INDIAN DENTAL ACADEMY
Leader in continuing dental education
Movements of a distal extension Rpd
Nature of load acting in distal extension partial
Treatment of distal extension partial denture
Altered cast impression procedure
Review of literature
Summary and Conclusion
A removable partial denture prosthesis as its name
implies is a prosthodontic restoration that supplies teeth
and its associated structures to a partial edentulous arch
and can be removed and inserted by the patient.
Removable partial dentures can be classified
according to the support they derive from the remaining
dentition and associated soft tissues.
Many RPD’s derive all their support from the
remaining natural teeth and are referred to as toothborne RPD’s.
RPD’s that derive their support from both the
teeth and associated residual ridge tissues are termed as
tooth-tissue borne RPD’s or distal extension RPD’
Movements of a Distal Extension RPD
Rotation of the prosthesis around a fulcrum line passing
through the two principal occlusal rests of the direct
retainer or through the points where the minor connectors
adjacent to the edentulous area break contact with the
Rotation of the prosthesis around the longitudinal axis
formed along the crest of the residual ridge.
Rotation of the prosthesis around an imaginary
perpendicular axis located along the center of the dental
FORCES AROUND THE FULCRUM
FORCES AROUND THE LONGITUDINAL AXIS
FORCES AROUND THE PERPENDICULAR AXIS
NATURE OF LOAD ACTING IN
DISTAL EXTENSION PARTIAL
The bilateral distal extension partial denture is the
most common design of partial denture and occurs more
often in the mandible than the maxilla.
considering the design of such a denture it is necessary to
understand what happens to it during function and in
particular under the vertical, lateral and anterior-posterior
loads to which it is subjected.
The vertical load that may be exerted on a partial
denture can be divided into parafunctional load and
functional load. In additional an uncomplicated vertical
load is likely to be applied intermittently throughout the
day in empty swallowing function.
It has been demonstrated that the degree of
displacement of the tissues under the saddle of the
denture is greater than that of the tooth within its
socket, and that the displacement increases towards the
When vertical load is applied to the saddle both
the abutment teeth and the soft tissue covering the
saddle area are displaced with the alveolar tissues
being displaced to a greater content than the tooth.
The result of this is rotation of the free end
saddle being displaced into the soft tissue posteriorly
and the clasp arm exerting leverage on the abutment
tooth in a distal direction.
With a rigid connector present between the saddle,
the same effect will occur on the opposite side of the
arch. This is such a design that application of the vertical
load will cause rotation of the free end saddles into the
tissues overlying the residual ridges and the line joining
the occlusal rest can be considered as the
At the same time as rotation of the saddles into the
supporting tissues occurs, so also is three rotation in the
opposite direction of the lingual bar connecting the
The amount of displacement of both the saddle
and the connector is however dependent upon the nature
and amount of the fibrous submucosa that covers that
covers the residual alveolar ridge and this can be assessed
Since increased vertical load causes increased
bony resorption it is wise to make the saddle cover as
large an area as possible in order to reduce the load per
unit area and ensure that the residual ridge is subjected to
It has been generally accepted that when the
saddle of a Kennedy class I denture with occlusal rest
placed distally on the abutment teeth is loaded vertically,
there is tendency to distal displacement of the abutment
tooth. This is not a bodily movement but rather one of
the tilting due to the arch of rotation of the saddle, which
in the gingival area of the abutment tooth is almost
parallel to the mucosa, resulting in minimal or no
support from the mucosa near the tooth.
This will result in distal bone loss, eventual
tooth mobility and of course denture movement,
dependent upon the state of the inter dental marginal
ligament and its regenerative capacity.
It has been shown that bilateral loading of the
denture saddles is more favorable to the abutment teeth
than unilateral loading and that loads applied to the
saddles are transmitted to the abutment teeth primarly
through the occlusal rests
The potential mobility of the abutment tooth will depend
Magnitude of the vertical load.
The physical characteristic of the overlying mucosa.
Angulation of the residual ridge to the horizontal plane.
The periodontal status of the tooth itself.
The effects of clasping are that
The more rigid the clasp, the greater the leverage on
the tooth and the less the load on the alveolar ridge.
The more flexible the clasp arms the less leverage on
the tooth and more load on the ridge.
