Retention/ Stability/ Support
Definition
Types
Factors affecting retention
Primary, secondary and mechanical retention
Retention in complete dentures refers to the ability of that denture to resist displacement in a direction
opposite the path of insertion.
Vertical forces are involved in retention e.g. sticky food gravity, chewing action and oral musculature tongue
cheeks …Etc.
Retention in complete dentures can be primary secondary.
Primary retention involves both physical and mechanical means.
Primary retention
1. Physical forces.
2. Cohesion:
o Force of attraction between two molecules of the same type.
o Molecules of saliva; force between them maintain its continuity enhancing retention.
3. Adhesion:
o Force of attraction between two unlike molecules.
o Denture-saliva-mucosa.
4. Interfacial surface tension:
o Force between two parallel surfaces separated by a thin film of liquid.
o Saliva acts as a separating media between denture flanges and the mucosa. A concave meniscus is
formed between saliva and air reducing their pressure on that side. When denture sits on that side, an
intimate contact is formed. This contribute to the retention of the denture.
5. Capillarity action:
o When the space between the denture and the mucosa is narrow, enough it acts as a tube that sucks
saliva and distributes it through the denture bearing area increasing retention.
6. Atmospheric pressure:
o Suction effect; when a force is exerted perpendicular and away from fully seated denture, the p
between the denture and the mucosa falls below the ambient pressure resisting displacement.
Proportional to the size of the denture bearing area.
o Good fit, bolder molding and good impression must be ensured.
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7. Gravity:
Beneficial for mandibular denture, but may be detrimental for the upper denture.
8. Muscular forces:
Harmony must be created between the denture and the oral musculature. Tongue frenal relieve
mylohyoid, buccinators masticatory muscles play a role. Denture must be well polished. Depend on the
ability of the patient to adapt to the new prosthesis.
Secondary retention
Indirect retention obtained when stability and support of the denture is optimum i.e. when other forces which
tend to unseat the denture are eliminated.
Factors affecting physical forces:
1. Saliva:
Quantity and quality. Xerostomia? Excessive salivation? Type of saliva?
2. Surface area:
The greater the surface area the better the retention maxillary denture mandibular denture.
3. Intimacy of contact:
The closer the denture and the denture bearing area are the better retention.
4. Peripheral seal:
Good peripheral seal improves retention; good bolder molding posterior seal and peripheral seal
prevent air entry into the denture and denture bearing area.
Mechanical retention
Modification made on complete dentures to enhance retention, they include:
1. Undercuts.
2. Mucosal inserts.
3. Over denture attachments.
4. Rubber suction discs.
5. Magnets.
6. Implants.
7. Denture adhesives and soft tissue liners.
Stability
The ability of a prosthesis to resist displacement by functional horizontal or rotational forces.
It is affected by:
1. Residual ridge size and contour.
2. Residual ridge quality.
3. Palatal vault.
4. Neutral zone and surrounding musculature.
5. Abnormal ridge relations.
6. Occlusal factors.
7. Intimate contact.
8. Direct bone anchorage.
9. Flange shape and contour.
Support
Resistance to vertical movement or displacement of the dentures towards the basal seat area.
Sources of support:
All denture bearing areas:
Maxilla--- hard palate, maxillary tuberosity, residual alveolar ridge.
Mandible--- buccal shelf, residual alveolar ridge.
Thus, impression must cover as much area as possible, with relief of the limiting structures.
Factors that enhance support:
1. Basal bone resistant to resorption
2. Firm, resilient and keratinized tissues well attached to the underlying bone.
3. Tissues of uniform thickness
4. Support should be at right angle or near right angle to the occlusal forces.