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RPD > Biomechanics of Removable Partial Dentures > Flashcards

Biomechanics of Removable Partial Dentures Flashcards

1
Q

What is biomechanics?

A
  • Application of mechanical engineering principles in the living organism
  • Mechanical forces exerted on RPD during functional & parafunctional mandibular movements should be properly directed to the supporting tissue to elicit the most favorable response
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2
Q

Alveolar bone provides support to the RPD via:

A

– Abutment teeth & periodontal ligaments
– Residual ridges through soft tissue covering

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3
Q

Why are teeth better able to tolerate vertical forces down the long-axis?

A

More PDL fibers activated to resist force

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4
Q

What forces on a tooth are deleterious?

A

off-axis
torque
horizontal

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5
Q

Excess for on the alveolar area may result in…

A

– Mucosal ulcerations
– Bone resorption

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6
Q

Whatare the forces acting on an RPD?

A
  • Vertical (Dislodging)
  • Horizontal (Lateral)
  • Vertical (Seating)
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7
Q

What are the requirements of an RPD?

A
  • Retention: Resistance to dislodging
  • Stability: Resistance to horizontal
  • Support: Resistance to vertical seating
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8
Q

What is retention?

A

Resistance to Vertical dislodging forces

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9
Q

What are the retention RPD components?

A

– Direct retainer: Retentive clasp
– Indirect retainer
– Proximal plates (Friction)

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10
Q

What is stability?

A

Resistance to horizontal, lateral, or torsional forces

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11
Q

What are the stability RPD components?

A

– Minor connectors
– Proximal plates
– Lingual plates
– Denture bases

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12
Q

What is support?

A

Resistance to vertical seating force and this is most important to oral health.

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13
Q

What are the support RPD components?

A

– Rests
– Major connectors: Maxillary tooth-tissue supported RPD
– Denture bases

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14
Q

What is reciprocation?

A

the means by which one part of a restoration is made to counter the effects created by another part

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15
Q

RPD’s true reciprocation can only be achieved if the reciprocating element touches the tooth _________ the retentive clasp

A

before

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16
Q

What are the biomechanical classificaiton of RPDs?

A
  • Tooth-supported RPD
    – Abutment teeth support RPD
    – Class III & IV RPD
  • Tooth-tissue supported RPD
    – Denture base is supported
    by both teeth & residual ridge
    – Class I, II, long-span IV RPDs
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17
Q

Class ____ RPDs best resist functional forces

A

III

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18
Q

What are the biomechanics of tooth-supported RPDs?

A
  • With occlusal loading, vertical seating forces directed down tooth long axis
    *Limited vertical dislodgement
    *Limited horizontal forces on Class III RPD
  • Class III RPDs best resist functional forces
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19
Q

What limits the vertical dislodgement of a tooth-supported RPD?

A

retentive clasp & proximal plates

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20
Q

What are the biomechanics of tooth-tissue supported RPDs?

A

– Subject to greater stress
– Combination of tooth & soft tissue support
– RPD extension movement permits rotational movement around fulcrums in 3 planes

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21
Q

How does rotation in Sagittal Plane around Horizontal Plane Fulcrum happen?

A
  • Fulcrum through rests closest to edentulous areas
  • Inferior-superior denture base movement of the distal end
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22
Q

What occurs when there is rotation in sagittal plane around horizontal plane fulcrum?

A

– Vertical seating force
– Vertical dislodgement force

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23
Q

What concepts allow for resistance to rotation around the horizontal fulcrum?

A
  • Retention: resistance to rotation away from ridge (Vertical dislodgement)
  • Support: resistance to rotation toward ridge (Vertical seating)
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24
Q

What parts of the RPD allow for resistance to rotation around the horizontal fulcrum?

A
  • Retention - Direct retainer, Indirect retainer, Proximal plates
  • Support - Rests, Major connector (Maxillary), Denture base
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25
Q

What occurs when there is rotation in vertical plane around longitudinal/sagittal fulcrum?

A
  • Fulcrum through crest of ridge
  • Rocking or side-to-side movement over the crest of the ridge
26
Q

What concepts allow for resistance to rotation in vertical plane around longitudinal/sagittal fulcrum?

A
  • Stability: resistance to rotation around ridge crest
27
Q

What parts of the RPD allow for resistance to rotation in vertical plane around longitudinal/sagittal fulcrum?

A
  • Rigid connectors
  • Clasps
  • Denture base
28
Q
A

Tooth-supported RPD forces

29
Q

What occurs when there is rotation in the horizontal plane around vertical fulcrum?