THE LATERAL COMPONENT
Lower distal extension saddles may be displaced
laterally as a result of the inclined plan action of the
cusps of the posterior teeth and the steeper the cusp
inclines the greater will be the load which acts laterally.
Lateral load may also act on the saddle during
these tooth contacts that may take place at times other
than during mastication and like the vertical forces will
be greater in magnitude.
The efficiency depends up on the anatomy of the
residual ridge and the condition of the soft tissue of the
Flat ridge with a marked fibrosis of the submucosa
offers comparatively little resistances, but if the ridge is
well formed and shows a thinner submucosa, resistance is
Lateral displacement have an adverse effect on the
residual alveolar ridge and in this respect the lateral
component of load is probably a major factors is ridge
resorption than the vertical component.
Stress Communicated by
Working side saddle.
Buccal ridge plate on working
Abutment tooth on working side.
Buccal arm of clasp on working
Balancing side saddle.
Lingual arm of claps on
Continuous clasp (if included in
Lingual plate (if included in
Lingual ridge plate on balancing
Abutment tooth on balancing
Teeth on balancing side.
Lingual plate of ridge supporting
teeth, and teeth themselves, on
Lateral loads will also be exerted on the denture by
the adjacent facial and lingual musculature particularly
during swallowing. These loads, which act through out
the day may total twice the load resulting from
masticatory function and their effects can be minimized
by using marrow posterior teeth and shaping the flanges
so that they do not extend beyond the zone of minimal
conflict. In addition the flanges should be kept thin in
order to give steam lined appearance to the denture.
ANTERO - POSTERIOR COMPONENT.
Posterior displacement of the mandible from the
inter cuspal position takes place only during the first
power strokes which are used when a hard or tough
bolus is being masticated. Although the magnitude of
the load involved in considerable and an anterior
displacing load on the lower denture results, it is
generally well resulted by the abutment teeth and those
anterior in the arch.
Although a masticatory performance a true
protrusive movement of the mandible is only used in
incision, there is often a protrusive element in grinding.
The cusp of the lower teeth, instead of being
accommodated in the fossae of the upper teeth, make a
contact on the slopes of the upper cusps. This results in a
inclined plane action which produces a distal force on the
lower denture, the magnitude of which will depend on
the musculature and the steepness of the cusp angles.
This backward force is in part resisted by the ridge
when it slopes upwards into the ascending ramus of the
mandible, but the greater part of the resistance comes
from the clasped abutment tooth.
The arms of the three arm clasp encompass the
tooth almost completely on its buccal and lingual
surfaces, and the tips of the arm lie on the mesial of the
crown. Consequently the abutment tooth tends to be
pulled in a distal direction. The magnitude of the force
applied will be greater if the clasp arm are cast alloy than
if they are wrought wire.
A greater problem arises if the abutment tooth is a
canine. Due to the crown morphology of this tooth it is
difficult to design a claps that will encompass the tooth
and also be an aesthetically acceptable. In such a
situations the clasped tooth is unable to offer resistance to
the distal displacement of the saddle, which is borne
entirely by the residual ridge.
TREATMENT OF DISTAL
KENNEDY CLASS I
The suggested methods of restoring the bilateral free end
saddle may be achieved by
1.Reducing the load
2.Distributing the load between teeth and residual ridges.
i) By varying the connector between clasp and saddle.
a) Stress breaking.
b) Combining rigid connection and gingivally
c) Combining rigid connection and occlusal
ii) By anterior placement of the occlusal rest :
a) The RPI system.
b) The balance of force system.
iii) By mucocompression
3. Distributing the load widely
i) Over more than one abutment tooth on each
ii) Over the maximal area of edentulous ridge.
Reducing the load
The vertical load on the saddle in mastication may be
reduced by decreasing the size of the occlusal table and also
by ensuring as wide a coverage of the residual ridge area by
the base of the saddle as is compatible with function.
Using canines and premolars instead of premolars
Using narrow teeth or reducing the width of
selected teeth by removing the lingual cusp (s).
Leaving a tooth off a saddle.
