Record Bases & Occlusion Rims - Key Points

Record Base

  • Definition: A temporary denture base used to hold the occlusion rim during recording and artificial teeth during trial denture.
  • Requirements:
    • Rigid, accurate, and stable.
    • Smooth, rounded borders.
    • Thin at crest, labial, and buccal slopes to allow space for teeth.

Types of Record Blocks

  • Temporary Base:
    • Discarded after use.
    • Examples: Shellac, reinforced shellac, self-cure acrylic resin, light-cure acrylic resin, vacuum-formed plastic sheets.
  • Permanent Base:
    • Becomes part of the final denture.
    • Examples: Heat-cure acrylic resin, metal (gold, chromium-cobalt, chromium-nickel).

Temporary Base Materials

  • Shellac:
    • Advantages: Adapts well, quick to construct, inexpensive.
    • Disadvantages: Warps easily, lacks rigidity, brittle.
  • Reinforced Shellac:
    • Lined with zinc oxide eugenol paste.
    • Still weak and prone to fracture.
  • Self-Cure Acrylic Resin:
    • Methods: Sprinkle-on, finger-adapted, flasking.
    • Advantages: Good strength and dimensional stability.
    • Disadvantages: Thickness control is difficult, residual monomer may cause irritation.
  • Light-Cure Acrylic Resin:
    • Cured with light after adaptation to cast.
  • Vacuum-Formed Plastic Sheets:
    • Advantages: Easy to fabricate, uniform thickness, accurate adaptation.
    • Disadvantages: Expensive, difficult to form smooth borders.

Permanent Base Materials

  • Heat-Cure Acrylic Resin:
    • Advantages: Rigid, accurate, stable, no distortion.
    • Disadvantages: Time-consuming, more expensive.
  • Cast Alloys:
    • Types: Cast gold, chromium-nickel, chromium-cobalt.
    • Advantages: Rigid, accurate, dimensionally stable, adds weight to mandibular dentures, enhances thermal conductivity in maxillary dentures.
    • Construction: Wax pattern on refractory cast, invested, wax burnout, molten metal casting.

Occlusion Rim

  • Definition: Occluding surfaces on denture bases used for recording jaw relations and arranging artificial teeth.
  • Uses:
    • Establish occlusal plane and arch form.
    • Record maxillo-mandibular relations.
    • Arrange teeth.
  • Requirements:
    • Securely attached to base without voids.
    • Positioned in the anticipated final position of artificial teeth.
    • Smooth surfaces that support lips and cheeks.

Measurements

  • Maxillary Wax Rim:
    • Anterior height: 20-22 mm.
    • Posterior height: 16-18 mm.
    • Anterior width: 3-5 mm.
    • Posterior width: 8-10 mm.
    • Occlusal plane parallel to Ala-Tragus line posteriorly and interpupillary line anteriorly.
  • Mandibular Wax Rim:
    • Anterior height: 16 mm.
    • Posterior height: 2/3 of retromolar pad.
    • Anterior width: 3-5 mm.
    • Posterior width: 8-10 mm.
    • Sealed to base without voids.

Construction Methods

  • Hand-made: Soften and fold wax to form a rim, then seal to base.
  • Ready-made: Adapt pre-made horseshoe-shaped rim to base.

Wax Rim Contour

  • Proper lip contour depends on labial wax surface contour.
  • Bone resorption patterns can affect ridge relations.
  • Mandibular cast should be mapped to aid in tooth arrangement.
  • Points and lines on cast and rim used for reference.

Preparation for Closure

  • V-grooves made on occlusal surface of wax to act as index during closure.

Cast Mounting

  • V-shaped grooves prepared on undersurface of cast.