Remove at night for tissue breathing.
• In-Office Care:
  • Ultrasonic cleaning for debris removal.
  • Must keep dentures wet during storage to prevent distortion.

Summary Topics

• Uses of acrylic resins (plastics).
• Definition of polymethyl methacrylate (PMMA).
• Various acrylic processing methods and benefits/drawbacks.
• Importance of denture relining.
• Expectations for new denture wearers.
• Home care tips for maintaining dentures.