DISTRIBUTION OF THE LOAD BETWEEN TEETH
i) By varying the connection between clasp and saddle.
a. Stress breaking
The principle of stress breaking in partial denture
design is the provision of some degree of movement or
flexibility between the clasp unit and the distal extension
saddle. The stress transmitted by the denture to the tissues
is distributed differently therefore and also reduced by the
energy absorbed in deformation than if the connection had
been rigid. Any device which allows movement between
the saddle unit and the retaining unit is known as a stress
Stress Breakers can be divided into two groups.
Those having a movable joint between the direct
retainer and the saddle.
Those having a flexible connection between the
direct retainer and the saddle.
The first group is necessary when a precision
attachment is used, but can also be used when a claps
is preferred. They vary in their range of movement,
some allowing only up and down and side to side
movements, whereas others also permit a vertical
hinge action. www.indiandentalacademy.com
Construction of a flexible or semi-flexible connector
between the direct retainer and tooth supported part of the
denture and the mucosally supported saddle is achieved
with a distally extended flexible bar connected to the rigid
The degree of flexibility will depend upon in its
length and cross sectional form.
Where a lingual bar connector has been used to join
the two saddles it should be distally extended on each side
and then re-curved along the residual ridge to allow
attachment into the matrix resin of the saddle.
Alternatively if a lingual plate connector is used a
split of an appropriate length can be made at its inferior
border. The saddle is attached to the more flexible bar
while the clasp units are attached to the rigid part of the
The use of such designs allows the mucosa
supported saddle a degree of movement which is
independent of the rigid tooth supported part of the denture
and therefore lessens the stress of the abutment teeth.
When a vertical load is applied the saddle is
displaced downward into the soft tissue covering the ridge
to a greater extend than where the retainer and occlusal
rest have direct connection with a saddle. This means that
the ridge bone has to withstand an increased vertical load
which is more evenly spread over the whole ridge rather
than concentrated at the free end of the saddle. Although
not quite accurate it may be assumed that the centre of
saddle rotation is at the portion of the connector lying
anterior to it.
The net result of the stress breaking action as far
as the vertical component is concerned is a greater
assignment of load to the edentulous ridge and less to
the abutment tooth.
The torque on the abutment is reduced markedly
in magnitude and is favorable in direction.
When a lateral component acts on the stress broken
saddle a greatly increased lateral stress is placed on the
alveolar bone. Less of the load falls on the abutment teeth
and consequently the magnitude of the damaging lateral
torque is reduced.
If a continuous clasp or lingual plate is included in
the design it is incorporated in the retainer unit and thus
plays less part in the distribution of lateral load.
Stress breaking has little effect on the anterior
component of force acting on the denture saddle during
the power strokes ; uninterrupted contact between tooth
and retainer and retainer and saddle ensures no saddle
movement in an anterior direction and load distribution is
accordingly not altered.
The dangerous horizontal torques acting on the
abutment teeth are reduced by stress breaking and that, in
consequence, their supporting structures are less liable to
However, the edentulous ridge is called upon to
accept more vertical and horizontal stress and as a result
tends to resorb more quickly.
COMBINING RIGID CONNECTION AND
GINGIVALLY APPRAOCHING CLASPING
When rigid connection between retainers and
saddles is used, with gingivally approaching clasps, a
condition may exist which is similar in principle to stress
breaking. The portion of this type of claps that is in
contact with the abutment tooth is at the end of a bar that
is resilient to a degree which depends upon its length and
cross section and the alloy used.
If the occlusal rest is allowed to move over the
occlusal surfaces of the tooth to a small degree in lateral
and antero-posterior directions (and this may occur when
saucer-shaped rest seat preparation are used), the action
of the clasp bar resembles a stress breaker, since its
resilience reduces the horizontal forces on the abutment
tooth. The effectiveness of the stress breaking actions of
these clasps may be increased by increasing the
resilience of the bar.
COMBINING RIGID CONNECTION AND
OCCLUSALLY APPROAHING CLASPING.
A combination of rigid connection and
occlusally approaching clasps is the opposite extreme to
stress breaking. In this condition more load is placed on
the abutment tooth and ridge is capable of variation and
depends on the ridge.
When the arm is resilient, a certain amount of
movement of the clasp over the surface of the tooth is
permitted. At one extreme a wrought gold wire clasp
allows most movement of the clasp over the enamel.
