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rpd > Biomechanics of Removable Partial Dentures > Flashcards

Biomechanics of Removable Partial Dentures Flashcards

1
Q

Biomechanics

A
  • Application of mechanical engineering
    principles in the living organism
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2
Q

Mechanical forces exerted on RPD during
functional & parafunctional mandibular
movements should be properly directed to

A

the supporting tissue to elicit the most
favorable response.

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3
Q

RPD Supporting Structures
* Alveolar bone provides support via:
(2)

A

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

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4
Q

RPD Tooth Support
* Teeth better able to tolerate — forces:
down long-axis

A

vertical
– More PDL fibers activated
to resist force

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5
Q

RPD Alveolar Support
* Excess force may result in:
(2)

A

– Mucosal ulcerations
– Bone resorption

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6
Q

Forces Acting on RPD
(3)

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

Requirements of RPD
* Retention:
–Resistance to —
* Stability:
–Resistance to —
* Support:
–Resistance to —

A

dislodging
horizontal
vertical seating

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8
Q

Retention:

A

Resistance to Vertical
dislodging forces

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9
Q

Retention: Resistance to Vertical
dislodging forces
* RPD components involved
(3)

A

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

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10
Q

Requirements of RPDs (continued)
* Stability:

A

Resistance to horizontal, lateral,
or torsional forces

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11
Q
  • Stability:
  • RPD components involved
    (4)
A

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

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12
Q

Requirements of RPDs (continued)
* Support:

A

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

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13
Q
  • Support:
  • RPD components involved
    (3)
A

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

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14
Q

Reciprocation:

A

is 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

A

touches the tooth
before the retentive clasp.

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16
Q

Tooth-supported RPD
(2)

A

– Abutment teeth support RPD
– Class III & IV RPD

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17
Q

Tooth-tissue supported RPD
(2)

A

– Denture base is supported
by both teeth & residual ridge
– Class I, II, long-span IV RPDs

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18
Q

Class — RPDs best resist functional forces

A

III

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19
Q

Tooth-supported RPD Forces
With occlusal loading, — seating forces
directed down tooth long axis
– Occlusal rests adjacent
to edentulous area

A

vertical

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20
Q

Tooth-supported RPD Forces
Limited (2)

A

*Limited vertical dislodgement
–Counteract through retentive clasp & proximal plates
*Limited horizontal forces on Class III RPD

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21
Q

Tooth-tissue supported RPD Forces
* Class I, II, & long-span IV RPDs
(3)

A

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

22
Q

Rotation in Sagittal Plane around
Horizontal Plane Fulcrum
(2)

A
  • Fulcrum through rests closest to
    edentulous areas
  • Inferior-superior denture base
    movement of the distal end
23
Q

Rotation in Sagittal Plane around
Horizontal Plane Fulcrum
* Occurs:
(2)

A

– Vertical seating force
– Vertical dislodgement
force

24
Q

Resistance to Rotation Around
Horizontal Fulcrum
* Retention:

A

resistance to rotation away from
ridge (Vertical dislodgement)
– RPD components involved
* Direct retainer, Indirect retainer, Proximal plates

25
Q

Resistance to Rotation Around
Horizontal Fulcrum
* Support:

A

resistance to rotation toward ridge
(Vertical seating)
– RPD components involved
* Rests, Major connector (Maxillary), Denture base

26
Q

Rotation in Vertical Plane through
Longitudinal/Sagittal Fulcrum
(2)

A
  • Fulcrum through crest of ridge
  • Rocking or side-to-side movement over the
    crest of the ridge
27
Q

Resistance to Rotation Around
Longitudinal Fulcrum
* Stability:

A

resistance to rotation around
ridge crest
–RPD components involved
* Rigid connectors, Clasps, Denture base

28
Q

Rotation in Horizontal Plane through
Vertical Fulcrum
(2)

A
  • Fulcrum at center of dental arch
  • Horizontal twisting results in buccolingual
    movement of RPD
29
Q

Resistance to Rotation Around
Vertical Fulcrum
* Stability:

A

resistance to horizontal
movement
–RPD components involved
* Minor connectors, Proximal plates, Rigid
portions of clasps, Lingual plates, Denture
base

