5

Assis.Prof.Radhwan Himmadi HasanB.D.S , M.Sc. , Ph.D. Prosthodontics2016

Principles of Removable Partial Dentures design with special emphasis on support and periodontal consideration of remaining teeth

PRINCIPLES OF DESIGN

1.Dentist should have thorough knowledge

2.Treatment plan must be based on complete examination and diagnosis of individual patient.
3.Dentist must correlate the pertinent factors and determine a proper treatment plan

4.RPD should restore the function without injury to remaining oral strutures

5.It is a form of treatment and not a cure.

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
2


STRESS CONSIDERATION IN A PARTIAL DENTURE
The stresses can be divided as:

Vertical

Horizontal

Torsional

Displacing stresses

Dislodging stresses

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
3

• VERTICAL STRESS

• Displacing stresses :
•



• These are the least harmful and are borne well if within physiologic limits
• Those forces which are the result of downward
• stresses along
• the long axis of
• the teeth in a crown
• to apex direction and
• the relatively vertical
• stresses on the ridge
• mucosa.
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
4

DISLODGING STRESSES :

These are the forces which tend to lift the partial denture from it’s rest position

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
5


HORIZONTAL STRESS





They originate as a component of rhythmic chewing stroke. These forces are effective in mesio-distal and buccolingual direction.
These lateral stresses are most damaging.

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
6

TORSIONAL STRESS

It is a twisting rotational type of force. It’s a combination of vertical and horizontal force
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
7

FORCES ACTING ON PARTIAL DENTURE

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
8

McCracken’s Removable Partial Prosthodontics 11th edition

Is a rigid bar supported somewhere along its length..

The point where the bar is supported is called the fulcrum

Three classes of levers (based on location of fulcrum, resistance and direction of effort (force).
Class I
Class II
Class III
LEVER

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
9


CLASS I LEVER

Fulcrum lies in the centre,

Resistance is at one
end and force at the other.

McCracken’s Removable Partial Prosthodontics 11th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
10

CLASS II LEVER

Fulcrum is at one end effort

at the opposite end and
resistance in the centre.

McCracken’s Removable Partial Prosthodontics 11th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
11

CLASS III LEVER

Fulcrum is at one end,

resistance at opposite
end and effort is in the centre.


McCracken’s Removable Partial Prosthodontics 11th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
12

Possible movements of partial denture.

Tooth –tissue supported partial
denture:

FULCRUM ON HORIZONTAL PLANE:

Extends through the rest of principle abutments.

Rotational movement of the denture in the sagittal plane.

Stewart’s clinical Removable Posthodontics 4th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
14

• DENTURE BASE MOVES AWAY FROM SUPPORTING TISSUES:

•

Counteracted by:

Direct retainer and
Indirect retainer
McCracken’s Removable Partial Prosthodontics 11th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
15

DENTURE BASE MOVES TOWARDS THE

SUPPORTING TISSUES:
Counteracted by:
• Occlusal rest.
• Tissues of supporting ridge

McCracken’s Removable Partial Prosthodontics 11th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
16

resulting forces on abutment teeth less damaging as it is in apical direction fibers of the periodontal ligament are so arranged that vertical forces are resisted greatly than horizontal forces

Dr.Radhwan Himmadi Hasan

17

Sunday, December 18, 2016

FULCRUM ON THE SAGITTAL PLANE




Extends through the occlusal rest on the terminal abutment and along the crest of the ridge.
Or Rotation about a longitudinal axis at the residual ridge
Movement is in the frontal plane

Stewart’s clinical Removable Posthodontics 4th edition

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
18

Counteracted by:

Rigidity of major and minor connector and their ability to resist torque.
Close adaptation of the denture base along the lateral slopes and the buccal slopes of the palate and ridge.
Direct retainer design

McCracken’s Removable Partial Prosthodontics 11th edition

Resulting forces more damaging as it is in horizontal direction
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
19


FULCRUM LOCATED IN MIDLINE JUST LINGUAL TO THE ANTERIOR TEETH (FULCRUM IS VERTICAL)

Rotational movement of denture in horizontal plane

or
flat circular movements of the denture
Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
20

Counteracted by :

Stabilizing components (reciprocal arm and minor connector)

Rigid major connector

Close adaptation of denture base

McCracken’s Removable Partial Prosthodontics 11th edition

Resulting forces more damaging as it is in horizontal direction
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
21


Tooth supported partial denture:
Movement :
Toward tissues resisted by rest on abutment teeth
Away from tissue resisted by retentive clasp arm
Horizontal movement resisted by stabilizing components

Rotation relatively non existent

Dr.Radhwan Himmadi Hasan
22

Sunday, December 18, 2016

• FACTORS INFLUENCING MAGNITUDE OF STRESSES TRANSMITTED TO ABUTMENT TEETH

• 1. Quality of support of ridge
• Form of residual ridge
• type of mucosal covering
• 2. Length of span
• 3. Clasp factor
• design
• length
• material
• amount of tooth contact
Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
23


4. Occlusion
Type of teeth
Harmony of occlusion

5. Areas of the base to which load is applied

Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
24

• QUALITY OF SUPPORT OF RIDGE

• Better support by ridge less stress on abutment teeth
• Large well formed ridges absorb greater stress less stress on abutment
• Broad ridges with parallel
• sides longer flanges on
• the denture base stabilize
• the denture against lateral
• forces.
•



Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
25

b. TYPE OF MUCOSA

Influences magnitude of stresses transmitted to abutment teeth.