Whereas a cast cobalt chromium clasp permits least
The extent of these clasp movements is small but
they may, however, be sufficient to reduce the torque
acting on the abutment and keep them within the
If the mucosal tissues covering the ridge areas are
highly displaceable and mobile,
then there may be an
indication for some type of movable or flexible connection
between the saddles and the retainer units.
d. THE DISJUNCT DENTURE
In the older patient it is not uncommon to find a
situation, particularly in the lower jaw, where the few
remaining teeth are anterior teeth with considerable
gingival recession and a generally poor periodontal
It has been suggested that such a problems may be
overcome by the construction of a two part denture,
composed separately of tooth borne and mucosa borne
sections each acting independently of each other on its
The tooth borne part comprises a lingual plate
which acts to protect the teeth and the gingivae from the
connector of the mucosa borne part, and which also
carries retention elements. In addition, it is constructed
with distally extending buccal bars which are designed
to engage a slot in the saddle of the mucosa borne part.
These are known as disjunct bars as they are not
attached directly and rigidly to the mucosa borne saddle
but allow some movement. They are however, necessary
for its retention.
The mucosa borne section of the denture are
essentially separate, there is no transfer of the vertical
masticatory load from the mucosa borne saddle to the
tooth borne section. In addition because of the absence of
a rigid connection between the two separate parts there is
little transfer of load by means of the disjunct bars. The
mucosa borne part can therefore move independently
according to the compressibility of the mucosa.
This technique has been suggested as particularly
useful in the treatment of the bilateral free end saddle,
where the support contribution of the remaining
standing teeth is poor and their periodontal health also
might be further compromised by a totally mucosally
borne designed denture.
The disadvantage of the denture is that is
technically difficult to construct and also that patients
occasionally complain it ‘rattling’ during function
which is of course due to the principles inherent in its
BY ANTERIOR PLACEMENT OF THE
The distribution of load between the abutment
teeth and residual ridge can sometimes be altered
favorably by anterior placement of the occlusal rest. This
has the effect of altering stresses on the saddle from a
Class I lever situation where the resistance to the applied
load lies on the opposite side of the fulcrum, to a Class
II lever where the resistance lies between the applied
load and the fulcrum. This permits more even
distribution of load and less stress on the abutment teeth
a. THE RPI SYSTEM
This system of partial denture design involving a
clasp unit comprised of a rest, proximal plate and “I” bar
An important consideration of this system is the
positioning of the occlusal rest to provide the element of
tooth support. If the rest is placed distally on the
abutment tooth and applied to the saddle, it has been
demonstrated that the arc of movement of the denture
base tends to the mainly perpendicular to the residual
ridge in the posterior region.
On moving anteriorly, however, the region near
the abutment tooth the saddle movement is almost
parallel to the ridge in an anterior direction. It is clear
that in this situations the mucosa adjacent to the tooth
can offer little resistance to the applied load, it and the
gingival margin being likely to be traumatized by the
horizontal movement of the denture against the abutment
tooth. This area, where tooth support ends and mucosa
support begins, should therefore be protected.
the occlusal rest is placed mesially on the
abutment teeth, it has been shown that the arc of
movement of the saddle under applied load will alter and
be more perpendicular to the mucosa throughout its
length, due to the presence of a mesial rather than a distal
This will increase the support provided by the
mucosa whilst reducing the anterior movement of the
saddle under applied www.indiandentalacademy.com
If the rest is placed distally then the tooth will tend
to tilt distally, where it has little support. If it is placed
mesially however, although there will be a tendency of
mesial tilting of the abutment tooth, this will be resisted
by other teeth in the arch anterior to it.
Potential damage to the gingival tissues distal to
the abutment tooth can be lessened if the distal surface of
the tooth is covered by a thin plate of cast metal (the
proximal plate) which extends on to the soft tissues. This
is relieved at the gingival margin.
Wear and damage will also be limited and the metal
will maintain a close adaptation so protecting the tissues
from food packing and preventing gingival hypertrophy.
In addition the plate should extend lingually on the
proximal surfaces of the tooth in order to provide some
reciprocation for the “I” bar clasp.
It has been argued that by constructing a
conventional occlusally approaching clasp the external
contour of the tooth is altered adversely, particularly in
relation to natural stimulation of the gingivae and in food
If its tip is placed towards the mesial portion of the
tooth it also serves to bring the proximal plate into tight
contact with the distal surface. As the denture is
depressed on to its basal seat the clasp will move towards
and downwards and out of contact with the tooth so
removing any possibility of leverage.
