Designing in removable partial dentures /certified fixed orthodontic courses by Indian dental academy

Designing in Removable partial
dentures
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com


Introduction
• Authorities in the field of removable partial
denture design may differ on their approach
in developing the design of each individual
prosthesis.
• There is however, complete agreement that
the correct design incorporates proper use
and application of mechanical and biologic
principles.

• Simple mechanical principles have to
understood and applied in designing of the
removable partial denture.
• Machines are classified into 2 categories as
simple and complex.
• Complex machines are combinations of
many simple machines.

Simple machines
• Lever, wedge,
screw, wheel and
axle, pulley and
inclined plane.
• A lever is a rigid
bar supported
somewhere along
its length.
• Support point of
the lever is called
the fulcrum.

• Of all simple
machines lever and
inclined plane
principle is
involved in partial
denture design.


Types of lever.


First class lever.


Location of stabilizing and retentive
components in relation to the horizontal
axis of rotation
• An abutment tooth will
better tolerate off vertical
forces if these forces
occur as near as possible
to the horizontal axis of
rotation of the abutment.


Tooth Vs tooth- tissue supported.
•
•
•
•
•
•

They differ in
Manner in which each is supported.
Method of impression registration.
Need for some indirect retention.
Denture base material. Acrylic/metal.
Difference in clasp design.

Forces acting on partial denture
• The all tooth supported RPD is rarely subjected to
induced stresses ,because leverage-type forces are
not involved and there are no fulcrums around
which the partial denture may rotate.
• The distal extension partial denture is subjected to
rotation around 3 principal fulcrums.


• During the formulation of design these
fulcrums and the movement that may take
place around them must be kept in mind and
components positioned to counteract the
movement.


Horizontal fulcrum line.
• It is in the horizontal
plane extending through
two principal abutments.
• Controls rotational
movement of denture in
sagittal plane (towards or
away from the ridge.)

• Magnitude of rotational
movement is greatest around
this fulcrum but not the most
damaging.
• Difficult to control
movement around this
fulcrum line
• Resultant forces are in the
apical direction.

Fulcrum on sagittal plane
• Extends through the occlusal
rest on the terminal abutment
and along the crest of the
residual ridge on one side of
the arch.
• Controls the rotational
movement in vertical
plane(rocking,or side to side
movements).

• Movements are easier to control around this
fulcrum.
• They are of lesser magnitude.
• More damaging forces as direction is
horizontal.


Vertical fulcrum line
• Located in midline
,lingual to anterior
teeth.
• Controls movement of
the denture in
horizontal plane (flat
circular movements of
the denture).

Principles by A.H. Schmidt (1956).
1. The dentist must have a thorough
knowledge of both the mechanical and
biologic factors involved in removable
partial denture design.
2. The treatment plan must be based on a
complete examination and diagnosis of the
individual patient.

3. The dentist must correlate the pertinent
factors and determine a proper plan of
treatment.
4. A removable partial denture should
restore form and function without injury
to the remaining oral structure.
5. A removable partial denture is a form of
treatment and not a cure.

Philosophy of design
• 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 .
• The challenge in design lies primarily in
class 1 and 2 arches and to some extent in
the class 4 arches.

• There are 3 basic , underlying approaches to
distributing the forces acting on partial
denture between the soft tissues and teeth.
– Stress equalization
– Physiologic basing
– Broad stress distribution.

Stress equalization
• 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.

• There fore , it is
believed that a a
type of stress
equalizer is needed
to replace the rigid
connection between
denture base and
direct retainer.

• Most common type
is a hinge device
which permits
vertical movement
of the denture base.
it can be adjusted to
control the amount
of vertical
movement.


Advantages.
1. Minimal direct retention is required- as
denture base acts more independently.
2. Has the massaging or stimulating effect on
the underlying bone and soft tissue.
Which minimizes tissue change and
resulting Rebasing procedures.

Disadvantages.
1. Construction of stress director is complex
and costly.
2. Constant maintenance required.
3. Difficult or impossible to repair.
4. Lateral movements of base can lead to
rapid resorption of the ridges.
This school of thought had got fewer
advocates.

Physiologic basing
• 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
– displacing or depressing the ridge mucosa
during the impression making procedure
– or by relining the denture base after it has been
constructed

• The tissue surface is
recorded in functional
form and not anatomic
form.
• Rpd constructed from
tissue displacing
impression will be
above the plane of
occlusion when the
denture is not in
function.


