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Fixed Prostodontics 2 > Biomechanics > Flashcards

Biomechanics Flashcards

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
Q

Pontics lying outside the inter-abutment axis act as a lever arm →

A

torqueing movement.

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26
Q

Gain additional resistance in opposite direction from lever arm; How?

A

-Axial grooves

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27
Q

Where would you place axial grooves to gain the additional resistance in preps to the right?

A

–Buccal and Lingual

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28
Q

— Grooves offset dislodgement in response to forces
outside the inter-abutment axis

A

F-L

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29
Q

Canine Replacement (Complex FDP)
(3)

A

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
Q

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 –

A

weak
canine
poor prognosis
restore with implants if possible
(Splint central incisors and premolar / molar)

31
Q

Double abutments help stabilize the prosthesis by

A

distributing forces over
more teeth (do not necessarily increase retention).
–This applies to especially to periodontally weakened teeth

32
Q

Criteria for secondary abutments
(3)

A

-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
Q

Pier Abutment:

A

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

34
Q

Pier Abutment:
Consider the Physiologic tooth movement

A

-Direction and amount varies from anterior to posterior

35
Q

Cause of failure in Peir Abutments is most often a —
(3)

A

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
Q

-Stresses can be concentrated around

A

the abutment teeth
and between retainers and abutment preps

37
Q

-Slight movement in non-rigid connectors can minimize the

A

transfer of stress from the particularly loaded segment to the
rest of the FPD

38
Q

If a non-rigid connector is placed on
the distal side of the retainer on a
middle abutment, movement in a
mesial direction will

A

seat the key into
the keyway.

39
Q

If a non-rigid connector is placed
on the mesial side of the middle
abutment, mesially-directed
movement will

A

un-seat the key.

40
Q

Non-Rigid Connectors - Indications:
(4)

A

-Pier abutment FPD
-Long span FPD with multiple abutments
-Non-parallel abutments – Tipped molar
-Planning for failure

41
Q

Non-Rigid Connectors-Contraindications:
(3)

A

-Long span FPD with two abutments
-Excessively mobile teeth
-Unopposed teeth

42
Q

Non-Rigid Connectors:
(2)

A

-Long span FDP with multiple abutments
-Combined anterior and posterior FDPs

43
Q

Special Considerations: Tilted Molar Abutments
-Discrepancy between
-Long axes of abutment teeth should converge by no more than

A

long axis of molar and premolar abutments
25o - 30o (maximum
angle of tilting) if FPD is made.

44
Q

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)

A

abutments
over-reduced / overtapered (↓ resistance)
the path of insertion
re-contouring or restoration or extraction
orthodontic

45
Q

-Occlusal reduction is not always the same as

A

clearance needed.
-Remove only enough tooth structure to provide necessary space for the restoration.

46
Q

-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

A

retention can be compromised with tilted molar
abutments

47
Q

-An — distributes forces favorably by directing forces in the long axis of the
abutment teeth.

A

FPD

48
Q

Well-aligned abutment teeth provide better support than

A

tipped abutment
teeth.

49
Q

-Non-axial loading (horizontal) often leads to

A

proximal crestal bone loss

50
Q

Molar uprighting (orthodontic movement)
(4)

A

-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
Q

Tilted Molar Abutments - Non-Rigid Connector
-Allows
-Keyway in distal of
premolar to avoid
-Must prepare box in —
of premolar preparation

A

slight movement -short span
intrusion of molar (mesial
seating action)
distal

52
Q

Non-Rigid Connectors:
(2)

A

-Non-parallel abutments –
tipped molar
-Buccal / lingual grooves
parallel with mesial wall
increase resistance form -
molar

53
Q

Proximal Half Crown –

A

does not involve
distal wall
-3/4 crown rotated 90o

54
Q

Proximal Half Crown –
Requirements:
(4)

A

-Caries-free distal surface
-Low incidence of caries
-Even marginal ridge height
-Short span length

55
Q

Tilted Molar Abutments - Copings and Crowns

A

Full crown preparation and
coping with path of insertion in
long axis of tooth.

56
Q

Tilted Molar Abutments - Copings and Crowns
Full coverage crown
compensates for

A

discrepancy
in paths of insertion.

57
Q

Must —reduce molar to
accommodate the thickness of
coping and crown.

A

over

58
Q

WHY would you do this?
(2)

A

Design for failure
Protect tooth (reduced
fracture of crown of
tooth with bridge
stresses

59
Q

Cantilever Fixed Partial Dentures
Primarily only for patients contraindicated for
implants. Why?
(2)

A

-Removing tooth structure on two teeth.
-Occlusal forces create guarded
prognosis

60
Q

Criteria for Cantilever:
(1)

A

-Replace only 1 tooth, and have at least 2
abutments

61
Q

Criteria for abutment teeth: Cantilever
(3)

A

-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
Q

Cantilever Fixed Partial Dentures
(3)

A

-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
Q

Replacement of
Lateral Incisor
-Only the — should be used as a solo abutment
(Why?)

A

canine
Long Root, Esthetics easier, occlusal forces more lateral and therefore protective of
pontic.

64
Q

A Rest can be placed on

A

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
Q

Cantilever Fixed Partial Dentures
(2) is necessary

A

Good clinical crown length / orthodontic position

66
Q

Cantilever FDP:
Replacement of First Premolar
(2)

A

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

67
Q

Cantilever: Premolars
—- rest used to
support premolar
cantilever pontic
-Either cemented or
bonded.

A

Mesial

68
Q

-When using a rest on a cantilever pontic,
place a rest seat in a —
—- can develop due to inadequate
cleansability.

A

restoration on the
abutment.
Caries

69
Q

First molar replacement with cantilever
-Unfavorable prognosis!!
(2)

A

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

70
Q

First molar replacement with cantilever
If absolutely necessary:
(5)

A

-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
Q

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?

A

-Root shape, occlusal
forces
-Occlusal forces
-Occlusal forces

72
Q

What other options could you have
done here to replace #9?
(2)

A

-Conventional bridge from #8-#10
-Single implant
-What else??

Fixed Prostodontics 2 (13 decks)

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