Indirect Retainers, denture Base Considerations Flashcards
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.
Indirect Retainer Prevents movement of:
the distal extension base away from the residual ridge
indirect retainer lever conversion
converts from class I lever to class II
Indirect Retainer Functions
❑Limit?
❑Reduce leverage?
❑Reduce tissue impingement?
❑Increase RPD?
❑use in relining?
Indirect Retainer Functions
❑Limit RPD vertical dislodgement
❑Reduce leverage on abutments
❑Reduce tissue impingement by
mandibular major connectors
❑Increase RPD stability & support
❑Stabilize the framework during relining
INDIRECT RETAINER is usually what?
assists what other component?
❑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 direction-
like when eating sticky food**
Requirements of an Indirect Retainer
❑ Usually in the form of?
❑ Ideal position?
❑ Place?
❑ Usually in the form of an auxiliary rest
❑ Ideal position is perpendicular
to fulcrum line
❑ Place as far forward of fulcrum line as
possible
effectiveness of an indirect retainer depends on?
❑ Properly prepared rest seats
❑ Distance from the fulcrum line
❑ Rigidity of the indirect retainer
The ________ the distance between the fulcrum line and the indirect
retainer, the more effective the direct retainer will be.
The greater the distance between the fulcrum line and the indirect
retainer, the more effective the direct retainer will be.
rigidity of indirect retainer:
the ideal component used?
can rugae be used?
what type of major connector alone is not acceptable as an indirect retainer? how can this be fixed?
❑ Rests are excellent
❑ Rugae are not good indirect retainers
❑ Lingual plating alone is not acceptable, must have rests on both ends
Forms/Location of Indirect Retainers
❑Occlusal rest/premolar
❑Lingual rest/Canine
❑Incisal rest/Incisor or Canine (less common)
❑Lingual plate major connector
lingual plate major connectors as indirect retainer must have:
ests at each end, otherwise lingual plate
IS NOT an indirect retainer
Indirect Retainer Placement
❑Anterior to horizontal fulcrum line
❑Perpendicular to fulcrum line
Class I/II indirect retainer numbers
❑Class I RPD: 2 indirect retainers
❑Class II RPD: 1 indirect retainer
Denture Base Movement Towards the tissue
❑ Rotation occurs around?
❑ Resisted by?
❑ Rotation occurs around
most distal rests
❑ Resisted by rests and
denture base
Denture Base Movement Away from the tissue
where is rotation?
resisted by?
❑ Rotation occurs around distal most retentive tips
❑ Resisted by retentive clasp when there is an indirect retainer
Denture Base Functions of
Tooth-supported RPD
- Support prosthetic teeth
- Esthetics: replace missing tissue
- Horizontal stability
denture base functions with tooth tissue supported RPD
- same as tooth supported plus the following:
- Vertical support
- Secondary retention: interfacial surface tension between base & underlying mucosa
Distal Extension RPD
Denture Base stress distribution Considerations
❑Distribute the forces of occlusion over as many teeth & as much soft tissue area as possible
❑Stress = Occlusal Force / Area
❑Increased Area: Decreased stress
soft tissue? bone? coverage? accuracy of fit?
Factors Affecting Denture Base Support of Distal Extension RPD
- Quality of soft tissue over residual
ridge
❑More displaceable tissue, less support - Type of bone
❑Cortical bone better support than cancellous - Amount of denture base tissue
coverage - Accuracy of fit of the denture base
❑Importance of accurate impression
Requirements of an Ideal Denture
Base Material
1. Accurate & dimensionally?
2. Tissue compatibility?
3. Thermal conductivity?
4. specific gravity?
5. strength?
6. Esthetic?
7. Potential for future what?
- Accurate & dimensionally stable
- Tissue compatibility
- Thermal conductivity
- Low specific gravity: light weight
- Sufficient strength: resist fracture
- Esthetic
- Potential for future reline
adjustment? estheitc? part of? thermal? thin? indication?
metal as a base material
❑Difficult to adjust
❑Poor esthetics
❑Part of cast framework
❑Good thermal conductivity
❑Can be kept thin:
❑Advantage where inadequate inter-arch space
common? reline/adjust? looks? attachment?
PMMA denture base
❑Acrylic resin
❑Most common
❑Easily adjusted & relined
❑Good esthetics
❑Attachment to framework by lattice or
mesh
distal extensions on both arches? how is this done? what type of connector is this considered?
Acrylic Resin Denture Base Retention
❑Considered a minor connector
❑Mandibular
❑Extend 2/3 distance to retromolar pad
❑Maxillary
❑Extend 2/3 distance to hamular notch
❑Types:
❑Lattice
❑Mesh
❑Retentive beads
Lattice Retention
❑Two struts of metal
❑Extend longitudinally along residual ridge
❑Positioned buccal & lingual to ridge crest
❑Avoid longitudinal strut along ridge crest
❑Interferes with tooth placement
❑Cleavage action occurs within denture base
❑Strongest attachment
❑Easiest to reline
❑Preferred retention
Mesh Retention
❑Thin sheet of metal with multiple
holes
❑Extension over ridge similar to lattice
❑Inferior attachment strength
❑Incorrect mesh construction: Longitudinal strut across
ridge crest, Interferes with tooth placement, or High stress site: Cleavage of denture base
Cast Stop on Mandibular Base
essential for?
Projects from?
A cast stop is essential to prevent displacement or deformation of the metal framework during resin-packing procedures.
Projects from the tissue surface of the minor connector to contact the dental cast.
joining of acrylic and metal on the internal surface
A butt joint should be used to join acrylic resin and metal components at the internal surface of a RPD. Each internal finish line should display an angle of 90 degrees.
internal line angles of external finish lines where acrylic and metal meet, why?
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 the finish lines
why should the acrylic have more bulk
acrylic denture teeth
❑Most common
❑Easily adjusted
❑Not wear opposing natural dentition
❑Chemical bond with denture base
porcelin denture teeth cons
❑Fracture?
❑Wear?
❑Difficult to?
❑Retention?
❑Fracture easily
❑Wear opposing dentition
❑Difficult to adjust
❑Mechanical retention only to denture base
Tube teeth
❑ Denture tooth with drilled channel
❑ Secured to metal post
❑ Used with metal base: inadequate interarch space
Reinforced acrylic pontics (RAPs)
where and why are these used?
❑ Composite resin polymerized around projections of metal from denture base
❑ Anterior teeth only
❑ Inadequate interarch space
Metal teeth
used when?
esthetics?
used where in arch?
adjustments?
Metal teeth
❑ Used with severely inadequate interarch space
❑ Poor esthetics
❑ Used only in posterior
❑ Difficult to adjust