• To permit vertical movement from rest
position to functional position the retentive
clasps have to have minimum retention and
also their number has to be less.


Advantages.
1. Intermittent base movement
has a physiologically
stimulating effect on the
underlying bone and soft
tissue.
2. Less need for relining and
Rebasing.
3. Simplicity of design and
construction because of
minimal retention
requirements.

4. Light weight prosthesis with minimal
maintenance and repair.
5. The looseness of the clasp on the
abutment tooth reduces the functional
forces transmitted to the tooth.


Disadvantages.
1. Denture is not well stabilized against
lateral forces.
2. There will be always premature contact
when mouth is closed .
3. It may be uncomfortable sensation to the
patient.
4. It is difficult to produce effective indirect
retention.

Broad stress distribution
• Advocates of this school of
thought believe that
excessive trauma to the
remaining teeth and residual
ridge can be prevented by
distributing the forces of
occlusion over as many
teeth and as much of the
available soft tissue area as
possible.
• Achieved by means of
additional rests,indirect
retainers,clasps and broad
coverage denture bases.

advantages
1. Teeth can be splinted .
2. Prosthesis are easier and less expensive to
construct.
3. No flexible or moving parts so less danger
of distorting the denture.


4. Indirect retainers and other rigid
components provides excellent horizontal
stabilization.
5. Less relining required.


disadvantages
1. Greater bulk may cause prosthesis to be
less comfortable.
2. Increased amount of tooth coverage can
lead to dental caries


Factors
influencing
magnitude of
stresses
transmitted to
abutment
teeth
1.
2.
3.

4.
5.

Length of span.
Quality of support
of ridge.
Clasp.
1. Qualities
2. Design.
3. Length
4. Material.
Abutment tooth
surface
Occlusal harmony.

Length of span
• The longer the edentulous span
,the longer will be the denture
base and the greater will be the
force transmitted to the abutment
teeth.


Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.

Quality of support of ridge
• Large well formed ridges are
capable of absorbing greater
amounts of stress than are
small,thin,or knife-edged ridges
• broad ridges with parallel sides
permit the use of longer flanges
which help in stabilizing the
denture against the lateral forces.
• Type of mucoperiosteum also
influences the magnitude of
stresses transmitted to abutment
teeth.

•Flat ridge will provide good support,poor
stability
•Sharp spiny ridge
will provide poor
support,poor to fair
stability.
•Soft ,flabby
displaceable tissuepoor support, poor
stability- leads to
vertical and lateral
instability and
transmission of stress
to the adjacent
abutment tooth.


Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.

Qualities of clasp
• More flexible the clasp
less stress is
transmitted to the
abutment tooth.
• But at the same time it
contributes less
resistance to the lateral
and vertical stresses
transmitted to the
residual ridges.

Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.

Design of clasp
• A clasp that is designed so that it
is passive when it is completely
seated on the abutment tooth
will exert less stress on the tooth
than one that is not passive.
• A clasp should be designed so
that during insertion or removal
of the prosthesis the reciprocal
arm contacts the tooth before the
retentive tip passes over the
greatest bulge of the abutment
tooth.

Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.

Length of clasp
• More flexible the clasp
less stress it will exert
on the abutment tooth.
• Flexibility can be
increases by
lengthening the clasp.


• Clasp length may be
increases by using a
curved rather than a
straight course on
an abutment tooth


Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Material used for clasp
fabrication
• Crome alloy being
more rigid will exert
greater stress on the
abutment tooth.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.


• Clasp arm of chrome
alloys are
constructed with a
smaller diameter
than a gold clasp


Amount of clasp surface in
contact with tooth


Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.

Abutment tooth surface
• Surface of gold crown or
restoration offers more
frictional resistance to clasp
arm movement than does the
enamel surface of the tooth.
• Greater stress is exerted on a
tooth restored with gold than on
a tooth with intact enamel.


Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
2.
3.

Length of span.
Quality of
support of
ridge.
Clasp.
1.
2.
3.
4.

4.
5.

Qualities
Design.
Length
Material.

Abutment tooth
surface
Occlusal
harmony.

Occlusal harmony.
• When deflective
occlusal contacts are
present between
opposing teeth
destructive horizontal
forces which are
magnified by leverage
are transmitted to the
abutment and ridge.

• Partial denture constructed opposing a
complete denture will be subjected to a
much less occlusal stress than one opposed
by natural dentition.
– Force exerted by natural teeth –300 pounds per
square inch.
– Complete denture – 30 pounds per square inch.

