Al Azhar university Removable Prosthodontics Lama El Banna Dr. Waseem Moshtaha

1. Retention and Stability
Dr. Waseem Bahjat Mushtaha
Specialized in prosthodontics

2. Retention

3. Retention
Retention:
it is the quality inherent in a denture
that resists the force of gravity,
the adhesiveness of food and the
forces associated with opening
the jaw

4. Factors affecting denture retention
1(Physical factors:
As adhesion, cohesion, interfacial surface
tension and atmospheric pressure.
2(Physiologic factors:
As the quality and quantity of the saliva,
nuromuscular control, habits and ridge.

5. 3(Characterization:
As (size, form and relationship) and health of the
patient.
4(Mechanical factors:
As occlusion, leverage an contour of denture bases
(polish surface(.
5(Surgical factors:
As ridge reconstruction, vistibuloplasty and implant.

6. 6(Psychological factors:
As the intelligence, expectation, apprehension
and gagging of the patient.
7(Retention aids:
As adhesives, springs and magnets.

8. Adhesive

9. Physical factors
1(Adhesion:
-Is the property of attraction between unlike
molecules ( the attraction of the saliva film
to the fitting surface of the denture on one
side and the attraction of the saliva film to
the mucosa on the other side.

10. -Adhesion is directly proportional to the area
covered by the denture.
-Adhesion depends on the close adaptation of
the denture to the supporting tissues and the
fluidity of the saliva.

11. 2(Cohesion:
It is the attraction between similar molecules.
)the attraction between the saliva molecules together
in the saliva film between the denture base and the
soft tissues.
3(Capillary attraction:
When the adaptation of the denture base to the
mucosa on which it rests is sufficiently close, the
space filled with a film of saliva acts like a
capillary tube and helps retain the denture.

12. 5(Atmospheric pressure:
When an upper denture is inserted in the mouth of
the patient, air is expelled out from underneath the
denture. If the border of the dentures are properly
adapted to the adjacent tissues, no air can get in,
this means that the pressure acting on the fitting
surface of the denture is less than that acting on
the polished surface. The difference between these
two pressure gives a positive force holding the
denture in place.
-For atmospheric pressure to be effective, the
denture must have a perfect seal around its entire
border.

13. 6(Viscosity:
The viscosity should be of medium type. Very
thin watery saliva does not seal the denture
well and the seal can be easily broken.
Although thick ropy saliva is excellent for
sealing the denture, however, it is not as
good as normal viscosity because it is likely
to cause gagging.

14. N.B
Maxillary dentures are mainly retained by
physical forces, mandibular dentures on the
other hand are poorly retained by physical
forces because of their small area of contact
and because the surface tension of the saliva
film under the denture is being constantly
transferred to the surface of the saliva in the
floor of the mouth . They are mostly
retained by mechanical factors.

15. Stability
Def:
Stability of a denture is its quality of being
firm, steady, and constant in position when
forces are applied to it.
-Stability refers to resistances against
horizontal movement and forces.

16. Mechanical factors influencing
stability of complete dentures
1(Retention:
For a denture to be stable it should be
retentive.
2(Balance occlusion:
This means harmonious contact between
upper and lower teeth in different positions
of the mandible. If there cusp interference,
stability will be impaired.

17. 3(Height of the occlusal plane:
The higher the occlusal plane in relation to the
residual ridge, the greater will be the
leverage action and the lesser will be the
stability of the denture. Therefore, the
occlusal plane should as near as possible to
the ridge to enhance denture stability.

18. 4(Position of the posterior teeth:
The posterior teeth should be set up over the crest of
the ridge. If the teeth are set up too far outside the
ridge, stability will be impaired.
5(Proper relief of hard areas:
Insufficient relief of hard areas under the denture
may cause rocking and instability of the denture.
Median palatine raphe, torus palatinus and torus
mandibularis are examples of hard areas that
should be considered.

19. 6(Ridge and palatal form:
Residual ridge with high vertical walls resist
lateral forces well and enhance denture
stability. On the other hand flat ridges often
minimal resistance to lateral stresses and so
decrease the denture stability.
-Considering the palatal form, a high arched
vault offers a good resistance to lateral
stresses, while a flat vault permits skidding
of the denture.

20. 7(Shape of the polished surface of the
denture:
The polished surface should be concave. The
muscles of the tongue, cheeks and lips when
acting on a concave polished surface will
tend to seat.
8(Shape and size of the tongue:
Broad and thick tongue enhance denture
stability on the other hand small narrow
tongue or extremely large tongue reduce
denture stability.