The mesial rest is linked to a minor connector
which also provides some reciprocation and is placed in
the mesio lingual embrasure but free of the adjacent tooth
anterior to it. With applied load to the saddle the rest acts
as a fulcrum point, ensuring mesial rather than distal
loading of the abutment tooth.
Under load it will be depressed tissue wards
further into the undercut area without exerting torque
or leverage on the abutment tooth.
The “I” bar crosses the gingival margin at right
angles and contacts the tooth in its gingival third and
at the greatest mesiodistal prominence of the tooth, its
precise position of contact immediately below and
above the survey line.
Besides being retentive, it will move mesio
gingivally away from the tooth under applied load.
The RPI system will result in a denture with
Enhanced mucosal support due to
Reinforcement against mesial tilting of the abutment
Adequate retention with minimal effect on natural tooth
No adverse stress on the abutment tooth during
Protection of the transitional region between the tooth
and the mucosal areawww.indiandentalacademy.com saddle.
of the edentulous
b. Balance of force system
The balance of force system, canbe considered as a
further refinement of the RPI system being based on the
mechanical principles of a class II lever. As the magnitude
of masticatory loads on the abutment teeth are much
greater than those of the forces of displacement and as the
tooth is less able to withstand this, the design has been
developed to ensure that loads during masticatory
performance are directed vertically along the long axis of
the tooth so avoiding torque and leverage.
A rest seat must be provided on the part of the
occlusal surface of the abutment tooth that is distant from
the saddle. This will act as the fulcrum point and ensure
vertical loading on the tooth during function. In distal
extension partial dentures this would be a mesially
placed support unit.
interproximal access area of about 1 mm must be created
between the abutment tooth and the anterior tooth
adjacent. It is in this area that reciprocation for the clasp
arm will be positioned together with the minor connector.
The clasp unit is designed so that retentive tip of the
claps arm is positioned on the interproximal surface of the
abutment tooth adjacent to the edentulous saddle. It should
lie below the maximum convexity of this surface engaging
a degree of undercut according to the physical properties
of the material.
The reciprocation for the retentive force of the clasp
arm in resisting displacement is provided by a vertical
plate in the prepared access area on the abutment tooth
above its maximum convexity. The vertical plate is joined
to the major connector.
The unit should be so designed that the flexible tip
of the clasp arm, the occlusal rest and the contact surface
of the vertical reciprocating plate are in line with the
crest of the edentulous ridge. Retention is therefore
achieved mesiodistally as opposed to bucco-lingually and
the design ensures that the greatest loads on the tooth are
applied mesio-distally where it is well supported.
When masticatory load is applied to the distal
extension saddle its downward movement towards the
underlying tissue is accompanied by a similar movement
of the retentive tip of the clasp arm. This allows the
clasp to disengage the tooth as it moves into an area of
increased undercut, this eliminating horizontal tooth
loading. The mesial occlusal rests will direct loads
vertically along the long axis of the tooth hence it is
better able to withstand them.
If a displacing force is applied to the denture, the
saddle and clasp tip once again move in the same
direction occlusally. The clasp tip will now engage the
proximal surface of the tooth below its maximum
displacement. Reciprocation during this action is
provided by the vertical interproximal plate on the
opposite side of the tooth.
III. BY MUCOCOMPRESSION
The greater the amount of displacement the less is
the magnitude of the torque and load on the abutment,
when a vertical load is placed on the saddle.
Different impression materials give varying
degrees of mucosal displacement
The saddle base fitted accurately against the
mucosa from which tissue fluid has already been
displaced sinks less under the masticatory load than if
fitted against an undisturbed mucosa.
distribution of load between abutment and ridge bone.
The greater the displacement the more evenly is
the stress distributed between the abutment and the
However, the mucosa cannot be continuously
subjected to such heavy pressure since this will result in
decreased blood supply to, and drainage from, the soft
tissues. Coupled with the fact that the tissue fluid is also
reduced, this may result in a tropic disturbance
The natural tendency of the displaced tissue is to
recoil in a visco-elastic manner. In assuming that the
saddle is maintained in the closest approximation with the
displaced mucosa, the presence of some force to hold it in
this position is also assumed.
