RPD DESIGN

SK EKRAMUR RAHMAN,
FINAL YEAR BDS
REGD. NO. – 1928 OF 2014- 15
DEPARTMENT OF PROSTHODONTICS
NORTH BENGAL DENTAL COLLEGE & HOSPITAL

 In class I, II & IV edentulous arches, the removable prosthesis combines the
support derived from the abutment teeth & soft tissues resulting in greater
stress during function.
 These forces need to be controlled by maximum coverage of the soft
tissues & the proper use & placement of components in the most favorable
positions.
 Proper design of the removable partial denture will contribute to the
preservation of remaining natural teeth, aid in the maintenance of tooth
position & occlusion & will restore mastication, improve phonation &
enhance appearance.
REMOVABLE PARTIAL DENTURE (RPD)
IT IS DEFINED AS ANY PROSTHESIS THAT REPLACES
SOME TEETH IN A PARTIALLY DENTATE ARCH. IT
CAN BE REMOVED FROM THE MOUTH & REPLACED
AT WILL- ALSO CALLED PARTIAL REMOVABLE
DENTAL PROSTHESIS

BIO-MECHANICAL
CONSIDERATION
FACTORS INFLUENCING MAGNITUDE OF STRESS
TRANSMITED TO ABUTMENT TEETH
CONTROLLING STRESS BY
DESIGN CONSIDERATION
FORCES ACTING ON PARTIAL
DENTURE

Horizontal Fulcrum line Vertical Fulcrum line Sagittal Fulcrum line
 The fulcrum occurs along the
horizontal line joining the
rests on two main abutments
on either side of the arch.
 Movement around this fulcrum
line occurs in sagittal plane
resulting in rotation of the
denture base away from or
towards the residual ridge
 These are vertical forces on
the abutment teeth directed
apically. The periodontal
ligament are better equipped
to resist the force.
 The fulcrum extends from occlusal
rest on the terminal abutment
along crest of the alveolar ridge on
one side of the arch.
 Movement around this fulcrum
occurs in the vertical plane
resulting in rocking or side to side
movement of denture base.
 This are vertical fulcrum line
located in the midline lingual to
anterior teeth.
 It controls rotational movement
of the denture in horizontal plane

More flexible –
1. Length of the span:
- α forces transmitted to abutment
2. Quality of support of ridge:
- well formed ridges
- type of mucoperiosteum
3. Clasp:
Compromised periodontal support Flexible clasp
1. Less stress transmitted to the abutment tooth
2.Less resistance to horizontal stresses. Therefore lateral and vertical
forces increase on the ridge.
Good periodontal support Less flexible clasp
a. Qualities of clasp
b. Clasp design
 Design should be passive on complete seating
 During insertion & removal of prosthesis the reciprocal arm should
contact the tooth before retentive tip passes over greatest bulge
A. FLAT RIDGE
B. SHARP & SHINY RIDGE
C. DISPLACEABLE TISSUE

c. Length of Clasp
 Length α Flexibility
 More flexible the clasp, less stress on abutment teeth
 Clasp length can be increased by using carved path
rather than straight path
d. Material
 Chrome alloy – more rigid – exert greater stress on the abutment
tooth
 Clasp arm of chrome alloy is constructed with small
diameter & also engage smaller undercut
3. Abutment tooth surface
 Surface of gold crown offer more frictional resistance on
clasp arm movement than enamel surface of tooth & thus
exerts greater stress on abutment tooth.
4. Occlusal Harmony
 A disharmonious occlusion with deflective occlusal
contact transmits destructive horizontal forces to the
abutment & ridge

1. Direct retention
 Minimum yet provide adequate retention
 Other components are used to contribute retention
a. Adhesion and cohesion: Maximum area and accurate adaptation
b. Neuromuscular control: Contour, extension, patient ability
c. Frictional control using guide planes
d. Atmospheric Pressure : Maxillary complete major connector &
posterior margin sealed by beading

2. Clasp position: Number of clasps – by classification
A) Quadrilateral configuration:
 Class III & Class III mod
 It is indicated in class 3 arches, particularly when modification
space exists on the opposite side.
 In this design Leverage is most effectively neutralized.
 Retentive clasp is positioned on each abutment teeth adjacent to
edentulous space
B) Tripod configuration:
 Class II & Class II mod
 All these adjacent to the edentulous space are clasped
 The design is not very effective as quadrilateral but most
effective in neutralizing leverage in class II situations
C) Bilateral configuration:
 Class I
 Terminal abutment on each side of arch must be clasped
 Little neutralization of leverage induced stresses

