Designing in Removable
partial dentures
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacadem...
Introduction




Authorities in the field of removable
partial denture design may differ on
their approach in developing...






Simple mechanical principles have to
understood and applied in designing of
the removable partial denture.
Machin...
Simple machines






Lever, wedge,
screw, wheel and
axle, pulley and
inclined plane.
A lever is a rigid
bar supported
...


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

www.indiandentalacade...
Types of lever.

www.indiandentalacademy.com
First class lever.

www.indiandentalacademy.com
components in relation to the
horizontal axis of rotation


An abutment tooth will
better tolerate off
vertical forces if...
Tooth Vs tooth- tissue
supported.







They differ in
Manner in which each is supported.
Method of impression regi...
Forces acting on partial
denture




The all tooth supported RPD is rarely
subjected to induced stresses ,because
levera...


During the formulation of design these
fulcrums and the movement that may
take place around them must be kept in
mind a...
Horizontal fulcrum line.




It is in the horizontal plane
extending through two
principal abutments.
Controls rotationa...






Magnitude of rotational
movement is greatest
around this fulcrum but
not the most
damaging.
Difficult to control
...
Fulcrum on sagittal plane





Extends through the
occlusal rest on the
terminal abutment
and along the crest of
the res...






Movements are
easier to control
around this
fulcrum.
They are of lesser
magnitude.
More damaging
forces as
direct...




Vertical fulcrum line

Located in midline
,lingual to anterior
teeth.
Controls
movement of the
denture in
horizontal...
www.indiandentalacademy.com
www.indiandentalacademy.com
Principles by A.H. Schmidt
(1956).
1.

2.

The dentist must have a thorough
knowledge of both the mechanical and
biologic ...
3.

4.

5.

The dentist must correlate the
pertinent factors and determine a
proper plan of treatment.
A removable partial...
Philosophy of design






Of the various schools of thought , none are
backed by scientific research or statistics.
Th...


There are 3 basic , underlying
approaches to distributing the forces
acting on partial denture between the
soft tissues...
Stress equalization


Resiliency of the tooth
secured by the
periodontal ligament in
an apical direction is
not comparabl...


There fore , it is
believed that a a
type of stress
equalizer is needed
to replace the rigid
connection between
denture...


Most common
type is a hinge
device which
permits vertical
movement of the
denture base. it
can be adjusted to
control t...
Advantages.
1.

2.

Minimal direct retention is required- as
denture base acts more
independently.
Has the massaging or st...
Disadvantages.

Construction of stress director is
complex and costly.
2.
Constant maintenance required.
3.
Difficult or i...
Physiologic basing




This school of thought too believes that
there is relative lack of movement in
abutment teeth in ...




The tissue surface is
recorded in
functional form and
not anatomic form.
Rpd constructed
from tissue
displacing
impr...


To permit vertical movement from rest
position to functional position the
retentive clasps have to have minimum
retenti...
1.

2.

3.

Advantages.

Intermittent base
movement has a
physiologically
stimulating effect on the
underlying bone and so...
4.

5.

Light weight prosthesis with minimal
maintenance and repair.
The looseness of the clasp on the
abutment tooth redu...
Disadvantages.
1.

2.

3.

4.

Denture is not well stabilized against
lateral forces.
There will be always premature
conta...
Broad stress distribution




Advocates of this school of thought
believe that excessive trauma to the
remaining teeth a...
advantages
1.

2.

3.

Teeth can be splinted .
Prosthesis are easier and less
expensive to construct.
No flexible or movin...
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 lea...
Factors
influencing
magnitude
of stresses
transmitted
to
abutment
teeth
1.
2.

3.

4.

5.

Length of span.
Quality of
supp...
Factors
influencin
g
magnitud
e of
stresses
transmitte
d to
abutment
teeth
1.

2.

3.

Length of
span.
Quality of
support ...
•Flat ridge will provide good support,poor
stability
•Sharp spiny ridge
will provide poor
support,poor to fair
stability.
...
Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
Length of
span.
2.
Quality of
support of
ridge....
Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
Length of
span.
2.
Quality of
support of
ridge....
Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
Length of
span.
2.
Quality of
support of
ridge....


