Retention /certified fixed orthodontic courses by Indian dental academy

ROLE OF THE OROFACIAL
STRUCTURES, SECRETIONS &
OTHER FACTORS AFFECTING
THE RETENTION IN COMPLETE
DENTURES
INDIAN DENTAL ACADEMY

Leader in continuing dental education
www.indiandentalacademy.com

INTRODUCTION


Optimal outcome of the prosthetic treatment
depends

on

the

successful

integration

of

the

prosthesis with patients oral functions as well as the
psychological acceptance of the prosthesis by the
patient. These parameters require that the patients
perceive their prosthesis as stationary & well
retained during function & that the prosthesis &
their effects on the face meet the psychodynamic
requirements of the patients.


• COMPLETE DENTURES RETENTION

•

Retention (G.P.T) has been defined as “That quality
inherent in the prosthesis acting to resist the forces of
dislodgement along the path of placement.”Complete
denture retention has been defined as “Resistance to
removal of the denture base in a direction opposite to
that of its insertion” and as “That quality inherent in
the

prosthesis

acting

to

resist

the

forces

of

dislodgment along the path of insertion”. In effect,
retention relates to the forces that are necessary to
completely remove the denture from its basal seat.

• From this it is clear that then, ordinarily retention is
regarded as a property of the denture rather than
that of the patient. If a denture is easily dislodged
during speech or eating, the embarrassment
experienced can be mentally traumatic. A retentive
denture contributes dramatically to the patients
acceptance of the finished prosthesis.


Historically, prosthodontists have sought

to

improve the quality of denture treatment through an
understanding and application of the factors involved
in retention. Disagreements regarding the relative
importance of various factors do exist.
Improvements in denture base materials and in
fabrication techniques stemmed from the simple
realization that better fit meant great comfort and
more efficient function.

• The prospect of retention without mechanical aid was
not seriously considered in the 18th and early 19th
centuries. With the advent of the well-fitting base
came the awareness that bases could be, and the
gradual acceptance that they should be, retained by
non-mechanical means, inevitably various efforts were
made to explain and better understand the physics of
the observed clinical phenomena.
•

Hence complete denture retention may be
described as that state of a denture where functional
forces are unable to destroy the attachment between
denture and mucoperiosteum.

It is difficult to consider stability and retention as
separate entities because of the close dependency of
the one upon the other. A lack of either property will
influence the effectiveness of the other to a great
extent.

Although

evaluation
precedence

of

a

over

both
good

are

indispensable

denture,

retention

as

prerequisite in denture construction.

stability
the

in

the
takes

paramount

Retention in a denture not only enhances its
stability, but also it helps to meet the various
psychologic problems encountered by the patient
during the learning or the re-educating period.
Such psychologic problems might include the fear,
apprehension,

and

embarrassment

caused

by

unsatisfactory denture retention. Thus, retention
supplementing

stability

will

achieve

finished

dentures which satisfies the physical, physiologic
and psychologic needs of the patient.

• FACTORS GOVERNING RETENTION OF
COMPLETE DENTURES:
I. Positive physical factors:
• Adhesion
• Cohesion
• Interfacial force
• Atmospheric pressure
• Gravity
II. Physiological factors:
• Role of saliva
• Neuro muscular control
• Ridge characteristics and relationships

III. Mechanical factors:
• Leverage
• Occlusion
• Shape of polished surface
• Under cuts
• Surface roughness

IV. Psychological factors
V. Surgical factors
• Ridge extension
• Implant supported dentures.


POSITIVE PHYSICAL FACTORS

Adhesion:
Adhesion is the physical force involved in the
attraction between unlike molecules. A drop of water
introduced on the surface of a solid glass plate will resist
movement away from the glass in proportion to the
adhesion between the unlike materials.
Fuller, A London dentist has been stated to mention
the word “Adhesion” in retention to maxillary denture
retention. Adhesion of salvia to the mucous membrane and
the denture base is achieved through ionic forces between
charged salivary glycoproteins and surface epithelium or
acylic resin. By promoting the contact of saliva to both oral
tissue and dentures base, adhesion works to enhance
further the retentive force of interfacial surface tension.

The quality of denture adhesion depends on the:
i. Close adaptation
supporting tissues:

of

denture

base

to

Impression techniques determine the degree of
intimate contact with the tissue at rest and during
function. It also prevents ingress of air which
decreases the retention.
ii. Fluidity of saliva:
Saliva should be search in nature and wet the
complete denture surface area.

iii. Area of contacting surface:
Greater the area of contact, greater will be
the retention. Mandibular dentures cover
less
surface area than maxillary prostheses and,
therefore, are subject to a lower magnitude of
adhesive (and other) retentive forces. Similarly,
patients with small jaws or very flat alveolar ridges
(small basal seats) cannot expect retention to be as
great as can patients with large jaws or prominent
alveoli. Thus, the dentures (and hence the
impressions that serve as the patient analogue for
their fabrication) should be extended to the limits
of the health and function of the oral tissues, and
efforts should at all times be made to preserve the
alveolar height to maximize retention.

iv. Shape of denture bearing area:
The forces act most powerfully at right
angles to the surface. So, flat palate will provide
good surface adhesion.
A version of adhesion is observed between
denture bases and mucous membranes themselves,
which is the situation in patients with xerostamia
(sparse or absent saliva). The denture base
materials seen to stick to the dry mucous
membrane of the basal seat and other oral
surfaces. Such adhesion is not very effective for
retaining dentures, and predisposes to mucosal
abrasions and ulcerations due to lack of salivary
lubrication.

It is annoying to the patients to have denture
bases stick to lips, cheek and tongue. An ethanol free
rinse containing aloe or lanolin, or a water soluble,
lubricating jelly, can be helpful in this situation. For
patients whose mouths are dry due to irradiation or
auto immune disorders like Sjogrens syndrome,
salivary stimulation through a prescription of 5-10mg
of oral Pilocarpine 3 times daily can be beneficial if
patient can tolerate likely side effects of increased
perspiration and excess lacrimation.

Cohesion:
Cohesion is the physical attraction of like molecules
for each other. It is a retentive force because it occurs
within the layer of fluid (saliva) that is present between
the denture base and the mucosa, and works to maintain
the integrity of the interposed fluid. The property of
cohesion is effective in direct proportion to the area
covered by the denture, if other factors are equal.
According to Jacobson and Krol, cohesion is a
physical factor of electromagnetic force acting between
the molecules of the same material. A molecule within a
fluid has an attraction exerted on it on all sides by
neighboring molecules.

