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partial removable > direct retainers pt. 2 the sequel > Flashcards

direct retainers pt. 2 the sequel Flashcards

1
Q

Clasp Types relative to HOC?

A

supra and infrabulge

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2
Q

other names?

  • Suprabulge
A

– Retentive arm approaches undercut from above the survey line
– Circumferential, Akers, Circlet= Synonyms

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3
Q

infrabulge

A

retentive cusp from below survey line
bar clasps

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4
Q

when are bar clasps indicated

A

distal extension RPD
tooth supported RPD (no distal extensions), esthetics

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5
Q

most common bar clasps

A

I bar and half modified T bar

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6
Q

esthetics? flex? caries? undercut adaptability/location for I/T bars?

bar clasp advantages

A

– More esthetic
– More flexible
– Less conducive to caries (less tooth coverage)
– Wider range of undercut adaptability
* MF, Mid-F (I-bar)
* DF ( ½ T-bar)

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7
Q

bracing? tissue? food? repair?

bar clasp disadvantages

A

– Less bracing (less encirclment)
– Possible tissue impingement
– Food impaction
– More difficult to repair or replace

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8
Q

Bar Clasps Rules for Approach arm
impinge soft tissue?
taper? why?
crossing gingival margin?
extending onto abutment tooth?
not positioned over?

A

– 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

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9
Q

Tooth-supported RPDs

A

Tooth-supported RPDs
– Class III RPD, short-span Class IV

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10
Q

Tooth-tissue supported RPDs

A

Tooth-tissue supported RPDs
– Class I & II RPD, long-span Class IV

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11
Q

Tooth-supported RPD Clasps most common type/ preferred?
undercuts location relative to edentulous area?
where is reciporacal clasp?

A

Circumferential (Circlet)
– Most common
– Retentive undercut away from edentulous area
– Reciprocal clasp on lingual

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12
Q

I bar with tooth supported RPD
where is undercut?
what prevents it use?

A

second choice behind circumferential
Mesiofacial, Midfacial undercuts
– Reciprocal clasp on lingual
– Tissue undercut prevents use

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13
Q

half t bar with tooth supported cases
undercut location relative to endentulous area?
reciprocal clasp located?
what prevents its use?

A

–Retentive undercut adjacent
to edentulous area
–Reciprocal clasp on lingual
–Tissue undercut prevents use

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14
Q

tooth supported RPD and hairpin/ reverse circlet clasp
rententive undercut location?
used when?
disadvantage?

A

–Retentive undercut adjacent
to edentulous area
–Used when tissue undercut present= ½ T or I-bar cannot be used
–Excess tooth coverage, disadvantage

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15
Q

Tooth-supported RPD Clasps: Embrasure clasp
used when? examples?

A

– Used when retainer is
necessary in a dentate area
–Class IV & Class III arch with no modification space
–Class II tooth-tissue supported RPD, when no modification space exists

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16
Q

Fulcrum Line

A

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

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17
Q

rotation around fulcrum line

A

• Rotation of the RPD toward the residual ridge around the horizontal fulcrum line while in function
– Factor in Class I & II extension RPDs
– RPD potentially functions as a lever
– Can result in detrimental clasp forces on the abutment teeth

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18
Q

Why rotation of the RPD toward the
residual ridge around the horizontal
fulcrum line?

A

– Difference in potential movement of abutment
& mucoperiosteum over residual ridge
– 0.25mm periodontal ligament, 2mm at mucoperiosteum
– 0.25mm = 0.01” (related to retentive clasp)

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19
Q

Distal Extension RPD Clasp Selection
class I vs II levers
where to put rests and guide planes

A

Distal abutment retentive clasp should NOT be anterior to terminal rest fulcrum line

– Distal rest/Distal guide plane
• Class I lever = Torquing force on abutment

– Mesial rest/Distal guide plane
• Class II lever
• Retentive tip disengages abutment
• Stress-release clasp design

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20
Q

Anterior placement of the rest helps to?

A

Anterior placement of the rest helps direct the forces more vertically onto the tissues of the residual ridge.
wider arc of rotation

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21
Q
  • Stress-release clasps types/ when used?
A
  • Stress-release clasps used on Class I & II RPDs distal abutments
    – RPI clasp assembly
    – RPC (A) clasp assembly
    – Combination clasp
    – ½ T clasp
    – Reverse circumferential clasp
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22
Q

RPI Clasp assembly
parts?
rest location?
undercuts location?
reciprocation from?

A
  • Rest (mesial), Proximal Plate, I-bar
  • Mesiofacial or Mid-facial retentive undercut
  • Reciprocation from:
    – ML Minor connector
    – Distal proximal plate
23
Q

prepping RPI guide planes
M or D?
where on tooth?
demensions?
how much is contacted by guide plate?
undercut necessary?

A

– Distal Guiding plane: Occlusal 1/3-1/2
* 2-3 mm
* Guide plate contacts ~1-1.5mm of plane, not whole plane
* Undercut is necessary below the guide plane

– ML Minor Connector GP: Occlusal 1/3
* 1-2 mm

24
Q

RPI Clasp assembly
* Structural Details:
I bar?
approach arm?
D PP width?
major connector?