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

www.indiandentalaca...
Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
Length of
span.
2.
Quality of
support of
ridge....


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

www.indiandentalacademy.com
Amount of clasp surface in
contact with tooth

www.indiandentalacademy.com
Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
Length of
span.
2.
Quality of
support of
ridge....
Factors
influencing
magnitude
of stresses
transmitted
to abutment
teeth
1.
Length of
span.
2.
Quality of
support of
ridge....


Partial denture constructed opposing a
complete denture will be subjected to a
much less occlusal stress than one
oppos...


Ideally,the occlusal
load should be
applied in the
center of the
denture –bearing
area, both anteroposteriorly and
bucc...
1.

1.

1.

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

Design considerations for
stress control

Direct retention
•
Adhesion ,cohesion
•
Fricti...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...
Adhesion and
Cohesion

Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhe...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...


The frictional
contact of the
prosthesis against
these parallel
surfaces can
contribute
significantly to the
retention ...
Function of guide planes
1.

2.

3.

To provide for one path of placement
and removal of the restoration.
To ensure the in...
Proximal guiding plane surfaces should be
about 2/3rd as wide as the distance between
the tips of adjacent buccal and ling...
Contact of guide planes

www.indiandentalacademy.com
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...
Design
consideratio
ns for stress
control
1.

1.

1.

1.

2.

3.
4.
5.

Direct
retention
•
Adhesion
,cohesion
•
Frictional...
Quadrilateral
configuration

Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.
6.

Direct retention
•
A...




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

When no modification space exists the
goal should be to place one clasp as far
posterior on the Dentulous side as
possi...
Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.
6.

Direct retention
•
Adhesion
,cohesion
•
Frictiona...


If there is no modification space present .

One clasp on the Dentulous side of the arch
should be positioned as far po...
Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.
6.

Direct retention
•
Adhesion
,cohesion
•
Frictiona...
The terminal
abutment
tooth on the
each side of
the arch must
be clasped
regardless of
where it is
positioned.

www.indian...
Design
considerations
for stress
control
1.

1.

1.

Direct retention
•
Adhesion
,cohesion
•
Frictional
•
neuromusc
ular
C...
1.

1.

1.

1.

2.

3.
4.
5.

6.

Design
considerations
for stress
control
Direct retention
•
Adhesion ,
cohesion
•
Fricti...


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

Alternatives
Reverse circlet clap




Approaches a distobuccal
undercut from the mesial
surfaces of a terminal
abutme...
Disadvantage
It may produce wedging force between 2
teeth's- can be countered by making rest
on the approximating surface ...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...


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

www.in...


One school of thought advocated
omitting of the distal rest in favour of a
mesial rest for the following reasons.



...
Disadvantage


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

www.indiandentalacademy.c...
What is the consensus?


Least unfavorable torque is when…..

…T clasp with distal -occlusal rest
and a rigid circumferen...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...






Wrought wire can flex in any spatial
plane and can absorb torosional stress
in both the vertical ad horizontal pl...
Advantages.





Flexibility.
Adjustability.
Minimum tooth contact.
Better esthetics.

www.indiandentalacademy.com
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...
Indications by crowns.
1.

2.

3.

Loss of periodontal
attachment by disease
or therapy.
Abutment has tapered
or short roo...




Splinting by crowns
stabilizes the teeth in
mesiodistal direction.
Splint should include
canine to achieve the
stabi...


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

www.indiandentalacademy.com
Splinting by clasps






Should not be done if fixed
splinting is possible.
More tan one teeth are
clasped on each sid...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...
Design considerations


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

www.indiandentalacademy.com
Class 1.


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

www.indiandentalacademy.com
Class 2








its use is not as critical as in
class 1.
If no modification space
exists .
An abutment tooth with
sui...






