pre clinical removable prosthodontics 3rd yr.

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PRINCIPLES OF

DESIGNING

REMOVABLE

PARTIAL DENTURE

All tooth supported RPD

Tooth and tissue supported RPD

All tooth supported RPD

Tooth and tissue supported RPD

Class I

Class II

Class IV

The forces generated in RPD’s can be understood by analyzing the action of two simple machines.

1.Liver and fulcrum

2. Inclined plane

Liver and fulcrum

First - class lever

Second - class lever

Third - class lever

Inclined plane

Forces acting on partial denture

This fulcrum controls the movement of denture in sagittal plane.

Movement is greatest in magnitude

• The second fulcrum line extends from occlusal rest of terminal abutment and along the crest of the ridge.

• Controls movement in vertical plane.

• Most damaging

The third fulcrum is located in the vicinity of midline just lingual to the anterior teeth.

Every effort should be made to design the

RPD to control or minimize rotational movement related to these three fulcrum lines

Factors influencing magnitude of stresses transmitted to abutment teeth

1. Length of span

2. Quality of support of the ridge

3. Qualities of the clasp

• Clasp design

• Length of clasp

• Material used

4. Abutment tooth surface

5. Occlusal harmony

BASIC PRINCIPLES

Thorough knowledge of mechanical & biological factors

Complete examination & diagnosis of patients

Restoration of form & functions of oral cavity

A removable partial denture is a form of treatment & not cure

PHILOSOPHY OF DESIGN

Various philosophies have been suggested related to removable partial denture, none has proved to be clinically advantageous over another

All of them have produced excellent results if physiological limit of supporting structures is observed

Occlusal forces should be distributed evenly and equally over the large supporting area.

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 Main factor which influences the design of removable partial denture is type of denture support; whether tooth supported or tissue supported or combination of both.

Accordingly, impression procedures will differ for both of them.

THREE BASIC APPROCHES TO

DISTRIBUTE OCCLUSAL FORCES

1. STRESS EQUALIZATION

2. PHYSIOLOGIC BASING

3. BROAD STRESS DISTRIBUTION

1. STRESS EQUALIZATION

According to this concept compressibility & resiliency of tooth periodontal ligament & mucosal tissue is different

It causes an unequal distribution of stress on abutment teeth & alveolar ridge resulting in weakening of abutment teeth

So it advocates use of Stress Director Or Stress

Equalizer

2. PHYSIOLOGIC BASING

This theory denies use of stress breaker in removable partial denture

It advocates use of functional impression procedure to record the tissue in its functional form

It will compress tissue even at rest , so occlusal loading can’t compress tissue further

Due to the rebound action of mucosa it will position the artificial teeth above occlusal plane

ADVANTAGES

Simplicity of design

Good adaptation to underlining mucosa

Minimum direct retention required

It decreases functional stresses on abutment teeth

DISADVANTAGES

Tissues are always in state of compression

It increases rate of Resorption of ridge

Denture teeth are always slightly above plane of occlusion

It causes instability of denture due to less number of retentive components

It does not provide stability against lateral forces

3. BROAD STRESS DISTRIBUTION

It advocates use of maximum soft tissue area & maximum no of teeth for even distribution of stress

It is achieved by use of additional rest, direct retainer & by increasing denture base area

Broad stress distribution

ADVANTAGES

It reduces forces on abutment teeth

Health of oral tissues & abutment teeth maintained.

 Additional rest seats or direct retainers reduces lateral forces on abutment teeth

It also acts as a splint

DISADVANTAGES

Due to greater amount of soft tissue coverage, it causes discomfort to patient

Difficult to maintain oral hygiene properly

ESSENTIALS OF DESIGNING

Key factors to be considered while designing of removable partial denture

Direct Retainers

Rest

Indirect Retainers

Major Connector

Minor Connector

Type Of Occlusion

Artificial Teeth

Indirect retainer

It is employed to neutralize unseating forces

Should be located as far anterior of fulcrum line as possible

Class I design -Two indirect retainers

Class II design -one on opposite side

Class II

Class I

CLASS III DESIGN

DIRECT RETAINER

1. Quadrilateral positioning of direct retainer

2. Bracing arm should be rigid

Rests

Prepared next to edentulous space

Indirect retention

Not required

Major & minor connectors

Same as class I & class II

Occlusion

Same as class I & class II

Denture base

Functional impression not required

Class IV design

Preserve labial alveolar bone

Direct retention – quadrilateral configuration

Major connector –should be rigid with broad palatal coverage

Indirect retention – should be as far posterior as possible functional impression – may required

Class IV

DESIGNS OF CLASP

A. Circumferential cast clasp

Bar clasp

DESIGNING PROCEDURE

Dentist should have thorough knowledge of all components of removable partial denture

The design of the removable partial denture should be simple & should follow mechanical & biological standards.

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