In the distal extension RPD support is derived from both the residual ridge and abutment

teeth. The variation in consistency providing this support allows some rotational

movements of the free-end base towards the soft tissues

Harmful Tissue-ward movements of distal

extension under occlusal load are

transmitted to the abutment teeth

resulting in loosening of these teeth

1.Broad tissue coverage, 2.The use of functional basing.3.Use of narrow teeth and harmonious occ. 4.Placing the artificial teeth on the anterior two-thirds of the base.5.Correct choice of direct retainer.

Strain on the abutment teeth is minimized through:

This principle is fulfilled by stress breaker design

It is a device or design, which allows movement between the denture base and the retainer to reduce lateral and tipping forces on abutment

teeth. It is also called "Stress director" or "Stress equalizer".

The stress breaker

Types of Stress Breakers

RPD having a movable joint between the direct retainer and the denture base

1-

Partial dentures having a flexible connection between the direct retainer and the denture base

2-

b-Wrought wire connectors soldered to the main major connector

c-Clasps having a stress breaking effect

a- Split major connectors

Types of Stress Breakers

RPD having a movable joint between the direct retainer and the denture base This joint may be in the form of

hinges, ball and socket devices or sleeves and cylinders

1-

Hinged type stress breakers allows vertical and hinge movement of the base

Hinged type stress breakers allows vertical and hinge movement of the base to prevent direct transmission of

tipping forces to the abutment

A- Dalbo extra-coronal precision attachment device

B- Chrisman intra-coronal retainer

Split major connectors

Partial dentures having a flexible connection between the direct retainer and the denture base

2-

(a)

A lower partial denture framework with partial division of a lingual plate to

achieve stress breaking action

(b) Wrought wire connectors soldered to the main major connector

c-Clasps having a stress breaking effect

1- R.P.I.

3 -R.P.A.4 -WROUGHT WIRE CLASP

2- Reverse Aker Clasp

Indications for the use of stress breakers:

2- Cases exhibiting well formed residual ridges and weak abutment teeth

3- If internal attachments are used to retain a distal-extension base

1- In distal extension RPDs

Distribution of stress between abutment teeth and the residual ridge.

The alveolar support of abutment teeth is preserved because horizontal forces acting on them are minimized.

Physiologic stimulation of the mucosa helps to minimize bone resorption due to the intermittent pressure caused by movement of the denture base.

If relining of the denture base is needed but not done immediately for any reason, the abutment teeth are not damaged.

Advantages of Stress Breakers

Disadvantages of Stress Breakers

Difficult to construct.If the intermittent pressure are beyond the physiologic tolerance;

ridge resorption results.

Easily distorted and difficult to repair.

Reducing the effectiveness of I.R.Expensive.Less tolerated by patients.Allow food trapping and occasionally tissue-trapping.If relining of the denture base is needed but neglected for a long

time , excessive ridge resorption results.

F (fulcrum): Indirect retention

Stress breaker

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