Forces of cohesion are responsible for maintaining
the continuity of a water droplet when placed in
contact with another material. Normal

saliva is not

very cohesive, so that most of the retentive force of
the denture – mucosa interface comes from adhesive
and interfacial factors unless the interposed saliva is
modified (as it an be with the use of denture
adhesive).


Thick high mucin saliva is more viscous
than thin watery saliva – yet thick secretions
usually do not result in increased retention for
the following reason – Watery, serous saliva
can be interposed in a thinner area than the
more cohesive mucin secretions. Stefans law
makes it clear, all other factors being equal,
that increase in fluid viscosity cannot be
accompanied by an equal increase in film
thickness if displacement force is to be kept
same.
The combined effect of adhesion and
cohesion will provide better retention.

Interfacial force:
It is the resistance to separation of two
parallel surfaces that is imparted by a film of
liquid

between

them.

A

discussion

of

interfacial forces is best broken into separate
comments on interfacial surface tension and
viscous tension.


Interfacial surface tension:
It is defined as the force that maintains the
surface continuity of a fluid. It results from a thin layer
of fluid that is present between two parallel planes of
rigid material. It is dependent on the ability of the fluid
to “wet” the rigid surrounding material. The cohesive
attraction between molecules is balanced in equilibrium
within the fluid. At the surface, the absence of the
neighboring molecules creates the one sided attraction
imbalance that causes surface tension. 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.

If the material, with the result that it will form
beads on the material’s surface. Most denture base
materials have higher surface tension than oral
mucosa, but once coated by salivary pellicle they
display low surface tension that promotes maximizing
the surface area between liquid and base. The thin
fluid film between denture base and the mucosa of
the basal seat therefore furnishes a retentive force
by virtue of the tendency of fluid to maximize its
contact with both surfaces. It is a relatively small
force when considered alone but by interaction with
other physical factors, it becomes an important
determinant.

Another method to explain the role of surface
tension in denture retention is by describing capillary
attraction or capillarity. Capillarity is what cause a liquid to
rise in a capillary tube, because in this physical setting the
liquid will maximize its contact with the walls of the
capillary tube, thereby rising along the tube wall at the
interface between liquid and air. 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 the liquid seeks to increase
its contact with both the denture and the mucosal surface.
In this way, capillarity will help to retain the denture.

Interfacial surface tension may not play as important
a role in retaining the mandibular denture as it does for the
maxillary one. Interfacial surface tension is dependent on
the existence of a liquid / air interface at the terminus of
the liquid/ solid contact; if the two plates with interposed
fluid are immersed in the same fluid, there will be no
resistance to pulling them apart. In many patients, there is
sufficient saliva to keep the external borders of the
mandible denture awash in saliva, thereby eliminating the
effect of interfacial surface tension. This is not so in the
maxilla. A simple system to explain interfacial surface
tension involves the attraction of two glass slabs placed in
direct apposition with an interposed fluid film. In 1948,
Stanitz27 used this model to explain the part played by the
fluid film in denture retention.

In review, the phenomenon of surface tension is defined
as the force that maintains the surface continuity of a fluid. This
results from the imbalance in cohesive forces between molecules
present at the surface. The cohesive attraction between
molecules is balanced in equilibrium within the fluid. At the
surface the absence of neighbouring molecules creates the onesided attraction and imbalance that causes a free potential
energy called surface tension.


When water rises vertically in a column within a capillary tube
standing in an open container of water, the fluid pressure
within the water at the height of the column is les that at the
base. The pressure at the base of the column is equal

to

atmospheric pressure, and therefore the pressure at the
height of the column is less than atmospheric pressure. This
phenomenon creates a pressure gradient across the meniscus.
Although it is the forces of adhesion and cohesion that cause
the water to rise in the tube, it is the forces of surface
tension that maintain the difference in pressure across the
meniscus.


Atmospheric pressure (Pa) is in equilibrium with fluid
pressure exerted on molecules within capillary tube at
level of liquid in container. Therefore
pressure on
molecules along dotted line (A) is equal to Pa. Fluid
pressure exerted on molecules at higher level (B) is less
than at level A in proportion to distance between A and B.
Because B is less than A, B is less than Pa, which indicates
presence of a pressure gradient across meniscus which is
maintained by surface tension.


Interfacial viscous tension:

It refers to the force holding two parallel plates
together that is due to the viscosity of the interposed
liquid. Viscous tension is described by Stefan’s Law. For two
parallel, circular plates of r that are separated by a
Newtonian (incompressible) liquid of viscosity k, and
thickness h, this principle states that the force (F)
necessary to pull the plates apart at a velocity V in a
direction perpendicular to the radius will be
F

=

(3/2) Π kr4
H3


x V

The relationship expressed by Stefan’s law makes it clear
that the viscous force increases proportionally to the increase in
the viscosity of the interposed fluid. The viscous force drops off
readily as the distance between the plates (i.e., the thickness of
the interposed medium) increases. The force increases
proportionally to the square of the area of the opposing surfaces.
When applied to denture retention, the equation demonstrates
the essential importance of an optimal adaptation between the
denture and the basal seat (a minimal h), the advantage of
maximizing the surface area covered by the denture (a maximum
r), and the theoretical improvement in retention made possible by
increasing the viscosity of the medium between the denture and
its seat. It also explains why a slow, steady displacing action
(small V) may encounter less resistance and, therefore, be more
effective at removing a denture than is a sharp attempt at
displacement (large V).
In application, interfacial forces are further enhanced
through ionic forces developed between the fluid and the
surrounding surfaces (adhesion) and the forces holding the fluid
molecules to each other (cohesion).

Atmospheric pressure:

Atmospheric pressure is the physical factor of
hydrostatic pressure due to the weight of the atmosphere
on the earth’s surface. At seal level this force amounts to
14.7 psi.
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; but there is no
suction or negative pressure, except when another force is
applied (suction alone applied to the soft tissues of the oral
cavity for even a short time would cause serious damage to
the health of the soft tissues under negative pressure).

