rpd design part 1

11/1/2013

1

11/1/2013

2

11/1/2013

3

Dr.Mostafa Omran Hussein Assistant Professor of Prosthodontics

Faculty of Dentistry Qassim University

11/1/2013

4

1) Recognize how to asses clinically magnitude of stress falling

on the partial denture.

2) Describe basic principles and philosophies used to design

partial denture that make those stresses within the

physiologic tolerance of the tissues.

3) Understanding problems associated different classes of

partial denture cases and methods to solve them.

4) Discussing methods of designing different classes of partial

dentures in different situations.

11/1/2013

5

RPD design

The denture must be adequately designed following

bio-mechanical principles. Proper design helps in

reducing the harmful effects on the oral tissues

especially those supporting the appliance.

Successful RPD design tends to keep the stresses

evoked during function and parafunction within the

physiologic limit of the stressed tissues.

11/1/2013

6

How to asses these stresses clinically ?

General musculature and health of the patient

wear facets and attrition on the remaining natural teeth

The type of opposing occlusion

Teeth inclination and cusp inclines

Width of occlusal table

Length and location of the saddle

Absence of posterior abutment

11/1/2013

7

Possible movements of RPD

1. Tissue ward movement

2. Tissue away movement

3. Lateral movement

4. Rotational movement

1. Around axis passing through abutment teeth.

2. Around axis passing through crest of the ridge.

3. Around center of the arch (fish tail movement).

11/1/2013

8

Rotation around fulcrum passing between principle abutments

11/1/2013

9

Rotation around crest of the ridge

11/1/2013

10

Rotation around fulcrum passing through center of the arch

11/1/2013

11

11/1/2013

12

11/1/2013

13

I. Design for support

Support is designed to counteract vertical

tissue- ward movement of the denture.

11/1/2013

14

Design for support

Removable partial dentures are divided according

to the type of support into:

Tooth supported RPD

Tooth-tissue supported

Tissue supported

11/1/2013

15

II- design for Retention

Retention is necessary to counteract

vertical displacing forces.

This can be achieved by mechanical

means e.g. Retentive clasp arms,,

attachments, guiding planes, and by

physical means as adhesion, cohesion

and interfacial surface tension.

11/1/2013

16

Design for retention

The selection of Clasp form depends on:

- Position of the tooth: I-bar clasps are indicated for

premolars for better esthetics.

- Condition of the abutment tooth: For strong abutment tooth

rigid clasp is preferred.

- Position of retentive undercut

11/1/2013

17

Undercut:

An area of tooth or soft tissue which is beyond the survey line when viewed from a particular direction. An undercut is formed when the base of an object is smaller than its top.

11/1/2013

18

Undercuts

Soft or bony

tissue

undercuts

Undercut due to tooth

inclination

Bulbous shape of the crown

11/1/2013

19

All the Undercuts are Undesirable undercuts Except that used for Denture

Retention

11/1/2013

20

Paralleling Instrument Used to Determine the Survey

Line, delineate and Measure area of Undercuts. It

may also determine the Relative Parallelism of the

Surfaces of Teeth and Other Areas on the Cast.

11/1/2013

21

1- Horizontal plateform.

2- Vertical column.

3- Horizontal or cross arm.

4- Vertical spindle.

5- Surveying table.

6- Base equipped with a

lock screw and universal

joint.

7- Surveying tools.

8- storage compartment,

9- tool rack.

1

2

3

4

6

5

8

9

11/1/2013

22

11/1/2013

23

Analyzing rod: is a rigid metal rod used for diagnostic purposes in the selection of the path of placement

Carbon marker: is used for the actual marking of the survey lines on the cast. A metal shield is used to protect it from breakage.

Undercut gauges: are used to measure the extent of the horizontal undercuts that are being used for clasp retention. Usually there are three sizes: 0.01, 0.02 and 0.03 of an inch

Wax trimmer is used to trim excess wax that may be inserted into those undercut areas, which are to be obliterated

11/1/2013

24

11/1/2013

25

Design for retention

- Position of retentive undercut

If the undercut is on the mesio-buccal side, I- bar,

combination wrought wire clasp, RPI RPA clasp

or back action can be used.

If the abutment tooth exhibits an undercut, on the

disto-buccal side, then a reverse circlet or

modified T clasp can be used.

11/1/2013

26

III- Design for bracing and denture stability

Bracing is necessary to counteract horizontal forces

generated due to lateral movement of the mandible

during mastication and the presence of cuspal inclines.

Rigid components placed on one side of the arch

stabilizes the denture against horizontal forces acting

on the opposite side i.e. bilateral stabilization.

11/1/2013

27

Design for bracing & stability

Bracing & stability achieved by:

Rigid part of retentive arm

Proximal plate

Buccal & lingual

flanges

Distal area of tuberosity

Slope of palatal

connector

Proper occlusion

Reciprocal arm

11/1/2013

28

IV- design for Reciprocation

Reciprocation is necessary to counteract forces acting

on one side of the tooth by an equal and opposite force.

This can be achieved by reciprocal clasp arms

contacting the tooth prior to or at the same time the

retentive tip crosses the survey line of the tooth.

Cross arch reciprocation should also be provided.

