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Fixed Prosth 2 > Biomechanics > Flashcards

Biomechanics Flashcards

1
Q

_____ FPD:

  • -1 or 2 missing teeth
  • -2 abutments
A

Simple FPD

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2
Q 
\_\_\_\_\_\_ FPD:
--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
A

Complex FPD

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3
Q

Abnormal stress created by_____ and _______ create material

failure and tooth failure

A

torque and leverage

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4
Q

What are the 4 Problems caused by bending and deflection?

A
  • Fracture of Porcelain
  • Connector breakage
  • Retainer loosening and subsequent caries
  • ”Unfavorable” tooth or tissue response
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5
Q

The ______ is directly proportional to the cube of

the length of its span.

A

deflection

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6
Q

The deflection is directly _______to the cube of

the length of its span.

A

proportional

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7
Q

Greater span/ interabutment space = _____ deflection

A

Greater deflection

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8
Q

_______ varies inversely by the cube of its

height (thickness).

A

Deflection

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9
Q

Deflection varies inversely by the cube of its

________

A

height (thickness).

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10
Q

The higher the occluso-cervical thickness of the connector, the _____ the FPD flexure

A

Less flexure

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11
Q

–FPD flexure is ______ to connector width

A

proportional

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12
Q

Is the width or height of connector more important to decreasing FPD flexure?

A

height

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13
Q

For PFM, what is the minimum height for connector?

A

3-4 mm

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14
Q

For ceramic FPDs, what is the minimum connector height needed?

A

4 mm

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15
Q

Use a bridge material with _____ yield strength (Yield strength refers to an
indication of maximum stress that can be developed in a material without
causing plastic deformation.)

A

high

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16
Q

_______ refers to an
indication of maximum stress that can be developed in a material without
causing plastic deformation.)

A

(Yield strength

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17
Q

Abutments and retainers in FPD receive ____ dislodging forces
than a single crown

A

greater

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18
Q

Occlusal force on
pontics can cause
______
torque.

A

Mesial-Distal

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19
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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20
Q

Grooves / boxes ______ to dislodgement.

A

increase resistance

21
Q

Is stress more favorable on the max or mand arch to stabilize and decrease likelihood of fracture?

A

Mand arch

22
Q

Canine replacing FPD is not a good idea in ____ arch?

A

Max arch

23
Q 
\_\_\_\_\_\_\_ help stabilize the prosthesis by distributing forces over 
more teeth (do not necessarily increase retention).
A

Double abutments

24
Q 
Double abutments help stabilize the prosthesis by distributing forces over 
more teeth (do not necessarily \_\_\_\_\_\_\_ )
A

increase retention).

25
Q

An edentulous space on both sides of a lone free-standing abutment

A

Pier Abutment:

26
Q

Cause of failure in Peir Abutments is most often a _______
-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)

A

loosened retainer

27
Q

-Stresses can be concentrated around the abutment teeth
and between retainers and abutment preps
-Slight movement in non-rigid connectors can minimize the
transfer of stress from the particularly loaded segment to the
rest of the FPD

A

Non-rigid connectors

28
Q 
If a non-rigid connector is placed on 
the \_\_\_\_\_ side of the retainer on a 
middle abutment, movement in a 
mesial direction will seat the key into 
the keyway.
A

distal

29
Q

If a non-rigid connector is placed
on the _____ side of the middle
abutment, mesially-directed
movement will un-seat the key.

A

mesial

30
Q
  • Indications:
  • Pier abutment FPD
  • Long span FPD with multiple abutments
  • Non-parallel abutments – Tipped molar
  • Planning for failure
A

Non-Rigid Connectors

31
Q
  • Contraindications:
  • Long span FPD with two abutments
  • Excessively mobile teeth
  • Unopposed teeth
A

Non-Rigid Connectors

32
Q

-Long axes of abutment teeth should converge by no more than _____ (maximum
angle of tilting) if FPD is made.

A

25o - 30o

33
Q

-Generally poor abutments
-Mesial wall must be over-reduced / overtapered (↓ resistance)
-Distal adjacent tooth may intrude on the path of insertion
Mesial surface may need re-contouring or restoration or extraction
Consider orthodontic uprighting (3rd molar extraction)

A

Tilted molars

34
Q

-Non-axial loading (horizontal) because of a tilted molar often leads to ________

A

proximal crestal bone loss

35
Q

-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?

A

Molar uprighting (orthodontic movement)

36
Q

If a molar is tilted, where would you have to reduce more occlusally for occlusion to be harmonious?

A

Distal

37
Q 
-Allows slight movement  -
short span
-Keyway in distal of 
premolar to avoid 
intrusion of molar (mesial 
seating action)
-Must prepare box in distal 
of premolar preparation
A

Non rigid connector used to accommodate a tilted molar

38
Q

If a non rigid connector is used, where should grooves/boxes be placed for retention of the FPD?

A

Facial and lingual surfaces

39
Q 
– does not involve 
distal wall
-3/4 crown rotated 90o
Used in case of tilted molars
Requirements:
-Caries-free distal surface
-Low incidence of caries
-Even marginal ridge height
-Short span length
A

Proximal Half Crown

40
Q 
Full crown preparation and 
coping with path of insertion in 
long axis of tooth.
Full coverage crown 
compensates for discrepancy 
in paths of insertion.
Must over-reduce molar to 
accommodate the thickness of 
coping and crown.
WHY would you do this?
Design for failure
Protect tooth (reduced 
fracture of crown of 
tooth with bridge 
stresses
A

Copings

41
Q 
Primarily only for patients contraindicated for 
implants. Why?
-Removing tooth structure on two teeth.
-Occlusal forces create guarded 
prognosis
Criteria :
-Replace only 1 tooth, and have at least 2 
abutments
Criteria for abutment teeth:
-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
A

Cantilever

42
Q

What are the 3 types of forces that can result from a cantilever placed in high occlusion?

A

Down, toward abutment or oblique twisting forces

43
Q

-Only the canine should be used as a solo abutment
(Why?) Long Root, Esthetics easier, occlusal forces more lateral and therefore protective of
pontic.
-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.
-Good clinical crown length / orthodontic position is necessary

A

Replacing lateral incisor

44
Q

Replacement of _______ using cantilever

  • Use full veneer retainers on the 2nd premolar and 1st molar.
  • Limit occlusion on the pontic.
A

First Premolar

45
Q 
-For premolar cantilevers for premolars, \_\_\_\_\_\_ used to 
support premolar 
cantilever pontic
-Either cemented or 
bonded.
A

Mesial rest

46
Q

What’s the 2
biggest problems
with this type of
restoration (mesial rest for PM cantilever?? -

A

OCCLUSION and Caries

47
Q

-Unfavorable prognosis!!
-Extreme leverage forces
generated by posterior position
-Occlusal forces place tensile stress
on 2o retainer

A

First molar cantilever

48
Q 
If absolutely necessary:
-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
A

Cantilever first molar indications

49
Q

-Lateral incisor abutment
-Why is this negative?
-Severe vertical overlap
-Why is this negative?
-Repeated de-cementation with
this particular case.
-Why would this keep
happening?
What other options could you have
done here to replace #9?
-Conventional bridge from #8-#10
-Single implant
-What else??

A

Central incisor cantilever

Fixed Prosth 2 (12 decks)

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