For example, a suction cup pressed against a pane of
glass stays in place because the rubber of the squeezed cup
elastically seeks to return to a larger shape, thereby
causing air pressure within the cup to be less than the
pressure outside the cup. A denture cannot be distorted
like a suction cup, but oral mucosa can be. 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.
Retention due to atmospheric pressure is directly
proportional to the area covered by the denture base. For
atmospheric pressure to be effective, the denture must
have a perfect seal around its entire border. Proper border
molding with physiological, selective pressure techniques is
essential for taking advantage of this retentive mechanism.

A conclusive clinical study by Snyder et al, in 1945
demonstrated the effect of reduced atmospheric pressure
on the retention of maxillary complete dentures
constructed for seven patients. Measurements made in a
pressure chamber at 4.7 psi simulating a 30,000 – foot
ascent above the earth demonstrated a decrease in
denture retention. With a 70% decrease in atmospheric
pressure, a 50% decrease in retention was noted.
At sea level the force of atmospheric pressure acts
with approximately 14.7 psi against the external surface of
the denture provided no air or gaseous pressure exists
between the denture base and the tissue surface.

Gravity:

The weight of the prosthesis constitutes a gravitational
force that is insignificant in comparison with the other forces
acting on a denture. But if a maxillary denture is fabricated
wholly or partially of a material that increases its weight
appreciably (eg., A metal base or precious metal posterior
occlusal surfaces), the weight of the prosthesis may work to
unseat, it, if other retentive forces themselves are suboptimal.
Increasing the weight of the mandibular denture (through
addition of a metallic base, insert or occlusal surfaces) may seem
theoretically capable of taking advantage of gravity. Anecdoteal
evidence suggest that this may indeed prove beneficial in case
where other retentive forces and factors of retention into play
when constructing a lower denture, gravity aids in providing the
necessary force to maintain the prosthesis in place at rest.
Grunewald recommended gold base complete dentures of a
weight similar to that of the lost teeth and alveolar tissues.
Such a technique would enhance the effectiveness of gravity on
the retentive properties of the prosthesis.

PHYSIOLOGIC FACTORS
Role of saliva:
Atmospheric pressure, or “suction” as it is
incorrectly called, contributes very little to the
retention of a denture until an attempt is made to
move it away from the tissue. Then, provided that the
saliva film remains intact, a reduction in pressure
occurs between denture and tissues and atmospheric
pressure resists displacement of the denture. If the
saliva film breaks down and air enters he space
between denture and tissues, the denture is no longer
retained. Hence it is important to exclude as much air
as possible from the saliva film.

Some dissolved air always remains, but if air
bubbles are present these expand rapidly and
connect

up

with

the

atmosphere

thus

producing a loss of retention. As pockets
remain in areas of poor adaptation, deep relief
chambers or places where the denture has
been adjusted away from a deep undercut.
When only a small space has been created, it
fills with saliva. A larger space, however,
usually contains air and this reduces denture
retention.


The internal pressure within a liquid
is slightly less than that of the
surrounding atmosphere, hence the
formation of a meniscus at the interface.
It is argued, therefore, that there is
slight retentive pressure from the
atmosphere provided that the saliva film
is intact. However other writers suggest
that no true meniscus is present, as the
entire surface of the denture is coated
with saliva.

Viscosity and volume of saliva:

The relationship between the denture
and the tissues is a dynamic one. Whenever
the denture tries to move, the viscosity of the
interposed saliva film resist or dampens this
movement.
Viscosity of the saliva depends upon its
mucin content. Parotid secretion is mainly
serous and therefore the secretion of the
mandibular and the sublingual glands is the
more important for denture retention.

Mucin is also secreted from the palatal glands
and lies between denture and tissues, flowing
slowly to the periphery. Here it remains in the
sulcus or on the soft palate until it is
swallowed.
A thin film of saliva resist flow much
more readily than a thicker film. Resistance to
flow varies inversely as the cube of the film
thickness. Thus by halving the gap between
denture and tissue, the retentive force due to

resistance to saliva flow is increased eightfold.

If the saliva itself has a high viscosity, it resists
flow more effectively. Hence the use of denture
fixatives or adhesives produce a large increase in the
viscosity of saliva. Unfortunately with the forces usually
generated in the mouth, a saliva of such high viscosity
cannot be compressed to a thin film. Therefore a marked
increase in viscosity is necessary to produce an effect
similar to that of decreasing the film thickness.
The danger of using denture adhesives is that
whilst a thin film of saliva is developed initially, this
gradually increases in thickness and the patient finds
difficulty in reducing it down again to a narrow section.

Unless there is plenty of further

highly viscous

saliva available in the mouth, then as soon as the
denture is tilted or is moved away from the tissues,
there is a shortage of saliva, air enters the space,
and the denture falls. This is what usually happens
when a denture adhesive is in use as the adhesive –
thickened saliva beyond the border of the denture is
swallowed and does not remain in the mouth.

If a denture is loaded at one side, then the saliva film
is thinned on this side and the denture may attempt to move
away from the tissues on the opposite side. Here any extra
saliva from the sulcus can flow in and so maintain the
continuity of the saliva film in the increasing space.
Adequate saliva volume is necessary and retention is
therefore poor in the mouths of patients whose saliva
volume is low.
The rate at which displacement of the denture is
attempted is also important. To a force applied suddenly,
there is little time for saliva flow to occur and the denture
is displaced. If a much smaller force is applied continuously,
however, flow takes place and the denture remains in place.
To study the influence that saliva might have on the
adhesion between on upper denture and the mucosa, we may
consider the adhesion mechanism between two glass plates
with a thin layer of fluid between them. Let us suppose that
the fluid consists of distilled water.

If the plates are held horizontally, the intermediate layer of fluid in
the periphery of the plate will be limited by a free layer of fluid, the so
called meniscus. The form of this meniscus depends on the pressure
within the fluid at the time of the examination. If the plates are closer
to one another (greater pressure in the fluid compared with the
atmospheric pressure), the meniscus will bulge out and attempts to
separate the plates will cause and inward bulge of the fluid meniscus
(reduced pressure).
The following physical factors must be considered in this
respect, viz., adhesion, cohesion, and surface tension. Measurable
factors active in the adhesion of two glass plates are adhesion and
surface tension.
The surface tension plays a role in the fixation has already been
stressed by various authors, including Schultze (1921), who formulated
the equation.
K= 2axy
b

Where
K = fixation force
a = surface tension coefficient
y = surface of the plates
www.indiandentalacademy.com between the plates
b = distance

Measurement of the force necessary to separate two
glass plates with an intermediate layer of water and fresh
mixed saliva, respectively, will show that separation requires
a greater force if the intermediate layer consists of saliva.
How can this be explained? Since the surface tension of
saliva is lower than that of the water?. The meniscus
created by the surface tension will act as spring all around
the edges of the plates, and the tension of that spring will
be directly correlated to the coefficient of the surface
tension. This is a very important factor that holds the
plates together. When a separating force exceeds the
elasticity modulus of the fluid meniscus, the meniscus
breaks and an intense flow in the intermediate layer of fluid
will occur. This divides the layer of fluid into two parts,
each of which adheres to the glass plates.

