Direct Retainers Part 2 Flashcards
–Retentive arm approaches undercut from below survey line
–Bar clasps
Infrabulge
Indications for _______
–Distal extension RPD
–Tooth-supported RPD, esthetics factor
Bar clasps
What is the most common bar clasp?
I-bar clasp
- Advantages–More esthetic–More flexible–Less conducive to caries (less tooth coverage)–Wider range of undercut adaptability (I-bar) •MF, Mid-F, DF
- Disadvantages–Less bracing–Possible tissue impingement–Food impaction–More difficult to repair or replace
Bar clasp
–Must not impinge on soft tissue
–Tapered •(Flexible minor connector: exception to rule)
–Cross gingival margin at 90 degrees
–Extend onto abutment tooth to the height of contour
–Not positioned over soft tissue undercut: food trap, tissue irritation
•Approach arm
–Class III RPD, short-span Class IV
Tooth-supported RPDs
–Class I & II RPD, long-span Class IV
•Tooth-tissue supported RPDs
For tooth supported cases, what clasp is described:
–Most common
–Retentive undercut remote from edentulous area
–Reciprocal clasp
- Less esthetic
-1st choice
Circumferential
For tooth supported cases, what clasp is described:
–Mesiofacial, Midfacial, Distofacial undercut
–Reciprocal clasp
–Tissue undercut prevents use
-More esthetic than circumferential
-2nd choice
I-bar
For tooth supported cases, what clasp is described:
–Retentive undercut adjacent to edentulous area
–Reciprocal clasp
–Tissue undercut prevents use
-3rd choice
1/2 T-bar
For tooth supported cases, what clasp is described:
–Retentive undercut adjacent to edentulous area
–Used when tissue undercut present
•½ T or I-bar cannot be used
–Excess tooth coverage, disadvantage
-Difficult to fabricate
-4th choice
Reverse Circlet (Hairpin)
For tooth supported cases, what clasp is described:
–Used when retainer is necessary in a dentate area
–Used in Class IV & Class III arch with no modification space
–Also used in Class II tooth-tissue supported RPD, when no modification space exists
•Embrasure clasp
•an imaginary line, connecting occlusal rests, around which a partial removable dental prosthesis tends to rotate under masticatory forces. The determinants for the fulcrum line are usually the cross arch occlusal rests located adjacent to the tissue borne components
Fulcrum line
_____ of the RPD toward the residual ridgearound the horizontal fulcrum line
–Factor in Class I & II extension RPDs
–RPD potentially functions as a lever
–Can result in detrimental clasp forces on the abutment teeth
Rotation
Is there a greater arch of rotation around the fulcrum line when the rest is on the mesial or distal causing more dislodgement?
Distal
______ placement of the rest helps direct the forces more vertically onto the tissues of the residual ridge.
Anterior placement
SHould the distal rest and distal guide plane be used in the distal extension RPD?
No
How much clearance is needed between vertical minor connectors?
5 mm
For the RPC, the middle 1/3 should be positioned how based on the survey line?
On the survey line
What class lever is created in RPI and RPC to ensure the RPD does not cause detrimental forces to the abutment teeth?
2
What are the 3 components of the RPI clasp desgin?
Mesial rest
Proximal plate
I Bar
What are the 3 components of the RPC clasp design?
Mesial rest
Proximal plate
Circumferential clasp
What are the 3 components of the combination clasp design?
Distal rest
Wrought wire
Cast reciprocal clasp
What component of the combination clasp is used to decrease torque of the class 1 lever created by the distal rest to decrease pressure on abutment teeth?
Wrought wire
What are the 4 ways to limit torquing forces in a class 2 RPD with posterior modification?
No clasp
Clasp in less undercut
Non-retentive clasp
Wrought wire clasp
In a distal extension RPD clasp selection, does the retentive clasp tip stay on the tooth or dislodge due to the class 2 lever created by the mesial rest?
Disengages
\_\_\_\_\_- clasp assembly •Mesiofacial or Mid-facial retentive undercut •Reciprocation –ML Minor connector –Distal proximal plate
RPI
Is the undercut necessary below the guiding plane on an RPI?
Yes
On the RPI clasp assembly, the distal plate and I bar move in what direction to relieve stress?
Mesiogingivally
On the RPI clasp assembly, the ML minor connector moves in what direction to relieve stress?
Mesio-occlusally
Should the ML minor connector on the RPI contact the adjacent tooth?
No; allows rotation
•Contraindications of \_\_\_\_\_\_ –Excess tissue undercut –Shallow vestibule •Tissue impingement –Abutment excess facial inclination •High survey line •Retentive undercut too high –Not in gingival 1/3
RPI
\_\_\_\_\_ •Mesiofacial retentive undercut •Circumferential retentive clasp–Cast round for Kennedy I•Reciprocation: –ML minor connector –Distal proximal plate•Wrap to lingual
RPC
–Hybrid clasp: RPI and circumferential concepts
–Similar criteria to Circumferential Retentive Clasp
•Proximal 2/3
–Middle 1/3 of tooth
–On the survey line
•Terminal retentive 1/3
–Gingival 1/3, Below survey line–Guide planes same as RPI
•Same criteria
RPC
- Distal rest, Wrought wire retentive clasp, Cast reciprocal clasp
- Mesiofacial undercut
- Indications–Mesial-inclination of abutment distal surface
- No undercut below guide plane
- RPC, RPI no stress release–Mesial rest cannot be used
- RPC, RPI no stress release
Combination clasp
Under what condition should you use a combination clasp?
Mesial inclination of abutment distal surface
What type of lever occurs with the combination clasp made from the distal rest?
Class I
•Mesial rest, Distal Proximal plate, ½ T-bar clasp •Indication: –Distofacial retentive undercut •Reciprocation: ML minor connector, Distal plate •Contraindications –Tissue undercut –Shallow vestibule –Abutment excess facial inclination •High survey line •Retentive undercut too high –Not in gingival 1/3
Modified (1/2) T Clasp
•Mesial rest, Distal guide plate, Reverse cast circumferential retentive clasp •Indications: –Distofacial retentive undercut –½ T clasp contraindicated •Reciprocation: –ML minor connector, Distal plate
Reverse Circumferential Clasp
\_\_\_\_\_\_ supported RPD •Rests adjacent to edentulous areas •Clasp by convenience –No fulcrum lines, no rotation –Determine by site of retentive undercut –Tissue undercut •Reciprocation rules still apply –Often Cast circumferential clasp
Tooth-supported
______ supported RPD
•Mesial rests preferred
•Stress-release clasps used
–Accommodate for rotation toward residual ridge around horizontal fulcrum
•Reciprocation still needed
–Often ML minor connector & Distal plate rather than circumferential reciprocal clasp
Tooth-tissue supported
