FORCES ACTING ON REMOVABLE

PARTIAL DENTURES

Fibers of periodontal ligament are arranged such that their resistance to

vertical forces is much greater

than that to horizontal forces

Tissues are adapted to Tissues are adapted to receive and absorb forces receive and absorb forces within their physiological within their physiological tolerancetolerance

POSSIBLE MOVEMENTS

OF THE PARTIAL

DENTURE

I- Tissue-ward movementsI- Tissue-ward movements

II- Tissue-away movementsII- Tissue-away movements

III- Horizontal movements:III- Horizontal movements: A) Lateral movementsA) Lateral movements

B) Antero-posterior movements.B) Antero-posterior movements.

IV- Rotational movementsIV- Rotational movements

At least four possible movements of the partial dentures exist

Vertical forces acting in gingival direction tending to move the denture towards the tissues

I- Tissue-ward movementsI- Tissue-ward movements

Vertical forces acting in gingival direction tending to move the denture towards the tissues

I- Tissue-ward movementsI- Tissue-ward movements

• Mastication, Swallowing And Aimless

Tooth Contact. Biting Forces

They occur during

• P.D. should be designed to resist this movement by providing adequate supporting components

•This function of the partial denture is called

“Support”

• The Resistance to Tissue Ward Movement

Support

• Distribute the Forces Over the Supporting Sttructure

• Transferring Occlusal Stresses to the Supporting Oral Structures

Distribute the Forces Over the Supporting Structure

II- Tissue-away movementsII- Tissue-away movements

Vertical forces acting in an occlusal direction tending to displace and lift the denture from its position

Tissue-away forces occur due to

The action of muscles acting along the periphery of the denture

•This function of the partial denture is called

“Retention”

Gravity acting on upper dentures or by

sticky food adhering to the artificial teeth or to the denture base.

Resistance to movement of the denture away from its tissue foundation (resistance of a denture to dislodgment)

Retention

This Function Is Mainly Provided By:

1-Mechanical Direct Retainers, Which Engage Undercuts On Abutment Teeth

2-Attachments.

3- physiologic forces on polished surfaces of denture bases

4- physical forces on fitting surfaces of denture bases

Horizontal movementsHorizontal movements A) Lateral movementsA) Lateral movements

Horizontal forces developed when the mandible moves from side to side

during function while the teeth are in contact

Lateral movements have a

destructive effect on teeth leading to tilting, breakdown of the periodontal ligament and looseness of abutment teeth.

Bracing

to Lateral Movement of the Partial Denture

Resistance

This Function Is Mainly Provided By:

Bracing clasp arms placed at or above the survey line of the tooth.

Minor connectors in contact with axial (vertical) surfaces of abutment teeth

Proximal plates

Adequate extension of the flanges

Horizontal movementsHorizontal movements B) Antero-posterior movementsB) Antero-posterior movements

There is natural tendency for the upper denture to move forward

and for the lower to move backward.

Horizontal forces which occur during forward and backward movement of the mandible

during function while the teeth are in contact

Horizontal movementsHorizontal movements B) Antero-posterior movementsB) Antero-posterior movements

Forward movement of the upper denture could be resisted by:

Anterior natural teeth. Palatal slope. Maxillary tuberosity. The natural teeth bounding the edentulous space.

The backward movement of the lower denture could be resisted by:

The slope of the retromolar pad. The natural teeth bounding the saddle area. Proximal plates.

From:From:• Guide planesGuide planes• Bracing clasp armsBracing clasp arms

•Reciprocation I barReciprocation I bar• Lingual platesLingual plates• RestsRests• Denture basesDenture bases

Active I-barActive I-bar

ReciprocationReciprocationI-barI-bar

BRACING AND STABILITYBRACING AND STABILITY

I- Tissue-ward movementsI- Tissue-ward movements

II- Tissue-away movementsII- Tissue-away movements

III- Horizontal movements:III- Horizontal movements: A) Lateral movementsA) Lateral movements

B) Antero-posterior movements.B) Antero-posterior movements.

IV- Rotational movementsIV- Rotational movements

At least four possible movements of the partial dentures exist

IV- Rotational movementsIV- Rotational movements

Rotational movements are due to

the variation in compressibility of

supporting structures, absence of

distal abutment at one end or more

ends of denture bases, and /or

absence of occlusal rests or

clasps at any end of the base

Periodontal ligamentPeriodontal ligament(0.25mm)(0.25mm)

MucosaMucosa(2.0mm)(2.0mm)

Different Displacement Between PDL & Different Displacement Between PDL & MucosaMucosa

1-Rotation of the extension denture base around transverse fulcrum axis:

Class I Lever:

fulcrum: between E and R

E

R

Free end saddle partial denture without indirect retention

1-Rotation of the extension denture base around transverse fulcrum axis:

A) Rotation of the denture base towards the ridge around the fulcrum axis joining

the two main occlusal rests

1-Rotation of the extension denture base around transverse fulcrum axis:

B) Rotation of the denture base away from the ridge around the fulcrum axis

joining the two main occlusal rests

Class I Lever: fulcrum: between E and R R X d1= E X d2

Direction of lever arm: E opposite R

Components of Removable Partial Denture That Are Used to Reduces the Tendency for a Removable Partial Denture to or Rotate in an Occlusal Direction About the Fulcrum Axis

Indirect Retention

when force is directed against unsupported end of beam cantilever can act as first class lever Torque

on the abutment tooth

F

A rigid major connector.

Balanced contact between upper and lower teeth.

Broad base coverage

This movement is counteracted by :

Providing adequate bracing

THANK THANK YOUYOU