• Occlusal load applied to the distal end of
denture base will result into more stress
transmitted to the abutment teeth.

• Ideally,the occlusal
load should be applied
in the center of the
denture –bearing area,
both antero-posteriorly
and bucco-lingually


1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
• Adhesion ,cohesion
• Frictional
• neuromuscular
Clasp position
– Quadrilateral
– Tripod
– bilateral
Clasp design
• Circumferential clasp
• Bar clasp.
• Combination clasp
Splinting of abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Design considerations for
stress control
• At present there is no way that
all forces can be totally negated
or countered.
• Long term clinical observations
have proved that a design
philosophy that strives to
control these forces within the
physiologic tolerance of the
teeth and supporting structures
can be successful.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Direct retention
• The retentive clasp arm is responsible
for transmitting most of the destructive
forces to the abutment teeth.
• Clasp retention should be kept at the
minimum yet provide adequate
retention to prevent dislodgement of
the denture.
• Other components should be used to
contribute for the retention so that
amount of retention provided by clasp
can be reduces

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Adhesion and
Cohesion
• For adhesion and cohesion to work
– Maximum area of available support should
be used.
– Denture base should be accurately adapted
to the underlying mucosa.

• Though peripheral seal cannot be
developed due to presence of teeth
.Atmospheric pressure helps in retention
of the maxillary partial denture when
metal casting is accurate and margins of
connector are beaded.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Frictional control
• The partial dentures should be
designed so that guide planes are
created on as many teeth as
possible.
• These planes can be on enamel
surfaces of the teeth or in
restorations placed on the teeth.


• The frictional
contact of the
prosthesis against
these parallel
surfaces can
contribute
significantly to the
retention of the
denture.

Function of guide planes
1. To provide for one path of placement and
removal of the restoration.
2. To ensure the intended actions of
reciprocal,stabilizing, and retentive
components.
3. To eliminate gross food traps between
abutment teeth and components of the
denture.

• Proximal guiding plane surfaces should be about
2/3rd as wide as the distance between the tips of
adjacent buccal and lingual cusps or
about 1/3rd of the buccal lingual width of the tooth.
Vertically it should extend 2/3rd of the length of the
enamel crown portion of the tooth from the
marginal ridge cervically.
Care must be taken to avoid creating buccal or
lingual line angles.

Contact of guide planes


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Neuromuscular control
• The innate ability of the patient
to control the action of the lips,
cheeks, tongue can be a major
factor in the retention of a
denture.
• A properly contoured denture
base, however, can aid the
patient’s neuromuscular control
of the prosthesis.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Clasp position
• The position of
retentive clasp is more
important than the
number of retentive
clasp used in any
design.
• The number of clasps
used is determined by
classification.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Quadrilateral configuration
• Is indicated in class 3 arches
particularly when modification
space exists on the opposite side.


• A retentive clasp is
positioned on each
abutment tooth
adjacent to the
edentulous spaces.
• In this design
leverage is
effectively
neutralized.

• When no modification space exists the goal
should be to place one clasp as far posterior
on the Dentulous side as possible and one
as far anterior as space and esthetics permit.


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Tripod configuration
• Used primarily for class 2 arches.
• If there is a modification space on
the Dentulous side .


• If there is no modification space present .
One clasp on the Dentulous side of the arch
should be positioned as far posterior, and
the other, as far anterior as factors such as
interocclusal space, retentive undercut, and
esthetics considerations will permit.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Bilateral configuration
• Used in class 1 cases.
– In this configuration the clasps exert
little neutralizing effect on the
leverage induced stresses generated
be the denture base. These stresses
must be controlled by other means.


The terminal
abutment tooth
on the each
side of the arch
must be clasped
regardless of
where it is
positioned.


Design
considerations
for stress
control
1.

1.

1.

Clasp design

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral

Clasp design
•

1.
2.
3.
4.
5.
6.
7.

Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Circumferential clasp
• Conventional circumferential
clasp originating from distal
rest and engaging mesiobuccal
retentive undercut should be
avoided at all cost in distal
extension removable partial
denture.


• As denture base
moves towards
the tissue the
clasp puts distal
tipping force on
the abutment
tooth.

Alternatives

• Reverse circlet clap

– Approaches a
distobuccal undercut
from the mesial surfaces
of a terminal abutment
tooth.
– As occlusal load is
applied, retentive
terminal moves
gingivally and loses
contact with the tooth
surface and no stresses
are transmitted.


