Denture Success: Retention and Stability

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).

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.

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.

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.

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.

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.

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.

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).