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DMD3 > Retainers > Flashcards

Retainers Flashcards

1
Q

What is the function of retainers?

A

Retainers are part of an RPD that engage the abutments and resist dislodging forces.

Provide resistance to displacement by deformation of the retentive arm.

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2
Q

What causes displacement of RPDs?

A

Can occur through gravity, sticky foods, or functional jaw movements

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3
Q

What are the types of direct retainers?

A

Intracoronal (Precision attachments)

Extracoronal (Retentive clasp assemblies and extracoronal attachments)

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4
Q

What are the disadvantages of clasp-retained partial dentures?

A

Strain on the abutment teeth often is caused by improper tooth preparation or clasp design.

Clasps can be unaesthetic, particularly when placed on visible tooth surfaces.

Caries may develop beneath clasp components, especially if patient fails to keep the prosthesis and the abutments clean.

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5
Q

What are the components of a clasp assembly?

A

Rest

Retentive arm

Reciprocating arm

Clasp body: Proximal plate

Minor connector

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6
Q

What are the types of extracoronal retainers?

A

Retentive clasp assemblies

Extracoronal attachments

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7
Q

What are the types of retentive clasp assemblies?

A

Suprabulge assemblies

Infrabulge assemblies

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8
Q

What is the difference between suprabulge and infrabulge assemblies?

A

Suprabulge: Retentive arm approach the region of the abutment from the occlusal direction.

Infrabulge: Retentive arm approach the undercut region of the abutment from the apical direction

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9
Q

What is the difference between a direct and indirect retainer?

A

Direct: Adjacent to edentulous area

Indirect: Away from edentulous area

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10
Q

How are retainers classified?

A

Based on retention (direct/indirect)

Based on construction (Adapted, wrought wire, cast)

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11
Q

What are the requirements of a retentive unit?

A

Support (Mainly by the rest distributing load through the abutment protecting soft tissues and periodontium)

Stabilization (Bracing effects resist horizontal forces evenly through all abutment teeth)

Retention (Resisting occlusal displacement)

Reciprocity (Insertion force of retention arm must be opposed by reciprocating arms and/or other components of the RPD)

Engagement (Components must encircle more than 180 degrees of the tooth to prevent movement of the abutment out of the assembly)

Passivity (When fully seated the clasp assembly exerts no force on the tooth)

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12
Q

Which parts of the retainer are responsible for stabilization of RPD?

A

Reciprocating arm

Proximal plate (Minor connector)

Initial third of the retentive arm

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13
Q

What components of the retainer provides retention of RPD?

A

Terminal third of the retentive arm

Should be distributed throughout the arch

Depth of the undercut should be determined by the flexibility of the alloy.

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14
Q

Where is the correct location of a retention arm?

A

Middle and/or gingival third (3 sections shoulder midsection and terminal third)

The terminal third should be flexible and should engage below the height of contour.

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15
Q

What is the ideal shape of the retention arm?

A

Tapered uniformly

Cross-sectional form: Half-round form

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16
Q

How can flexibility of the retention arm be modified?

A

Length of the arm (Longer = more flexible)

Degree of taper (Lengthwise and widthwise)

Cross-sectional form (greater diameter = less flexible)

Material type used

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17
Q

How does kind of material affect the flexibility of the retention arm?

A

All cast gold alloys show some degree of flexibility

Cast gold alloys have greater resiliency than Cr-Co alloys.

Cast alloys flexibility is inversely proportional to bulk

Wrought wire clasp has higher tensile strength than cast clasps. For this reason it can be used in smaller diameter to provide greater flexibility without fatigue and fracture.

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18
Q

What is the function of the reciprocal arm?

A

To resist movement in response to deformation of the retentive arm.

Must be in contact during entire period of retentive clasp deformation

Stabilization of framework against horizontal movements during deformation of retentive arm

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19
Q

What are the features of the reciprocating arm?

A

Rigid

Half-round form

Average diameter greater than the retentive arm opposing it

No taper or taper in one dimension (lengthwise)

Above height of contour

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20
Q

What is the function of the clasp body?

A

Unites the arms and rest with the framework.

21
Q

What are the features of the clasp body?