This force can only come from rigid clasping of the
abutment tooth and results in a continuous force acting on
It is thus seen that the use of rigid connection and
clasping together with mixture displacement leads to an
unacceptable situation in respect of potential damage to
the abutment and covering mucosa.
If maximum displacement is to be used,
arrangement must be made to allow some recoil of the
This can be achieved either by very light
clasping, generally wrought gold wires of thin gauge,
or by a stress breaker giving flexible connection
between the saddles and retainer units.
The method of maximum displacement coupled with
light clasping directly attached to the saddles is not used
Retention of such a denture is inadequate because of
the light clasping and poor adhesion, the latter being due to
the uneven thickness of saliva film between the mucosa and
the fitting surface of the denture after recoil of the tissues.
Lateral stresses are resisted largely by the edentulous
ridge, which is, therefore, liable to resorb.
With mucostasis, even when cast clasps are
directly attached to the saddles, no forces act either on
the ridge or abutment when the saddle is not under load.
In the resting stage, too, adhesion is maximal.
With this type of impression too, the bone is not
evently stressed, the areas underlying thinner mucosa
receiving an increased share of the load.
With such a technique and where rigid clasping
directly attached to the saddle is used, maximal leverage
and torque is placed on the abutment teeth, which are,
therefore, predisposed to periodontal breakdown.
With this type of impression too, the bone is not
evenly stressed, the areas underlying thinner mucosa
receiving an increased share of the load.
There is however, a condition intermediate
between maximum displacement and mucostasis that has
Thus a compromise between stasis and maximum
displacement seems to give a result with the advantages
of each present to some degree.
3. WIDE DISTRIBUTION OF LOAD
I)WIDE DISTRIBUTION OF LOAD OVER THE
When clinically circumstances permit, the procedure
is to move the occlusal rest anteriorly so that it lies not
on the tooth that immediately bound the saddle, but on
the occlusal surface of the tooth that lies immediately
If a rest is placed on this tooth some of the vertical
load is placed upon it and its marginal ridge becomes
the fulcrum point.
If two flexible arms now arise from this and its
encompass the buccal and lingual surfaces of the
posterior tooth and if these arms lie above the survey
lines then some of the vertical load is dispersed.
Part is dissipated in opening the clasp arms and
part is directed down the long axis of the tooth.
The retaining clasp is on the rested tooth. Which
accepts vertical load through the occlusal rest. Lateral
load is distributed to the two teeth by the clasp arms.
II.) WIDE DISTRIBUTION OF LOAD OVER THE
The saddles of the denture should always cover the
largest possible area, so that the pressure falling on any
unit area of the edentulous ridge is reduced under vertical
and horizontal loading.
While full coverage over the
retromolar area and the buttress bone both buccally and
lingually is desirable for load distribution it may not
always be acceptable to the patient.
Modification of the bilateral
free end saddle
Modification of the bilateral free end saddle
1) An anterior saddle present in addition to 2 free
2) Long free end saddle interrupted by a single
An anterior saddle present in addition to 2 free end
The stress on the abutment tooth depends on
• saddle length and shape
•Displaceability of mucosa
A rigid construction is advisable
By clasping the 4 abutment teeth , vertical and
horizontal forces are resisted by 2 teeth on each side
. This facilitates wide distribution of load
a)If only 2 premolars remain bilaterally
• Lingual bars and continuous clasps
The clasps are constructed in wrought wire but if
ridges are well formed they may be constructed in cast
b)if premolars are severely inclined lingually
• Buccal bar
• Back action clasp
c)Only 2 canine remain
•Simple acrylic resin mucosa supported denture
2)Long free end saddle interrupted by a single
b)Retain if healthy .
This reduces length of saddle thereby reduces
Wide distribution of load since clasping on 2
c)when molar is single long standing tooth it is
sensible to dispense with the small free
Bilateral free end saddle upper denture
The basic problem encountered with Bilateral free end
saddle upper denture is similar to those found with
Indirect retention is more necessary with the upper
than with the lower
Indirect retention is obtainable in these cases by.