Healthy mucosa capable

of bearing greater functional
loads than thin atrophic
mucosa

Soft, flabby, displaceable mucosa

Contribute little to vertical support of denture allows excessive movement of denture stress transmitted to abutment teeth

Stewart’s clinical Removable Posthodontics 4th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
26


2. LENGTH OF SPAN

Longer edentulous span

longer denture base

greater force transmitted to

abutment teeth

Every effort be made to retain a posterior abutment to avoid class I and class II situation.

Stewart’s clinical Removable Posthodontics 4th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
27

3. CLASP AS A FACTOR IN STRESS

More flexible the retentive arm of claspless stress to abutment tooth


But, flexible clasp arm  provides less stability against horizontal forces increase stress on residual ridge.

Decision should be made whether abutment or ridge requires more protection

Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
28

In examination phase decide whether ridge or abutment tooth require more protection

If periodontal support good

less flexible clasp like vertical projection clasp

If periodontal support weak

use more flexible clasp like

combination clasp

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
29


AMOUNT OF CLASP SURFACE IN CONTACT WITH TOOTH

Greater the area of tooth to metal contact between clasp and tooth

more will be stress exerted on the tooth.

Stewart’s clinical Removable Posthodontics 4th edition

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
30

OCCLUSION AS A FACTOR

Disharmonious occlusion

generate horizontal stresses

when magnified by factor of leverage

can transmit destructive forces to both abutment teeth and residual ridge.

Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
31

TYPE OF OPPOSING OCCLUSION

Play important role in determining amount of stress generated by occlusion

Natural teeth can exert closing force upto 300(136.078 kilograms) pounds/inch square, whereas, complete denture upto 30 (13.6. kilograms) pounds/inch square.

Therefore RPD constructed against removable prosthesis is subjected to much less occlusal stress than one opposed by natural dentition.
Stewart’s clinical Removable Posthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
32

AREA OF DENTURE BASE TO WHICH LOAD IS APPLIED

Less movement of base if load applied adjacent to the abutment tooth than if it is applied to the distal end of the base.


movement may be 4 times greater at distal end of base than next to the clasp.

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
33

STRATEGIC CLASP POSITIONING AS A MEANS OF STRESS CONTROL

Leverages can be controlled to a large extent by means of clasps, if there are sufficient abutment teeth and they are strategically distributed in the dental arch.

If number and location of potential abutments is less than ideal harmful effects can be decreased by strategic placement of clasps.
Stewart’s Clinical removable partial Prosthodontics 4th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
34

Indicated most often in class III arches (with modification space on opposite side)

QUADRILATERAL CONFIGURATION

McCracken’s Removable Partial Prosthodontics 11th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
35

TRIPOD CONFIGURATION

Class II situations

Distal abutment on one

side of arch missing
leverage controlled to
some extent by creating
tripod configuration
of clasp placement.





McCracken’s Removable Partial Prosthodontics 11th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
36

BILATERAL CONFIGURATION

For class I situations

Not considered ideal, but best option available

Stress must be controlled by other means.

McCracken’s Removable Partial Prosthodontics 11th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
37

ESSENTIALS OF PARTIAL DENTURE DESIGN

Should be systematically developed on the diagnostic cast based on the following.


• Where is the prosthesis supported.
• How the support is connected.
• How the prosthesis is retained.
• How the retention and support are connected.
• How the edentulous base support is connected
McCracken’s Removable Partial Prosthodontics 11th edition
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
38

WHERE IS THE PROSTHESIS SUPPORTED.

Tooth supported

Tooth - tissue supported:

Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
39

TOOTH SUPPORTED

• The most ideal support units are the RESTS.
• The abutment selected for the support has to be evaluated for
Periodontal health.
Crown- root ratio.
Crown –root morphology
Location of the tooth in the arch
The opposing dentition


Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
40

TOOTH- TISSUE SUPPORTED

Depends on 6 factors:-

• Quality of residual ridge

• The extent to which the ridge will be covered by mucosa
• The accuracy and type of impression registration
• The design chracteristics
• The occlusal load applied
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
41

Design of the removable partial denture

Simple

Comfortable.

Harmless to the remaining tissues.
Sunday, December 18, 2016
Dr.Radhwan Himmadi Hasan
42

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
43

1-Name the minor connectors that appear in these case(6 marks)

2- What are the Methods of recording the degree of tilt(4 marks)

Sunday, December 18, 2016

Dr.Radhwan Himmadi Hasan
44