Direct Retainers

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Direct Retainers
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Retention

• Denture base
• mechanical (undercuts)
• physical (adhesion, cohesion, etc.)
• Direct retainers (clasp assembly)
• mechanical

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Direct Retainers
Buccal

• Retention
• Composed of
• rest
• retentive element
• reciprocal (bracing) element
• minor connector

Lingual
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Direct Retainers

• Passive at rest
• Activated only during dislodgement

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Direct Retainers
Suprabulge

• Infrabulge

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Direct Retainers
Suprabulge

• Infrabulge

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Direct Retainers

• Suprabulge
• Begin above height of contour (rigid)
• Tip in gingival 1/3 of tooth (flexible)
• Middle portion as low as possible for esthetics
• Infrabulge
• Tip in gingival 1/3 of tooth

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Placement of Retentive Arms

• Middle to Lower 1/3 of Tooth
• Tipping forces
• Esthetics
• Occlusal interferences

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Requirements of Direct Retainers

• 1. Support
• rests

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Requirements of Direct Retainers

• 2. Reciprocity
• bracing arms, minor connectors

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Requirements of Direct Retainers

• 3. Stability
• resist horizontal movement
• rest, minor connector, bracing arm

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Requirements of Direct Retainers

• 4. Retention
• retentive arm

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Requirements of Direct Retainers

• 5. Encircle gt 180
• prevents tooth migration
• clasp arms, minor connectors

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Requirements of Direct Retainers

• 6. Passivity
• prevents discomfort, orthodontic tooth movement

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Magnitude of Retention

• Angle of Convergence
• Depth into angle

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Magnitude of Retention

• Clasp Flexibility
• Length
• proportional
• measured from taper

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Magnitude of Retention

• Clasp Flexibility
• Length
• increased by curvature
• molar allows greater length

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Magnitude of Retention

• Clasp Flexibility
• Diameter
• inversely proportional
• use uniform taper

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Magnitude of Retention

• Clasp Flexibility
• Cross Sectional Form
• Round is most flexible
• cast or wrought
• 1/2 round flexes in two directions
• cast only

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Magnitude of Retention

• Clasp Flexibility
• Material
• Cast is less flexible
• Wrought wire
• greater tensile strength
• flexibility without fatigue

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Direct Retainer Selection

• Principal
• Pick a retainer to suit the existing teeth
  rather than prepare the tooth to fit a particular
  direct retainer design

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Direct Retainer Selection

• Class I II (Tooth Tissue-Borne)
• Stress releasing direct retainers
• Class III IV (Tooth-Borne)
• Non-stress releasing direct retainers

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RPD Stress Distribution

• Stress Releasing Retainers
• Compensate for difference in movement of teeth
  and mucosa

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RPD Stress Distribution

• Stress Releasing Retainers
• Consider when
• Distal extension (Cl I II)
• Abutment periodontally involved
• Displaceable mucosal support
• Extensive edentulous space

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Retainer Selection Tooth-Borne RPDs

• Minimal rotation
• Stress release usually unnecessary
• Choose non-stress releasing retainers
• Cast Circumferential
• Ring Clasp
• Embrasure Clasp (Double Akers)
• Reverse Action (C) Clasp

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Rest Placement Tooth-Borne RPDs

• Adjacent Edentulous Space
• Most effective placement of support
• Ease of preparation
• Reduces minor connectors
• Very rare exceptions

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Rest Placement Tooth/Tissue-Borne RPDs

• Mesial Rest
• Reduced rotational forces
• Exceptions Mesial rest not indicated
• Mesial Restorations
• Rotations
• Mesial plunger cusp opposing

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Direct Retainers for Tooth-Borne RPDs

• Non-Stress Releasing Direct Retainers
• Cast Circumferential
• Ring Clasp
• Double Embrasure Clasp
• Reverse Action (C) Clasp

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Cast Circumferential (Akers)
Buccal

• Clasp of choice
• Retentive bracing arms originate from rest

Lingual
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Cast Circumferential

• Simple to construct
• Hygienic
• Excellent stabilization

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Cast Circumferential

• Less esthetic than bar clasps
• Less hygienic than bar clasps
• More difficult to adjust than wrought wire

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Ring Clasp

• Tilted abutments
• Usually mesially / lingually tilted mandibular
  molars
• Undercut directly adjacent the rest

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Ring Clasp

• Supporting strut and auxiliary rest
• resists flexure
• Excellent bracing
• Allows use of available undercut

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Ring Clasp

• Poor hygiene
• Very difficult to adjust
• Contraindicated with excessive tissue undercuts
  (support strut)