If modification space
exists.
The most anterior
abutment on the tooth
supported side, with its
rest and clasp
ass...
Class 3






Indirect retention is not
ordinarily used.
Auxillary rests must for
lingual plate major
connector.
Auxill...




If the contours of the
posterior abutment
teeth in class 2 or 3
partial denture are not
suitable for retention
In su...
Class 4


The indirect
retainer
must be
located as
far posterior
as possible.

www.indiandentalacademy.com
Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.
6.

Direct retention
•
Adhesion
,cohesion
•
Frictiona...
Design considerations






The initial occlusal contact should always
be in the remaining natural teeth.
Mandible shou...






if number of teeth replaced is reduced
stress transmitted will be less
Sharp cutting surfaces and sluiceways
can ...
Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.
6.

Direct retention
•
Adhesion
,cohesion
•
Frictiona...
Design considerations….








Distal extension denture base should cover the
retro molar area and tuberosity of maxi...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...
Design considerations

Mandibular arch.






Lingual plate major connector can aid in
distribution of functional stres...




Added rigidity provided by lingual plate
also helps in distributing stress created
on one side of the arch to the ot...
Maxillary arch.




Broad palatal major connector that connects
several of the remaining natural teeth
through lingual p...
Design
considerations
for stress
control
1.

1.

1.

1.

2.
3.
4.
5.

6.
7.

Direct retention
•
Adhesion
,cohesion
•
Frict...




If more guiding planes are incorporated in
design the force transmitted to each teeth can
be minimized.
When crown r...
design modification of minor
connector.
Places the minor
connector in the center of
the lingual surface of the
abutment to...
Disadvantages.





Increases encroachment of tongue
space
More obvious borders.
potentially greater space between the
...
Design
considerations
for stress
control
1.

1.

1.

1.

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

Direct retention
•
Adhesion
,cohesion
•
Fricti...
Design considerations
Floor of rest seat preparation must be less
than 90 degrees with long axis of tooth as
this design g...




Rest should be free to move within the
rest seat to release the stresses which
would otherwise transmit to the 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....



If tooth and tissue supported.
Also Consider
1.

2.
3.

4.
5.

6.

Quality and contour of supporting bone
and mucosa
...




Denture base areas adjacent to
abutment teeth are primarily tooth
supported.
As we proceed away from abutment
teeth,...
Second step




Connect the tooth and tissue support
units.
These connection is facilitated by
designing and locating ma...
Third step.




Determine how the partial denture is to be
retained.
Selecta clasp design that will

1.

2.

3.

4.

Avo...
Fourth step.


Connect the retention units to the
support units

www.indiandentalacademy.com
Fifth step.


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

www.indiandentalacademy.c...
To be continued ……




Designing of major connectors .
Designing of minor connectors
Miscellaneous factors in designing...
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandentalacademy.com
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Designing in removable partial dentures /certified fixed orthodontic courses by Indian dental academy

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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.

Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
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Designing in removable partial dentures /certified fixed orthodontic courses by Indian dental academy

