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Fixed Prosthodontics II > L2- Biomechanics and FPD Problems > Flashcards

L2- Biomechanics and FPD Problems Flashcards

1
Q

What are the two types of FPDs?

A

Simple FPD & Complex FPD

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2
Q

List the parameters for a simple FPD:

A
  • 1 or 2 missing teeth
  • 2 abutments
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3
Q

If someone has two abutments they would be a candidate for a:

A

simple FPD

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4
Q

If someone has only 2 missing teeth, they would be a candidate for a:

A

simple FPD

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5
Q

List the parameters for a complex FPD:

A
  • 3 or more missing teeth
  • missing canine
  • 1, 3, or greater than 3 abutments
  • splinted, pier, cantilever
  • non-parallel abutments
  • combined anterior and posterior FPD
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6
Q

Would the following image be classified as simple or complex?

A

simple FPD

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7
Q

Would the following image be classified as simple or complex?

A

complex FPD

(replacing more than 3 teeth)

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8
Q

Would the following image be classified as simple or complex?

A

complex FPD

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9
Q

Would the following image be classified as simple or complex?

A

complex FPD

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10
Q

Abnormal stress created by tongue and leverage create:

A

material failure and tooth failure

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11
Q

Failure in FPD’s are more due to ____ factors such as:

A

Biomechanical
- caries
- gingival inflammation
- poor framework design
- poor occlusion
- material failure

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12
Q

Bending or deflection of the FPD is a result of:

A

abnormal stress

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13
Q

List the problems caused by bending and deflection:

A
  1. fracture of porcelain
  2. connector breakage
  3. retainer loosening and subsequent caries
  4. “unfavorable” tooth or tissue response
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14
Q

In this image we see that the connector is broken, this is likely due to:

A

flexure

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15
Q

The law of beams states that:

A

Deflection = Load (length) ^3 / 4e Width (Height) ^3

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16
Q

According to the law of beams, the deflection is ____ proportional to the cube of the length of its span

A

directly

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17
Q

According to the law of beams, the ___ is directly proportional to the cube of the length of its span

A

deflection

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18
Q

FPD flexure varies directly by x^3 where x is the:

A

inter abutment distance

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19
Q

Increased pontics = increased length -

A

increased deflection

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20
Q

If 1p results in a deflection of x; 2p results in a deflection of __x, and 3p results in a deflection of __x

A

8x; 27x

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21
Q

Deflection varies ___ by the cube of its height (thickness)

A

inversely

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22
Q

____ varies inversely by the cube of its height

A

defelction

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23
Q

FPD flexure varies inversely by t^3 where t is the:

A

occlusal-cervical thickness of the connector

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24
Q

1/2t= ___ times increase in flexure
1/3t= ___times increase in flexure

A

8 times
27 times

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25
Q

Achieving the connector height needed can be:

A

clinically challenging

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26
Q

When achieving the connector height, what dimensions must be considered?

A
  1. FL
  2. occlusal cervical
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27
Q

A connector can be:

A

rigid or non-rigid

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28
Q

A rigid connector is:

A

cast or soldered

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29
Q

Connector requirements include:

A
  1. OC height
  2. FL width
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30
Q

The minimum height for a metal (rigid) connector =

A

3-4mm x 3-4 mm

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31
Q

The minimum height x width for a ceramic/zirconia (rigid) connector =

A

4mm x 4mm

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32
Q

The Pontic/connector design needs an adequate ___ thickness

A

O-C

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33
Q

How can you determine if a Pontic/connector design has an adequate OC thickness?

A

wax up and complete abutment evaluation to see what connector measurements are possible

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34
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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35
Q

Yield strength refers to an indication of ____ that can be developed in a material without causing plastic deformation

A

maximum stress

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36
Q

T/F: You should use a bridge lateral with intermediate yield strength

A

False-high yield strength

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37
Q

If concerns exist with connector strength, considering using an ____ for increased retention on abutments

A

adhesive cement (bond)

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38
Q

Why might you use an adhesive cement (bond) with a connector?

A

for increased retention on abutments

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39
Q

T/F: Abutments and retainers receive greater dislodging forces than a single crown

A

True

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40
Q

Where should boxes and grooves be placed in regards to the connector design?

A

in response to direction of anticipated torque

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41
Q

Occlusal forces on pontics can cause:

A

medial-distal torque

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42
Q

With a downward force on the middle two units, what results?

A

MD Torque

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43
Q

Forces at an oblique angle or outside the center of the restoration as seen in the image below causes ____ around the ____ axis of rotation

A

FL torque; MD

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44
Q

Grooves/Boxes ____ resistance to enlargement

A

increase

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45
Q

When placing boxes & groove to increase resistance to dislodgment, place them in response to:

A

director of anticipated torque

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46
Q

Ideally you would place boxes and grooves in response to direction of anticipated torque, this is located:

A

perpendicular to the movement around the axis of rotation

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47
Q

What features aid in the appropriate retention and resistance of a retainer?

