Indirect Retainers Flashcards by sophie rosen

Indirect Retainer

The component of a RPD that assists the direct retainer
in preventing displacement of the distal extension
denture base by functioning through lever action on
the opposite side of the fulcrum line when the denture
base moves away from the tissues in pure rotation
around the fulcrum line.

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Indirect Retainer
❑Prevents

movement of the distal
extension base away from the residual
ridge

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Indirect Retainer
❑Converts

Class I lever to Class II lever

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Indirect Retainer Functions
(5)

❑Limit RPD vertical dislodgement
❑Reduce leverage on abutments
❑Reduce tissue impingement by
mandibular major connectors
❑Increase RPD stability & support
❑Stabilize the framework during relining

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INDIRECT RETAINER
❑ Usually a rest located on the

opposite
side of the fulcrum line that assist the
direct retainer in resisting movement
of the RPD in an occlusal directionlike when eating sticky food

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Requirements of an Indirect
Retainer
(3)

❑ Usually in the
form of an
auxiliary rest
❑ Ideal position
is
perpendicular
to fulcrum line
❑ Place as far
forward of
fulcrum line as
possible

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Effectiveness of an Indirect Retainer
(3)

❑ Properly prepared rest seats
❑ Distance from the fulcrum line
❑ Rigidity of the indirect retainer

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Distance from the fulcrum line
The greater the distance between the fulcrum line and the indirect
retainer, the

more effective the direct retainer will be.

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Rigidity of the indirect retainer
(3)

❑ Rests are excellent
❑ Rugae are not good indirect retainers
❑ Lingual plating alone is not acceptable

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Forms/Location of Indirect Retainers
(4)

❑Occlusal rest/premolar
❑Lingual rest/Canine
❑Incisal rest/Incisor or Canine (less common)
❑Lingual plate major connector

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Lingual plate major connector
❑ MUST have rests at each end, otherwise

lingual plate
IS NOT an indirect retainer

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Indirect Retainer Placement
(2)
❑Class I RPD: – indirect retainers
❑Class II RPD: – indirect retainer

❑Anterior to horizontal fulcrum line
❑Perpendicular to fulcrum line

2
1

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Denture Base
Movement
❑ Towards the tissue
(2)

❑ Rotation occurs around
most distal rests
❑ Resisted by rests and
denture base

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Denture Base
Movement
❑ Away from the
tissue
(2)

❑ Rotation occurs
around distal
most retentive
tips
❑ Resisted by
retentive clasp
when there is an
indirect retainer

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Denture Base Functions
Tooth-supported RPD
(3)

Support prosthetic teeth
Esthetics: replace missing tissue
Horizontal stability

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Denture Base Functions
Tooth-tissue supported RPD
(3)

All of the above plus the following:
Vertical support
Secondary retention: interfacial surface
tension between base & underlying mucosa

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Broad-stress distribution

❑ Distribute the forces of occlusion over as
many teeth & as much soft tissue area as
possible

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❑ Stress =

Occlusal Force / Area

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❑ — Area: — stress

Increased
Decreased

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Factors Affecting Denture Base
Support of Distal Extension RPD
(4)

Quality of soft tissue over residual
ridge
Type of bone
Amount of denture base tissue
coverage
Accuracy of fit of the denture base

Quality of soft tissue over residual
ridge

❑ More displaceable tissue, less support

Type of bone

❑ Cortical bone better support than cancellous

Accuracy of fit of the denture base

❑ Importance of accurate impression

Requirements of an Ideal Denture
Base Material
(7)

Accurate & dimensionally stable
Tissue compatibility
Thermal conductivity
Low specific gravity: light weight
Sufficient strength: resist fracture
Esthetic
Potential for future reline

Denture Base Materials Metal (5)

❑Difficult to adjust ❑Poor esthetics ❑Part of cast framework ❑Good thermal conductivity ❑Can be kept thin:

❑Can be kept thin: Advantage where

inadequate inter-arch space

Denture Base Materials ❑Polymethyl methacrylate (PMMA) (5)

❑Acrylic resin ❑Most common ❑Easily adjusted & relined ❑Good esthetics ❑Attachment to framework by lattice or mesh

Acrylic Resin Denture Base Retention ❑Considered a --- connector

minor

Acrylic Resin Denture Base Retention ❑Mandibular

❑ Extend 2/3 distance to retromolar pad

Acrylic Resin Denture Base Retention ❑Maxillary

❑ Extend 2/3 distance to hamular notch

Acrylic Resin Denture Base Retention ❑Types: (3)

❑ Lattice ❑ Mesh ❑ Retentive beads

Lattice Retention (4)

❑Two struts of metal ❑Strongest attachment ❑Easiest to reline ❑Preferred retention

Two struts of metal (3)

❑ Extend longitudinally along residual ridge ❑ Positioned buccal & lingual to ridge crest ❑ Avoid longitudinal strut along ridge crest

❑ Avoid longitudinal strut along ridge crest (2)

- Interferes with tooth placement - Cleavage action occurs within denture base

Mesh Retention (3)

❑Thin sheet of metal with multiple holes ❑Extension over ridge similar to lattice ❑Inferior attachment strength

❑Incorrect mesh construction (3)

❑ Longitudinal strut across ridge crest ❑ Interferes with tooth placement ❑ High stress site: Cleavage of denture base

Cast Stop on Mandibular Base ❑ A cast stop is essential to

prevent displacement or deformation of the metal framework during resinpacking procedures

Cast Stop on Mandibular Base Projects from the tissue surface of the minor connector to

contact the dental cast.

A butt joint should be used to join acrylic resin and metal components at the --- surface of a RPD. Each internal finish line should display an angle of -- degrees.

internal 90

❑ The internal angles of external finish lines should be

slightly less than 90 degrees. This results in improved mechanical retention for acrylic resin components.

purpose of finish lines

to create a distinct resin-metal interface and to prevent the acrylic resin from becoming too thin

because acrylic resin gains its strength with increasing bulk, it should not be

finished to a thin edge

if this is attempted, the material may

chip or fracture

this can create...

unhygenic and potentially irritating conditions

Tooth Replacement ❑ Acrylic (4)

❑ Most common ❑ Easily adjusted ❑ Not wear opposing natural dentition ❑ Chemical bond with denture base

Tooth Replacement ❑ Porcelain (4)

❑ Fracture easily ❑ Wear opposing dentition ❑ Difficult to adjust ❑ Mechanical retention only to denture base

Tooth Replacement ❑ Tube teeth (3)

❑ Denture tooth with drilled channel ❑ Secured to metal post ❑ Used with metal base: inadequate interarch space

Tooth Replacement ❑ Reinforced acrylic pontics (RAPs) (3)

❑ Composite resin polymerized around projections of metal from denture base ❑ Anterior teeth only ❑ Inadequate interarch space

Tooth Replacement ❑ Metal teeth (4)

❑ Used with severely inadequate interarch space ❑ Poor esthetics ❑ Used only in posterior ❑ Difficult to adjust