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Removable Partial Prosthetics > Direct Retainers Part 1 > Flashcards

Direct Retainers Part 1 Flashcards

1
Q

Intracoronal Direct Retainers

A

Advtantages:
+Internal attachment
+Most esthetic

Disadvantages:

  • Costly
  • Requires Crown
  • Complex fabrication (not all dental labs can process)
  • High Maintenance
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2
Q

Extracoronal Direct Retainers

A

Clasp Assembly

More commonly used

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3
Q

Extracoronal Clasp Types

A

Suprabulge
&
Infrabulge

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4
Q

Suprebulge

A

Top portion above the contour of the abutment type
Retentive arm approaches undercut from above the height of the contour (above the survey line)

Circumferential, Akers, Circlet

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5
Q

Infrabulge

A

The retentive arm approaches the undercut from BELOW the survey line

Has Bar Clasps

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6
Q 
******Where are these located:
Rest
Reciprocal Clasp
Retentive Clasp
Proximal Plate

go over this question again

A

Rest ~ on the occlusal

Reciprocal Clasp - on the lingual

Retentive Clasp ~ on the buccal

Proximal Plate (guide plate) ~ type of minor connector

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7
Q

Clasp Assembly

A

Lies on the:
occlusal, lingual, or incisal surface

~Prevent tissue ward movement of clasp

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8
Q

Reciprocal Components

A

~Rigid Component

~Above height of contour

~Reciprocal Clasp, Lingual Plate, Proximal Plate, Guide Plate (minor connectors)

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9
Q

Retentive Clasp Arm

A

~Proximal 2/3 of tooth (which is rigid)

~Rigid portion, above the height of the contour

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10
Q

Retentive Terminal

A

~Distal 1/3

~Is Flexible

~Below the height of contour

~Provides a direct retention

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11
Q

Minor Connector

A

~Joins the body of the clasp to the framework

~Is Rigid

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12
Q

Approach Arm

A

~Is a component of the bar clasp

~Connects the clasp to the framework

~Flexible minor connector
~Exception to the rule

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13
Q

What are the requirements of Clasp Assembly?

A
  1. Support
  2. Stability
  3. Encirclement of more than 180 degrees
  4. Reciprocation
  5. Passivity
  6. Retention
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14
Q

What is Support for Clasp Assmebly?

A

~Resists vertical movement toward tissues

~Rests

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15
Q

What is Stability for Clasp Assembly?

A

~Resists horizontal displacement

~Areas above the survey line

~All rigid components of direct retainer

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16
Q

What is Encirclement?

A

– May be continuous or broken
– Minimum of 3 points used
– Prevents tooth from moving away from the
clasp

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17
Q

What is Reciprocation?

A 
– Reciprocal component 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
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18
Q

What is Passivity?

A

– Components of direct retainer exert no force

when fully seated

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19
Q

What is Retention?

A

– 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

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20
Q

Retention portion of tooth must be _____ in relation

to path of prosthesis insertion

A

undercut

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21
Q

Retention amount minimum necessary to resist

reasonable ____

A

dislodging forces

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22
Q

Undercut must always

A

come from below the height of the contour

1mm from the gingival margin on the apical 1/3

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23
Q

What are the 3 Retention Factors?

A

• Angle of convergence of the undercut

• Depth of undercut
– 0.010”, 0.020”, 0.030”
(undercuts we are looking for)

• Flexibility of the retentive clasp

~Retention should not be too much or too little~

24
Q

Retentive Clasp

A

• Retentive 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

25
Q

Longer Cusp arm =

A

more flexible

26
Q

Retentive Clasp Flexibility Factors

A
  1. Length
  2. Diameter
  3. Taper
  4. Cross-sectional form
  5. Material
27
Q

Retentive Clasp Flexibility Factors

Length

A

– Flexibility = length3
• Double length,
8x more flexible

– Increase length, curve clasp

28
Q

Retentive Clasp Flexibility Factors

Diameter

A

– Flexibility = 1/diameter3

• Double diameter,
8x less flexible

29
Q

Retentive Clasp Flexibility Factors

Taper

A

– Clasp terminal ½ as thick as origin
• 1mm to 0.5 mm

– Clasp terminal ½ as wide as origin
• ~2mm to 1mm

30
Q

Retentive Clasp Flexibility Factors

Cross-sectional form

A

– Round clasp more flexible than halfround
• Round flexes in all spatial planes
• Half-round flexes in one plane

31
Q

Retentive Clasp Flexibility Factors

Material

A

– Cast chromium alloys less flexible than cast gold
alloys

– Wrought alloys more flexible than cast alloy

– Cast Chromium

32
Q

What alloy is used in casting the Clasp Framework?

