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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
Resistance to Rotation Around Horizontal Fulcrum * Support:
resistance to rotation toward ridge (Vertical seating) – RPD components involved * Rests, Major connector (Maxillary), Denture base
26
Rotation in Vertical Plane through Longitudinal/Sagittal Fulcrum (2)
* Fulcrum through crest of ridge * Rocking or side-to-side movement over the crest of the ridge
27
Resistance to Rotation Around Longitudinal Fulcrum * Stability:
resistance to rotation around ridge crest –RPD components involved * Rigid connectors, Clasps, Denture base
28
Rotation in Horizontal Plane through Vertical Fulcrum (2)
* Fulcrum at center of dental arch * Horizontal twisting results in buccolingual movement of RPD
29
Resistance to Rotation Around Vertical Fulcrum * Stability:
resistance to horizontal movement –RPD components involved * Minor connectors, Proximal plates, Rigid portions of clasps, Lingual plates, Denture base
30
Extension RPD Rotation through Horizontal Fulcrum (2)
* RPD functions as a lever * Can result in deleterious effects on teeth –Magnified loading forces
31
Lever Function * Lever system can magnify force through --- advantage
mechanical
32
Class I & II levers encountered in
tooth-tissue supported (Extension) RPDs
33
Fulcrums & levers are not usually a factor in
tooth-supported RPDs
34
Class I lever occurs during
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
Extension RPD Levers: Effect of Rest/Retentive Clasp Positions Class I: * Distal rest/Distal Guide Plate/Distal extension RPD: (3)
– Circumferential clasp tip anterior to rest/ fulcrum. – Circumferential clasp moves occlusally during function. – Directs detrimental distal torquing force to abutment.
36
Extension RPD Levers: Effect of Rest/Retentive Clasp Positions Class II: * Mesial rest/Distal Guide Plate/Distal extension RPD: (3)
– 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
Effect of Abutment Position Class I Lever occurs when abutment with retentive clasp --- to horizontal fulcrum line/axis of rotation (AR) in
anterior Class II arch with posterior modification space.
38
During RPD rotation toward ridge, anterior clasp produces
detrimental torquing force on this abutment.
39
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)
1. No clasp 2. Clasp in less undercut 3. Non-retentive clasp (tip not in undercut) 4. Wrought wire clasp
40
Extension RPD Levers: Effect of Indirect Retention * NO Indirect retention – Class I Lever occurs with – Disadvantages (2)
Vertical dislodgement forces. (Rotation at horizontal fulcrum) * Allows greater vertical dislodgement to occur. * Potential for tissue impingement under mandibular major connector.
41
Extension RPD Levers: Effect of Indirect Retention * Indirect Retainer present – Class II Lever occurs with Limited Vertical dislodgement – Advantages (2)
* Vertical dislodgement limited * Potential for tissue impingement by major connector reduced
42
Class III RPD (2)
– No fulcrums or levers – Design by convenience
43
Class I, II & long-span IV RPDs (Extension RPDs) (2)
– Consideration of rotation toward & away from residual ridge at Horizontal fulcrum – Potential Class I & II Levers
44
Factors Influencing Magnitude of Stress Transmitted to Abutment Teeth (2)
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
1. Length of extension span
– Correlates to length of lever effort arm
46
2. Quality of Support Ridge
– Broad ridge better support than thin, knife- edge ridge * Better resistance to both vertical & horizontal force
47
3. Flexural qualities of clasp (4)
– 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
4. Clasp design (2)
– Clasp passive when completely seated – Reciprocal arm contacts tooth before retentive tip passes height of contour * Neutralize stress from retentive tip
49
5. Abutment tooth surface (1)
– Gold greater frictional resistance to clasp arm movement than enamel * Greater stress on gold restored tooth
50
6. Occlusal Harmony (2)
– 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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