A
  • Fulcrum at center of dental arch
  • Horizontal twisting results in buccolingual movement of RPD
30
Q

Where is the fulcrum line through?

A

rest seats

31
Q

What concepts allow for resistance to rotation in the horizontal plane around vertical fulcrum?

A
  • Stability: resistance to horizontal movement
32
Q

What parts of the RPD allow for resistance to rotation in the horizontal plane around vertical fulcrum?

A
  • Minor connectors
  • Proximal plates
  • Rigid portions of clasps
  • Lingual plates
  • Denture base
33
Q

When extension RPD rotates through horizontal fulcrum it acts as a…

A

lever

34
Q

If the RPD acts as a level (horizontal fulcrum) when is the result?

A

deleterious effects on teeth (magnified loading force)

35
Q

______ system can magnify force through mechanical advantage

A

Lever

36
Q

Class I & II levers encountered in what kind of RPDs?

A

tooth-tissue supported (Extension)

37
Q

Fulcrums & levers are not usually a factor in what kind of RPDs?

A

tooth-supported RPDs

38
Q

Class __ lever occurs during rotation around horizontal fulcrum line through terminal rests

A

I

39
Q

Retentive clasp should or should not be anterior to terminal rest fulcrum line?

A

SHOULD NOT

40
Q

What can happen if the retentive clasp is anterior to terminal rest fulcrum line?

A

Detrimental torquing forces applied to abutment

41
Q

What clasp is a class I lever type?

A
  • Distal rest/Distal Guide Plate/Distal extension RPD:
    – Circumferential clasp tip anterior to rest/ fulcrum.
    – Circumferential clasp moves occlusally during function.
    – Directs detrimental distal torquing force to abutment
42
Q

What clasp is a class II level type?

A
  • Mesial rest/Distal Guide Plate/Distal extension RPD:
    – Circumferential clasp tip slightly posterior to rest/fulcrum.
    – Circumferential clasp moves more mesially during function.
    – Clasp tip tends to move into deeper undercut
  • Produces less leverage on abutment than with distal rest.
43
Q

What are the alternatives to class I lever clasps?

A
  1. No clasp
  2. Clasp in less undercut
  3. Non-retentive clasp (tip not in undercut)
  4. Wrought wire clasp
44
Q

_____________ occurs when abutment with retentive clasp anterior to horizontal fulcrum line/axis of rotation (AR) in Class II arch with posterior modification space

A

Class I Lever

45
Q

slide 27-29

A
46
Q

Class I Lever occurs with _______ dislodgement forces

A

Vertical

47
Q

What are the disadvantages of a class I lever?

A
  • Allows greater vertical dislodgement to occur
  • Potential for tissue impingement under mandibular major connector
  • No indirect retention
48
Q

What are the advantages of a class II lever?

A
  • Vertical dislodgement limited
  • Potential for tissue impingement by major connector reduced
  • Indirect retainer present
49
Q

What kind of RPD has no fulcrum or lever?

A

Class III RPD

50
Q

What kind of RPDs have fulcrums and potential levers?

A

Class I, II & long-span IV RPDs (Extension RPDs)

51
Q

What are the characteristics of RPD horizontal fulcrums?

A
  • Longer modification space
  • More complicated
  • 2 fulcrums
52
Q

What are factors Influencing Magnitude of Stress Transmitted to Abutment Teeth?

A
  1. Length of extension span
  2. Quality of Support Ridge
  3. Flexural qualities of clasp
  4. Clasp design
  5. Abutment tooth surface
  6. Occlusal Harmony
53
Q

The length of extension span correlates to the length of the…

A

lever effort arm

54
Q

What type of ridge is better?

A

Broad ridge better support than thin, knife-edge ridge
* Better resistance to both vertical & horizontal force

55
Q

If a clasp is more flexible, _____ stress transmitted to abutments

A

less

56
Q

If a clasp is more flexible, ____ horizontal stability

A

less

57
Q

If a clasp is more flexible, _____ stress transmitted to residual ridge

A

more

58
Q

Flexural qualities of a clasp are determined by…

A
  • Clasp length & diameter
  • Clasp material
59
Q

A disharmonious occlusion may generate ________ forces

A

horizontal

60
Q

When magnified by the factor of RPD leverage, horizontal forces
may be destructive to…

A

abutment teeth & residual ridges

61
Q

What is stress control by RPD design?

A

Forces exerted through RPD can be widely distributed, directed, & minimized by the selection, the design, & the location of the RPD components, in conjunction with the development of harmonious occlusion

RPD (25 decks)

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