Disadvantage
It may produce wedging force between 2 teeth'scan be countered by making rest on the
approximating surface too.


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Vertical projection or Bar
clasp.
• It is used in distal extension partial
denture when retentive undercut is
located on the distobuccal surface.
• Never when tooth has a mesiobuccal
undercut.


• Functions similar to the reverse
circumferential clasp with the advantage of
not producing any wedging forces .


• One school of thought advocated omitting of
the distal rest in favour of a mesial rest for
the following reasons.
– As the fulcrum line is still distal to the clasp
terminal when distal rest is used .
– With use of mesial rest the lever arm is increases
and forces are directed to the ridge in more
vertical direction which are better tolerated by
the ridge.


Disadvantage
• a space is created
between framework
and tooth surface
leading to food
trapment


What is the consensus?
• Least unfavorable torque is when…..
…T clasp with distal -occlusal rest and a
rigid circumferential reciprocating clasp.


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Combination clasp
• It is used when mesiobuccal undercut
exists on an abutment tooth adjacent to
a distal extension edentulous ridge.
• Only the retentive arm is wrought
metal.
• Reciprocation and stabilization against
lateral movement must be obtained
through the use of the rigid cast
elements that make up the remainder of
the clasp.

• Wrought wire can flex in any spatial plane
and can absorb torosional stress in both the
vertical ad horizontal planes.
• A cast clasp flexes in the horizontal plane
only.
• A short wrought wire arm can be
destructive element because of its reduced
ability to flex compared with a longer
wrought –wire arm.


Advantages.
•
•
•
•

Flexibility.
Adjustability.
Minimum tooth contact.
Better esthetics.


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Splinting of abutments
• Rationale
– It increases the periodontal ligament
attachment area and distributes the
stress over a larger area of support.


Indications by crowns.
1. Loss of periodontal
attachment by disease
or therapy.
2. Abutment has tapered
or short roots
3. Second premolar as
abutment with
edentulous space
anterior to it- splinted
with canine by FPD.

• Splinting by crowns
stabilizes the teeth in
mesiodistal direction.
• Splint should include
canine to achieve the
stabilization in
buccolingual direction
as well.

• An extremely week
teeth should not be
splinted with a
strong teeth.


Splinting by clasps
• Should not be done if fixed
splinting is possible.
• More tan one teeth are 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 arm will not
be retentive.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Indirect retention
• Indirect retainer.
– 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)

• Indirect retainer also contributes to a
lesser degree, to the support and
stability of the denture.

Design considerations
• Should never be
on an inclined
tooth or on a
single weak
incisor.


Class 1.
• It must always
be used and
positioned as far
anteriorly as
possible.


Class 2
• its use is not as critical as in
class 1.
• If no modification space exists .
• An abutment tooth with suitable
contours for clasping should be
selected as far anterior on the
tooth-supported side as possible.
• This rest and clasp assembly,
may serve as the indirect
retainer if it is located far
enough anterior to the fulcrum
line.

• If modification space
exists.
• The most anterior
abutment on the tooth
supported side, with its
rest and clasp assembly,
may be located far
enough anterior to the
fulcrum line to serve as
the indirect retainer.
• A definite rest seat
positioned even farther
anterior,if possible,may
increase the effectiveness
of the indirect retention.


Class 3
• Indirect retention is not
ordinarily used.
• Auxillary rests must for
lingual plate major
connector.
• Auxillary rests may be
needed to provide additional
vertical support for a long
lingual bar major connector
or an extensive palatal major
connector.

• If the contours of the
posterior abutment
teeth in class 2 or 3
partial denture are not
suitable for retention
• In such case non
retentive stabilizing
clasp are designed for
posterior teeth and
anterior indirect
retention is a must.

Class 4
• The indirect
retainer must
be located as
far posterior
as possible.


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

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.
• Reduced buccolingual width of replaced teeth
reduces the stress transmitted.


• if number of teeth replaced is reduced stress
transmitted will be less
• 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 .

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Denture base
• ….to reduce the stress to the
abutment teeth?
– denture base should cover
maximum area of the supporting
tissue as possible.
– Denture base flanges should be
as long as possible-to help
stabilize against horizontal
movements.

