4. RETENTION
– Complete denture retention is the resistance to
displacement of the denture base away from the
ridge.
– The resistance in the movement of a denture
away from its tissue foundation especially in a
vertical direction. (GPT 9)
5. STABILITY
– Stability is the resistance to horizontal and
rotational forces.
– It is the resistance of a denture to movement on
its tissue foundation, especially to lateral
(horizontal) forces as opposed to vetical
displacement. (GPT 9)
6. SUPPORT
– Support is the resistance to vertical movement of
the denture base toward the ridge.
18. CAPILLARITY
– Another way to understand Interfacial Surface
Tension is by describing capillary action or
capillarity.
– Capillarity causes a fluid to rise in a capillary
tube because in this physical setting the fluid will
maximize its contact with the walls of capillary
tube, thereby rising along the tube wall at the
interface between liquid and glass.
19. – When the adaptation of the denture base to the
mucosa on which it rests is sufficiently close , the
space filled with a thin film of saliva acts like a
capillary tube in that liquid seeks to increase it’s
contact with both the denture and the mucosal
surface.
– In this way, capillarity will help to retain the
denture.
20. Interfacial Viscous Tension
Interfacial Viscous Tension refers to the force
holding two parallel plates together that is due to
the viscosity of the interposed liquid.
Stefan’s law-
F= (3/2)pkr4 V
h3
21. – r- Radius of two parallel, circular plates
– k- viscosity of liquid between two circular plates
– h- Distance between two circular plates
– V- velocity of displacing force
– F a square of area of opposing surface
– a(k) viscocity of interposed fluid
– a1/(h) distance between plates
– a Velocity of displacing action (V)
22. ATMOSPHERIC PRESSURE
– Atmospheric pressure can act to resist dislodging
forces applied to dentures, if the dentures have an
effective seal around their borders.
– This resistance force has been called suction
because it is a resistance to the removal of
dentures from their basal seat.
23. – When a force is exerted perpendicular to and
away from the basal seat of a properly extended
and fully seated denture, pressure between the
prosthesis and the basal tissues drops below the
ambient pressure, resisting displacement.
24.
25. GRAVITY
– When a person is in an upright posture, gravity
acts as a retentive force for the mandibular
denture and a displacive force for the maxillary
denture.
– In most cases, the weight of the prosthesis
constitutes a gravitational force that is
insignificant in comparison with the other forces
acting on the denture.
26. BIOLOGIC FACTORS
– Neuromuscular control- Neuromuscular control
refers to the functional forces exerted by the
musculature of the patient that can affect
retention.
– Muscular forces are exerted by the muscles of the
lips, cheeks and tongue upon the polished surface
of the denture and by the muscles of mastication
indirectly through the occlusal surface.
27. – Individuals appear to vary in their ability to
develop the motor coordination and conditioned
reflexes necessary to manipulate intraoral
prostheses.
– While some patients are able to adapt to
prostheses that seem to be unacceptable, others
appear to have difficulty learning to control any
dentures, regardless of the contours, design, or
occlusion.
28. QUALITY AND QUANTITY
OF SALIVA
– Saliva, a relatively viscous liquid, is present in
the space between the denture base and the
mucous membrane. The viscosity depends on the
proportion of secretion of the serous and mucous
glands.
– For the greatest retentive force, the film of saliva
should be thin and continuous.
29. – Excessive saliva that is thick and ropy,
accumulates between the tissue surface of the
denture and the palate leading to loss of
retention.
– The absence of saliva (Xerostomia) affects
retention and can also cause irritation and
soreness of the denture bearing tissues.
30. CONDITION OF MUCOSA
AND SUBMUCOSA
– Firm, keratinized tissues provide maximum
retention in comparison to tissues that get easily
displaced during function.
31. ORAL AND FACIAL
MUSCULATURE
– For oral and Facial musculature to provide
retention-
– Denture Base must be extended properly to cover
the maximum surface area without hampering the
normal health and function of the oral structures.