  1. 1. Designing in Removable partial dentures INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. 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. www.indiandentalacademy.com
  3. 3.    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. www.indiandentalacademy.com
  4. 4. 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. www.indiandentalacademy.com
  5. 5.  Of all simple machines lever and inclined plane principle is involved in partial denture design. www.indiandentalacademy.com
  6. 6. Types of lever. www.indiandentalacademy.com
  7. 7. First class lever. www.indiandentalacademy.com
  8. 8. 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. www.indiandentalacademy.com
  9. 9. 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. www.indiandentalacademy.com
  10. 10. 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. www.indiandentalacademy.com
  11. 11.  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. www.indiandentalacademy.com
  12. 12. 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.) www.indiandentalacademy.com
  13. 13.    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. www.indiandentalacademy.com
  14. 14. 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). www.indiandentalacademy.com
  15. 15.    Movements are easier to control around this fulcrum. They are of lesser magnitude. More damaging forces as direction is horizontal. www.indiandentalacademy.com
  16. 16.   Vertical fulcrum line Located in midline ,lingual to anterior teeth. Controls movement of the denture in horizontal plane (flat circular movements of the denture). www.indiandentalacademy.com
  17. 17. www.indiandentalacademy.com
  18. 18. www.indiandentalacademy.com
  19. 19. 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. www.indiandentalacademy.com
  20. 20. 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. www.indiandentalacademy.com
  21. 21. 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. www.indiandentalacademy.com
  22. 22.  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.  www.indiandentalacademy.com
  23. 23. 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. www.indiandentalacademy.com
  24. 24.  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. www.indiandentalacademy.com
  25. 25.  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. www.indiandentalacademy.com
  26. 26. 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. www.indiandentalacademy.com
  27. 27. 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. www.indiandentalacademy.com
  28. 28. 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 www.indiandentalacademy.com
  29. 29.   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. www.indiandentalacademy.com
  30. 30.  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. www.indiandentalacademy.com
  31. 31. 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. www.indiandentalacademy.com
  32. 32. 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. www.indiandentalacademy.com
  33. 33. 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. www.indiandentalacademy.com
  34. 34. 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. www.indiandentalacademy.com
  35. 35. 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. www.indiandentalacademy.com
  36. 36. 4. 5. Indirect retainers and other rigid components provides excellent horizontal stabilization. Less relining required. www.indiandentalacademy.com
  37. 37. disadvantages 1. 2. Greater bulk may cause prosthesis to be less comfortable. Increased amount of tooth coverage can lead to dental caries www.indiandentalacademy.com
  38. 38. 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. www.indiandentalacademy.com
  39. 39. 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. www.indiandentalacademy.com
  40. 40. •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. www.indiandentalacademy.com
  41. 41. 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. www.indiandentalacademy.com
  42. 42. 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. www.indiandentalacademy.com
  43. 43. 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. www.indiandentalacademy.com
  44. 44.  Clasp length may be increases by using a curved rather than a straight course on an abutment tooth www.indiandentalacademy.com
  45. 45. 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. www.indiandentalacademy.com
  46. 46.  Clasp arm of chrome alloys are constructed with a smaller diameter than a gold clasp www.indiandentalacademy.com
  47. 47. Amount of clasp surface in contact with tooth www.indiandentalacademy.com
  48. 48. 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. www.indiandentalacademy.com
  49. 49. 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. www.indiandentalacademy.com
  50. 50.  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. www.indiandentalacademy.com
  51. 51.  Ideally,the occlusal load should be applied in the center of the denture –bearing area, both anteroposteriorly and bucco-lingually www.indiandentalacademy.com
  52. 52. 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. www.indiandentalacademy.com
  53. 53. 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 www.indiandentalacademy.com
  54. 54. 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. www.indiandentalacademy.com
  55. 55. 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. www.indiandentalacademy.com
  56. 56.  The frictional contact of the prosthesis against these parallel surfaces can contribute significantly to the retention of the denture. www.indiandentalacademy.com
  57. 57. 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. www.indiandentalacademy.com
  58. 58. 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.
  59. 59. Contact of guide planes www.indiandentalacademy.com
  60. 60. 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. www.indiandentalacademy.com
  61. 61. 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. www.indiandentalacademy.com
  62. 62. 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. www.indiandentalacademy.com
  63. 63.   A retentive clasp is positioned on each abutment tooth adjacent to the edentulous spaces. In this design leverage is effectively neutralized. www.indiandentalacademy.com
