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Removable Partial Dentures > 14- Biomechanics and Principles of RPD Design > Flashcards

14- Biomechanics and Principles of RPD Design Flashcards

1
Q

what does biomechanics consider

A

mechanical forces exerted on RPD during functional and 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 via:

A
  • abutment teeth and 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 are deleterious forces

A
  • off axis
  • torque
  • horizontal
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5
Q

excess force may result in:

A
  • mucosal ulcerations
  • bone resorption
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6
Q

what are the forces acting on RPD

A
  • vertical (dislodging)
  • horizontal (lateral)
  • vertical (seating)
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7
Q

what are the requirements of RPD

A
  • retention: resistance to dislodging
  • stability: resistance to horizontal
  • support: resistance to vertical seating
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8
Q

what are the RPD components involved in retention

A
  • direct retainer- retentive clasp
  • indirect retainer
  • proximal plates (friction)
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9
Q

what are the RPD components involved in stability

A
  • minor connectors
  • proximal plates
  • lingual plates
  • denture bases
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10
Q

what are the RPD components involved in support

A
  • rests
  • major connectors: maxillary tooth tissue supported RPD
  • denture bases
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11
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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12
Q

RPDs true reciprocation can only be achieved if:

A

the reciprocating element touches the tooth before the retentive clasp

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13
Q

what class RPD best resists functional forces

A

class III

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14
Q

what helps vertical seating forces direct down tooth long axis with occlusal loading

A

occlusal rests adjacent to edentulous area

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15
Q

describe horizontal and vertical forces in tooth supported RPD

A
  • limited vertical dislodgment- counteract through retentive clasp and proximal plates
  • limited horizontal forces on class III RPD
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16
Q

describe class I, II and long span IV RPDs

A
  • subject to greater stress
  • combination of tooth and soft tissue support
  • RPD extension movement permits rotational movement around fulcrums in 3 planes
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17
Q

where is the horizontal plane fulcrum

A

through rests closest to edentulous area

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18
Q

where does rotation in sagittal plane around horizontal plane fulcrum occur

A
  • inferior- superior denture base movement of the distal end
  • vertical seating force
  • vertical dislodgment force
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19
Q

what helps resistance to rotation around the horizontal fulcrum

A
  • retention: resistance to rotation away from ridge (vertical dislodgment)
  • support: resistance to rotation towards ridge (vertical seating)
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20
Q

what are the RPD components involved in retention in the horizontal fulcrum

A

-direct retainer
- indirect retainer
- proximal plates

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21
Q

what are the RPD components involved in support in the horizontal fulcrum

A

-rests
- major connector in maxillary
- denture base

22
Q

describe rotation in vertical plane through longitudinal/sagittal fulcrum

A
  • fulcrum through crest of ridge
  • rocking or side- to- side movement over the crest of the ridge
23
Q

what principle is involved in resistance to rotation around longitudinal fulcrum and what components are involved

A
  • stability- resistance to rotation around ridge crest
  • rigid connectors, clasps, denture base
24
Q

describe rotation in horizontal plane through vertical fulcrum

A
  • fulcrum at center of dental arch
  • horizontal twisting results in buccolingual movement of RPD
25
what principle is involved in resistance to rotation in vertical fulcrum
- stability - minor connectors, proximal plates, rigid portions of clasps, lingual plates, denture base
26
what does the RPD function as and in horizontal fulcrum and what can this result in
- lever - can result in deleterious effects on teeth
27
lever system can magnify force through:
mechanical advantage
28
what is the formula for mechanical advantage
effort arm/ resistance arm
29
what is the order of resistance arm, fulcrum and effort arm in a class I lever from left to right
- resistance arm (going up) - fulcrum on bottom - effort arm (going down)
30
what is the order of resistance arm, fulcrum and effort arm in a class II lever from left to right
- fulcrum on bottom - resistance arm ( going up) - effort arm (going up)
31
what is the order of resistance arm, fulcrum and effort arm in a class III lever from left to right
- resistance arm (going up and out) - effort arm (going up and out) - fulcrum on top
32
when are class I and II levers encountered
in tooth tissue supported RPDs
33
retentive clasp should not be: and why
anterior to terminal rest fulcrum line - detrimental torquing forces applied to abutment
34
in class I lever, distal rest/distal guide palte/distal extension RPD
- circumferential clasp tip anterior to rest/fulcrum - circumferential clasp moves occlusally during function - directs detrimental distal torquing force to abutment
35
in class II lever, 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 deeper underuct: produces less leverage on abutment than with distal rest
36
during RPD rotation toward ridge what produced detrimental torquing forces on the abutment
the anterior clasp
37
what are the alternatives to effect of abutment position
- no clasp - clasp in less undercut - non retentive claso - wrought wire clasp
38
what is the effect of no indirect retention on extension RPD levers
class 1 lever occurs with vertical dislodgment
39
what are the disadvantages of no indirect retention in extension RPD levers
- allows greater vertical dislodgment to occur - potential for tissue impingement under mandibular major connector
40
what are the effects of the presence of an indirect retainer in extension RPD levers
- class II lever occurs with limited vertical dislodgment
41
what are the advantages of indirect retainers in extension RPD levers
- vertical dislodgment limited - potential for tissue impingement by major connector reduced
42
what are the factors influencing magnitude of stress transmitted to abutment teeth
- length of extension span - quality of support ridge - flexural qualities of clasp - clasp design - abutment tooth surface - occlusal harmony
43
what does the length of extension span correlate to
length of lever effort arm
44
which has better support: broad ridge or thin, knife edge ridge
broad ridge
45
more flexible the clasp:
- less stress transmitted to abutments - less horizontal stability - more stress transmitted to residual ridge
46
what are flexural qualities determined by
- clasp length and diameter - clasp material
47
describe the ideal clasp design
- clasp passive when completely seated - reciprocal arm contacts tooth before retentive tip passes height of contour - neutralize stress from retentive tip
48
which material has greater frictional resistance to clasp arm movement than enamel
gold
49
greater ____ on gold restored tooth
stress
50
what does a disharmonious occlusion generate
- horizontal forces - may be destructive to abutment teeth and residual ridges
51
describe stress control by RPD design
forces exerted through RPD can be widely distributed, directed and minimized by the selection, the design and the location of the RPD components in conjunction with the development of harmonious occlusion

Removable Partial Dentures (21 decks)

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