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Alternative to Ring Clasp

• When possible
• Cast circumferential with lingual retention
• Requires lingual undercut remote from rest
• More hygienic
• Easier to adjust

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Double Embrasure Clasp
Buccal

• Two rests, two retentive arms, two bracing arms
• Used in quadrants with no edentulous space
• Distal approach cannot be used on most posterior
  tooth

Lingual
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Double Embrasure Clasp

• Allows placement where no other useable undercut
  is present
• Requires extensive preparation
• Rests must be positive to prevent wedging
• Hygiene

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Reverse Action Clasp ("C"Clasp)

• Undercut adjacent edentulous space
• Almost impossible to adjust
• Poor esthetics, hygiene
• Clearance from opposing occlusion
• Poor flexibility (esp. short crowns)

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Tooth-Borne Direct Retainers

• Cast suprabulge clasps
• Exceptions
• Use stress-releasing clasps when
• Esthetics
• use infrabulge or w.w.
• Poor prognosis for posterior abutment
• allows conversion to distal extension

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Tooth-Tissue Borne Direct Retainers

• Denture base moves toward tissue in function
• Rotation around rests
• Use stress-releasing direct retainers

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Stress-Releasing Direct Retainers

• Mesial Rest Concept
• Rotation retentive tip, proximal plate
• Move mostly down (and forward)
• Into more undercut (release of tooth)

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Non-Stress-Releasing Direct Retainers

• Distal Rest
• Rotation retentive tip, proximal plate
• Move mostly forward (tip rotates up)
• Toward height of contour (activate or bind)

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Distal Rest Concept

• Long Guiding Planes
• Binding, torque
• Not advisable

• Short Guiding Planes
• proximal plate moves into space, escape of rest
• Acceptable, if mesial rest not possible

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Tooth-Tissue -Borne RPD's

• Use mesial rest to reduce torque
• Exceptions
• Large mesial restoration
• Heavy mesial occlusion
• Insufficient room for rest or minor connector
  (rotations)
• Modification spaces

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Retainer Selection Tooth-Tissue Borne RPDs

• Stress-releasing Clasps
• RPI Clasp
• RPA Clasp
• Combination Clasp

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Infrabulge (Bar) Clasps

• Approaches undercut from gingival direction
• Best esthetics

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Infrabulge (Bar) Clasps

• I - bar most common
• S - bar used to avoid large soft tissue undercut
• "Y", "T", "L", and "U" less useful

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Infrabulge Clasps Contraindications

• Shallow vestibule
• Requires 4 mm from free gingival margin - 3 mm
  for clearance, 1mm for thickness of arm
• Pronounced frenal attachments
• No labial tooth undercut

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Infrabulge Clasps Contraindications

• Large soft tissue undercut
• food impaction
• Disto-buccal undercut
• 180 encirclement

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RPI Clasp

• "R" Rest (always mesial)
• "P" Proximal Plate (distal)
• "I" I - Bar (buccal)

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RPI Clasp

• Rest minor connector and proximal plate
  reciprocate
• Proximal plate toward lingual
• Retentive arm mid-buccal except canines
  (mesio-buccal)

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RPI Clasp

• Minimum of 4 mm in vestibule
• (3mm from FGM, 1mm for bar)
• Distobuccal undercut not useful
• less than 180

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Bar Clasp with Mesial Rest

• When I-bar cant access undercut while
  encircling gt 180
• Or avoiding soft tissue undercut

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RPA Clasp

• Similar to RPI with wrought wire suprabulge
  retentive arm
• Used where infrabulge approach not possible

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RPA Clasp

• "R" Rest (always mesial)
• "P" Proximal Plate (distal)
• "A" Aker's retentive arm (always wrought wire)

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Combination Clasp

• Circumferential clasp with wrought wire clasp
• Bracing and retentive arms originate from distal
  rest
• Guideplane must not run entire occluso-gingival
  height

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Combination Clasp

• Tooth-borne cases with poor prognosis for
  posterior abutments
• Mesial rest and infrabulge approach not possible

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Indirect Retainers

• Prevent rotational displacement of denture from
  tissue base
• Rotation occurs around rests

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Indirect Retainers

• Should be 90 from primary fulcrum line (usually
  most posterior rests)
• As far from primary fulcrum as possible

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Primary Fulcrum Lines
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Indirect Retainers

• Usually rests
• Also lingual plate major connector

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Indirect Retainers

• Auxiliary functions
• Reduces torquing of 1 abut.
• Increases stability
• Increase strength of lingual bar