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Removable Partial Dentures > Direct Retainers > Flashcards

Direct Retainers Flashcards

1
Q

what does retention do

A

resists dislodging forces

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2
Q

what is primary retnetion

A

mechanical from retaining elements on abutment teeth

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3
Q

what is secondary retention

A
  • intimate contact of minor connector with guide planes
  • intimate contact of denture base and maxillary major connector with underlying tissues
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4
Q

what is a direct retainer used for

A

retain and prevent dislodgment

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5
Q

what are the type of direct retainers

A
  • intracoronal
  • extracoronal
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6
Q

describe intracoronal direct retainers and disadvatnages

A
  • internal precision attachment: key/keyway
  • most esthetic
  • disadvantge: require crown, complex fabrication and high maintenance
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7
Q

describe extracoronal direct retainers

A
  • clasp assembly
  • more commonly used
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8
Q

what are the clasp types

A
  • suprabuldge and infrabuldge
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9
Q

describe suprabuldge clasps and their names

A

-retentive arm approaches undercut from above the survey line
- circumferential, akers or circlet

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10
Q

describe infrabuldge clasps

A

retentive arm approaches undercut from below survey line
- bar clasps

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11
Q

where is the retentive clasp usually located

A

buccal/facial side

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12
Q

what are the components of a suprabuldge or infrabuldge clasp assembly

A
  • rest
  • retentive clasp
  • reciprocal element
  • one or more minor connector
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13
Q

what are the specific design features of the various components in a clasp

A
  • vertical and horizontal approach arms
  • clasp termini
  • clasp bodies
  • clasp shoulders
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14
Q

where is the rest located

A

on occlusal, lingual and incisal surfaces

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15
Q

what does the rest do

A

prevent tissueward movement of clasp

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16
Q

what are the reciprocal components

A
  • rigid component
  • above height of contour
  • reciprocal clasp, lingual plate, proximal plate, guide plate
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17
Q

describe the retentive clasp arm

A

-proximal 2/3
- rigid portion above the height of contour

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18
Q

describe the retentive terminal

A
  • distal 1/3
  • flexible
  • below height of contour
  • provides direct retention
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19
Q

describe the minor connector

A

joins body of clasp to framework
- rigid

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20
Q

describe the approach arm

A
  • component of bar clasp
  • connects clasp to frameowrk
  • flexible minor connector
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21
Q

what does support do and what part of the clasp provides support

A
  • resists vertical movement towards tissue
  • rests
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22
Q

what does stability do and what part of the clasp provides stability

A
  • resists horizontal displacement
  • areas above the survey line
  • all rigid components of direct retainer
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23
Q

encirclement of more than ____ degrees

A

180

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24
Q

describe encirlemnet

A
  • may be continuous or broken
  • minimum of 3 points used
  • prevents tooth from moving away from the clasp
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25
Q

describe reciprocation

A
  • reciprocal component contact tooth at the same time or sooner than the 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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26
Q

what is passivity

A

components of direct retainer exert no force when fully seated

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27
Q

what does retention do

A

resists displacement of RPD away from supporting tissues

28
Q

where is retention located

A

area below survey line ideally in gingival 1/3

29
Q

where is the clasp arm tip located

A

terminal 1/3 below survey line

30
Q

retention portion of tooth must be _____ in relation to path of prosthesis insertion

A

undercut

31
Q

what are retention factors

A
  • angle of convergence of the undercut
  • depth of undercut (0.01”, 0.02”. 0.03”)
  • flexibility of the retentive clasp
32
Q

when should retentive clasps become active

A

only when disclosing forces are apllied to them

33
Q

a retentive clasps ability to provide retention is based on what?

