Lec 8 (easy)

Support - Definition

• Support, in general, is the area a dental prosthesis rests on.
• It also refers to the resistance the prosthesis can handle against occlusal/functional forces.
• In complete dentures, it's the available mouth area for support.
• Supporting areas are the mouth areas best at absorbing functional forces during chewing.

Parts of a Complete Denture

• Denture base/denture foundation: The part of the denture that contacts the supporting area (denture bearing area). Also called the impression/intaglio surface, recorded and reproduced by the final impression. It has three subdivisions:
  • Support areas
  • Relief areas
  • Peripheral seal/border areas
• Denture flange: The surface outside the denture base. Called the cameo/art surface. Primarily influences the esthetic appeal and doesn't impact function.
• Occlusal surface: The surface formed by the artificial teeth. Used to create balance for the denture during chewing.

Denture Bearing Area

• Refers to the surfaces contacted by the denture base.
• The picture shows the denture base's fitting surface, which contacts the oral tissues.
• Denture bases are usually made of hard materials (like acrylic) and don't change shape during function.
• 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 during chewing.
• 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 (reduced blood flow).
• Bone resorption and ischemia are long-term problems.
• Pain, ulceration, and irritation can occur (sometimes immediately or shortly after use).

What Happens When We Make an Impression?

• A dental impression records the oral cavity's anatomy using appropriate materials (carried by impression trays).
• The material presses against oral structures to record them (compression).
• It is assumed that the denture base applies as much force as used during impression making.
• Some structures (like teeth and bone) can withstand the pressure, while others (mucosa, muscle attachments) cannot.

How to Manage Compression in Denture Bases

• A customized tray is needed, contacting only pressure-resistant areas.
• This tray is made from a first duplicate or primary cast from the initial/preliminary impression.
• Wax sheets (relief wax) are placed on the duplicate in areas where pressure reduction is needed during impression-making.
• A special acrylic tray is then made and, finally, the wax is removed before final impression.
• Pressure can also be reduced by creating holes in the tray (relief holes).

Anatomical Landmarks

• Visible/palpable anatomical structures are present in the edentulous oral cavity.
• These structures are appreciated in both impressions and casts.
• Knowledge of how these structures are classified is important in making custom trays to apply selective pressure during impression making.
• Key classifications for support include:
  • Support areas (primary and secondary)
  • Relief areas
  • Border areas/peripheral seal areas

Favorable Characteristics of Supporting Areas

• Thick cortical bone, which is avascular: Resistant to resorption, providing excellent support.
• Thick keratinized attached mucosa: Resists trauma and ulceration due to denture base movements.
• Direction related to occlusal plane: Optimal support and resistance are when the supporting area is parallel or perpendicular to occlusal forces.

Relief Areas

• Some areas might have favorable support criteria but not be used for support.
• Key areas needing relief include:
  • Nerve canals (e.g., mental or incisive)
  • Sharp bony edges (e.g., canine prominence, interdental bony peaks)
  • Fresh extraction socket spaces
  • High frenal attachments
  • Ridge crest with soft medullary bone
  • Areas of thin mucosa (e.g., mid-palatine raphae, external oblique ridge)

Peripheral Seal Areas

• These areas determine denture flange length and thickness.
• Classified as:
  • Frenal areas (where muscles attach)
  • Sulcus areas (between attachments where muscles move)

Maxilla - Support and Relief

• Primary Support:
  • Horizontal surface of the 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

Maxilla - Peripheral Seal 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

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

This quiz covers essential concepts of complete dentures, including definitions of support and the various parts of a denture. You will learn about the denture base, flanges, and occlusal surfaces, as well as their significance in functionality and aesthetics. Test your knowledge on these fundamental components and their roles in dental prosthetics.