– Occlusal plane at correct level.
– Teeth arranged in neutral zone i.e. the zone where
forces from both the cheeks and tongue
equalizes.
32. RIDGE CHARACTERISTICS
– The ideal ridge is with adequate vertical height
and flat crest. This type of ridge provides
maximum amount of retention.
– There should be adequate inter-ridge distance
between the upper and lower ridges.
33. UNDERCUTS,
ROTATIONAL INSERTION
PATHS
– The resiliency of the mucosa and submucosa
overlying basal bone allows for the existence of
modest undercuts that can enhance retention.
– If the undercut area is seated first and the
remainder of the denture base can be brought into
proximity with the basal seat on rotation of the
prosthesis around the undercut part that is already
seated, this “rotational path” will provide
resistance to vertical displacement.
34.
35. CHEMICAL FACTOR-
Denture adhesive
– Denture adhesive is used to refer to a
commercially available, nontoxic, soluble
material (Powder, cream or liquid) that is applied
to the tissue surface of the denture to enhance
denture retention, stability, and performance.
36.
37. – They enhance retention through optimizing
interfacial forces by
– 1) increasing the adhesive and cohesive
properties and viscosity of the medium lying
between the denture and its basal seat.
– 2) Eliminating voids between the denture base
and its basal seat.
38. PSYCHOLOGICAL
FACTOR
– The process by which edentulous patient learns
to use complete denture is complex.
– It requires-
– Willingness to learn.
– Expectation
– Apprehension
39. MECHANICAL FACTORS
– Retentive Springs- These are made up of
coiled stainless steel, gold plated base metal
or nylon and have their ends attached to
swivels in the premolar areas, on both the
sides of the upper and lower denture.
40.
41. – The dentures are thus permanently attached to
each other and are held in occlusion for insertion
in the mouth, as soon as they are released they
are forced back into their supporting basal areas
due to action of spring and are held together to
their respective places.
42. – Disadvantages:
– Continuous pressure helps in rapid ridge
resorption
– Inner surface of cheeks get injured due to
frictional forces with the spring.
– Lateral movements are totally restricted and
hence efficiency of denture is hampered.
– Maintaining Oral hygiene is a problem.
43. SUCTION DISC
– They consist of a rubber disc which is affixed to
a stud on the fitting surface of a denture.
– The partial vacuum created within the perimeter
of this disc holds the upper denture suspended
from the hard palate.
– They cause a constant irritation and serve no
useful purpose.
44.
45. SUCTION CHAMBER
– When the denture is inserted the patient creates a
partial vacuum in this chamber by sucking and
swallowing and this small area of reduced
pressure helps to keep the denture in place.
46.
47.
48. MAGNETS
– From time to time the use of small magnets
embedded beneath the premolar and molar teeth
and arranged with similar poles opposite to each
other has been advocated.
– In theory the repulsion effect will keep both the
dentures in place but in practice it has been found
that this repulsive force is undetectable when
dentures are separated by more than 1 or 2 mm.
49. IMPLANT SUPPORTED
DENTURES
– It was proposed in the McGill Consensus
statement (2002) and again in the york consensus
statement (2009) that 2-implant supported
overdentures should be the minimum offered to
edentulous patients as the first choice of
treatment.
50. SURGICAL FACTORS
– Usually we use these factors to increase the
retention of the dentures through various
procedures, like vestibuloplasty, ridge
augmentation, frenectomy & dental implants.
51. ULTRASUCTION
CHAMBER
– Ultra Suction system increases the retention of
complete dentures.
– Ultra Suction works on a simple mechanical
principle: Suction.
52.
53. CONCLUSION
– Establishing optimal complete denture retention
requires an understanding of the factors
discussed. Incorporation of these determinants
into the prosthesis through proper design and
technique contributes to the success of complete
dentures.