A
  1. wall length
  2. occlusal convergence
  3. geometric resistance form
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48
Q

Adhesive cement (bonding) can be considered for increased:

A

retention

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49
Q

Pontics lying outside the inter-abutment axis act as a ____ resulting in ____

A

lever arm; torquing movement

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50
Q

How might you gain additional resistance in opposite direction from lever arm?

A

axial grooves

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51
Q

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

A

buccal & lingual

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52
Q

____ offset dislodgment in response to forces outside the inter-abutment axis

A

facial & lingual grooves

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53
Q

What would this grooves in this image offset?

A

dislodgment in response to forces outside the inter-abutment axis

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54
Q

If a canine has to be replaced, this is considered:

A

complex FPD

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55
Q

Canine pontics lie:

A

outside the inter abutment axis

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56
Q

Because canine pontics lie outside the inter abutment axis, ____ is greater and therefore:

A

stress; less favorable on maxillary arch

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57
Q

Forces inside the arch push the canine pontic ___ resulting in ___

A

bucally; weak-tension

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58
Q

Is a canine Pontic more favorable in the maxillary or mandibular arch?

A

mandibular

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59
Q

Why is a canine Pontic more favorable in the mandibular arch?

A

Because forces outside the arch act to seat the Pontic (strong- compression)

(stress more favorable in mandibular arch)

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60
Q

Canines are considered to be complex because when you bite on the maxillary canine, this tooth wants to be forces ____, putting pressure on ____

A

outward; lateral & premolar

61
Q

For mandibular canines, the occlusal force is being pushed:

A

inward towards the arch

62
Q

T/F: For a maxillary canine replacement, the Pontic lies outside the inter-abutment axis

A

true

63
Q

For canine replacement, the adjacent teeth (lateral and premolar) serve as:

A

weak abutments

64
Q

When replacing a canine, you should not replace:

A

more than one additional tooth

65
Q

Canine + 2 contiguous teeth=

A

poor prognosis

66
Q

Canine + 2 contiguous teeth = poor prognosis so you should instead try to restore with:

A

implants when possible

(splint central incisors and premolar/molar)

67
Q

Double abutments may also be referred to as:

A

splinting

68
Q

What can help problems caused by poor crown/root ratio and long spans?

A

splinting (double abutments)

69
Q

Double abutments (splinting) helps stabilize the prosthesis by:

A

distributing forces over more teeth (does not necessarily increase retention)

70
Q

Double abutments (splinting) helps to stabilize the prosthesis by distributing forces over more teeth (though it does not necessarily increase retention). This applies especially to:

A

periodontally weakened teeth

71
Q

List the criteria for secondary abutments:

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
72
Q

When we have a tooth in between two pontics:

A

pier abutment

73
Q

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

A

pier abutment

74
Q

When considering the physiologic tooth movement, direction and amount varies from:

A

anterior to posterior

75
Q

The cause of failure in Pier abutments is most often a:

A

loosened retainer

76
Q

List three causes of a loosened retainer in a pier abutment:

A
  1. PROSTHESIS FLEXURE creatine movement of teeth
  2. TENSILE STRESSES between terminal retainers and abutments (intrusion of abutments under loading)
  3. DIFFERENCE IN RETENTIVE CAPACITIES between abutments (relative to size)
77
Q

The following image shows:

A

pier abutment bridge

78
Q

_____ in non-rigid connectors can minimize the transfer of stress from the particularly loaded segments to the rest of the pier abutment FPD

A

slight movement

79
Q

A ____ or ____ can minimize problems often encountered with pier abutments

A

nonrigid connector or cantilever

80
Q

What does the key in the image function to do?

A

it will allow some movement so the bridge isnt taking so much force, as well as removes stress

81
Q
A
82
Q

When making a pier abutment with a NON-RIGID connector, the key is put on the ____ of the pier abutment

A

distal

83
Q

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

A

seat the key into the key way

84
Q

If a non-rigid connector is placed on the ____ side of the retainer on a middle abutment, movement in the mesial direction will seat the key into the keyway

A

distal

85
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

86
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

87
Q

What does the arrow indicate in the following image?

A

pier abutment with decay; pier abutments are hard to clean under

88
Q

Non-rigid connector indications include:

A
  1. pier abutment FPD
  2. long span FPD with multiple abutments
  3. non-parallel abutments (tipped molar)
  4. planning for failure
89
Q

Non-rigid connector contraindications include:

A
  1. long span FPD with two abutments
  2. excessively mobile teeth
  3. unopposed teeth
90
Q

Why are unopposed teeth a contraindication for non-rigid connectors?

A

no occlusal forces so you wouldn’t need a key way

91
Q

The follow are reasons you (should/should not) choose a NON-RIGID connector:

  1. long span FPD with two abutments
  2. excessively mobile teeth
  3. unopposed teeth
A

should not!

92
Q

The follow are reasons you (should/should not) choose a NON-RIGID connector:

  1. pier abutment FPD
  2. long span FPD with multiple abutments
  3. non-parallel abutments (tipped molar)
  4. planning for failure
A

should!

93
Q

If you have to bridge 18-20 and only have two abutments , what option would be CONTRAINDICATED?

