The document discusses factors that influence retention of complete dentures. It defines retention as the resistance of a denture to dislodging forces. Retention is provided by physical factors like adhesion, cohesion, and surface tension; physiological factors like muscle control and saliva; and mechanical factors like undercuts, occlusion, and denture adhesives. Proper design of denture surfaces and incorporation of these retention factors is necessary for optimal denture function and patient satisfaction.
3. INTRODUCTION
Optimal outcome of complete denture
treatment depends on the successful
integration of the prosthesis with the
patients oral function plus psychological
acceptance of the dentures by the
patients. These parameters requires
that patient perceive their dentures as a
stationary or well retained during
function.
4. DEFINITIONS
GLOSSARY OF PROSTHODONTIC TERMS;
It’s the quality inherent in the prosthesis acting to
resist the forces of dislodgement.
BOUCHER;
It’s the resistance to removal in a direction
opposite to that of its insertion.
It’s the quality in a denture that resists the forces
of gravity, the adhesiveness of foods, and the
forces associated with the opening of the jaws.
5. Fish was among the Ist
to discuss the
determinants of retention and differentiate
between the tissue, polished and occlusal
surfaces of a complete dentures.
The proper design of the tissue,
polished and occlusal surfaces of the
complete denture permits the dentist to
incorporate the mechanical, biological, and
physical factors of denture retention.
6.
7. FACTORS IN THE RETENTION OF
DENTURES
PHYSICAL
PHYSIOLOGICAL
MECHANICAL
PSYCHOLOGICAL
11. ADHESION
Its the attraction of unlike molecules for each other .
Adhesion of saliva to the mucous membrane and denture
is achieved through ionic forces between charged salivary
glycoproteins and surface epithelium or acrylic resin.
In case of Xerostomia adhesion is observed between
denture base and mucous membrane.
Retention provided by adhesion is proportionate to the
area covered by the denture.
Therefore dentures should be extended to the limits of the
health and function of the oral tissues.
12. COHESION
It’s the attraction of like molecules for each other.
It’s a retentive force because it occurs within the layer of
saliva that is present between the denture base and the
mucosa and maintains the integrity of the saliva.
13. INTERFACIAL FORCES
It’s the resistance to separation of two
surfaces that is imparted by a film of liquid
between them.
It can be discussed under
Interfacial surface Viscous tension
tension
14. INTERFACIAL SURFACE TENSION
It results from a thin layer of fluid that is present between
two parallel planes of material.
It depends on the ability of the fluid to wet the rigid
surrounding material-WETABILITY
If the material has low surface tension fluid will maximize its
contact with the material.
15. CAPILLARITY-Is what causes a liquid to rise in a capillary
tube. The space between the denture base and the
mucosa ,when its sufficiently close acts like a capillary tube
in which the saliva tends to maximize contact and aid in
retention
16. Interfacial surface tension plays a important role in the
retention of maxillary denture.
Its totally dependant on the presence of air at the
margins of liquid and solid interface.
17. GLASS SLAB MODEL
When two glass slab is interposed with a thin film of water its
difficult to separate them. But when the glass slabs are
placed under water, it can be easily separated.
This is because, there is no liquid-air interface under water
and hence no surface tension
18. VISCOUS TENSION – STEFAN’S LAW
(3/2) πkr4
F = x V
h3
F – Force necessary pull the circular plates
r – The radius of the circular plates
k – Viscosity of the liquid between the
plates
h – Thickness of the liquid
V – Velocity in a direction perpendicular to
radius
19. ATMOSPHERIC PRESSURE
Its an emergency retentive factor.
Its due to the pressure of atmosphere on the earth surface.
At sea level its 14.7lb/in2
.
Atmospheric pressure resists dislodging forces applied to the
denture if the dentures have an effective seal around their
borders.
This resisting force is called suction. But there no suction , or
negative pressure ,unless a dislodging force is applied.
20. BORDER SEAL
The contact of the denture border with the underlying or adjacent
tissue to prevent the passage of air or other substances.
Border seal is achieved by border molding.
Posterior palatal seal area is important in getting a proper border
seal.
This maintains the tissue contact during soft palate function and
compensates for processing changes.
This area extends between the hamular notches along the flexural
line of soft palate
21. A region that often causes problem in maintaining border
seal is the retrozygomatic space.
The remaining border of denture can be recorded by
draping effect of the lips and cheek and is not a problem
when overextension is avoided
22. The mandibular denture presents a major problem
with regard to retention.
Reasons for this are -
- Movable floor of the mouth.
-
Lack of ideal ridge height and conformation.
Border seal - facial
flanges
- retromolar pad
- lingual flange
23. Lingual flange –
Distolingual flange-Adequate seal can be obtained by gently
compressing the lateral wall of the retromylohyoid fossa
lingual to the retromolar pad and tucking the distolingual
flange laterally against the mucosa.
The contour and inferior extension of the lingual flange are
dependent on anatomy of the mylohyoid muscle.
24. GRAVITY
It’s the force exerted by the earth on all objects
towards its centre.