30
Q

Extension RPD Rotation through
Horizontal Fulcrum
(2)

A
  • RPD functions as a lever
  • Can result in deleterious effects on
    teeth
    –Magnified loading forces
31
Q

Lever Function
* Lever system can magnify force through
— advantage

A

mechanical

32
Q

Class I & II levers encountered in

A

tooth-tissue
supported (Extension) RPDs

33
Q

Fulcrums & levers are not usually a factor in

A

tooth-supported RPDs

34
Q

Class I lever occurs during

A

rotation around
horizontal fulcrum line through terminal
rests. (Rotation toward ridge)
* Retentive clasp should NOT be anterior to
terminal rest fulcrum line.
– Detrimental torquing forces applied to
abutment.

35
Q

Extension RPD Levers:
Effect of Rest/Retentive Clasp Positions
Class I:
* Distal rest/Distal Guide Plate/Distal extension RPD:
(3)

A

– Circumferential clasp tip anterior to rest/ fulcrum.
– Circumferential clasp moves occlusally during function.
– Directs detrimental distal torquing force to abutment.

36
Q

Extension RPD Levers:
Effect of Rest/Retentive Clasp Positions
Class II:
* Mesial rest/Distal Guide Plate/Distal extension RPD:
(3)

A

– 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 res

37
Q

Effect of Abutment Position
Class I Lever occurs when abutment with retentive clasp
— to horizontal fulcrum line/axis of rotation (AR) in

A

anterior
Class II arch with posterior modification space.

38
Q

During RPD rotation toward ridge,
anterior clasp produces

A

detrimental
torquing force on this abutment.

39
Q

Extension RPD Levers:
Effect of Abutment Position
Class I Lever occurs when abutment with retentive clasp
anterior to horizontal fulcrum line/axis of rotation (AR) in
Class II arch with posterior modification space.
During RPD rotation toward ridge,
anterior clasp produces detrimental
torquing force on this abutment.
Alternatives:
(4)

A
  1. No clasp
  2. Clasp in less undercut
  3. Non-retentive clasp (tip not in undercut)
  4. Wrought wire clasp
40
Q

Extension RPD Levers:
Effect of Indirect Retention
* NO Indirect retention
– Class I Lever occurs with
– Disadvantages
(2)

A

Vertical dislodgement
forces. (Rotation at horizontal fulcrum)

  • Allows greater vertical dislodgement to occur.
  • Potential for tissue impingement under mandibular
    major connector.
41
Q

Extension RPD Levers:
Effect of Indirect Retention
* Indirect Retainer present
– Class II Lever occurs with Limited Vertical
dislodgement
– Advantages
(2)

A
  • Vertical dislodgement limited
  • Potential for tissue impingement by major
    connector reduced
42
Q

Class III RPD
(2)

A

– No fulcrums or levers
– Design by convenience

43
Q

Class I, II & long-span IV RPDs (Extension
RPDs)
(2)

A

– Consideration of rotation toward & away from
residual ridge at Horizontal fulcrum
– Potential Class I & II Levers

44
Q

Factors Influencing Magnitude of Stress
Transmitted to Abutment Teeth
(2)

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
45
Q
  1. Length of extension span
A

– Correlates to length of lever effort arm

46
Q
  1. Quality of Support Ridge
A

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

47
Q
  1. Flexural qualities of clasp
    (4)
A

– More flexible, less stress transmitted to
abutments
– More flexible, less horizontal stability
– More flexible, more stress transmitted to
residual ridge
– Flexural qualities determined by:
* Clasp length & diameter
* Clasp material

48
Q
  1. Clasp design
    (2)
A

– Clasp passive when completely seated
– Reciprocal arm contacts tooth before
retentive tip passes height of contour
* Neutralize stress
from retentive tip

49
Q
  1. Abutment tooth surface
    (1)
A

– Gold greater frictional resistance to clasp arm movement
than enamel
* Greater stress on gold restored tooth

50
Q
  1. Occlusal Harmony
    (2)
A

– A disharmonious occlusion may generate horizontal forces
– When magnified by the factor of RPD leverage, these forces
may be destructive to abutment teeth & residual ridges

rpd (22 decks)

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