A

the resistance of the metal to deformation

34
Q

what are the retentive clasp flexibility factors

A
  • length: the longer the more flexible
  • diameter: the thicker the clasp the less flexible
  • taper: clasp terminal 1/2 as thick as origin (1mm-0.5mm) and clasp terminal 1/2 as wide as origin (2mm to 1mm)
    4. cross sectional form: round clasp more flexible than half round
35
Q

what planes do round clasp flex in

A

spatial

36
Q

what planes do half round clasps flex in

A

one plane

37
Q

desscribe half round clasps

A
  • almost always as in circumferential clasp
38
Q

describe round clasps

A

in wrought wire clasps
- provides maximum flexibility

39
Q

what materials are the most to least flexible

A

wrought > cast gold > cast chromium

40
Q

what undercuts should you use with each material

A
  • cast chrome alloy: 0.01”
  • cast gold alloy: 0.015”
  • wrought wire: 0.02”
41
Q

what alloy is used in casting the framework

A

usually ticonium (NiCr) or vitallium (CoCr)

42
Q

how is wrought wire produced

A

by drawing metal through dies of smaller diameter

43
Q

what are the retentive qualities of circumferential clasps

A
  • approaches undercut from above the survey line
  • pulls toward occlusal to resist displacement
44
Q

what are the retentive features of 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
45
Q

describe the reciprocal clasp

A
  • must be rigid
  • shaped different than flexible retentive clasp
  • not tapered
46
Q

what is reciprocation

A

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

47
Q

how is reciprocation achieved

A
  • rigid plating (lingual plate)
  • minor connectors
  • guide planes extend around the vertical line of abutments
  • reciprocal clasp arms
  • contact areas of proximal teeth
48
Q

what type of RPD are circumferential clasps used in

A

tooth supported RPD - kennedy class III

49
Q

what are the advantages of circumferential clasps

A
  • excellent stabilization, support, bracing
  • easiest to design and construct
  • easier to repair
50
Q

what are the disadvantages to circumferential clasps

A
  • covers more tooth surface: more conducive to caries by more plaque retention
  • increases tooth circumference: may cause greater occlusal force on tooth
  • more difficult to adjust
51
Q

why is the circumferential clasp kept as low on crown as survey line permits

A
  • less torquing on tooth
  • less interference with occlusion
52
Q

what do you do if survey line is too hgih

A

recontour enamel surface to lower it

53
Q

what do you do if survey line is too low

A

surveyed crown required

54
Q

describe the retentive clasp in circumferential clasp configuration

A
  • cast 1/2 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 (2mm) to tip (1mm)
55
Q

describe the reciprocal clasp in circumferential clasp configuration

A
  • cast 1/2 round
  • entire clasp in middle 1/3
  • above survey line
  • no taper: unifrom width 1.5- 2 mm
56
Q

what are the types of circumferential clasps

A
  • circlet
  • embrasure clasp
  • ring clasp
  • combination clasp
57
Q

describe the circlet clasp

A
  • circumferential clasp of choice Class III RPD
  • engage undercut remote from edentulous area
58
Q

describe embrasure clasps

A
  • 2 circlet clasps joined at body
  • used when retainer is necessary in a dentate area : Class III with no mods, Class II with no mods, Class IV
  • requires heavy reduction of abutment adequate clasp bulk
59
Q

when are ring clasps indicated

A

mesiolingually tipped mandibular molars Class III RPD

60
Q

describe the ring clasp

A
  • engage mesiolingual undercut
  • auxillary bracing arm for reciprocity
  • additional occlusal rest: support, prevent further mesial movement
  • avoid if possible
61
Q

when are reverse circlet clasps indicated

A

retentive undercut adjacent to edentulous space
- class III RPD
- tooth-tissue supported RPD (Class I or II distal extension
- 1/2 T bar clasp preferred, if no tissue undercut at approach arm

62
Q

describe reverse circlet clasps

A
  • difficult to obtain adequate occlusal clearance
  • avoid if possible
63
Q

describe combination clasp

A
  • wrought round wire retentive clas
  • cast 1/2 round reciprocal clasp
64
Q

what is the indication for combination clasp-

A
  • distal extension RPD class I and II
  • mesial rest not possible, distal rest must be used
  • mesiofacial undercut
65
Q
A

Removable Partial Dentures (21 decks)

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