Lec 8 3 (medium)

Prosthodontics Lecture 8 & 9 - Denture Bearing Areas

• Module: Prosthodontics 3 (BDS IV/Semester 7)
• Lecturer: Dr Vinothkumar Sengottaiyan (@Dr_VK)
• Institution: Oman Dental College

Learning Outcomes

• Differentiate denture bearing areas of maxillary and mandibular arches into supporting, relief, and limiting areas.
• Plan and condition denture bearing areas for complete dentures.
• Understand possible preprosthetic surgeries for denture construction.
• Identify situations requiring specialist referral for further management.

Support - Definition

• General: Foundation area for a dental prosthesis.
• Also refers to resistance that a prosthesis can have against occlusal/functional forces.
• In complete dentures: Area of the mouth available for support.
• Supporting areas in the mouth are best suited for absorbing functional forces during mastication.

Parts of Complete Denture

• Denture Base/Foundation: Part of the denture that contacts the supporting area (denture bearing area).
• Also called impression surface or intaglio surface.
• Recorded and reproduced by final impression.
  • Subdivisions: Support areas, relief areas, and peripheral seal/border areas.
• Denture Flange: Surface outside the denture base.
  • Also called cameo/art surface.
  • Developed by the dentist – influences aesthetics, not function.
• Occlusal Surface: Surface formed by artificial teeth.
  • Used for creating balance for dentures during mastication.

Denture Bearing Area

• Refers to all surfaces contacted by the denture base.
• The denture base (fitting surface) contacts oral tissues.
• Denture bases, typically made of hard materials like acrylic, do not change shape during function.
• All occlusal forces are transferred completely to the denture bearing areas by the denture base.

Forces in Complete Dentures

• Forces perpendicular to the occlusal plane are generated in complete dentures during mastication.
• These forces are transmitted as compressive forces to the underlying supporting tissues.
• In bone, these forces cause bone resorption.
• In tissues, these forces cause ischemia (reduction of blood flow).
• Bone resorption and ischemia are long-term problems.
• However, some pain, ulceration, and irritation can occur instantly or in short-term use.

What Happens When We Make an Impression?

• A dental impression records the anatomy of the oral cavity using impression trays and appropriate materials.
• Pressing materials against structures in the oral cavity is compression.
• Denture base applies similar force for making an impression.
• Some structures (teeth, bone) withstand pressure, others (mucosa, muscles) are compressed.

How to Manage Compression in Denture Bases?

• Fabricate a customized tray contacting only pressure-resistant areas.
• Fabricate the tray with a primary cast from an initial/preliminary impression.
• Implement wax sheets (called relief wax) in areas needing pressure reduction.
• Fabricate a special tray with acrylic.
• Remove wax before the final impression.
• Use relief holes in the tray to further reduce pressure.

Anatomical Landmarks

• Visible/palpable structures in the edentulous oral cavity.
• Important for impressions and casts.
• Knowledge of classification is essential for making custom trays for selective pressure applications during impression making.
  • Support areas (primary and secondary).
  • Relief areas.
  • Border areas/peripheral seal areas.

Tissues of Edentulous Oral Cavity

• Mucosa:
  • Keratinized attached mucosa (residual ridge and palate).
  • Non-keratinized unattached mucosa (vestibule, cheeks, floor of mouth, soft palate, uvula, tonsillar pillars).
• Submucosa: Fibrous tissue (anterior palate, tuberosities, residual ridges).
• Fatty/glandular tissue: (posterior palate, some areas of floor of mouth).
• Muscular tissue: (along vestibule, cheek, floor of mouth).
• Bone:
  • Cortical bone (most areas except crest of residual ridges).
  • Medullary bone (along crest of residual ridges).

Favourable Characteristics of Supporting Areas

• Thick cortical bone: Avascular, resistant to resorption, excellent supporting structure.
• Thick keratinized attached mucosa: Resists trauma/ulceration from denture base movements.
• Direction relative to occlusal plane: Maximum support and resistance when parallel (or perpendicular) to occlusal forces.

Maxillary Anatomical Landmarks

• Detailed list of landmarks (e.g. Tuberosity, Buccal frenum, Crest of residual ridge).

Mandible Anatomical Landmarks (Self-Assessment)

• Detailed list of landmarks (Refer to the next slide and label the picture).

Classification of Anatomical Landmarks - Mandible

• Supporting Structures: (provide resistance to masticatory forces), specific characteristics like cortical bone, keratinized mucosa, perpendicular to occlusal forces. Categorized into primary and secondary, including the buccal shelf and slopes of residual ridge.
• Limiting Structures: (limit denture base extension), including labial frenum, labial/buccal vestibule, pterygo-mandibular raphe, lingual frenum, and lingual vestibule.
• Relief Areas: (require relief from denture base pressure during function), including areas like mental foramen, crest of residual ridges, canine and premolar eminences, genial tubercles, and mylohyoid ridges..

Pre-Prosthetic Surgeries

• Alveoloplasty: Reduce sharp bony extensions of the alveolar ridge.
• Vestibular Extension/Sulcus Deepening: Increase sulcus depth, often via skin/mucosal grafting.
• Tuberosity Reduction: Create space in posterior ridge for posterior denture base extensions.
• Debulking of Flabby Tissues: Achieve firm mucosal support.
• Ridge Augmentation: Increase alveolar ridge height to improve denture stability. Implants may be considered, depending on the type of augmentation.

Textbook for Reference

• Zarb, G.A., 2012. Prosthodontic Treatment for Edentulous Patients: South Asia Reprint-E-book. Elsevier Health Sciences.

Explore the denture bearing areas in the maxillary and mandibular arches through this quiz based on Prosthodontics Lectures 8 and 9. You'll learn about supporting, relief, and limiting areas, alongside preprosthetic surgeries essential for complete dentures. Perfect for BDS IV students looking to enhance their understanding of denture construction.