Direct Retainers Part 1 Flashcards
____ retention:–Mechanical from retaining elements on abutment teeth
Primary Retention
____ retention:–Intimate contact of minor connector with guide planes–Intimate contact of denture base & maxillary major connector with underlying tissues
Secondary Retention
______: •RPD component used to retain and prevent dislodgement
Direct Retainer
•______ direct retainer
–Internal precision attachment: key/keyway
–Most esthetic
–Disadvantages: require crown, complex fabrication, & high maintenance
Intracoronal
•________ direct retainer
–Clasp assembly
–More commonly used
Extracoronal
–Retentive arm approaches undercut from above the survey line
–Circumferential, Akers, Circlet•Synonyms
Suprabulge
_____–Retentive arm approaches undercut from below survey line
–Bar clasps
Infrabulge
Which portion of the tooth is the reciprocal arm usually found on?
Lingual
Which portion of the tooth is the retentive arm usually found on?
Buccal
Which portion of the tooth is the rest usually found on?
Occlusal/Incisal
______ lies on occlusal, lingual, incisal surface–Prevent tissueward movement of clasp
Rest:
_____ components of direct retainer:
–Rigid component
–Above height of contour
–Reciprocal clasp, Lingual plate, Proximal plate, Guide plate (minor connectors)
Reciprocal components
_____ components of direct retainer:
•Proximal 2/3
•Rigid portion, above height of contour
Retentive clasp arm
_____ components of direct retainer:
•Distal 1/3
•Flexible•Below height of contour•Provides direct retention
Retentive terminal
- Joins body of clasp to framework
* Rigid
Minor Connector
- Component of bar clasp
- Connects clasp to framework
- Flexible minor connector
- Exception to rule
Approach arm
–Resist vertical movement toward tissue
–Rests
Support
–Resist horizontal displacement
–Areas above the survey line
–All rigid components of direct retainer
Stability
The class assembly should provide Encirclement of more than ____ degrees
–May be continuous or broken
–Minimum of 3 points used
–Prevents tooth from moving away from the clasp
180
–The component that contact tooth at same time or sooner than retentive clasp
–Remain in contact while retentive tip passes over height of contour
–Resist retentive tip lateral forces
–Requires parallel surface to path of insertion
Reciprocation
–Components of direct retainer exert no force when fully seated
Passivity
–Resists displacement of RPD away from supporting tissues
–Area below survey line: ideally in gingival 1/3
•Clasp arm tip: Terminal 1/3 below survey line
Retention
_____ clasps should become active ONLY when disclosing forces are applied to them.
•Their ability to provide retention is based on the resistance of the metal to deformation.
Retentive
If there is more length on the retentive clasp, is it more or less flexible?
More flexible
If there is more diameter on the retentive clasp, is it more or less flexible?
Less flexible
Is a round clasp or half-round clasp more flexible?
Round
-material for clasps
‣Produce by drawing metal through dies of smaller diameter
‣Most flexible of all clasps
Wrought wire
______ clasp:
–Approaches undercut from above the survey line
–“Pulls” toward occlusal to resist displacement
Circumferential clasp
______ clasp:
–Approaches undercut from below survey line–“Pushes” toward occlusal to resist displacement–Easier to seat, more difficult to remove than circumferential clasp
Bar clasp
_____ clasp:
•Must be rigid
•Shaped different than flexible retentive clasp•Not tapered
Reciprocal Clasp
______ is the means by which one part of the framework opposes the action of the retainer in function.
Reciprocation
•Most logical clasp for tooth-supported RPD (Class III)
•Advantages
–Excellent stabilization, support, bracing
–Easiest to design & construct
–Easier to repair
•Disadvantages
–Covers more tooth surface: more conducive to caries by more plaque retention
–Increases tooth circumference
•May cause greater occlusal force exerted on tooth
–More difficult to adjust
Circumferential clasp
Clasp kept as_____ on crown as survey line permits
–Less torquing action on tooth
–Less interference with occlusion
–If survey line is too high, enamel surface must be recontoured to lower the survey line
–Survey line too low, Surveyed crown required
Low
Should retentive clasp be whole round or half round?
1/2 round
- In middle 1/3of tooth
* Above the survey line
–Proximal 2/3
- In gingival 1/3•Below survey line
* Tip curves to occlusal
–Terminal retentive 1/3
\_\_\_\_ clasp –Cast ½ round –Entire clasp in middle 1/3 –Above the survey line •If survey line too high, must recontour •Prepare surface parallel to path of insertion–No taper: Uniform width 1.5 –2.0 mm
•Reciprocal clasp
- Circumferential clasp of choice Class III RPD
* Engage undercut remote from edentulous area
Circlet
•2 circlet clasps joined at body
•Used when retainer is necessary in a dentate area
–Class III with no modification space
–Class II with no modification space
–Class IV
•Requires heavy reduction of abutment teeth for adequate clasp bulk
–Inadequate preparation, clasp fracture common
Embrasure Clasp
•Engage undercut adjacent to edentulous area Class III RPD
•Covers extensive tooth surface, increased caries risk
•Difficult to fabricate
•Indication: Mesially-tipped mandibular molar with mesiofacial undercut
–½ T preferred for this situation, if no tissue undercut at approach arm
•“Last choice” for mesially-tipped molars
Reverse Circlet (Hairpin Clasp)
- Indication: Mesiolingually-tipped mandibular molars Class III RPD
- Engage mesiolingual undercut
- Auxiliary bracing arm for reciprocity
- Additional occlusal rest: –support, prevent further mesial movement
- Avoid if possible
- Incorrect Ring clasp: No reciprocation No support
Ring Clasp
•Indication:
Retentive undercut adjacent to edentulous space
–Class III RPD
–Tooth-tissue supported RPD (Class I or II distal extension)
–½ T bar clasp preferred, if no tissue undercut at approach arm
•Difficult to obtain adequate occlusal clearance
•Avoid, if possible
Reverse Circlet Clasp
•Wrought round wire retentive clasp
•Cast ½ round reciprocal clasp
•Indication: Distal extension RPD(Class I & II)
–Mesial rest not possible, distal rest must be used
–Mesiofacial undercut
•Wrought wire soldered to framework
Combination Clasp
•Indication: –Class I, II RPDs–Mesiofacial retentive undercut•Circumferential retentive clasp–Cast ½ round (ALWAYS) except in periodontally compromised teeth, cast round.•Reciprocation:–Distal proximal plate–ML minor connector
RPC
