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Fixed Prostodontics 2 > Biomechanics > Flashcards

Biomechanics Flashcards

(72 cards)

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1
Q

Simple FPD:
(2)

A

–1 or 2 missing teeth
–2 abutments

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2
Q

Complex FPD:
(5)

A

–3 or more missing teeth
–Missing Canine
–1,3, or greater than three abutments
Splinted, pier, cantilever
–Non-parallel abutments
–Combined anterior and posterior FPD

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3
Q

FPD Failure
Abnormal stress created by (2) create material
failure and tooth failure

A

torque and leverage

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4
Q

”Failure in FPD’s are more due to biomechanical factors like:
(5)

A

–caries
–gingival inflammation
–poor framework design
–poor occlusion
–material failure.”

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5
Q

Problems caused by bending and deflection
Problems caused by bending and deflection
(4)

A

Problems caused by bending and deflection
-Fracture of Porcelain
-Connector breakage
-Retainer loosening and subsequent caries
-”Unfavorable” tooth or tissue response

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6
Q

Law of Beams

A

-Deflection = Load (Length)^3
4e Width (Height)^3

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7
Q

The deflection is directly proportional to the

A

cube of
the length of its span.

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8
Q

FPD flexure varies directly by — where x is the inter-
abutment distance.

A

x^3

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9
Q

Deflection varies — by the cube of its
height (thickness).

A

inversely

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10
Q

Deflection =

A

Load (Length)^3
4e Width (Height)^3

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11
Q

FPD flexure varies — by t^3 where
t is the occluso-cervical thickness of
the connector

A

inversely

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12
Q

1/2t = – times increase in flexure
1/3t = – times increase in flexure

A

8
27

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13
Q

Connector Design – Rigid vs Non-Rigid
Rigid =

A

Cast or Soldered

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14
Q

Connector requirements – O-C Height vs F-L Width
-Minimum Height (Metal):
-Minimum Height x Width (ceramic/Zirconia):

A

3-4mm x 3-4 mm
4mm x 4mm

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15
Q

Pontic/Connector design needs adequate O-C thickness
-How do you know what’s adequate?

A

-Wax up and complete abutment evaluation to see what connector
measurements are possible.

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16
Q

Use a bridge material with high yield strength (Yield strength refers to an

A

indication of maximum stress that can be developed in a material without
causing plastic deformation.)
-Zirconia with appropriate size or a PFM alloy with high yield strength

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17
Q

If concerns exist with connector strength, consider using

A

an adhesive cement
(bond) for increased retention on abutments

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18
Q

Abutments and retainers receive — dislodging forces
than a single crown

A

greater

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19
Q

Modify preparations to increase

A

retention and resistance
form / structural durability

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20
Q

Place — in response to direction of
anticipated torque

A

boxes / grooves

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21
Q

Occlusal force on
pontics can cause

A

Mesial-Distal
torque.

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22
Q

Forces at an oblique
angle or outside the
center of the restoration
cause

A

F-L torque (around
M-D axis of rotation) .

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23
Q

Grooves / boxes increase resistance to dislodgement.
(2)

A

-Place boxes / grooves in response to direction of anticipated
torque.
-Perpendicular to the movement around the axis of rotation

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24
Q

skipped
Use retainer with appropriate retention / resistance
(2)

A

-Wall length / occlusal convergence / geometric resistance
form
-Consider adhesive cement (bonding) for ↑ retention.

