Dental Prosthetics: Occlusion Blocks and Bases

Record Bases and Occlusion Blocks

• Definition: Occlusion blocks consist of occlusion rims attached to well-fitting trial denture bases.
• Functions:
  • Establish facial contours
  • Aid in tooth selection
  • Establish and maintain vertical dimension of occlusion during record making
  • Make interocclusal records
  • Arrange denture teeth
  • Waxed-up mold for the external surface of the complete denture

Requirements of a Trial Denture Base

• Characteristics:
  • Rigid
  • Accurately adapted to the cast with proper extensions
  • Dimensionally stable with minimal warpage
  • Relieved from any undercuts to avoid scraping the cast during insertion and removal
  • Clean and smooth for patient comfort
  • Proper and uniform thickness (2mm)
  • Easy to construct

Wax Block Out

• Purpose: Protect master casts, tissue undercuts and irregularities are blocked out with base plate wax.
• Locations:
  • Maxillary casts: Labial of the anterior ridge, rugae areas, sometimes in the tuberosity areas laterally.
  • Mandibular cast: Retromylohyoid areas.

Record Base Fabrication Procedure

• Soak Cast: The cast is soaked in room temperature water for 5 minutes to expel air and minimize defects.
• Separating Medium: A tinfoil substitute is used as a separating medium to protect the cast and allow separation of the record base.
• Tinfoil Substitute Application: It is applied twice, allowing the first layer to dry before applying the second. A thin film is applied to all surfaces of the cast including land areas.
• Record Base Material: Autopolymerizing acrylic resin is used to fabricate the record base.
• Record Base Thickness: Thinner on the crest of the ridges and buccal to the crest of the ridges because space may be limited for tooth arrangement.

Occlusion Rim Fabrication

• Material: Occlusion rims are generally made of pink modeling wax.
• Functions:
  • Registration of jaw relationships
  • Choice of artificial teeth:
    • Midline is determined
    • High and low lip lines are determined to indicate tooth length
    • Canine lines indicate tooth width
    • Distance between canine line and posterior end of occlusion rim determines the mesiodistal (M-D) width of posterior teeth
  • Setting-up of teeth
  • Support for lip and cheeks

Occlusion Rim Dimensions

• Width:
  • Approximately 8-10 mm in width posteriorly.
  • 6-8 mm in width anteriorly.
• Maxillary Occlusion Rim Vertical Height: The labial surface in the central area is approximately 6-8 mm anterior to the middle of the incisive papilla and is inclined labially
• Mandibular Occlusion Rim Vertical Height: About 18mm.
  • In the posterior lower region, the height is equal to two-thirds the height of the retromolar pad (middle to upper third).

Important Patient Considerations

• Information: Patients should be informed that the record bases and occlusion rims are not part of the completed dentures. They may feel a little loose due to the blocked-out undercuts.

References

• Rahn, A.O., Heartwell, C.M. (1993). Textbook of complete dentures. (5th ed.). Philadelphia: Lea & Febiger.
• Sowter, J.B. (1986). Baseplates. In R.E. Barton (Ed.), Removable Prosthodontic Techniques (Revised edition). Chapel Hill: University of North Carolina Press.
• Zarb, G.A., Bolander, C.L. (2004). Prosthodontic treatment for edentulous patients. (12th ed.). St. Louis: Mosby Inc.