Lec 8 (medium)

Support - Definition

• Support, in general, is the base area where a dental prosthesis rests.
• It also refers to the resistance a prosthesis can withstand against occlusal/functional forces.
• In complete dentures, support is the available area in the mouth to support the denture.
• In other cases, supporting areas are locations in the mouth best suited to absorb the functional forces during chewing.

Parts of Complete Denture

• Denture base/denture foundation: The part of the denture contacting the supporting area (denture bearing area).
  • Also known as the impression surface or intaglio surface.
  • Recorded and reproduced from final impressions.
  • Has subdivisions:
    • Support areas
    • Relief areas
    • Peripheral seal/border areas
• Denture flange: The surface outside the denture base.
  • Also called cameo/art surface.
  • Created by the dentist.
  • Affects aesthetics, not function in most cases.
• Occlusal surface: The surface formed by artificial teeth.
  • Used to create balance for dentures during chewing.

Denture Bearing Area

• Refers to all surfaces the denture base contacts.
• The image shows the denture base's fitting surface, which contacts oral tissues.
• Denture bases are typically made of hard materials like acrylic.
• They maintain shape during function.
• All occlusal forces are transferred to the denture bearing areas via the denture base.

Forces in Complete Dentures

• Forces perpendicular to the occlusal plane are generated during chewing.
• These forces are transmitted to supporting tissues as compressive forces.
• Compressive forces in bone cause bone resorption.
• Compressive forces in tissues cause ischemia (reduced blood flow).
• Bone resorption and ischemia are long-term problems.
• Sometimes, pain, sores, and irritation occur immediately or shortly after use.

What Happens When We Make an Impression?

• A dental impression records the oral anatomy.
• Appropriate impression materials are carried by impression trays.
• The material is pressed against oral structures to create a record.
• Pressing against these structures constitutes compression.
• The denture base should apply as much force as used to create the impression.
• Some structures like teeth and bone withstand pressure.
• Other structures (mucosa, muscle attachments) compress easily.

How to Manage Compression in Denture Bases

• To manage pressure, a customized tray should be made.
• The tray contacts only pressure-resistant areas.
• The tray is made from a duplicate (primary cast) of an initial/preliminary impression.
• Wax (relief wax) is placed in areas requiring pressure reduction during impression taking.
• A special acrylic tray is created following wax removal.
• Further pressure reduction can be achieved through holes in the tray (relief holes).

Anatomical Landmarks

• Anatomical structures in the edentulous mouth are visible and palpable.
• These structures are visible in impressions and casts.
• Understanding these structures and how they are classified aids in custom tray creation, allowing for selective pressure application during impressions.
• Key classifications:
  • Support areas - primary, secondary
  • Relief areas
  • Border areas/peripheral seal areas

Favorable Characteristics of Supporting Areas

• Thick cortical bone: Avascular, resistant to resorption, excellent support.
• Thick keratinized attached mucosa: Resists trauma and ulcers caused by denture movement.
• Direction relative to the occlusal plane: Optimal support and resistance when the area is parallel to the occlusal plane.

Relief Areas

• Sometimes, favorable support criteria are present, but these areas do not provide support.
• Key relief areas:
  • Nerve canals (mental, incisive)
  • Sharp bony edges (canine prominence, interdental peaks)
  • Fresh extraction socket spaces
  • Frenal attachments
  • Areas with soft medullary bone
  • Areas of thin mucosa (mid palatine raphe, external oblique ridge).

Peripheral Seal Areas

• These areas determine denture flange length and thickness.
• Classification:
  • Frenal areas: Where muscles attach.
  • Sulcus areas: Spaces between attachment points where muscles move.

Maxilla - Support and Relief

• Primary support: Horizontal surface of posterior 2/3 of the palate.
• Secondary support: Anterior and lateral slopes of the palate, residual ridge slopes.
• Relief areas: Residual ridge crest, incisive papilla, mid palatine raphae, canine eminence, undercuts (if any).

Maxilla - Peripheral Seal Areas

• Key areas:
  • Labial sulcus
  • Labial frenum
  • Buccal sulcus
  • Buccal frenum
  • Hamular notch
  • Posterior palatal seal area

Mandible - Support and Relief

• Primary support: Buccal shelf.
• Secondary support: Residual ridge slope.
• Relief areas:
  • Residual ridge crest
  • Mental foramen
  • Mylohyoid ridge
  • Genial tubercles

Mandible - Peripheral Seal Areas

• Key areas:
  • Labial frenum
  • Labial sulcus
  • Buccal frenum
  • Buccal sulcus
  • Retromolar pad area
  • Lingual frenum
  • Alveolo-lingual sulcus