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25
Pontics lying outside the inter-abutment axis act as a lever arm →
torqueing movement.
26
Gain additional resistance in opposite direction from lever arm; How?
-Axial grooves
27
Where would you place axial grooves to gain the additional resistance in preps to the right?
–Buccal and Lingual
28
--- Grooves offset dislodgement in response to forces outside the inter-abutment axis
F-L
29
Canine Replacement (Complex FDP) (3)
Canine pontic lies outside the inter-abutment axis Stress is greater and therefore less favorable on maxillary arch Forces inside arch push the pontic buccally (weak - tension) Stress more favorable in mandibular arch Forces outside arch act to seat the pontic (strong – compression)
30
Canine Replacement FDP Pontic lies outside the inter-abutment axis Adjacent teeth (Lateral and 1st premolar) are --- abutments Should not replace more than one additional tooth when replacing a --- Canine plus 2 contiguous teeth –
weak canine poor prognosis restore with implants if possible (Splint central incisors and premolar / molar)
31
Double abutments help stabilize the prosthesis by
distributing forces over more teeth (do not necessarily increase retention). --This applies to especially to periodontally weakened teeth
32
Criteria for secondary abutments (3)
-Root surface area and C:R must equal to the primary abutments --Secondary retainers must have greater than or equal to retention of primary retainers --Long crown length and adequate interproximal space for connectors
33
Pier Abutment:
An edentulous space on both sides of a lone free-standing abutment
34
Pier Abutment: Consider the Physiologic tooth movement
-Direction and amount varies from anterior to posterior
35
Cause of failure in Peir Abutments is most often a --- (3)
loosened retainer -Prosthesis flexure creating movement of teeth -Tensile stresses between terminal retainers and abutments; intrusion of abutments under loading -Differences in retentive capacities between abutments (relative to size)
36
-Stresses can be concentrated around
the abutment teeth and between retainers and abutment preps
37
-Slight movement in non-rigid connectors can minimize the
transfer of stress from the particularly loaded segment to the rest of the FPD
38
If a non-rigid connector is placed on the distal side of the retainer on a middle abutment, movement in a mesial direction will
seat the key into the keyway.
39
If a non-rigid connector is placed on the mesial side of the middle abutment, mesially-directed movement will
un-seat the key.
40
Non-Rigid Connectors - Indications: (4)
-Pier abutment FPD -Long span FPD with multiple abutments -Non-parallel abutments – Tipped molar -Planning for failure
41
Non-Rigid Connectors-Contraindications: (3)
-Long span FPD with two abutments -Excessively mobile teeth -Unopposed teeth
42
Non-Rigid Connectors: (2)
-Long span FDP with multiple abutments -Combined anterior and posterior FDPs
43
Special Considerations: Tilted Molar Abutments -Discrepancy between -Long axes of abutment teeth should converge by no more than
long axis of molar and premolar abutments 25o - 30o (maximum angle of tilting) if FPD is made.
44
Special Considerations: Tilted Molar Abutments -Generally poor --- -Mesial wall must be -Distal adjacent tooth may intrude on Mesial surface may need Consider --- uprighting (3rd molar extraction)
abutments over-reduced / overtapered (↓ resistance) the path of insertion re-contouring or restoration or extraction orthodontic
45
-Occlusal reduction is not always the same as
clearance needed. -Remove only enough tooth structure to provide necessary space for the restoration.
46
-Occlusal reduction is not always the same as clearance needed. -Remove only enough tooth structure to provide necessary space for the restoration. -Allows for longer axial wall length because
retention can be compromised with tilted molar abutments
47
-An --- distributes forces favorably by directing forces in the long axis of the abutment teeth.
FPD
48
Well-aligned abutment teeth provide better support than
tipped abutment teeth.
49
-Non-axial loading (horizontal) often leads to
proximal crestal bone loss
50
Molar uprighting (orthodontic movement) (4)
-Places abutment in better position for preparation -Distributes forces under loading through long axis of tooth (helps prevent/eliminate mesial bony defects) -Enables replacement of optimum occlusion -Requires EXCELLENT communication and treatment planning skills to educate patient. Often extra 1-2 years of ortho prior to bridge placement. And then maybe an implant would be better? Hmm....
51
Tilted Molar Abutments - Non-Rigid Connector -Allows -Keyway in distal of premolar to avoid -Must prepare box in --- of premolar preparation
slight movement -short span intrusion of molar (mesial seating action) distal
52
Non-Rigid Connectors: (2)
-Non-parallel abutments – tipped molar -Buccal / lingual grooves parallel with mesial wall increase resistance form - molar
53
Proximal Half Crown –
does not involve distal wall -3/4 crown rotated 90o
54
Proximal Half Crown – Requirements: (4)
-Caries-free distal surface -Low incidence of caries -Even marginal ridge height -Short span length
55
Tilted Molar Abutments - Copings and Crowns
Full crown preparation and coping with path of insertion in long axis of tooth.
56
Tilted Molar Abutments - Copings and Crowns Full coverage crown compensates for
discrepancy in paths of insertion.
57
Must ---reduce molar to accommodate the thickness of coping and crown.
over
58
WHY would you do this? (2)
Design for failure Protect tooth (reduced fracture of crown of tooth with bridge stresses
59
Cantilever Fixed Partial Dentures Primarily only for patients contraindicated for implants. Why? (2)
-Removing tooth structure on two teeth. -Occlusal forces create guarded prognosis
60
Criteria for Cantilever: (1)
-Replace only 1 tooth, and have at least 2 abutments
61
Criteria for abutment teeth: Cantilever (3)
-Long roots w/ good configuration -Long clinical crown -Resistance form for preparations O-C height for connectors w/o impinging on interdental papilla -Favorable crown:root ratio and healthy periodontium
62
Cantilever Fixed Partial Dentures (3)
-Occlusal forces on standard FPD direct forces along long axis of abutment teeth. -Cantilever pontic without abutment root directs occlusal forces apically putting both vertical and lateral forces on abutments. -Abutment choice is VERY important!
63
Replacement of Lateral Incisor -Only the --- should be used as a solo abutment (Why?)
canine Long Root, Esthetics easier, occlusal forces more lateral and therefore protective of pontic.
64
A Rest can be placed on
mesial of pontic against a rest prep in a restoration in the distal of the central incisor or slight wrap-around of proximal contact.
65
Cantilever Fixed Partial Dentures (2) is necessary
Good clinical crown length / orthodontic position
66
Cantilever FDP: Replacement of First Premolar (2)
-Use full veneer retainers on the 2nd premolar and 1st molar. -Limit occlusion on the pontic.
67
Cantilever: Premolars ---- rest used to support premolar cantilever pontic -Either cemented or bonded.
Mesial
68
-When using a rest on a cantilever pontic, place a rest seat in a --- ---- can develop due to inadequate cleansability.
restoration on the abutment. Caries
69
First molar replacement with cantilever -Unfavorable prognosis!! (2)
-Extreme leverage forces generated by posterior position -Occlusal forces place tensile stress on 2o retainer
70
First molar replacement with cantilever If absolutely necessary: (5)
-Pontic size small (premolar) -Light occlusal contact; no excursive contact -Pontic and connector need maximum O-G height for rigidity -Good crown:root ratio of abutments -Clinical crowns - maximum preparation length and resistance form
71
Central incisor replacement with cantilever Pontic -Unfavorable Prognosis!!: 1. Lateral incisor abutment -Why is this negative? 2. Severe vertical overlap -Why is this negative? 3. Repeated de-cementation with this particular case. -Why would this keep happening?
-Root shape, occlusal forces -Occlusal forces -Occlusal forces
72
What other options could you have done here to replace #9? (2)
-Conventional bridge from #8-#10 -Single implant -What else??

Fixed Prostodontics 2 (13 decks)

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