3. Clasp design:
a) Cast Circumferential clasp:
Simple circlet clasp – not indicated for distal extension
Reverse circlet clasp – preferred in distal extension situation
b) Bar clasp:
T- bar clasp with a distal occlusal rest & rigid
circumferential arm causes least stress on abutment.
c) Combination clasp
Wrought wire retentive arm more flexible will exert less
stress on abutment teeth

4. Splinting
 Adjacent teeth may be splinted to increase the periodontal ligament attachment
area and distribute the stress over a larger area of support.
 An extremely week tooth should not be splinted with a strong tooth.
Fixed Splinting
•There is loss of periodontal attachment by disease or therapy.
•Abutment has tapered or short roots.
•The terminal abutment stands alone
•Edentulous space distal to canine and lateral incisor is also missing.
•The canine is splinted to central incisor by making a three-unit
FIXED partial denture replacing lateral incisor
.•The distal space is replaced with removable partial denture.
Removable Splinting
•It should not be done if fixed splinting is possible
.•It is used when more than one tooth is clasped on each side of the arch,
using a number of rests for additional support and stabilization of the
teeth and prosthesis.
•Most of the clasp arms will not be retentive.
•The main advantage of removable splinting is cross-arch stabilization.

INDIRECT RETAINER
It is the component of removable partial denture that assists the direct retainer
in preventing displacement of the distal extension denture base by functioning through
lever action on the opposite side of the fulcrum line when the denture base moves away
from the tissues in pure rotation around the fulcrum line (GPT 7).
5. Indirect Retention
In Class 1
 IR is mandatory.
 One on each side of arch is placed as far anteriorly as possible.
In Class 2
 Its use is not as critical as class 1.
 The opposite arch will be clasped to make a tripod configuration and the
most anterior clasp with its rest will function as indirect retainer.
In Class 3
 In class 3, indirect retainer is not necessary as there are no rotational
forces.
In Class 4
 The consideration is reverse of classes 1 and 2. •The indirect retainer
is placed as far posteriorly as possible on either side.

6. Occlusion
 Occlusion which is in harmony with movements of TMJ and neuromusculature will minimize the
stress transferred to the abutment teeth and residual ridge.
 The initial occlusal contact should always be in the remaining natural teeth.
 Mandible should not be guided into protrusive or lateral movements by the metal or artificial teeth
 .Reducing the buccolingual width and the number of replaced teeth reduces the stress transmitted
 .Contact of the natural teeth should be the same, regardless of whether denture is in mouth or not.
 Sharp cutting surfaces and sluiceways can help relive some unnecessary force during mastication.
 Steep cuspal inclines on the artificial teeth should be avoided because they tend to introduce
horizontal forces detrimental to the abutment.
 It should cover as maximum area of the supporting tissue as possible.
 Flanges should be as long as possible –tohelp stabilize against horizontal movements
 Overextension should be avoided.
 Distal extension denture base should cover the retro molar area and tuberosity of maxilla
as these structures better absorb stress.
 Contour of the polishedsurfaces also helps in reducing the stress transmitted
 Accurate adaptation of denture base also lessens the movement of the same and reduces
stress.
7. Denture Base
 Some major connectors can control stress effectively
 .In the mandibular arch, the lingual plate major connector properly supported by rests aids in
the distribution of functional stress. It also supports periodontally weakened anterior teeth, and
helps in cross-arch stabilization.
 In the maxillary arch, a broad palatal major connector can distribute stress over a large area by
covering a hard palate and contributing to support, stability and retention of the prosthesis.
8. Major Connectors

 Intimate tooth to partial denture contact is brought about by contact of minor
connectors with tooth (guiding planes)
 .It offers horizontal stability to partial denture and abutment tooth against lateral
forces.
9. Minor Connector
 It controls stress by directing stress along the long axis of abutment teeth.
 Periodontal ligament is better suited to withstand vertical than
horizontal forces.
 Floor must form angle < 90 degree
 In distal extensions, the rest seat should be saucer shaped to allow some
movement of the rest so that forces are not transmitted to the abutment.
10. Rests

 The treatment plan must be based on a complete examination and diagnosis of the individual patient.
 Dentist must correlate the pertinent factors and determine a proper plan of treatment.
 The prosthesis should restore form and function without injury to the remaining oral structure.
 A removable prosthesis is a form of treatment and not a cure.
 Dentist must have a thorough knowledge of both the mechanical and biologic factors involved in removable partial
denture design.
Developed by A.H. Schmidt in 1956:
 Of the various schools of thought , none are backed by scientific research or statistics.
 They are ideas of dentists who by extensive clinical experience have formulated rules by which
they produce a design .
 If the physiologic limits of the supporting tissues are respected, then almost any design can
be successful.
 The challenge in design lies primarily in class 1 and 2 arches and to some extent in the class
4 arches and distributing the forces acting on the removable partial denture between the
soft tissues and teeth.
Philosophy of Design