A

– I-bar 2mm contact at retentive undercut
– Approach arm : ~3mm from gingival margin, Crosses gingival margin 90°
– Distal proximal plate width: Line angle to line angle
– Major connector: 3mm from gingival margin: mandible OR 6mm from gingival margin: maxilla

25
Q

RPI Clasp assembly Stress release:

A

– Rotation around mesial rest/fulcrum
– Distal guide plate & I-bar move mesiogingivally
• I-bar disengages from tooth (Stress release)
– ML minor connector rotates mesio-occlusally
Disengage abutment tooth= release

26
Q

RPI Clasp assembly Stressm release design criteria:
relief is below?
undercut below?
allow what component to move?
ML minor conn shouldnt contact what?

A

– Relief below distal plate, Undercut below guide plane
* Allow proximal plate movement

– ML minor connector not contact adjacent tooth to allow rotation

27
Q

Need ____ separation between
vertical minor connector with RPI
* If not?

A

Need 5mm separation between
vertical minor connector with RPI
* If not 5mm, then should use lingual plate

28
Q

RPI Clasp RPI Clasp assembly
• Contraindications

A

Excess tissue undercut

– Shallow vestibule
• Tissue impingement

– Abutment excess facial inclination
• High survey line
• Retentive undercut too high
– Not in gingival 1/3

29
Q

RPC Clasp assembly (RPA)
components?
undercut where?
type of retentive clasp?

A

• Rest (mesial), Proximal Plate,
Circumferential (Akers) clasp (not I bar)
• Mesiofacial retentive undercut
• Circumferential retentive clasp

30
Q

RPC(A) Reciprocation:

A

Reciprocation:
– ML minor connector
– Distal proximal plate
* Wrap to lingual

31
Q

RPC Clasp assembly (RPA)• Structural Details:

A

– 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

32
Q

RPC Clasp assembly (RPA)
• Stress release:

A

– Rotation around mesial rest/fulcrum
– Circumferential clasp & distal guide plate move
mesiogingivally
• Clasp disengages from tooth
• ML minor connector rotates
mesio-occlusally

33
Q

RPC Clasp assembly (RPA) Stress release design criteria

relief where?
prox 2/3 retentive clasp where?
relief provided by?
failure to follow these criteria?

A

– Relief below distal guide plate, undercut below plane
– Proximal 2/3 of retentive clasp exactly on survey line
* Relief is provided below proximal 2/3
* Allow clasp to disengage during rotation

– Failure to follow criteria
* Fulcrum moves to proximal area of clasp
* Class I lever with detrimental force

34
Q

Combination Clasp
parts?
undercut?
indications

A

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

35
Q

combination clasp stress release

A

comes from the flexibility of matieral
– Rotation occurs at distal rest minor connector
– Clasp moves occlusally
• Class I lever occurs
• Distal torquing force occurs
• Flexibility of wrought wire limits torque

36
Q

RP? indication? reciprocation?

Modified (1/2) T Clasp

A
  • Mesial rest, Distal Proximal plate, ½ T-bar clasp
  • Indication:
    – Distofacial retentive undercut
  • Reciprocation: ML minor connector, Distal plate
37
Q

Stress release:Modified (1/2) T Clasp

A
38
Q

Modified (1/2) T Clasp
• Contraindications

A

– Tissue undercut
– Shallow vestibule
– Abutment excess facial inclination
• High survey line
• Retentive undercut too high
– Not in gingival 1/3

39
Q

Clasp Selection: Abutment Anterior to Horizontal Fulcrum

A

Class I lever occurs in Class II RPD with posterior modification
Limit torquing forces by:
1. No clasp
2. Clasp in less undercut
(i.e. MB tooth #6)
3. Non-retentive clasp (tip not
in undercut)
4. Wrought wire clasp

40
Q

Overview Tooth-supported RPD Clasp
Selection
• Rests ?
• Clasp by?
• Reciprocation rules?

A

• 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

41
Q

Tooth-supported RPD Clasp Selection table:
RPI, 1/2 T, circlet, reverse, embrasure
where is undercut?
indications/contra?

A

w

42
Q

Overview Tooth-Tissue Supported
(Distal Extension) RPD Clasp Selection
rests preferred?
stress release?
reciprocation?

A

• 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

43
Q

RPI? RPC? combo clasp? 1/2 t bar? Reverse?

undercuts? when used/not

Distal Extension RPD Stress-Release Clasp Selection: table

A
44
Q

prefered clasp assembly for dista; extensions

A

RPI

45
Q

why must the retentive clasp be posterior to occlusal rests in distal extension cases

A

must be posterior to fulcrum line to prevent dislodging forces on the tooth
I bar will disengage with function

46
Q

where is the reciprocation with RPI

A

rest minor connector and prox plate

47
Q

how long should the RPI approach arm be?

A

1 PM

48
Q

deminsions of the approach arm for RPI

A

top: 3mm from margin
bottom: 6mm

49
Q

what if its too big?

area of I bar touching tooth, deminsions

A

the pod
1.5- 2mm in width and 2-3 mm tall
can impinge on gingival margin if too large

50
Q

i bar contraindications

A

tissue undercut greater than 1.5mm at the approach arm
high frenum (impingment)

51
Q

when beading the maxillary cast when should it fade out? why?

A

6mm from margin to avoid excessive pressure on tissues

52
Q

Reverse Circumferential Clasp
* components?
* Indications:
* Reciprocation:

A
  • Mesial rest, Distal guide plate, Reverse cast
    circumferential retentive clasp
  • Indications:
    – Distofacial retentive undercut
    – ½ T clasp contraindicated
  • Reciprocation:
    – ML minor connector, Distal plate
53
Q

Reverse Circumferential Clasp stress release

A

similar to others

partial removable (14 decks)

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