Principles of Removable Partial Denture
Dr. Shujah A Khan
Department of Prosthodontics,
Difference In Prosthesis Support
Requirements for movement control are generally
functions of whether the prosthesis will be tooth
supported or tooth tissue supported
For a tooth-supported prosthesis, the movement potential is less
because resistance to functional loading is provided by the teeth
For a tooth-tissue supported prosthesis, the residual ridge
presents with variable potential for support
Differentiation Between Two Main Types
of Removable Partial Dentures
Certain points of difference are present between
Kennedy Class I and Class II types of partial dentures and
the Kennedy Class III type of partial dentures
Manner in which each is supported:
Class I and distal side extension of Class II Primary Support
Tissues underlying the base and Secondary Abutment teeth
Class III All support from Abutment Teeth
Secondly, the method of impression registration and jaw record
required for each type will vary.
Thirdly the need for some kind of indirect retention exists in the
distal extension type of partial denture.
Fourth, the use of a base material that can be relined to
compensate for tissue changes
•Differences in Support
The distal extension partial denture derives its major
support from the residual ridge with its fibrous
connective tissue covering.
The length and contour of the residual ridge significantly
influence the amount of available support and
The longer the edentulous area covered by
the denture base, the greater the potential
lever action on the abutment teeth.
Good Support, but
Poor Support and
Poor to Fair Stability
Poor Support and
Two requirements need to be fulfilled
1. The anatomic form, relationship of remaining teeth and
surrounding soft tissues must be recorded accurately.
• Impression material that can be easily removed from undercuts
without distortion used to fulfil this requirement
• Irreversible hydrocolloid, mercaptan rubber base, silicone
impression materials and polyethers
2. The supporting form of the soft tissues underlying the
distal extension base of the partial denture should be
recorded so firm areas are used as primary stress–bearing
areas and readily displaceable tissues are not overloaded
- Muco-displacive impression ?
• An impression material capable of displacing tissue sufficiently to register the
supporting form of the ridge will fulfil this second requirement.
No single impression material can satisfactorily fulfil both
of the previously mentioned requirements!!!
Hence a combination of materials or same type of material with
differing viscosities used?
•Differences in Clasp Design
The tooth-supported partial denture, which is totally
supported by abutment teeth, is retained and stabilized
by a clasp at each end of each edentulous space.
Only requirement for such clasps is that they flex
sufficiently during placement and removal of the denture
to pass over the height of contour of the teeth in
approaching or escaping from an undercut area.
While in its terminal position on the tooth, a retentive
clasp should be passive and should not flex except
when one is engaging the undercut area of the tooth
for resisting a vertical dislodging force.
Cast retentive arms are generally used for this
Advantages and Disadvantages
In the combination tooth and tissue supported RPD, the
direct retainer must perform still another function in
addition to resisting vertical displacement
Stress Breaker – Combination Clasp
The amount of stress transferred to the supporting
edentulous ridge(s) and the abutment teeth will depend
1. Direction and magnitude of the force;
2. Length of the denture base lever arm(s);
3. Quality of resistance (support from the edentulous
ridges and remaining natural teeth); and
4. Design characteristics of the partial denture.
The greater the surface area contact of each minor
connector to its corresponding guiding plane, the more
horizontal the distribution of force.
Maximum contact of
the proximal plate
minor connector with
the guiding plane
produces a more
horizontal distribution of
stress to the abutment
Minimum contact or
disengagement of the
minor connector with
the guiding plane
allows rotation around
the fulcrum located on
the mesio-occlusal rest,
producing a more
vertical distribution of
stress to the ridge
contact with the
guiding plane from
the marginal ridge
to the junction of
the middle and
gingival thirds of the
vertically to the
ridge and horizontally
to the abutment
•Essentials of Partial Denture Design
Design of the partial denture framework should be
systematically developed and outlined on an accurate
diagnostic cast based on the following concepts:
1. Where the prosthesis is supported?
2. How the support is connected?
3. How the prosthesis is retained?
4. How retention and support are connected?
5. How edentulous base support is connected?
It is first necessary to determine the support; tooth
borne or distal extension base?
Potential support the abutment can provide,
1. Periodontal health
2. Crown and root morphologies
3. Crown to root ratio
4. Bone Index Area (how tooth has responded to previous stress)
5. Location of tooth in arch
6. Relationship of tooth to other support units (edentulous span)
7. Opposing dentition
In evaluation of potential support from the edentulous
ridge areas, consideration should be given to:
1. Quality of residual ridge contour and quality of supporting
2. Extent to which the residual ridge will be covered by the
3. Type and accuracy of impression registration
4. Accuracy of denture base
5. Design characteristics of the component parts of framework
6. Anticipated occlusal load
The second step in systematic development of the design
is to connect the tooth and tissue support units.
Major and Minor connectors
The third step is to determine the how the RPD is to be
retained Placement of Direct retainers
The key to selecting a successful clasp design for any
given situation is to choose one that will
1. Avoid direct transmission of tipping or torquing forces to the
2. Accommodate the basic principles of clasp design by definitive
location of component parts correctly positioned on abutment
3. Provide retention again reasonable dislodgement
4. Be compatible with undercut location, tissue contour and
esthetic desires of the patient
The fourth step is to connect the retention units to the
support units, direct and indirect retainers must be
rigidly attached to the major connector
The fifth and last step is to outline and join the
edentulous area to the already established design
•Components of Partial Denture Design
All partial dentures have two things in common:
1. They must be supported by oral structures
2. They must be retained against reasonable dislodging
In Class Kennedy III partial dentures three components
Support provided by Rests
Connectors (Stabilizing Components)
Kennedy Class I and II support comes from both the
teeth and underlying ridge tissues.