Thin fluid film exists (shaded area) between denture
base and tissues of residual ridges. Meniscus develops at
border of denture. Note that position of meniscus will
depend on where soft tissue loses contact with denture
border. Draping effect of cheeks may provide a meniscus
along polished surface of denture border (A). When cheek
is retracted, meniscus is developed at denture border (B).
The flow of the fluid is, however, diminished by an
increased viscosity. This explains why fresh saliva, despite
its lower surface tension, gives stronger adhesion between
the glass plates, i.e., the rate of flow is lowered by the
high viscosity of the saliva owing to its mucoid content. The
higher the viscosity, the lower the rate of flow and the
greater the fixation power.

Conditions which increase retention. From an analysis of the
effects of the saliva film on retention, there are three
important factors. The thickness of the saliva film:
Retention

∝

1
Saliva film thickness3

The viscosity of the fluid film:
Retention ∝ saliva viscosity.
The larger the surface area, the better the retention:
Retention ∝ area2

The best conditions for denture retention
are therefore:
• A fully extended denture (with border
seal, including post dam).
• A closely adapted denture (minimal
saliva film thickness)
• A saliva of medium viscosity which can
be compressed to a very thin film by
the normal intra-oral forces.
• A saliva of adequate volume.

Neuro muscular control:
Dentures are always foreign bodes in the mouth and when fitted
for the first time, most muscular actions tend to expel them. Gradually
however the wearer learns to differentiate between the food and
denture Dentures are always foreign bodes in the mouth and when fitted
for the first time, most muscular actions tend to expel them. Gradually
however the wearer learns to differentiate between the food and
denture and at first consciously but later subconsciously, to control and
stabilize them.
Neuromuscular control refers to the functional forces exerted
by the musculature of the patient that can affect retention. This is
primarily a learned biologic phenomenon. Certain characteristics can be
incorporated into the external controls of the denture base to promote
neuromuscular control.

The oral and facial musculature
supply
supplementary retentive forces, provided (i) the
teeth are positioned in the ‘neutral zone’ between
the cheeks and the tongue (ii) the polished
surfaces of the dentures are properly shaped. (iii)
the denture bases must be properly extended to
cover the maximum area possible without
interfering in the health and function of the
structures that surround the denture (iv) the
occlusal plane must be at the correct level and (3)
the arch form of the teeth must be in the “neutral
zone” between the tongue and the cheeks.

This is not to say that patients must hold their prosthetic
teeth in place by conscious effort, only that the shape of the
buccal and lingual flanges must make it possible for the
musculature to fit automatically against the denture and
thereby to reinforce the border seal. One of the objectives in
impression making and arch form design is the harnessing of a
patients unconscious tissue behaviour

to enhance both

retention and stability of the prosthesis. If the buccal flanges
of the maxillary denture slope up and out from the occlusal
surface of the teeth and the buccal flanges of the mandibular
denture slope down and out from the occlusal plane, the
contraction of the buccinator will tend to seat both dentures
on their basal seats.


The lingual surfaces of the lingual flanges should
slope towards the center of the mouth so that the tongue
can fit against them and perfect the border seal on the
lingual side of the denture. The base of the tongue is
guided on top of the lingual flange by the lingual side of the
distal end of the flange, which turns laterally toward the
ramus. This part of the denture also helps ensure the
border seal at the back end of the mandibular denture.
The base of the tongue also may serve as an
emergency retentive force for some patients. It rises up at
the back and presses against the distal border of the
maxillary denture during incision of food by the anterior
teeth. This is done without conscious effort. It is seldom
that a patient needs to be taught to do this. For the oral
and facial musculature to be most effective in providing
retention for complete dentures, the following conditions
must be met:

Every prosthodontist recognize the ability
of certain patients to wear their dentures and
function without complaint despite the fact that
they may be extremely ill fitting, unstable, or
even broken. The biologic 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.
The fields of oral perception, sensation and
proprioception are currently being researched.

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 restorations that
seem to be unacceptable, others appear to have
difficulty learning to control any dentures, regardless
of the contours, design, or occlusion. It is muscular
control that enables patients to function with
dentures that rest on basal tissues that have
undergone resorptive changes and no longer related
to the intaglio of the denture base.

Studies by Brill et al demonstrate that older
patients have more difficulty adjusting to new
complete dentures. This may result from the
progressive cerebral atrophy that affects related
neurologic systems. They also demonstrated the
dramatic
denture

decrease
retention

in
that

mandibular
accompanied

complete
local

anesthesia of the oral mucosa in experienced
denture patients. This was especially marked in
those

patients

with

severely

compromised

residual ridge height and conformation.

The normal activity of muscle is dependent on
different

impulses

originating

in

proprioceptors

recording changes in muscle tendons and joints. More
over they depend on other different impulses
originating in exteroceptors, which record changes in
the oral environment. The touch receptors found in
the oral cavity, including those of the tongue, are
particularly concerned with denture retention. It is
believed

that

importance

in

these

receptors

properly

are

adjusted

coordination of lips,www.indiandentalacademy.com
cheeks and tongue.

of

great

muscular

Ridge characteristics and relationship :
Types of alveolar ridges and palate formation
and their significance on retention.

Maxillary denture bearing area:
1. Well developed but not abnormally thick ridges and
a palate with a moderate vault.
2. High V – shaped palate usually associated with thick
bulky ridges.
3. Flat palate with small ridges and shallow sulci
4. Ridges

exhibiting undercut areas:

Mandibular denture bearing area:
1. Broad and well –developed ridges:
2.Ridges exhibiting undercut areas:
3.Well –developed but narrow or knife-like
ridges.


Ridge forms and
retention of denture:

their

influence

on

In a discussion of physical considerations of
retention, ridge forms and their influence on the
retention of dentures should be considered. One
should be able to predict the degree of retention by
the shape of the ridge.