 Resiliency of the tooth secured by the periodontal ligament in an apical
direction is not comparable to the greater resiliency and displaceability of the
mucosa covering the edentulous ridge.•
 Therefore, it is believed that a type of stress equalizer is needed to replace the
rigid connection between denture base and direct retainer.
 It is also called a stress breaker or articulated prosthesis.
A. Stress Equalization
 They may be hinges, sleeves and cylinders or ball and socket joints.
 They allow vertical movement and hinge action of the
distal extension denture base and help transfer load from the
abutment to the ridge.
 Examples are Dalbo, Crismani and ASC 52 attachments.
Stress Equalizer Having a Movable Joint Between the Direct Retainer and
Denture Base
 Wrought wire connector
 Divided major connector
Stress Equalizer Having a Flexible Connection Between the
Direct Retainer and Denture Base
Advantages
•Minimal direct retention is required as denture base acts more
independently.
It minimizes tipping forces on abutments, thus preserving its
alveolar bone support.
It is proposed that the force is evenly distributed between
abutment and ridge.
Disadvantages
•Construction is complex and costly
•Constant maintenance is required, and it is difficult or impossible to
repair.
•Vertical and horizontal forces are concentrated on the ridge, which
leads to rapid resorption of the ridges
. •If relining is needed but not done, there will be excessive ridge
resorption.
Stress Equalizer Having a Movable Joint Between the Direct Retainer
and Denture Base
Stress Equalizer Having a Flexible Connection Between the
Direct Retainer and Denture Base

This school of thought too believes that there is relative lack of movement in abutment teeth
in an apical direction
But it believes that stress equalization can be best achieved by either
a.Displacing or depressing the ridge mucosa during the impression making procedure
b.Relining the denture base after it has been constructed
The tissue surface is recorded in functional form and not anatomic form.
Prosthesis constructed from tissue displacing impression will be above the plane of
occlusion when the denture is not in function.
To permit vertical movement from the rest position to functional position, the retentive clasps
have to have minimum retention and also their number has to be less.
B. Physiologic Basing
Advantages
•Intermittent base movement has a physiologically stimulating effect on the
underlying bone and soft tissue.
•There is less need for relining and rebasing.
•There is simplicity of design and construction because of minimal retention
requirements.
•The looseness of the clasp on the abutment tooth reduces the functional forces
transmitted to the tooth.
Disadvantages
•Denture is not well stabilized against lateral forces.
•There will be always premature contact when the mouth is closed, which
is uncomfortable to the patient.
•It is difficult to produce effective indirect retention.

•It involves distribution of forces of occlusion over as many teeth and as much of
the available soft tissue area as possible
•It is achieved by means of additional rests, indirect retainers, clasps and broad
coverage denture bases.
C. Broad Stress Distribution
Advantages
•Teeth can be splinted.
•Prosthesis are easier and less expensive to construct.
•There are no flexible or moving parts so less danger of distorting the denture.
•Indirect retainers and other rigid components provide excellent horizontal
stabilization.
•Less relining is required
Disadvantages
•Greater bulk may cause prosthesis to be less comfortable.
•Increased amount of tooth coverage can lead to dental caries

•Clasp retention should not be considered the prime objective of design.
•Proper contour of an adequately extended denture base and accurate fit of the framework
against multiple, properly prepared guide planes should be used to help the retentive clasp
arms retain the prosthesis.
Classes 1 and 2
1. Direct Retention
Class 1 prosthesis usually requires two retentive clasp assemblies –one on each terminal
abutment.
The type of clasp depends on the location of undercut,
a. distobuccal–reverse circlet and bar clasp
b. mesiobuccal–combination clasp.
•Reciprocal arms should fulfill all its requirements.
2. Clasps
Class 2 should have three retentive clasp arms.
Type and location on distal extension side are similar to class 1.
On the other side, if modification is present, a simple circlet clasp is on the teeth anterior and
posterior to edentulous space.
If there is no modification, then there are one anterior and one posterior embrasure clasps.
Reciprocal arms should fulfill all the requirements
•Teeth selected for rest preparation should provide maximum possible
support for the prosthesis.
•Rests should be placed next to the edentulous space with few
exceptions.
3. Rests