It helps in retaining the mandibular denture in
position.
When its difficult to bring other factors of
retention into play, gravity aids in retention of
mandibular retention.
25. SALIVA
All the physical factors of retention comes into play
when saliva is interposed between mucosa and
denture.
Many studies have been conducted to determine the
role of saliva in denture retention.
According to Stefan’s law the saliva should be viscous
enough to aid in retention.
Camphell observed that decrease in a fluid film
thickness increases denture retention.
Wilhelm H.W. showed that minor salivary glands had
great importance for denture retention.
The saliva should have optimum viscosity to
incorporate the physical factors of retention.
26. OROFACIAL MUSCULATURE
They provide supplementary retentive forces.
The teeth should be positioned in the neutral
zone and the polished surface should be properly
shaped.
The buccal flanges -
The lingual
flanges -
The base of the tongue serves as a emergency
retentive force in maxillary denture.
28. NEUROMUSCULAR CONTROL
Neuromuscular forces refers to the functional forces
exerted by the musculature of the patient that can affect the
retention.
This is primarily a learned biological phenomenon.
Certain patients have the ability to wear their dentures and
function without complaint despite the fact that they may be
extremely ill-fitting, unstable or even broken.
The biological factor of neuromuscular control gradually
becomes a major determinant in complete denture
retention as experienced patients learn to alter their
muscular function to harmonize with the prosthesis.
29.
30. INTIMATE TISSUE CONTACT
It’s the biological factor that refers to the close adaptation
of the denture base to the underlying soft tissue.
The impression technique will determine the degree of
intimate tissues contact.
The impression material should have adequate flow
properties, accuracy and dimensional stability to provide
intimate tissue contact.
32. ELASTICITY OF THE TISSUES
Elasticity is the property of a body, which enables
it to return to its original form after being
distorted or deformed
Reasons for elasticity of tissues are their cellular
structure and the presence of elastic fibers.
If the submucous membrane are soft and flabby
and are displaced during impression making,
the tendency will be for them to resume their
rest position , unseating the denture.
34. BALANCED OCCLUSION
It’s the bilateral, simultaneous, anterior and posterior
occlusal contact of teeth in centric and eccentric
position.
Balanced functional occlusion is critical in promoting
denture retention. The occlusion must be free of
interference within functional range of movement of the
patient to avoid dislodging forces.
35. SPRINGS
Springs are attached to the premolar region on both sides of
upper and lower dentures. The dentures are thus permanently
attached to each other and are held in occlusion for insertion
into the mouth. As soon as they are released the dentures are
forced apart by the action of springs and held in place.
Disadvantages
- Lateral movements are restricted
- Soreness of mucosa due to irritation
- Excessive alveolar resoption
- Unhygienic
36. MAGNETS
Small magnets are fixed on the maxillary and
mandibular dentures with like pole facing each other.
The repulsive forces developing between like poles,
forces the denture to press against the basal seat. This
aids in retention
Magnets can be surgically embedded in the edentulous
ridge
37. DENTURE ADHESIVES
Refers to commercially available non- toxic, soluble material
that is applied to the tissue surface of the denture to enhance
denture retention, stability & performance
Ingredients
Mechanism of action
Indications: - Xerostomia
- Lack of neuromuscular control
- Cerebro-vascular accidents
- Neuro epileptic patients
- Patients under gone resective surgery
It is emphasized denture adhesives is not indicated for
retention of improperly fabricated or poorly fitting
prosthesis
38. SUCTION CHAMBERS
A relief chamber with definite margin is made on
the palatal aspect of the denture.Such denture
creates a partial vacuum & aids in retention
Disadvantage:
Irritation & proliferation of the soft tissue into the
chamber
39. RUBBER SUCTION DISCS
It consists of a rubber disc which is buttoned onto a stud
into the fitting surface of the maxillary denture
Disadvantage; It causes constant irritation & damage to
soft tissue & even epithelioma
On prolonged use causes perforation of palate
40. SURGICAL METHODS
VESTIBULOPLASTY:
It is any series of surgical procedure described to restore
alveolar ridge height or width by lowering mucosal
attachments & unattached mucosa form the ridge crest to
a position deeper into the labial, buccal, lingual sulcus.
Objectives:
- To extend the denture bearing area
- To reposition muscle attachments
- To provide better foundation for the prosthesis
41. IMPLANTS
In case of resorbtion of the residual alveolar ridge &
deformities of the jaws, where other surgical procedures
cannot be used to correct the defect, implants are used
to aid in retention of the prosthesis
42. RIDGE AUGMENTATION PROCEDURE
It’s a surgical procedure, where in the width & height of
the residual ridge is increased by placing the bone
material or alloplast material or combination of both
Materials used:
Bone & Cartilage
Alloplastic materials: Proplast
Hydroxyappatite
Tricalcium phosphate
43. SUMMARY AND CONCLUSION
Several factors have been described as
determining the relationship of the tissue
surface of the denture base to the
underlying soft tissues that will provide
optimal retention.
It’s the understanding and incorporation of
these determinants that may ultimately
govern the success or failure.