A

Above height of the contour

Rigid

It will be in contact with guiding planes (frictional retention)

22
Q

What are guiding planes and what is their function?

A

Flat parallel surfaces prepared on abutment teeth (occlual one/two thirds)

Guide planes provide a single path of insertion

GP are used to control and limit directions of movement of RPD during insertion removal or function

Components of the denture start contacting the abutments at the guiding plane area.

23
Q

How are guiding planes made most effective?

A

Parallel

Include more than one common axial surface (proximal and lingual surfaces)

Placed on several teeth

Cover a large surface area (long and/or broad)

24
Q

What are the types of suprabulge assemblies?

A

Circumferencial clasp types include:

Simple

Reverse

Embrasure

25
Q

What are the features of a simple circumferential clasps made?

A

The most simple and versatile clasp

Clasp assembly has one retentive arm opposed by a reciprocal arm originating from the rest

26
Q

What are the indications of a simple circumferential clasp?

A

Molars and premolars

Intercalated edentulous area

Canines with no aesthetic restriction

27
Q

What limits ability to use the simple circumferential clasp?

A

Tilting of the tooth towards the edentulous space

28
Q

What are the features of reverse circumferential design?

A

Rest and body are opposite to the edentulous area

The arms run towards the edentulous space

A proximal plate is needed

29
Q

What are the limitations of a reverse circumferential design?

A

Short clinical crown

No space for the connector

30
Q

What are the features of the ring clasp design?

A

Mesial and distal rests

Encircles almost all of the tooth

31
Q

What are the indications for ring clasps?

A

Intercalated edentulous area

Molars tipped in a mesiolingual direction

32
Q

When should a ring clasp not be used?

A

Free end saddle

33
Q

What are the types of infrabulge clasps?

A

T-bar clasp

Modified T-clasp

I-clasp

RPI clasp

34
Q

What are the features of a T-bar clasp?

A

Approach arm originates from components in the edentulous area

Retention arm cross gingival margin at 90 degrees

Two horizontal projections

35
Q

What are the indications of a T-clasp design?

A

Intercalated or free end edentulous area

36
Q

What are the contraindications for a T-clasp design?

A

Interference with frenulum

Height of contour near the occlusal surface

Severe soft tissue undercut (metal can irritate the soft tissue and can cause food entrapment)

37
Q

What is the modified T-clasp design used for?

A

Avoiding the significant soft tissue undercuts

38
Q

What are I clasp designs used for?

A

Both intercalated and free end saddle.

39
Q

What are the features of I-clasp designs?

A

Crosses perpendicular to the gingival margin

Should be placed mesially to the midfacial prominence of the abutment

40
Q

What are the limitations of the I-clasp designs?

A

Same as other bar clasp designs:

Interference with frenulum

Height of contour near the occlusal surface

Severe soft tissue undercut (metal can irritate the soft tissue and can cause food entrapment)

41
Q

What are the components of an RPI clasp?

A

Rest, proximal plate, and I bar

I bar is located in the mesio-buccal undercut

42
Q

What is needed for an RPI clasp design?

A

Guiding planes

43
Q

When is an RPI clasp used?

A

For Kennedy class I and class II designs.

44
Q

What are the limitations of RPI clasp designs?

A

Need to reduce tooth structure

Tipped teeth require severe axial reduction

45
Q

What are the features of the proximal plate in an RPI?

A

Wide minor connector touching the distal guiding plane

Junction of the occlusal and middle third of the guiding plane

1 mm thick

Joins the framework at a 90 degree angle.

46
Q

What are the benefits of the proximal plate in an RPI clasp design?

A

Improves stabilization of the prosthesis

Improves retentiveness by limiting the path of insertion and removal

Provides reciprocation

Reduces food impaction if the guiding planes are done properly

47
Q

What are telescopic crown retained removable partial dentures?

A

Parallel-sided inner and outer crowns that are rigidly connected to abutment teeth. The denture is slotted into these crowns for stability.

48
Q

What are the limitations of telescopic crowns?

A

High treatment costs

Increased risk for tooth fracture

Treatment and laboratory procedures are highly complex

DMD3 (53 decks)

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