Denture Success: Retention and Stability

Denture Success

• Retention, Stability, and Support are key concepts.
• Retention is the resistance to vertical tissue away movement (dislodgement).
• Stability is the resistance to horizontal or rotational forces (tipping or rocking).
• Support is the resistance to vertical tissue-ward forces (tissue ward movement).

Retention

• Factors:
  • Physical
  • Mechanical
  • Anatomical & Physiological
  • Psychological Acceptance
  • Retentive aids
  • Surgical factors

Physical Factors

• Adhesion: Attraction between unlike molecules (mucosa and denture base).
  • Retention depends on:
    • Area covered by the denture
    • Adaptation of the denture to tissues
    • Saliva fluidity
• Cohesion: Attraction between like molecules (within saliva film).
  • Cohesion maintains the integrity of the saliva film.
• Interfacial Surface Tension: Combination of adhesion and cohesion.
• Atmospheric pressure: Pressure difference between fitting and non-fitting denture surfaces.
  • Expelled air creates a seal and a positive force holding the denture in place.
• Capillary attraction: Saliva rising through the space between denture and mucosa, increasing contact.
• Viscosity: Resistance of a liquid to flow.
  • Thick ropy saliva seals well but can cause gagging.
  • Thin watery saliva seals poorly.
• Gravity: Plays a role in retention for mandibular dentures, but is less impactful.

Mechanical Factors

• Undercuts: Mechanical locking of the denture.
  • Common sites: Distobuccal vestibule and tuberosity (maxilla), Distolingual vestibule (mandible).
• Occlusion: Enhances retention and stability.
  • Examples: Balanced occlusion and Monoplane occlusion.
• Leverage: Height of the occlusal plane should be as close to the base as possible.
• Contour of denture base: Accurate fit, polished surfaces.

Anatomical and Physiological Factors

• Quality and quantity of saliva: Xerostomia (dry mouth) and excessive saliva decrease retention.
• Arch relationship: Ideal jaw relations improve retention.
  • Retrognathic or prognathic ridges can compromise treatment.
• Neuromuscular control: Muscular forces can affect retention.
  • Design considerations:
    • Teeth in the neutral zone
    • Occlusal plane in relation to the tongue
    • Shape of the polished surface.
• Buccinator muscle: Anteroposterior muscle, minimizing dislodging forces during mastication.
  • Concave polished surface helps retain the denture.

Retentive Aids

• Springs: Stainless steel coils attached to premolars on both sides, enhancing retention.
• Rubber suction discs: Attach to the denture for improved retention.
• Adhesives: Temporary bonding agents (strips, paste, powder) for holding dentures in place.
• Magnets: Placed under molar and premolar teeth, opposing poles repel each other.
  • Disadvantages: Corrosion, remedied by encapsulation in stainless steel, titanium, or palladium.

Surgical Factors

• Vestibuloplasty: Surgical procedure to restore alveolar height and width by lowering muscle attachments.
• Ridge augmentation: Increasing alveolar ridge height and width.
  • Methods: Autogenous bone grafting, non-autogenous bone grafting, synthetic hydroxyapatite.
• Distraction osteogenesis: Using a distractor to slowly pull bone apart (lengthening surrounding tissue).
  • Advantages: No donor site required, simultaneous soft tissue lengthening.
  • Disadvantages: Long treatment period, risk of infection.
• Implant-supported overdenture: Used when other options are insufficient.
  • Types: Ball and socket, Bar and clip, Magnet.

Stability

• Factors affecting denture stability:

  • Retention
  • Occlusion
  • Leverage (height of occlusal plane)
  • Position of posterior teeth
  • Proper relief of hard areas
  • Ridge and palatal form
  • Shape of the polished surface
  • Shape and size of the tongue

• Retention: Better retention contributes to better stability.

• Occlusion: Balanced occlusion enhances stability by distributing forces.

• Leverage: Lower occlusal plane improves stability.

  • Occlusal plane should be parallel to the residual ridge crest.

• Position of posterior teeth: Teeth placed on the crest (center) of the ridge promote stability.

  • Neutral zone concept balances buccal and lingual forces.

• Relief of hard areas: Relieving hard spots prevents denture instability and rocking.

• Ridge and palatal form: High vertical ridge walls resist lateral forces, enhancing stability.

• Shape of polished surfaces: Concave surfaces direct muscular forces to stabilize the denture.

  • Convex surfaces can lead to denture displacement.

• Tongue size and position: A well-placed tongue benefits stability.

Support

• Snowshoe principle: Wide denture base coverage maximizes support.
• Effective Support Factors:
  • Maximum surface coverage without impinging on movable tissues.
  • Selective loading of primary stress-bearing areas (minimizing bone resorption).