Alternatives to Clasp-Retained
Removable Partial Dentures
Rotational Path
Hidden Clasp/Twin Flex/Saddle Lock
Equipoise
Virginia Partial
‘Invisible’ Clasps (Optiflex)
Attachment Partial Dentures
Fractured Abutments
Kennedy Class IV (Category I)
Rotational Path RPD
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Elimination of clasps
on one side of RPD
Place rigid element
into undercut
Rotate other end into
place (clasps)
Place in Undercut, Rotate Clasp into Place
Principles
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Large deep rests to
provide support,
reciprocation
Reciprocation from
adjacent teeth
End that rotates must
not have rigid
elements in undercut
Preparations
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Sufficient reduction if
placing a crown
Avoid undercuts in rests
Prepare axis close to
rotational axis
Dovetail if no other
element to keep
abutment from moving
Effective RPD Design
Underutilized
Potential Problems
Impossible to adjust
 Modification spaces (large blockout)
 Require sufficient undercut
 Require ability to hide metal
guiding plate
 Requires good laboratory support

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Blockout
Hidden Clasp/Twin Flex
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Uses retentive
undercut on proximal
surface
Requires sufficient
undercut
Space for clasp
movement - hygiene
Hidden Clasp

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Designed by lab
(retentoscope)
If insufficient
retention, labs tend to
bring the clasp
around to facial
Variable retention
(Soo et al, 1996)
Hidden Clasp Results
Equipoise
Lingual back-action clasp
reciprocated
Minimal facial clasp display.
1mm
Equipoise
Equipoise
Greater preparation
 Minimal Stress release
 Kennedy Class III situations
 Visible metal mesial embrasure display

Flexible ‘Gasket’ RPD’s
Virginia Partial - elastomeric
 Cu-Sil - elastomeric
 Flexite/Valplast - thermoplastic
 No clasps
Cu-Sil

Flexible ‘Gasket’ RPD’s
Difficult to adjust, polish
 Tend to tear, rough surface

Cu-Sil
Virginia Removable Partial Denture
Silicone gasket around teeth
 Compensates for lost bone/gingival height
 Patients generally favour

Virginia Removable Partial Denture
Hygiene
 Caries potential
 Liner lifespan

Virginia Removable Partial Denture
Hygiene
 Caries potential
 Liner lifespan

‘Invisible’ Clasps (Optiflex)


Non-metal, white
Opti•Flex
Coating
applied to metal
clasps
‘Invisible’ Clasps (Optiflex)
Thick, white, ugly clasp?
 Porous (plaque)
 Fatigue
 Bulky (comfort)

Other alternatives
Bonding composite to clasp arm
 Anodizing clasp arm
 Precision & Semi-Precision Removable
Partial Dentures

Overview of Prosthetic Attachments
Attachments


Type of direct retainer
Metal receptacle (matrix =
female) attached to
• An abutment or
• A prosthesis

Closely fitting component
(Patrix = male) mates with
the receptacle
Uses for Attachments

Fixed Partial Dentures

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Lack of draw between
abutments
Stress distribution
Uses for Attachments

Removable partial dentures

Comfort
• Less Bulk
• Within confines of Crown
Uses for Attachments
Removable partial dentures
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
Esthetics
Retention
Uses for Attachments
 Overdentures
• Retention
Classifications of Attachments
By type of Prosthesis
 Intracoronal / Extracoronal
 Precision / Semi-Precision

Intracoronal Attachments
Female portion of attachment within a crown
Extracoronal Attachments
Portion of attachment outside of crown/retainer contours
Precision Attachments
Box or key way
 One path of insertion
 Allows minimal to no rotation

Precision Attachments
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Milled prostheses
Semiprecision Attachments
Less intimate fit
 Some leeway or resilience
 Principle to relieve stress

Overdenture Attachments
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Bars
Balls
Studs
Magnets
Overdenture Attachments
Scope of Practice
Generally beyond scope of GP
 GP’s should be aware of possibilities

Advantages
Esthetics
 Hygiene

Advantages

Stress distribution

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
deep rest
directs stress along long axis
Single path of movement
Advantages
Comfort - fewer lingual components
Disadvantages
Cost
 Maintenance

Critical
 More complex types
need more
maintenance
 If poorly maintained

• Catastrophic failures
• Patient response
Disadvantages
Extra tooth preparation
for intracoronal
 If insufficient reduction

• over-contoured retainer

Major reduction of
non-restored teeth
Disadvantages
Overdenture
flange must draw
with attachments
 Can’t place
flange in some
undercuts

Disadvantages
Technique sensitive
 Lab

Parallelism
 Casting
 Processing
acrylic

Disadvantages
Technique sensitive
 Dentist

Tissue base
impression
 Relating Base to teeth

Contraindications
Short clinical crowns
 Large pulps
 Dexterity problems
 Bruxers?

Design Considerations
 Tissue Health
 Critical
 Compressible tissue - recovery
 Affects occlusion
Patient Instructions

Routine adjustments required

Prevent major problems

Dental checkups twice a year

Advise type of attachments

Record attachment type and replacement #
in chart
Summary - Attachment RPD’s
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Attractive Advantages
Maintenance critical and costly
Long term success if:
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Dentist uses utmost care
Patient follows care & maintenance regime
If dentist or patient careless, ultimately
fails
Summary - Esthetic Alternatives
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No panacea
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significant disadvantages with some designs
Costs
Managing expectations is important
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Initially
Long-term