Class IA: Inverted U-shaped ridge:

The inverted U-shaped ridge permits a very
retentive lower denture. The sides are parallel and
when the denture slides upward it hugs them. At the
crest, there is fairly lat surface being pulled apart at
right angles to the surface. This resists separation.

Class IB: Flat inverted U-Shaped ridge:

The flat inverted U-shaped ridge presents
shorter parallel walls. It, therefore, resist
dislodgment for a short distance only when the pull is
on a upward direction. After that the entire denture
leaves the ridge. There is a tendency for the denture
to slide since the flange are short.

Class IC: U-Shaped:

The U-shaped ridge presents very little
retention in comparison with class IA, but it will
resist displacement in a upper direction. It will have a
tendency to slide. Articulation must be very accurate
in these cases to prevent movement.

Class 2: Inverted V-shaped ridge:

The inverted V-shaped ridge is probably the
least retentive of all. The moment the denture moves
in an upward direction it leaves the entire ridge at
once. There is no parallelism. Also, the direction of
force is such that separation from the ridge is
easier.

Class 3A : Parallel walled thin ridge:

The retention is not very great in a parallel walled
thin ridge because of the small area at the crest of
the ridge. Although the parallel walls of the denture
hug the sides of the ridge and create some
vaccumatic space, this is too small to account for
much of the retention.

Class 3B: Parallel walled ridge, broad crested:
The broad crested parallel walled ridge is the
most retentive of all. It is a combination of the
longer parallel walls and the broad crest. The broader
crest has the two features of creating a vacuumatic
space as well as resisting separation with the
direction of force at right angles.

Class 4: Flabby tissue:
Flabby ridges play very little part in disturbing
stability and retention.

Classification based on ridge relations
and retention:
The relations of the residual ridges may be
classified as:
1. Protruded residual ridge.
2.Both residual ridges are protruded
3.Mandibular residual ridge is protruded.
4.Under developed mandible.
5.Retruded mandible.

The maxillary and mandibular ridges should be
observed at he appropriate occlusal vertical dimension.
The amount of inter ridge distance should be noted. An
excessive amount of space due to resorption will result in
poor stability and retention because of the increased
leverage. A small amount of interridge distance will lead
to difficulty in setting teeth and maintaining a poor free
way space. However this condition greatly enhances the
stability of the dentures because the occlusal surfaces of
the teeth are close to the ridge minimizing leverage, tilt
and tongue forces.
Ridges that are not parallel to each other will cause
movement of the bases when the teeth occlude because of
an unfavourable direction of forces.

The ridges should also be observed in their anteroposterior and lateral relationships. As the maxilla resorbs,
the crest of the ridge appears to move downward, forward
and laterally because it is wider at its inferior border than
at its occlusal border. This condition could be further
compromised by a prognathtic jaw relationship and this
accentuates the importance of tooth placement to maintain
esthetics and minimize undesirable leverage.
When maxillo mandibular or ridge relations are not
normal, they dictate a different occlusal relation of the
teeth. One must remember that the medial and lateral
positions of the teeth must provide acceptable anatomic and
physiologic limits.

Peripheral seal
Border seal: The border or periphery of the denture
provides ample opportunity for the ingress of air. Correct
adaptation of the sulcus tissues to the inside of the cheeks
and lips insures a border or valve seal. During a small
displacement of the denture, the soft tissue of lips and
cheeks move inwards under atmospheric pressure and
maintain contact with the denture, thus preventing the
ingress of air. Overtrimming of the border to provide
relief for frena allows easy ingress of air as does an under
extension of the denture into the sulcus.
Both extension and width of the border are
important. If the denture flange does not fill the sulcus
laterally, air collects in the space left and valve seal is lost.
Lateral filling of the sulcus is particularly important in the
upper tuberosity regions.

In the lower jaw there is a relatively long border for
a small area. Consequently the potentially for air leakage is
high. Seal of the tissue against the lingual aspect of the
lower denture is difficult to achieve as also is seal at the
distal end of a lower denture where it covers part of the
retromolar pad. Usually, therefore, border seal in the case
of the lower denture is poor.
In the upper jaw, the posterior palatal border is
similarly the weakness part of the border seal, as only as
slight movement of the denture away from the tissue allows
the ingress of air and breakdown of the saliva film. A
correctly positioned and shaped post dam is therefore
essential to maintain retention. Increased pressure on the
retromolar pads by the lower denture may have a similar
effect.

MECHANICAL FACTORS
LEVERAGE:
The three classes of levers are well known and are
used in many operations. Although many simple tasks, such as
using a crowbar to lift a rock and squeezing on a nutcracker,
are accomplished by simple levers in one of these three
classes, the act of chewing with artificial dentures involves a
multiple lever system. It is the problem of the dentistengineer to prevent or minimize leverage when its operation
would be unfavourable and to establish or increase it when
its operation would be beneficial.
Anteroposterior point of application of muscle pull on
mandible. This point should be known in order that the
working occlusal surfaces may be placed in their most
favourable positions on the lower alveolar ridge (The upper
areas of support extend further, both anteriorly and
Posteriorly, than the lower ones and ordinary need not be
considered in this connection).

The point of application is controlled to some
degree by the patient as a result of nerve impulses
acting more or less independently on the various
muscle fiber groups. However, the significant fact in
connection with artificial denture restoration is that
the point where muscle pull is applied on the mandible
is always behind the center of the denture
supporting areas and probably is always behind the
distal ends of these areas. Thus, as pointed out
previously, with the resistance on the anterior teeth
the mandible is a leaver of the third class, the point
of application of muscle pull lies between the condyle
head and the resistant mass of food, resulting in
pressure upon both.www.indiandentalacademy.com

Yielding of foundation – the tissues covered by the
denture base are neither rigid nor uniformly yielding.
They are neither permanently nor even temporarily
stable

in form. Under intermittent chewing force

they change form, both because of their elasticity
and because of changes in volume of the contained
liquid. The fact that the denture base rests on a
more or less yielding support causes it to become a
lever under certain conditions. This presents the
dentist – engineer with problems that he aims to
solve with his knowledge of lever action.