Design considerations….
– Distal extension denture base should cover the
retro molar area and tuberosity of maxilla as
these structures better absorb stress.
– Overextension should be avoided as
interference with functional movements of
surrounding tissues will transmit stresses to the
remaining teeth.
– Accurate adaptation of denture base leads to
less tendency for movement during function.
– Contour of the polished surfaces also helps in
reducing the stress transmitted.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Major connector


Mandibular arch.
• Lingual plate major connector can aid in
distribution of functional stress and so is advised
if anterior teeth are periodontally weakened.
• Also indicted in class 1 arches when the need for
additional resistance to horizontal rotation of the
denture is required because of excessively
resorbed residual ridges.
• Another indication is in shallow floor of mouth.

• Added rigidity provided by lingual plate
also helps in distributing stress created on
one side of the arch to the other side
(CROSS ARCH STABILIZATION).
• A lingual bar should be tapered superiorly
with a half pear shape in cross section and
should be relived sufficiently.

Maxillary arch.
• Broad palatal major connector that connects
several of the remaining natural teeth through
lingual plating can distribute stress over a large
area.
• Major connector covering hard palate contributes
to support, stability, and retention of the
prosthesis.and reduces the stress that is transmitted
to the abutment teeth.

Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscular
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferentia
l clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector

6.

Minor
connector

7.

Rests

Minor connector
• The intimate tooth to partial
denture contact is brought by
minor connector
• It serves too purposes .
– Provides horizontal stability to the
partial denture against lateral forces
on the prosthesis.
– Through this contact, the tooth
receives stabilization against lateral
stresses.

• If more guiding planes are incorporated in
design the force transmitted to each teeth
can be minimized.
• When crown restorations are used, a lingual
reciprocal clasp arm may be inset into the
tooth contour by providing a ledge on the
crown on which the clasp arm may rest.

design modification of minor
connector.
• Places the minor connector
in the center of the lingual
surface of the abutment
tooth.
Advantage:
it reduces the amount of
gingival tissue coverage.
Provides enhanced bracing and
guidance during placement.

Disadvantages.
• Increases encroachment of tongue space
• More obvious borders.
• potentially greater space between the
connector and abutment tooth.


Design
considerations
for stress
control
1.

1.

1.

1.
2.
3.
4.
5.
6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscul
ar
Clasp position
–
Quadrilateral
–
Tripod
–
bilateral
Clasp design
•
Circumferent
ial clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests

Rests
• Control stress by directing stress
along the long axis of abutment
teeth.
• Periodontal ligament is better
suited to withstand vertical than
horizontal forces.


• Floor of rest seat preparation must be less than 90
degrees with long axis of tooth as this design
grasps the tooth to prevent its migration.
When an angle is more than 90 degrees inclined
plane effect is set up and stress on abutment is
magnified.
• in class 1 and 2
– Preparation should be saucer shaped without any sharp
angles and ledges.

• Rest should be free to move within the rest
seat to release the stresses which would
otherwise transmit to the tooth.
• More the no of teeth that bear rest seats, the
less will be the stress places on each
individual tooth.

Essentials of partial denture
design.
• It should be systemically developed and
outlined on an accurate diagnostic casts.


First step
•
•

Decide how the partial denture has to be
supported.
If Tooth supported.
–

Evaluate
1.
2.
3.
4.
5.
6.
7.

Periodontal health
Crown and root morphologies
Crown to root ratio.
Bone index area.
Location of tooth in arch.
Length of edentulous span.
Opposing dentition.

•
•

If tooth and tissue supported.
Also Consider
1. Quality and contour of supporting bone and
mucosa
2. Extend to planned coverage of ridge.
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.

• Denture base areas adjacent to abutment
teeth are primarily tooth supported.
• As we proceed away from abutment teeth,
they become more tissue supported.


Second step
• Connect the tooth and tissue support units.
• These connection is facilitated by designing
and locating major and minor connectors in
compliance with the basic principles and
concepts.


Third step.
•
•

Determine how the partial denture is to be
retained.
Selecta clasp design that will
1. Avoid direct transmission of tipping for torquing
forces to the abutment
2. Accommodate the basic principles of clasp design by
definitive location of components parts correctly
positioned on abutment tooth surfaces.
3. Provide retention against reasonable dislodging
forces.
4. Be compatible with undercut locations,tissue
contour,and esthetic desires of the patient.

Fourth step.
• Connect the retention units to the support
units


Fifth step.
• Outline and join the edentulous area tote
already established design components.


To be continued ……
• Designing of major connectors .
• Designing of minor connectors
• Miscellaneous factors in designing.


• Leader in continuing dental education
•


Designing in removable partial dentures /certified fixed orthodontic courses by Indian dental academy

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