• Continuous clasp
•Anterior extension of palatal bar
•Extension of any palatal plate to cover the rugae
Modifications of the Bilateral free end saddle
a)Long free end saddle interrupted by a single
b)Anterior natural teeth missing
c)Series of single tooth saddles separated by single
If no teeth are to be extracted a horse shaped
metal base covering hard palate is often the treatment
ALTERED CAST PROCEDURE
The purpose of altered cast procedure is to obtain the
maximum support from the edentulous area of the extension
partial denture. This procedure applies the principal of
recording the edentulous tissue in a form that provides the
proper denture base extension without distortion or
displacement of the tissues.
The objective is to ensure the best possible
relationship between the casting framework, properly fitted
on the teeth and the denture base thereby deriving the
greatest support potential from both teeth and edentulous
THE LOADED IMPRESSION TECHNIQUE FOR
THE DISTAL EXTENSION REMOVABLE
In order to obtain an optimum impression of an
arch that will receive a Kennedy class I or II RPD, a dual
impression technique must be employed. The final
impression combine an elastomer to register the anatomic
form of the teeth and surface detail of the residual ridge
and a more viscous material to load the residual ridge.
Review of Literature
Stress analysis is distal extension partial dentures.
George W. Hindels J. Prosthet Dent. 7; 197 – 205, 1952.
He described the load distribution in extension saddle partial
dentures. He said that the method used to make impression of
the supporting and retaining anatomic status of the mouth is of
basic importance for obtaining optimum distribution of the
masticatory load in the construction of remarkable partial
denture, especially those of the lower extension saddle type.
His opinion is that there are three definite requirement that
must be fulfilled to assure proper load distribution in extension
saddle partial denture.
The tissue surface of the saddle should be negative reproduction
of the anatomic, undisturbed surface of the alveolar mucosa.
The masticatory load should be distributed between the ridge
and the abutment teeth during function and cannot be left to be
carried by alveolar ridge alone.
The denture saddle should be related to the metal frame work in
such a way as to be similar to the relationship existing between the
supporting teeth and the supporting mucosa when latter is a
The Bilateral free end saddle lower denture.
Lamme G.A. and John Osborne
J. Prosthet Dent 4 : 640 – 652, 1954.
They stated that the bilateral free end saddle lower denture (class I
lower denture of the kennedy’s classification) always presents a
treatment problem. A free end saddle can have tooth support at only
one extremity and this at least part of lead falling upon it must be
resisted by the edentulous alveolar bone. This is in contra distinction
to the bounded saddle, which has anteriorly and posteriorly placed
abutment teeth. in this he given following methods for the treatment
of the free and saddle. The following method of attempting to control
the vertical load are designed to give the optimal reaction in both
1.Reducing the load directly.
2.Distributing the load between teeth and alveolar
i) By varying the nature of the connection between
clasp and saddle.
b)Combining rigid connection and gingivally
c)Combining rigid connection and occlusal
ii) By anterior placement of the occlusal rest.
iii) By mucocompression.
3. Distributing the load widely
i) Over more than one abutment tooth on each side.
ii) Over the maximal area of edentulous alveolar
Stress analysis is distal extension partial dentures.
George W. Hindels J. Prosthet Dent. 7; 197 – 205, 1957.
He did a stress analysis in distal extension partial dentures, he
said that masticatory stresses exerted on the base of a distal
extension partial denture are transmitted to the supporting
anatomic structures through contacting parts of the appliance.
If the parts are incorrectly designed or constructed, they will
alter the direction and force of these masticatory stresses and
may create stresses which are not within the physiologic limits
of tissue tolerance. The partial denture should be constructed.
So this movement is vertical is relation to the supporting bone.
Clasp and rest should be designed to allow for this vertical
movement of the denture base. Stress other than those vertical to
the abutment teeth should be reciprocated. Reciprocation is best
obtained by contact of rigid parts of the partial denture with
modified axial surface of the abutment teeth which are made
parallel to each other and the path of insertion
A study of partial denture design and masticatory pressure
in the mandibular bilateral distal extension case.
Anthony K. Karies :
J. Prosthet dent. 8: 340-350, 1958
In a study of masticatory performance, he found out that the
The reduction of the size of the occlusal table reduces the forces
acting on the partial denture and lessens the stresses on the
abutment teeth and supporting tissues.