Consider the analogy of a saucer resting on a glass surface
the saucer remains stable when downward pressure is
applied at any point within the circumference of the base.
On the other hand, when downward pressure is applied at
any point outside the supporting base the saucer becomes a
lever, the edge of the base acts as a fulcrum and the
opposite side of the saucer is raised.
If instead of resting on a glass surface, the saucer
rests on a yielding surface ( a layer of soft rubber, for
example) tilting of the saucer result whenever downward
force is applied at any point except the very center. The
further from the center a force is applied, the greater will
be the tilting effect. Even when pressure is applied inside
the base but not in the exact center, the saucer becomes a
lever.

This principle applies also to a denture base but not
to the same degree, for although the supporting
tissues are never so rigid as glass, they are not often
so yielding as soft rubber. Because of the yielding of
the denture base’s support, the base becomes a lever.
Often the upper base acts as one lever, the lower
base is another lever, and the mandible itself as a
third lever. Thus, we have a multiple lever system. It
is impossible to eliminate leverage in this system ; our
problem is to control it.

Leverage of the mandible is made more favourable by placing
the working occlusal surfaces back in the mouth nearer the
line of force, but leverage of the base on yielding tissues is
made more favourable by placing these surfaces at the center
of the foundation. Since these two ideals are in conflict, the
occlusal areas on which closing force is exerted should be
placed in most instances some where between the best
position with respect to the bases. This is another situation
that demands compromise on the part of the dentist –engineer
who respects the requirements of the living tissues with which
he is dealing.

Under cuts:
Under cuts of the ridge are acceptable if they can be
utilized fully by the denture. Unilateral under cuts can be
accommodated by selecting a suitable path of insertion of the
denture. Bilateral undercuts can only be used to the extent by
which the soft tissues over them can be compressed. The
resistance of the mucous and sub mucosa overlying the basal
bone allows for the existence of modest undercuts that can
enhance retention.

Although exaggerated bony undercuts or less obvious
ones covered by thin epithelium may compromise denture.
Generally bilateral undercuts of 1-2 mm can be used.
Trimming the denture to fit partially into the under cut
area produces a space. If this is filled only with saliva, then
little retention is lost. If space produced in large, however, an
air bubble remains and this reduces retention.
Some “undercuts” are only undercut in relationship to a
linear path of insertion or relative to a presumed vertical path
of insertion. But if the undercut area is seated first (usually in
a direction that deviates form the vertical), 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

Surface Roughness:
In so far as increasing roughness would increase the
interfacial area for adhesion between saliva and denture, the
strength of that union would be improved. However, since, as
stated above, failure does not occur at this site in this way,
roughness is irrelevant and can be discounted.


PSYCHOLOGICAL FACTORS
Psychological effects on retention:
The dentures may have an adverse psychological effect
on the patient, and the nervous influences that result may
affect the salivary secretions and thus affect retention.
Eventually, patients acquire an ability to retain their dentures
by means of their oral musculature. This muscular stabilization
of dentures is probably accompanied by a reduction in the
physical forces used in retaining their dentures. Quite
clearly, the physical forces of retention can be improved and
reestablished, up to a point, by careful and frequent attention
to the denture status. This is done by periodic inspection and

by relining and rebasing procedures.

Dentures are always foreign bodies in the mouth and when
fitted for the first time most muscular actions tend to expel
them. Gradually, however, the wearer learns to differentiate
between the food and the dentures and, at first consciously
but later subconsciously, to control and stabilize them with
the tongue and cheeks. The tongue, by resting on top of the
lower denture and pressing it downwards and forwards, can
control its tendency to rise, and also counterbalance to a large
degree un stabilizing masticatory forces. The tongue can also
be unconsciously trained to prevent the back edge of the
upper denture dropping while the front teeth are incising.The
muscular cheeks can be trained, again unconsciously, to press
downwards on the buccal flanges of the lower denture, while
still carrying out their function of placing food between the
teeth.

SURGICAL FACTORS

Ridge extension:
Alveoloplasty, the surgical reshaping of the
alveolar ridge, is indicated where uneven interseptal
spines or bilateral bony undercuts exist. Bone
removal should always be done with prudence
because it is accompanied by varying degrees of
bone resorption. The use of ridge augmentation with
implant materials should be considered when removal
of bony undercuts will results in a deficient ridge.

The use of these materials can both preserve
bone and correct the anatomic defect.
Removal

of

interseptal

bone

and

gentle

compression of the expanded socket is often all that
is required to achieve the goal of a well contoured
ridge with the conservation of bone. Excessive
removal of bone during multiple extractions should be
avoided as a ridge with an inverted “V” shape may
result.

In the mandibular arch, an area which often
requires alveoloplasty but is frequently overlooked is
the lingual aspect at the posterior termination of the
mylohyoid ride. The denture flange should extended
below

this

projections

area.

The

should

be

removal

of

bilateral.In

these
the

bony

atrophic

mandible the alveolar processes, because of lateral
resorption, frequently presents a thin bony ridge
called a “Knife-edge ridge’. The overlying soft tissue
is often rolled with www.indiandentalacademy.com base.
a mobile fibrous

Denture tooth contact may cause pain and require
extensive modification of the denture bas in this
area. Previously, surgical procedures to remove or
stabilize the mobile soft tissue and recontour the
sharp bony ridge left the patient with less vertical
tissue

height

and

continued

bone

resorption

frequently leading to a recurrence of the “knife-edge
ridge”. Today, ridge augmentation with synthetic
implant materials shows great promise to correct this
inadequacy.

In the maxillary arch, an area which often requires an
alveloplasty is the alveolar tubercles. The tubercles often
present opposing bilateral buccal undercuts that become a
problem

in impression making and, if reproduced, with the

insertion and removal of the denture.
Removal of these undercuts by grinding form the tissue
surface of the denture can lead to retention and food
accumulation problems

.

If no undercuts are present in the anterior section of

the arch, it is not always

necessary to remove the

undercuts from both tubercles. Before an undercut is
allowed to remain one should be sure to check that
adequate exists in a horizontal direction to allow free
passage of the coronoid process without crushing or
trapping sensitive cheek tissues between it and the
denture base.
In a vertical direction, the alveolar tubercles
frequently approximate the retromolar papilla and pad
area to the extent that adequate denture base coverage
and correct placement of the occlusal plane is not
possible.


Both bony and soft tissue removal should be accomplished
where possible

to allow adequate vertical height for the

denture bases. Care should be exerted to avoid damaging the
greater palatine artery or entering the maxillary sinus.
Careful presurgical examination to determine the location of
the sinus floor is necessary. Gentle repositioning of the sinus
floor superiorly and medially can also be accomplished when an
enlarged tubercle with a thin sinus wall is evident.


