indirect retainers

INDIRECT RETAINERS

DefinitionsIndications for I. R.

Types

Factors Affecting I.R.

Tipping (Rocking)Is the Rotation of Partial Denture around a Fulcrum

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DEFINITIONS

Tooth-tissue supported partial dentures are subjected to vertical displacing forces acting in an occlusal direction. These forces may totally displace the denture if the direct retainers are not functioning adequately. However if the direct retainers are adequate, rotation of the denture around a fulcrum axis rather than total displacement occurs. This rotation is counteracted by the unit of the partial denture called "Indirect retainer".

In tooth supported partial dentures; tissue away movement of the prosthesis is prevented by the action of direct retainers and rests placed on the abutment teeth (self indirect retainer).

In mucosa supported partial dentures;(full palatal coverage) tissue away movement of the prosthesis is prevented by mechanical means (clasps) and by the action of physical means of retention on a well fitting denture base and the connector (direct indirect retention).

Indirect Retainers are “components of removable partial denture that are used to reduces the tendency of the denture to rotate in an occlusal direction about the fulcrum axis”

Retentive fulcrum line is the line joining the retentive tips of the clasps holding the principal abutments (Diagonally placed).

Supportive Fulcrum Line Is the Line Joining the Occlusal Rests Supported by Principal Abutments.

Fulcrum Lines

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This Movement Is Related To Quality Of The Tissue, Extent Of Denture Base And Its Fit And The Amount Of Force Applied

Components of RPD That Are Used to Reduces Its Tendency to Rotate in an Occlusal Direction About the Fulcrum AxisSupportive Elements (Rests) Used to Retain Far Ends of Partial Dentures

Indirect Retention

Retaining Elements (Clasps) Used to Retain Near Ends of Partial Dentures

DIRECT RETAINERS

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This Movement Is Related To Quality Of The Tissue, Extent Of Denture Base And Its Fit And The Amount Of Force Applied Support

Indications for Indirect Retainers

Tooth-tissue Supported Partial Dentures Are Subjected to Vertical Displacing Forces Acting in an Occlusal Direction. If the Direct Ret. Are Adequate, Rotation of the Denture Around a Fulcrum Axis Rather Than Total Displacement Occurs

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Class I

Class II

Class IV

Long Span Class III

Factors Influencing the Effectiveness of Ind.Ret.

1-Effectiveness of the Direct R.

• Well-supported I. R. Should Be Placed As Far From the Fulcrum Line As Possible. The Greater the Distance, the More Effective Is the Indirect Retention

•A Perpendicular Line Projecting Anteriorly From the Fulcrum Axis Is the Most Effective Location of I. R. And Affords the Best Resistance Against Vertical Dislodging Forces

2- Proper Location of I.R

3- Effectiveness of the Supporting Structures

• Definite, Properly Prepared Rest Seat

• Should Never Be Placed on Weak Teeth or on Inclined Surfaces

• I.R. In the Form of Rest Should Be Placed in a Definite, Properly Prepared Rest Seat That Allows Transmission of the Forces Along the Long Axis of the Tooth Without Slippage of the Rest or Movement of the Tooth

• The Minor Connector Joining the I. R. to the Framework Should Be Rigid. Flexing of the Connector Multiplies Rather Than Dissipates the Applied Forces

4- Rigidity of the Denture Frame

Factors Influencing the Effectiveness of Ind.Ret.

1- Effectiveness of the D. R.2- Proper Location of I.R

4- Rigidity of the Denture Frame

3- Effectiveness of the Supporting Structures

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Forms of I.R.1-Rests2-Connectors

Forms of Ind.Retainers

1-Auxiliary Occlusal or Canine Rests

A- R. Used In Mandibular P. D.

2- Principal Occlusal Rest of Modification Area

2- Principal Occlusal Rest of Modification Area

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3- Embrasure Hooks

4- Auxiliary Rests at the Terminal Ends of Ling. Plate or Kennedy Bar

Forms of Ind.Retainers

1-Auxiliary Occlusal or Canine Rests

A- R. Used In Mandibular P. D.

2- Principal Occlusal Rest of Modification Area

3- Embrasure Hooks4- Auxiliary Rests at the Terminal Ends

of Ling Plate or Kennedy Bar

B- Indirect Retainers Used in Maxillary Partial Dentures

1) Cummer Arm

2) Palatal Arm

3) Anterior Palatal Bar

4) Posterior Palatal Bar

7) Auxiliary Occlusal or Canine Rests

8) Principal Occlusal Rest of Modification Area

6) Direct-indirect Retainer (Full Palatal Coverage)

5) Palatal Strap and Rugae Support

1) Cummer Arm

2) Palatal Arm

3) Anterior Palatal Bar

4) Posterior Palatal Bar

5) Palatal Strap and Rugae Support

6) Direct-indirect Retainer (Full Palatal Coverage)

Auxiliary Occlusal or Canine Rests

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