11/1/2013

29

Retentive

Reciprocal

Reciprocal

Retentive

11/1/2013

30

VI- design for Indirect retention

Indirect retention should be designed in

free-end saddle cases to counteract

rotation of the partial denture away

from the underlying tissues.

This is mainly achieved by using rests

located on the opposite side of the

fulcrum axis and/or unrelieved

maxillary major connectors.

11/1/2013

31

VII- design for connection

Saddles are joined together by a suitable rigid

major connector.

Other components as clasps. additional rests or

indirect, retainers are joined to the saddle or to

the major connector by minor connectors.

11/1/2013

32

11/1/2013

33

1. Lack of posterior abutment

2. Support is derived from both the residual ridge and abutment teeth

3. Major support is obtained from the residual ridge

4. If resorption occurs and relining of the denture is neglected further bone

resorption occurs with subsequent torque acting on the abutments.

Mucosa 2 mm

PDL 0.2 mm

bone

11/1/2013

34

Reduction of the load.

Distribution of the load between abutment teeth and residual ridges.

Wide distribution of the load.

Providing posterior abutments.

11/1/2013

35

I- Reduction of the load

This can be achieved by:

1- The use of small and narrow teeth to increase the masticatory

efficiency and reduce the masticatory load.

2-Developing harmonious occlusion and reducing the cusp angle of

artificial teeth.

3- Leaving a tooth off the saddle.

4-Placing the artificial teeth on the anterior two-thirds of the base (no

3rd molar).

11/1/2013

36

II. Distributing the load between abutments

and residual ridge

This could be achieved by:

Correct choice of the abutment tooth with suitable crown and root morphology and efficient alveolar

bone support.

Correct choice of direct retainer (clasps having stress releasing action) and using stress equalizing

design.

11/1/2013

37


and residual ridge Clasps that have stress releasing action:

RPI clasp

Wrought wire clasp RPA clasp

Gingivally approaching clasp Back action clasp

11/1/2013

38

Mesial placement of the occlusal rest

provides the following advantages:

1. Changing the direction of torque on the abutment from the

distal to the mesial side of the tooth, where the resistance

to torque action will be applied to the neighboring teeth.

2. Achieving mechanical advantage from class I to class II lever

F

F

R

R

11/1/2013

39

3. Clasp disengagement from the tooth during function provides

less stresses on the abutment.

Buccal view

Occlusal view

11/1/2013

40

4. The farther the anterior placement of the rest, the more vertical will be the

forces, the less is the horizontal component of force falling on the ridge.

5. As rest is moved anteriorly, this will increase the area of, support (decrease

the force /unit area) and hence less stresses on the ridge and less torque

on the abutments.

6.The bone near the abutment will thus share the distal part of the ridge in

bearing the occlusal load.

11/1/2013

41


and residual ridge The use of :

Physiologic impression

Selective pressure impression

Functional reline method

Before metal framework construction

After metal framework construction

After denture construction

11/1/2013

42

Ill- Wide Distribution of Load

Wide distribution of the load over the ridge. The broader the coverage, the greater the distribution of load,

that provides more denture ability to withstand vertical and horizontal stresses.

Wide distribution of load over the teeth

Placing additional rests on the teeth adjacent to the abutment.

Splinting of one or more teeth, either by fixed partial dentures or by an embrasure or multiple clasp.

Using a kennedy bar to distribute the lateral load on multiple teeth.

11/1/2013

43

IV- Providing Posterior Abutments

Using an implant at the distal part of the ridge.

Salvaging a hopeless posterior tooth to be used

as a partial overdenture abutment.

11/1/2013

44

1. Lack of posterior abutment

2. inadequate physical means of retention.

11/1/2013

45

11/1/2013

46

11/1/2013

47

Designing Kennedy class I

1- Denture base:

A combined metal-acrylic base is used to:

Allow further relining

Allow mechanical retention with the acrylic

base.

Make physiologic basing more applicable.

11/1/2013

48


2- Rests :

Mesially placed saucer-shaped rest seats is used

to:

Allow dissipation of stresses

Allow transmission of stresses along the long

axes of teeth.

11/1/2013

49


3- Direct retainers :

Diagonally placed clasp with stress releasing action to:

Reduce torque to the abutment tooth

Minimize interference with normal stimulation of gingiva.

Good stabilizing components.

11/1/2013

50


4- Indirect retention:

In the form of rests or maxillary major connector

located as far anterior to the fulcrum axis as possible on a strong tooth.

Preferably bilateral.

11/1/2013

51


5- connectors:

Lingual bar is preferred than lingual plate and sublingual bar?

Middle palatal strap is preferred than anteroposterior palatal strap?

Any condition prevent their use change to another choice.

11/1/2013

52


6- Artificial teeth:

Small narrow teeth bucco-lingual.

Teeth with sharp cutting edges.

Centric occlusion is in harmony with centric relation.

Lower teeth over crest of the ridge.

11/1/2013

53

How to design this maxillary arch

11/1/2013

54

Class I Kennedy With Anterior Modification

It is wise to restore modification space with

fixed restoration?

When the remaining teeth are weak swing lock

design could be used to aid in splinting.

rpd design part 1

Documents