Exostoses are bony nodules located on the alveolar process
of the mandible and the maxilla. The buccal aspect in the
molar region of the mandible and the buccal aspect from the
premolars Posteriorly to the alveolar tubercle in the maxilla
are the most frequent locations. These exostoses usually
present undercuts to the path of insertion and removal of the
denture and should be removed by alveoloplasty techniques.


Tori are bony hyperostoses common to both maxilla and
mandible. Small tori that do not act as fulcrum points under a
denture may not require removal. The torus, however, even
when small, may act as a fulcrum under a denture if the
mucosal covering of the crest and slopes of the ridges are
displaceable to a greater extent than the mucosal covering of
the torus. In these instances, the denture base over the area
must be relieved to compensate for the difference or the
torus should be surgically removed.
When a torus

is large, grossly undercut, or located

Posteriorly where the post palatal seal is to be placed, it
should be surgically removed.

Genial tubercles are neither exostoses nor tori but are
often prominent following advanced alveolar ridge resorption
in the anterior area of the mandible. They are covered by
thin tissue which will not bear the pressure of a denture
flange located in this area. The superior portion of these
prominences may be removed in a

fashion similar to the

mandibular torus. That portion of the genioglossus muscle
with attached in the area is usually left free.


ANATOMIC INFLUENCES ON MAXILLARY
DENTURE RETENTION

Considerations unique to the maxillary
complete denture include the incorporation of
a posterior palatal seal to complete the border
seal. The posterior palatal seal maintains
tissue contact during base movement or soft
palate
function
and
compensates
for
processing changes. This critical area extends
between the hamular notches
along the
flexure line of the soft palate.

The posterior palatal seal of the denture must
extend horizontally beyond

the supportive hard

palate to include the muscular aponeurosis of the
soft palate. This area is not susceptible to pressure
atrophy

and therefore allows moderate tissue

displacement to maintain the thin fluid film. To obtain
the proper amount of tissue displacement, the
posterior palatal seal must be deeper as the palatal
vault becomes steeper to compensate for greater
processing error.

Patients exhibiting highly tapered steep palatal
vaults, present a special problem. The processing error
may be so severe that no amount of posterior palatal seal
can compensate for the resulting deficiency in intimate
tissue contact. In these situations a metal base or
subsequent bench-cure reline procedure

would be

incorporated into the initial treatment plan.
A region that often causes problems in maintaining
border seal is the buccal space or retrozygomatic space.
This varies in size and shape but must be filled to avoid
ingress of air beneath the denture base.

Care should be taken to fill the entire buccal space
during border molding and subsequently impression
making as limited by the normal functional range of
movement of the coronoid process.
The remaining border of the maxillary denture
benefits from a draping effect of the lips and cheek
and is not usually a problem in maintaining border seal
if overextension is avoided.

ANATOMIC INFLUENCES ON MANDIBULAR
DENTURE RETENTION

The mandibular denture generally presents
the major problem with regard to retention.
Reasons for this include a movable floor of the
mouth, which causes difficulty in establishing a
lingual border seal, and lack of ideal ridge height
and

conformation,

which

minimizes

stability.

denture

Intimate tissue contact of the mandibular denture
can be achieved through sound impression procedures
as outlined above. The elimination of dislodging
forces by accurate border molding that prevents
overextension can also be accomplished. Special
attention to the triangular buccal frenum, and the
mentalis muscle, which may active in the region of
the labial flange, should accompany any border –
molding procedure. The border seal of the entire
facial flange of the denture depends on accurate
border molding and is enhanced by the dropping
effect of the lips and cheek.

A slight posterior seal may be necessary on the
distal border of the mandibular denture at the point
where the cheek no longer provides contact along the
denture border. The denture base should cover the
posterior extension of the firmly bound, keratinized
tissue of the pear – shaped pad. Craddock coined the
term “pear –shaped pad”, which refers to the area
formed by the residual scar of the extracted third
molar and the associated retro molar papilla.

Clinically the pear shaped pad is distinguishable by
the lighter color and firmly bound nature of the
overlying mucosa. Immediately distal to the area is
the less keratinized more resilient, and more vascular
retro molar pad. It contains glandular tissue and a
sub mucosa layer that can tolerate a gentle posterior
seal. Lamie and Krol suggest beading this region at
the junction of the pear – shaped and retro molar pad
to

ensure

peripheral

dentures border.

seal

along


the

posterior

Mandibular lingual anatomic influences:
The border seal along the distal extension of the lingual
flange requires an understanding of the anatomy and dynamic
muscle physiology of the region. The posterolateral portion of
the retromylohoid curtain overlies the superior constrictor
muscle, and the posteromedial aspect covers the palatoglossus
muscle and lateral surface of the tongue. The inferior wall of
the retromylohoid fossa overlies the submandibular gland,
which fills the gap between the superior constrictor and the
most distal attachment of the mylohyoid muscle. Border
molding must allow for the muscular function in this region. It
is possible that medial pterygoid contraction could influence
the contours of the distolingual flange by causing a bulge in
the posterior wall of the retromlohyoid space.

Adequate seal can be obtained by gently
compressing the tissues of the lateral wall of the
retromylohyoid fossa lingual to the retromolar pad
and tucking the distolingual flange laterally against
the mucosa overlying the superior constrictor muscle
superiorly and the loose connective tissue of the
mandible inferiorly. Maximum posterior extension
into the fossa is not necessary. Once the border seal
is established, further posterior extension adds little
to the support, stability, or retention.

The contour and inferior extension of the lingual
flange are dependent on the action and anatomy of
the mylohoid muscle. The lingual flange slopes
medially away from the mandible to allow for the
action of the mylohoid muscle. This inclination also
enhances the ability of the tongue to control the
mandibular denture, providing a seating force to the
denture.

The mandibular attachment of the mylohoid muscle
extends anterioinferiorly along the mylohyoid ridge from
the lingual tuberosity in the molar region to the genial
tubercles

at

the

midline.

Posterior

fibers

extend

vertically to attach to the hyoid bone, while the anterior
fibers extend horizontally to meet the fibers of the
contralateral side to form a midline

tendinous raphe.

This explains why the lingual flange can be made longer
Posteriorly despite a more superior mylohyoid muscle
attachment.