  64. 64.  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. www.indiandentalacademy.com
  65. 65. 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 . www.indiandentalacademy.com
  66. 66.  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. www.indiandentalacademy.com
  67. 67. 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. www.indiandentalacademy.com
  68. 68. The terminal abutment tooth on the each side of the arch must be clasped regardless of where it is positioned. www.indiandentalacademy.com
  69. 69. 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. www.indiandentalacademy.com
  70. 70. 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. www.indiandentalacademy.com
  71. 71.  As denture base moves towards the tissue the clasp puts distal tipping force on the abutment tooth. www.indiandentalacademy.com
  72. 72.  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. www.indiandentalacademy.com
  73. 73. Disadvantage It may produce wedging force between 2 teeth's- can be countered by making rest on the approximating surface too. www.indiandentalacademy.com
  74. 74. 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. www.indiandentalacademy.com
  75. 75.  Functions similar to the reverse circumferential clasp with the advantage of not producing any wedging forces . www.indiandentalacademy.com
  76. 76.  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. www.indiandentalacademy.com
  77. 77. Disadvantage  a space is created between framework and tooth surface leading to food trapment www.indiandentalacademy.com
  78. 78. What is the consensus?  Least unfavorable torque is when….. …T clasp with distal -occlusal rest and a rigid circumferential reciprocating clasp. www.indiandentalacademy.com
  79. 79. 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. www.indiandentalacademy.com
  80. 80.    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. www.indiandentalacademy.com
  81. 81. Advantages.     Flexibility. Adjustability. Minimum tooth contact. Better esthetics. www.indiandentalacademy.com
  82. 82. 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. www.indiandentalacademy.com
  83. 83. 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. www.indiandentalacademy.com
  84. 84.   Splinting by crowns stabilizes the teeth in mesiodistal direction. Splint should include canine to achieve the stabilization in buccolingual direction as well. www.indiandentalacademy.com
  85. 85.  An extremely week teeth should not be splinted with a strong teeth. www.indiandentalacademy.com
  86. 86. 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. www.indiandentalacademy.com
  87. 87. 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. www.indiandentalacademy.com
  88. 88. Design considerations  Should never be on an inclined tooth or on a single weak incisor. www.indiandentalacademy.com
  89. 89. Class 1.  It must always be used and positioned as far anteriorly as possible. www.indiandentalacademy.com
  90. 90. 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 www.indiandentalacademy.com fulcrum line.
  91. 91.    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
  92. 92. 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. www.indiandentalacademy.com
  93. 93.   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. www.indiandentalacademy.com
  94. 94. Class 4  The indirect retainer must be located as far posterior as possible. www.indiandentalacademy.com
  95. 95. 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. www.indiandentalacademy.com
  96. 96. Design considerations    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. www.indiandentalacademy.com
  97. 97.    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 . www.indiandentalacademy.com
  98. 98. 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. www.indiandentalacademy.com
  99. 99. 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. www.indiandentalacademy.com
  100. 100. 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 www.indiandentalacademy.com
  101. 101. Design considerations 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. www.indiandentalacademy.com
  102. 102.   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. www.indiandentalacademy.com
  103. 103. 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. www.indiandentalacademy.com
  104. 104. 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. www.indiandentalacademy.com
  105. 105.   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. www.indiandentalacademy.com
  106. 106. 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.  www.indiandentalacademy.com
  107. 107. Disadvantages.    Increases encroachment of tongue space More obvious borders. potentially greater space between the connector and abutment tooth. www.indiandentalacademy.com
  108. 108. 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. www.indiandentalacademy.com
  109. 109. Design considerations 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. www.indiandentalacademy.com
  110. 110.   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. www.indiandentalacademy.com
  111. 111. Essentials of partial denture design.  It should be systemically developed and outlined on an accurate diagnostic casts. www.indiandentalacademy.com
  112. 112. 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. www.indiandentalacademy.com
  113. 113.   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. www.indiandentalacademy.com
  114. 114.   Denture base areas adjacent to abutment teeth are primarily tooth supported. As we proceed away from abutment teeth, they become more tissue supported. www.indiandentalacademy.com
  115. 115. 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. www.indiandentalacademy.com
  116. 116. 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. www.indiandentalacademy.com
  117. 117. Fourth step.  Connect the retention units to the support units www.indiandentalacademy.com
  118. 118. Fifth step.  Outline and join the edentulous area tote already established design components. www.indiandentalacademy.com
  119. 119. To be continued ……    Designing of major connectors . Designing of minor connectors Miscellaneous factors in designing. www.indiandentalacademy.com
  120. 120. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com
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