However provision must be made for three other factors:
1. Best possible support from resilient tissues
accomplished by Impression technique primarily and
secondarily by area covering the denture base area.
2. Method of direct retention
• Direct transmission of load to long axis of abutment teeth
instead of leverage
3. Distal extension bases movement of extension base
away from tissues is minimum Indirect retainers
Support of RPD by the abutment teeth is dependent on
the alveolar support, crown and root morphology,
rigidity of the framework and design of occlusal rests
Through clinical and roentgenographic interpretation the
dentist may evaluate the abutment teeth and decide
whether they will provide adequate support?
The dentist is responsible for preparation and restoration
of abutment teeth to accommodate the most ideal
design of the partial denture
Effectiveness of tissue support is dependent upon:
1. Quality of the residual ridge
2. Extent to which it will be covered by the denture base
3. Accuracy and type of impression registration
4. Accuracy of denture bases
5. Design characteristics of the component parts
6. Occlusal load applied
Quality of residual ridge cannot be influenced, except it
can be improved by tissue conditioning or modified by
Accuracy of impression technique is entirely in the hands
of the dentist
Accuracy of denture base is influenced by the choice of
materials and the exactness of processing techniques
Total occlusal load applied to the residual ridge may be
influenced by reducing the area of occlusal contact
Fewer or narrower teeth, more effectively shaped teeth?
Opposing natural teeth vs opposing artificial teeth?
Ridge tissues recorded in their resting or non functioning
form are incapable of providing the composite support
for distal extension bases
Three factors must be considered in the acceptance of an
1. Primary stress bearing areas recorded in their supporting form
2. Tissues other than primary stress bearing areas recorded in
their anatomic form
3. Total area covered by the impression should be sufficient to
distribute load over large area tolerated by tissues – Snowshoe
Denture base processed to the functional form is
generally less irregular and provides greater area
coverage than does a denture base processed to the
anatomic or resting form.
A denture base made to anatomic form exhibits less
stability under rotating and/or torquing forces than does
a denture base processed to functional form and thus
fails to maintain its occlusal relation with opposing
•Major and Minor Connectors
A major should be properly located in relation to gingival
and moving tissues and should be designed to be rigid
provides proper distribution of forces to and from the
Minor connectors arise from the major connectors and
join it with other parts of the denture; serve to connect
tooth and tissue support units
For Tooth Supported prosthesis:
1. Retain prosthesis against reasonable dislodging forces without
damage to abutment teeth
2. Aid in resisting any tendency of the denture to be displaced in a
For Distal Extension Partial Dentures
While retaining the prosthesis, it must also be able to flex or
disengage when the denture moves tissue-ward under function
Stabilizing components of the removable partial
denture framework are those rigid components that
assist in stabilizing the denture against horizontal
All stabilizing components should be able to distribute
stresses equally to all supporting teeth without
overworking any one tooth.
It is necessary that minor connectors have sufficient bulk
to be rigid and yet present as little bulk to the tongue as
Two or more parallel, vertical surfaces of abutment
teeth, so shaped to direct a prosthesis during placement
1. Provide for one path of placement and removal of the
2. To ensure the intended actions of reciprocal/stabilizing,
3. Eliminate gross food traps between abutment teeth and
components of denture
Proximal guiding plane surfaces should be about one-half
the width of the distance between the tips of adjacent
buccal and lingual cusps
Or it should be one-third the buccal lingual width of the
And should extend vertically about two-thirds the length
of the enamel crown portion of the tooth from the
marginal ridge cervically.
A guiding plane should be located on the abutment
surface adjacent to an edentulous area.
However, excess torquing is inevitable if the guiding
planes squarely facing each other on a lone standing
abutment adjacent to an extension area are used
An indirect retainer must be placed as far anterior from
the fulcrum line as adequate tooth support permits.
It must be placed on a rest seat prepared in an abutment
tooth that is capable of withstanding the forces placed
An indirect retainer cannot function effectively on an
inclined tooth surface, nor can a single weak incisor
tooth be used for this purpose.
•Implant Considerations In Design
Kennedy Class III presents less of a challenge to Oral
Tissues and patient accommodation than Class I and II.
The challenge is chiefly related to prosthesis movement
to an extent allowed by tissue displaceability under an
Use of implants can significantly benefit tissue
tolerability and reduce any challenge to accommodation
presented by prosthesis movement
•Examples of Systemic Approach to Design
Class III RPD
Entirely tooth supported, may be made to fit the prepared
surfaces of the anatomic form of the teeth and surrounding
It does not require an impression of the functional form of the
ridge tissues, nor does it require indirect retention.
Cast clasps of the circumferential variety, the bar type, or the
combination clasp may be used.
Unless the need for later relining is anticipated, as in the
situation of recently extracted teeth, the denture base may be
made of metal, which offers several advantages.
The Class III partial denture can frequently be used as a valuable
aid in periodontal treatment because of its stabilizing influence
on the remaining teeth.
Kennedy Class I – Bilateral Distal Extension RPD
Because it derives its principal support from the tissues
underlying its base, a Class I partial denture made to anatomic
ridge form cannot provide uniform and adequate support.
Yet, unfortunately, many Class I mandibular removable partial
dentures are made from a single irreversible hydrocolloid
both the abutment teeth and the residual ridges suffer
because the occlusal load placed on the remaining teeth is
increased by the lack of adequate posterior support
Kennedy Class II RPD
Combination of tissue supported and tooth supported
Principles of Design for both Class I and II collectively used