The effect of the partial denture on masticatory performance did
not reveal any significant relationship.
The rigid design of the partial denture were more desirable than
the flexible are specifically the rigid lingual bar is more
desirable than a flexible bar in withstanding horizontal stresses.
Preparation of abutment teeth for removable partial
J. Prosthet Dent. 20: 396 – 406, 1968.
He mentioned about the preparation of abutment teeth for
dentures, he says that the preparation of spoon shaped or
rounded rest seat areas that direct forces towards the long axes
at abutment teeth provides positive support for the partial
denture. The location of rest areas affects the movements of
abutment teeth by changing the direction of force applied to the
teeth and to the denture base.
Metal guiding planes that contact the proximal surface of the
abutment teeth and extend 1 to 2 mm onto the residual ridge
lessen the possibility that debris will collected around the denture
the residual ridge and the abutment. The development of adequate
support for partial denture without applying under torquing force
to the abutment and the maintenance of the health of the
periodontal supporting structure pre vital to the success of partial
Clasp design for extension base removable partial
Arthur J. Krol
J. Prosthet Dent. 29:408-416, 1973.
He mentioned that clasp design for extension base partial
dentures is one of the more fascinating and thought provoking
subject in dentistry. Many types of clasp for unilateral and
bilateral distal extension base partial dentures are consult
being and by dentist and dental laboratories throughout the
work in an attempt to prolong the life of the remaining teeth.
The clasp returd to as an R.P.I. clasp is introduced which
minimizes tooth coverage and reduces stress on the abutment
RICHARD P. FRANK in 1986 in his clinical observation
indicated that the wrought wire clasp assembly. The I-bar clasp
assembly and the L-bar clasp assembly yield similar results. Several
thousand observations have been made by the faculty and no special
trend of problems has been noted that would cause one clasp
assembly to be favoured over another. These three types of clasp
assemblies work satisfactorily when properly chosen and carefully
RONALD E. MYERS
in 1986 in his photoelastic study of rests
found out that with a distal extension removable partial denture,
maximum use of existing oral structure can aid in the total support
of the prostheses and reduce the force on the solitary abutment.
Four rests with relieved and unrelieved guide plates were
evaluated for optimum stress distribution around the root of a
solitary premolar abutment. The rest were the mesial, the distal.
The mesial and distal and the continuous rest.
The findings demonstrated that :
1.The continuous rest had the most favourable stress
2.All other rest design demonstrated more lateral stress than the
3.Relieved guide planes demonstrated 58% less maximum shear
stress in the apical portion than unrelieved guide planes.
An analysis of rotational movements of asymmetrical
destal extension removable partial dentures.
Aviv I. Et al
J. Prosthet Dent 61; 211 - 214, 1989.
He states that an axis of rotation is created through the most
distally placed occlusal rest. When a distal extension removable
partial denture is loaded. If the residual ridges are of unequal
length, the axis of rotation may not be perpendicular to the
residual ridge. Movements of I bar retainers loaded on the
mesiobuccal aspect of asymmetrical abutment teeth may torque
the abutment teeth as the denture base moves tissues wards. Use
of L shaped direct retainer on the distobuccal surveyed undercut
will create a more favourable class II lesser effect on the
Comparison of vertical movements occurring during
loading of distal extension RPD bases made by three
Richard J Leupold, Robert J Flinton, David L Pfiefer
The study clinically compared the vertical displacement
of the distal extension RPD made from altered cast
impression, an impression from border molded custom
tray. Stock tray irreversible hydrocolloid was used as a
control. Although statistically significant 0.19mm
difference between impression techniques may or may
not be clinically significant.
Sectional impression for mandibular distal extension
Hanaa Al Shiekh, Adel M Abdul Hakim
The final impressions made in border molded full
arch custom tray clinically comparable to sectional
impression for distal extension mandibular RPD.
reduction in vertical movement when analyzed
statistically. However this finding maybe clinically
Clinical outcome of altered cast impression procedures
compared with the use of a one piece cast.
Richard P Frank , James S Brudvik, Karleen G Noonan
The altered cast impression procedure does not have
significant advantages over the one piece cast provided
standards in this study are met. These include completely
extended impression, use of a magnification to ensure
complete seating of the frame work and coverage of the
retromolar pad and buccal shelf by the base.
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