•
In Class 1•
 IR is mandatory.
 One on each side of arch is placed as far anteriorly as possible.
In Class 2
 Its use is not as critical as class 1.
 The opposite arch will be clasped to make a tripod configuration and the
most anterior clasp with its rest will function as indirect retainer.
These should fulfill all requirements specifically for distal extensions.
5. Major Connector
These must fulfill all the requirements.
6. Minor Connector
If there are sufficient centric stops, then MIP is utilized. If there are
insufficient centric stops, then centric occlusion is given (MIP at
centric relation).
7. Occlusion
A selective pressure impression should record the residual ridge in a
functional form.
8. Denture Base

Class 3
1. Direct Retention
2. Clasps
3. Rests
Retention can be achieved with much less potential harmful effect on
the abutment teeth than with the Class 1 or 2 arch.
The position of the retentive undercut on abutment teeth is not critical
The quadrilateral positioning of direct retainers is ideal.
Tooth and tissue contours and aesthetics should be considered, and the
simplest clasp possible selected
Rest seats should be prepared next to the edentulous space when
possibleand fulfill all requirements.
5. Major & Minor connector
6. Occlusion
7. Denture Base
Indirect retention is usually not required
They must meet the requirements and used as per indication
Given in MIP
A functional-type impression is not required.

Class 4
 The movements of this type of removable partial denture and the resulting stresses transmitted to the
abutment teeth are unlike the pattern seen in any other type of prosthesis.
 The design is unique.
 The aesthetic arrangement of the anterior replacement teeth may necessitate their placement anterior
to the crest of the residual ridge, resulting in potential tilting leverage.
 Planning should begin to reduce these stresses even before extraction is planned by considering the
following:
 Preservation of labial alveolar process
 Retaining teeth to serve as an intermediate abutment or as an overdenture abutment
 Shorter edentulous span leading to less tilting leverage
Clasps
The quadrilateral configuration, with the anterior clasps placed as far anterior and the posterior clasps
placed as far posterior as possible, would be the ideal.
Should be rigid, and broad palatal coverage should be used in the maxillary arch
Major Connector
Indirect Retention
Should be used as far posterior to the fulcrum line as possible
Denture Base
A functional type of impression may be indicated if the edentulous area
is extensive.

Armamentarium:
• Surveyor with its tools
•Articulator –plasterless if possible or any simple hinge or
mean value articulator
•Colour pencils – red, blue, black, brown
Colour Coding
•It allows for easy understanding of the design marked on the diagnostic
models by the technician and improves the communication.
•Commonly red, black, blue and brown colours are used.
•Red means ‘required action’ or the teeth require some preparation.
•Black denotes survey lines on teeth and soft tissues. Instructions on cast are also
written in black.
•Blue denotes portions that will be made of acrylic.
•Brown denotes all-metallic portions.

PROCEDURE
1. Occluded Diagnostic Casts
 Proposed rests are as remarked on the cast base below the tooth with a short line.
 Any cuspal relief needed to provide adequate occlusal clearance for the rest is marked in
red on the tooth to be prepared.
 Line marked on the lingual surface of upper anterior teeth demarcates incisal limits of
metal extensions and gingivo-occlusal limits of proposed rests and indirect retainers
•This is indicated by marking the type of replacement on the labial side
of ridge of the missing tooth
•The following symbols are used:
Denture tooth –no symbol
Tube tooth –T
Facing –F
Metal pontic –M
Reinforced acrylic pontic –RAP
2. Type of Tooth Replacement
•The final tilt is selected by placing the cast on the surveyor at
horizontal tilt and tilting the cast to consider –retentive
undercuts, interferences, aesthetics and guiding planes
•The cast is locked in position once the final tilt is determined.
•The areas that require modification are marked in red.
3. Select the Final Tilt of Cast

The tilt of cast is recorded by tripoding for future reference.
4. Tripod the Cast
The carbon marker is placed and survey line is marked in black on all the teeth.
Soft tissue undercuts are also scribed for designing bar clasps
5. Mark the Survey Lines and Soft Tissue Undercuts
Rests and indirect retainers are then marked in red
Areas to be recontoured are also marked in red as evenly spaced diagonal
lines..
6. Mark the Areas to Be Prepared in the Mouth
Outline the exact position and extent of the denture base area in blue.
7. Mark the Denture Base Area

With a brown pencil, the clasp arms are drawn to the correct size,
shape and location and are connected to the other components.
If wrought wire clasp is used, the symbol WW is marked on the cast
base.
10. Draw the Clasp Arms
The framework with major and minor connectors is marked in brown
to join the already marked rests, indirect retainers, denture base and
replacement teeth.
8. Mark the Major and Minor Connectors
Desired undercut is measured with an undercut gauge, and the location
of retentive terminal is marked as a red line of 2 mm.
9. Mark the Retentive Terminal

RPD DESIGN

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