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.


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.

2.

The dentist must have a thorough
knowledge of both the mechanical and
biologic factors involved in removable
partial denture design.
The treatment plan must be based on a
complete examination and diagnosis of
the individual patient.

3.

4.

5.

The dentist must correlate the
pertinent factors and determine a
proper plan of treatment.
A removable partial denture should
restore form and function without
injury to the remaining oral structure.
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.

2.

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

Disadvantages.

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.
1.


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.


1.

2.

3.

Advantages.

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


4.

5.

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


Disadvantages.
1.

2.

3.

4.

Denture is not well stabilized against
lateral forces.
There will be always premature
contact when mouth is closed .
It may be uncomfortable sensation to
the patient.
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.

2.

3.

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


4.

5.

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


disadvantages
1.

2.

Greater bulk may cause prosthesis to
be less comfortable.
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
influencin
g
magnitud
e of
stresses
transmitte
d to
abutment
teeth
1.

2.

3.

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

Qualities
Design.
Length
Material.

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.
Length of
span.
2.
Quality of
support of
ridge.
3.
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.
Length of
span.
2.
Quality of
support of
ridge.
3.
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.
Length of
span.
2.
Quality of
support of
ridge.
3.
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.
Length of
span.
2.
Quality of
support of
ridge.
3.
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.
Length of
span.
2.
Quality of
support of
ridge.
3.
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.
Length of
span.
2.
Quality of
support of
ridge.
3.
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 anteroposteriorly and
bucco-lingually


1.

1.

1.

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

Design considerations for
stress control

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

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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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

Adhesion and
Cohesion

Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests



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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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.

2.

3.

To provide for one path of placement
and removal of the restoration.
To ensure the intended actions of
reciprocal,stabilizing, and retentive
components.
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 www.indiandentalacademy.com
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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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
consideratio
ns for stress
control
1.

1.

1.

1.

2.

3.
4.
5.

Direct
retention
•
Adhesion
,cohesion
•
Frictional
•
neuromus
cular
Clasp position

Quadrilat
eral

Tripod

bilateral
Clasp design
•
Circumfer
ential
clasp
•
Bar clasp.
•
Combinati
on clasp
Splinting of
abutments
Indirect
retention
Occlusion
Denture base
Major

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.


Quadrilateral
configuration

Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.
6.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector



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.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector

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.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector

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.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral

Clasp design

Clasp design

Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector
Rests
•

1.

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


1.

1.

1.

1.

2.

3.
4.
5.

6.

Design
considerations
for stress
control
Direct retention
•
Adhesion ,
cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinati
on clasp
Splinting of
abutments
Indirect
retention
Occlusion
Denture base
Major
connector
minor

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's- can 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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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.

2.

3.

Loss of periodontal
attachment by disease
or therapy.
Abutment has tapered
or short roots
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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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 toothsupported 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. ww.indiandentalacademy.com
w

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.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector

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.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector
minor connector

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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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.

6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromuscula
r
Clasp position

Quadrilateral

Tripod

bilateral
Clasp design
•
Circumferenti
al clasp
•
Bar clasp.
•
Combination
clasp
Splinting of
abutments
Indirect retention
Occlusion
Denture base
Major connector

Minor
connector
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
•
neuromusc
ular
Clasp position

Quadrilater
al

Tripod

bilateral
Clasp design
•
Circumfere
ntial clasp
•
Bar clasp.
•
Combinatio
n 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.

2.
3.

4.
5.

6.

Quality and contour of supporting bone
and mucosa
Extend to planned coverage of ridge.
Type and accuracy of impression
registration.
Accuracy of denture base.
Design characteristics of the component
parts of framework.
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.

2.

3.

4.

Avoid direct transmission of tipping for torquing
forces to the abutment
Accommodate the basic principles of clasp
design by definitive location of components parts
correctly positioned on abutment tooth surfaces.
Provide retention against reasonable dislodging
forces.
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.


Thank you
For more details please visit


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

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