A

Usually Ticonium (NiCr) or Vitallium (CoCr)

Is easy to fabricate

33
Q

How is Wrought wire produced?

A

‣ Produce by drawing metal through dies of smaller

diameter

34
Q

Wrought wire is ….

A

the most flexible of all clasps

35
Q

What are other Clasp Materials?

A

Stainless steel, type IV gold

36
Q

The design of a retentive clasp arm should be ____

A

‣ Produce by drawing metal through dies of smaller

diameter

37
Q

Circumferential Clasp should ____

A

– Approach undercut from above the survey line

– “Pull” toward occlusal
to resist displacement

38
Q

The Bar Clasp ____

A

– Approaches undercut from below survey line
– “Pushes” toward occlusal to resist displacement
– Easier to seat, more difficult to remove than
circumferential clasp

39
Q

The Reciprocal Clasp must be ____

A

Rigid

40
Q

The Reciprocal Clasp is

A

is shaped different than the flexible retentive clasp

and Not tapered

41
Q

What is Reciprocation?

A

Reciprocation is the means by which one part of the
framework opposes the action of the retainer in
function.

42
Q

How can Reciprocation be achieved?

A

Reciprocation may be achieved by:

• Rigid plating (LINGUAL PLATE)
• Minor connectors 
• Guide planes extended around the vertical line of 
abutments
• Reciprocal clasp arms
• Contact areas of proximal teeth
43
Q

Circumferential Clasps are the most logical clasp for

A

tooth-supported RPD (CLASS III)

44
Q

What are the advantages of Circumferential CLasps?

A

~Excellent Stabilization, support and bracing

~Is the easiest to design and construct

~Is the easiest to repair

45
Q

What are the disadvantages of Circumferential Clasps?

A

~Covers more tooth surface; is more conducive to caries by more plaque retention

~Increases tooth circumference
>May cause greater
occlusal force exerted on
tooth

~More difficult to adjust

46
Q

Circumferential Clasp is kept ____

A

as low on the crown as the survey line permits

because of:
~Less torquing action on tooth
~Less interference with occlusion
~If the survey line is too high, the enamel surface must be recontoured to lower the survey line
~the survey line being too low, so surveyed crown will be required

47
Q

Describe a Retentive Circumferential Clasp

A 
– Cast ½ Round
– Proximal 2/3 
• In middle 1/3 of tooth
• Above the survey line
– Terminal retentive 1/3 
• In gingival 1/3
• Below survey line
• Tip curves to occlusal
– Tapers from origin (2.0mm) 
to tip (1.0 mm)
48
Q

Describe a Reciprocal Circumferential Clasp

A

• Reciprocal 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

49
Q

What are the types of Circumferential Clasps?

A
  1. Circlet
  2. Embrasure clasp
  3. Reverse Circlet (hairpin) clasp
  4. Ring clasp
  5. Reverse Circlet clasp
  6. Combination Clasp
  7. RPC clasp
50
Q

What is Circlet Circumferential Clasp?

A

• Circumferential clasp of choice Class III RPD
• Engage undercut remote from edentulous
area

51
Q

What is Embrasure Circumferential Clasp?

A

• 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

52
Q

What is Reverse Circlet (Hairpin) Circumferential Clasp?

A

• 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

53
Q

What is Ring Circumferential Clasp?

A 
• Indication: Mesiolingually-tipped mandibular 
molars Class III RPD
• Engage mesiolingual undercut
• Auxillary bracing arm for reciprocity
• Additional occlusal rest: 
– support, prevent further mesial movement
• Avoid if possible
• Incorrect Ring clasp: No reciprocation
No support
54
Q

What is a Reverse Circlet Circumferential Clasp?

A

• 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

55
Q

What is Combination Circumferential Clasp?

A

• 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

56
Q

What is RPC Clasp (RPA)?

A 
• Rest (mesial), Proximal Plate, Circumferential 
(Akers) 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

Removable Partial Prosthetics (5 decks)

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