Certain authors believe that adequate inferior extension of
the flange can provide continuous contact regardless of tongue
position or mobility of the floor of the mouth. However, the
inferior

extension

of

the

posterior

determined by the displaceability

lingual

flange

is

of the soft tissue and

underlying mylohyoid muscle when the floor of the mouth is at
its most superior position. In addition, the flange is molded by
a contracted mylohyoid muscle. At rest the level of the floor
of the mouth may be inferior to the lingual flange and the
mucosa may drop laterally away from the intaglio as the
mylohyoid muscle relaxes.

In such situations the border seal occurs at the border of the
lingual flange when the mylohyoid muscle is active. When it is
inactive, with the tongue retracted or at rest, the seal may
occur as high as along the contact of the intaglio with mucosa
overlying the mylohyoid ridge. Fortunately, the tongue often
occupies the entire superor to the floor of the mouth at rest.
By contacting the lingual denture surface, it is able to
promote a seal in this region and enhance retention. Accurate
border molding and impression procedures ensure adequate
border seal.


Mandibular anterior lingual influences:
The most difficult region in which to obtain a
border seal is the anterior lingual border. The mylohyoid
muscle acts anteriorly as well as Posteriorly to raise the
floor of the mouth, and the genioglossus muscle functions
in the region underlying the lingual frenum. The superior
fibers of the genioglossus muscle attach to the superior
genial tubercles and function in depressing the body of
the tongue. Activation of the inferior fibers of the
genioglossus muscle that pulls the tip of the tongue
posterosuperiorly, depresses the central part of the
tongue to form a concavity during bolus formation, and
causes the anterior floor of the mouth to reach its most
superior position.

Several methods may be used to establish and
maintain border seal throughout the functional range
of movement of the anterior floor of the mouth.
Some techniques recommend the horizontal extension
of the anterior lingual flange sublingually. Here the
lingual flange is extended inferiorly to contact the
highest level of the floor of the mouth. The flange
can then be extended


Posteriorly to contact the sublingual folds and there by
establish a seal when the tongue is at rest and the floor of
the mouth drops. Care is taken not to impinge on the
submandibular or sublingual gland ducts.
Another technique involves a similar method of border
molding to determine the inferior extension of the flange.
However, a slight displacement of the mucosa anteriorly can
be tolerated and provides a seal when the muscular floor of
the mouth is at rest. This is accomplished by adding a slight
additional amount of softened border-molding material to the
inner surface of the previously molded anterior lingual area
and reseating the custom tray. Again, the tongue at rest aids
in maintaining the border seal by contacting the polished

lingual flange as well as the mandibular anterior teeth.

Relationship of the external surface and periphery to
surrounding orofacial musculature:
Some important yet easily overlooked determinants of both
denture stability and retention involve the relationship of the
polished surface of the denture base to the surrounding
musculature on the denture base generally result in lateral and
vertical dislodging forces.
Certain factors involving the musculature and the polished
surface of the denture can facilitate stability in two ways. First, the
action of certain muscle groups must be permitted to occur without
interference by the denture base so that they will not dislodge the
prosthesis during function or compromise stability. Second, the
dentist must recognize that normal functioning of some muscle
groups can be used to enhance stability. Alterations in external
denture base contours can lead to a dynamic seating and stabilizing
action directed towards the prosthesis.

MECHANICAL AIDS TO RETENTION:
There are certain devices which are intended
to keep complete dentures in place but their
permanent use should only be employed as a last
resort, and some not at all.

I] Springs: These are made of coiled stainless
steel, gold-plated base metal or nylon and have
their ends attached to swivels in the premolar
areas on both sides of the 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 the springs and held in place .

Disadvantages:
1. The constant pressure may cause mucosal irrita
tion and excessive alveolar resorption.
2. The inner surfaces of the cheek are

frequently

injured from frictional contact with the springs
3. Lateral movements are extremely restricted and
hence

the

efficiency

of

the

dentures

impaired.
4. They are generally inefficient and unhygienic.

is

II]

Denture fixatives:
The powder form consists of natural gums such as

tragacanth or karaya with cellulose added. It is sprinkled
on the moist, fitting surface of the denture which will
then usually stick in place for several hours. Gradually
the sticky jelly is pressed from underneath the denture
or washed away by the saliva, and for this latter reason
is rarely of any use for holding lower dentures. Even with
prolonged use it does not appear to affect the mucosa.
Creams and liquids, containing the same substances as

are in artificial saliva, are also available.

Uses
1.To hold the upper record block in position when

securing

intra-oral record
2. To prolong the usefulness, for a short time, of an
immediate upper denture which is becoming loose through
alveolar resorption.

.

3. To enable a patient to wear an old, ill-fitting
denture, while a denture in normal use is

upper

being repaired.

4. Sometimes used by public speakers, such as actors or
clergymen, to give them the assurance that the upper
denture will not move while they are addressing their
audiences.


Disadvantages:
1. It has an unpleasant feel as soon as it is pressed
out from beneath the denture.
2. It is only a temporary expedient and the less
accurate the fit of the denture the more rapidly is
the fixative washed away.
3. It,is of little use for retaining lower dentures.

III] Suction chambers: These often resemble
relief areas in shape but differ from them in having
a clearly defined outline instead of merging into
the surrounding surface. 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.
The mucosa in this area of reduced pressure
proliferates to form a mass of dentureinduced hyperplasia. For this reason the
technique should not be used.

Disadvantages:
1. It has an unpleasant feel as soon as it is
pressed out from beneath the denture
2. It is only a temporary expedient and the less
accurate the fit of the denture the more
rapidly is
the fixative washed away
3. It,is of little use for retaining lower
dentures.

Suction chambers :These often resemble relief areas
in shape but differ from them in having a clearly
defined outline instead of merging into the
surrounding surface . When the denture is inserted
the patient creates a partial vacuum in this chamber
by sucking.
Rubber suction discs :Although these are still used in
practice they are only included in this list in order to
condemn them. 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.

IV] Magnets: From time to time the use of small
magnets embedded beneath the molar and premolar teeth
and arranged with similar poles opposite each other, has
been advocated. In theory the repulsion effect will keep
both dentures in place but in practice it will be found
that, owing to magnetic force being inversely proportional
to the square of the distance and also the small size of
the magnets which it is possible to fit, the repulsive
effect is undetectable when the dentures are separated
by more than 1 or 2mm.

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