prosthodontic-lec3 Retention stability-and-support

1. Retention, Stability and Support
in Complete Denture

2. • retention is the resistance to removal in a
direction opposite that of insertion.
• Stability is the quality of the denture to be
firm, steady and constant to displacement by
functional, horizontal or rotational stresses.
• Support is the resistance to vertical movement
of the denture base, towards the ridges.

3. Factors affecting retention of Dentures:
• A-Interfacial Surface Tension
It is the resistance to separation developed between two well
adapted surfaces by a thin film of fluid.
It is dependent on the ability of the fluid to wet the rigid
surrounding material. If the surrounding material has low surface
tension as oral mucosa does, fluid will maximize its contact with
the material, thereby wetting it readily and spreading out in a
thin film.

4. • B-Adhesion
• It is the physical force of attraction between
unlike molecules between the surfaces in
close contact.
• Adhesion of saliva to the mucous membrane
& the denture base achieved through ionic
forces between charged salivary glycoproteins
& surface epithelium or acrylic resin.
• Xerostomia-ethanol free rinse containing aloe
or lanolin or a water soluble lubricating jelly.
• oral pilocarpine 3times daily 5to 10 mg

5. • It acts when saliva sticks to the denture base
and to the mucous membrane of the basal
seat. It depends on:
• Close adaptation of the denture base
• Size of denture bearing area
• Type of saliva

6. • C-Cohesion
• It is the physical attraction
of like molecules for each other.
Cohesion is the physical factor
of electromagnetic force acting between
molecules of the same material.

7. D -Atmospheric Pressure
It is the physical factor of hydrostatic pressure
due to weight of the atmosphere on the earth’s
surface. When a dislodging force is applied on
the denture having good border seal, a negative
pressure develops in the space created
between
the denture base and the mucous membrane.

8. Factors affecting retention of denture
depend on:
-Shape of the palate
Flat palate increases retention and decrease
stability while V- shaped palate decreases
retention and increase stability.
Surface area
The force of adhesion is proportional to the area
of the surfaces in contact. Denture bearing of
maxilla is 22.96cm²and mandible is 12.255cm².

9. - Closeness of the denture adaptation
Adhesion depends on the closeness of the
denture to the tissues. Fit of the denture
depends on the accuracy for denture
construction.
-Direction of displacing forces
Adhesion acts almost powerfully at right angles
to the surface.

10. Factors relating to denture periphery:
• Atmospheric pressure
When an upper denture is inserted air between
it and the mucous membrane is expelled and
when the fit of the periphery to the tissues is
good no air can get in because there is an
efficient seal. This means that the pressure
acting on the fitting surface of the denture is
less than that acting on the non-fitting surface
(atmospheric pressure).

11. Intra oral factors and biomechanical
considerations:
• Undercut
• Jaw size
• Disharmony in jaw sizes
• Arch shape
Square, ovoid, or tapered
• Ridge form
high ridge with flat crest and parallel sides

12. • The vault form
A flat vault resists vertical displacement but it
provides little resistance to lateral displacement.
The narrow V- shaped vault is also unfavorable for
the retention of dentures.
• The soft palate
The width of the post dam depends upon the
curvature and functional activity of the soft palate.

14. Aids of retention
• Certain aids have been used to improve
retention of complete dentures:
• Vestibuloplasty.
• Ridge Augmentation Procedure
• Implant
• Over denture
• denture adhesives

15. denture adhesives
• nontoxic, soluble material available either in
form as powder or cream that is applied to the
tissue surface of the denture to enhance
denture retention, stability, & performance

16. It augment the retention through
1-increasing the adhesive & cohesive properties &
viscosity of the medium lying between the denture
& the basal seat
2-eliminating the voids between the denture base
& the basal seat.
3-because adhesives are more cohesive than saliva,
intrinsic physical forces of adhesive resist the pull
more than would similar forces within saliva.

17. Indications:
1-improve the stability of the denture for patient
with new denture.
2-pateint with xerostomia
3-provide psychological sense
4-pateints with resection surgery.
5-pateint with poor muscle tone such as Parkinson's
disease
6-patient with neurological disorder i.e.
cerbrovascular accident.

18. Contraindications:
1-they are not indicated for retention of
improperly fabricated or poorly fitting
prosthesis.
2-should not be used as a substitute to a relining
materials or tissue conditioner.

19. Stability

20. • Denture stability depends on:-
1-the size & form of the basal ridge (loss of
vertical high of the ridge & increase flabby
movable tissue decrease stability). Maximum
coverage of denture bearing area within the
physiological limit
2-the quality of final impression.
3-the form of polished surface.

21. • 4-the proper location & arrangement of the artificial
teeth. should be located at the neutral zone so the teeth
are subjected to equal and opposite forces from
surrounding muscles. also correct occlusal plane should
be establishing of if too high occlusal plane will force
the tongue into new position i.e. higher position leads
to loss of tongue accuracy causes raise of floor of
mouth & pressure on the border of the lingual flange
cause partial loss of border seal. If the occlusal plane
too low causes destabilizing the denture.
• 5-pateint education regarding tongue position & diet
habit
•

22. support
• Effective support is realized when:
1. Denture is extended to cover maximum surface area
Snow Shoe principle: Increased surface area decreases
the stress/unit area leading to decreased tissue
displacement which in turn causes denture movement.
2. Those tissues most capable of resisting resorption are
selectively loaded during function.
3. Compensation is made for varying tissue resiliency to
provide for uniform denture base under function and
maintain harmonious occlusal relationship.