A

non-rigid connector

94
Q
  • Long span FPD with multiple abutments
  • Combined anterior and posterior FPDs

These would be reasons to choose a:

A

pier abutments with non-rigid connectors

95
Q

What step is essential I the case of a pier abutment with a non-rigid connector?

A

metal framework try in

96
Q

What is seen in the following image?

A

Pier-abutment

97
Q

What is seen in the following image?

A

pier-abutment with non-rigid connector

98
Q

What can be noted in this case?

A

pretty significant difference in path of insertions (due to tipped molar)

99
Q

Long axes of abutment teeth should converge by NO MORE than: _____ (maximum angle of tilting) if FPD is made

A

25-30 degrees

100
Q

Tilted molars are generally ____ abutments

A

poor

101
Q

With a tilted molar as an abutment tooth, the ___ must be over-reduced/ overtapered which results in ___.

A

mesial wall; decreased resistance

102
Q

With a tipped molar abutment tooth, ____ may intrude on the path of insertion and require mesial surface re-contouring or extraction

A

adjacent tooth

103
Q

With a tilted molar as an abutment tooth, if the distal adjacent tooth intrudes on the path of insertion, what might some options be?

(consider tilted molar and adjacent tooth)

A
  1. orthodontic uprighting of tilted molar
  2. mesial surface re-contouring of distal adjacent tooth
  3. extraction of adjacent tooth (esp 3rd molars)
104
Q

T/F: Occlusal reduction is always the same as clearance needed in regards to tilted molar abutments

A

False- occlusal reduction is NOT always the same as clearance needed

105
Q

Because occlusal reduction is NOT always the same as clearance needed in regards to tilted molar abutments, you should remove only enough tooth structure to:

A

provide necessary space for the restoration

106
Q

By removing only enough tooth structure to provide the necessary space for the restoration on a tilted molar abutment, this allows for ___ because retention can be compromised with tilted molar abutments

A

longer axial wall length

107
Q

What can be compromised with tilted molar abutments?

A

retention

108
Q

An FPD distributes forces favorably by directed forces in the:

A

long axis of abutment teeth

109
Q

_____ abutment teeth provide better support than ___ abutment teeth

A

well-aligned; tipped

110
Q

_____ (horizontal) often leads to proximal crystal bone loss

A

non-axial loading

111
Q

non-axial loading (horizontal) often leads to:

A

proximal crystal bone loss

112
Q

In the following image, what does the colored area indicate?

A

bone loss associated with tilted molar

113
Q

An orthodontic movement to correct tilted molars (so they are better abutments)

A

molar uprighting

114
Q

Distributes forces under loading through long axis of tooth (helps prevent/eliminate mesial bony defects)

A

molar uprighting

115
Q

____ enables replacement of optimum occlusion in the case of a tilted molar

A

molar uprighting

116
Q

What is a proximal half crown and in what case would this be utilized?

A

3/4 crown that is rotated to 90 degrees that does not involve the distal wall of the TIPPED molar abutment

117
Q

What are the requirements for a proximal half crown?

A
  1. caries-free distal surface
  2. low incidence of caries
  3. even marginal ridge height
  4. short span length
118
Q

When might you use a proximal half crown?

A

On a tipped molar in a patient with optimal home care

119
Q

When considering copings and crowns on a tilted molar abutment, you would need to:

A

communicate with the patient that this is NOT an ideal treatment & there is a failure risk

120
Q

Full crown coping with path of insertion in longs of tooth where the full coverage crown compensates for discrepancies in path of insertion caused by a tilted molar:

A

Copings and crowns on tilted molar abutment

121
Q

What must be done to the molar in order to accommodate the thickness of a coping & crown?

A

over-reduction

122
Q

Why would you consider coping & crown on a tilted molar abutment?

A
  • design for failure
  • protect tooth (reduced fracture of crown with tooth and bridge stresses)
123
Q

What is primarily only for patients contraindicated for implants?

A

Cantilever FPD

124
Q

Why is a cantilever FPD primarily ONLY an option for patients contraindicated for implants?

A
  1. removing tooth structure on TWO teeth
  2. Occlusal forces created GUARDED PROGNOSIS
125
Q

Criteria for cantilever?

A

Replace only 1 tooth, and have at least 2 abutments

126
Q

The criteria for abutment teeth with a cantilever FPD:

A
  1. long roots with good configuration
  2. long clinical crown
  3. favorable crown root ratio
  4. healthy periodontium
127
Q

Why is a long clinical crown a requirement for the abutment teeth with a cantilever FPD?

A
  • resistance form for preparations
  • O-C height for connectors without imprinting on interdental papilla
128
Q

What can be seen in the following image?

A

cantilever FPD

129
Q

What can be seen in the following image?

A

coping and crown

130
Q

Because most of us don’t have laterals in occlusion, this makes it one area where a ____ is a more ideal option:

A

cantilever FPD

131
Q

Occlusal forces on a STANDARD FPD directs forces along the:

A

long axis of abutment teeth

132
Q

Cantilever pontic without abutment root directs occlusal forces ___ putting both -__ and ___ forces on abutments

A

apically; vertical & lateral

133
Q

What tooth is commonly replaced with a cantilever FPD?

A

lateral incisor

134
Q

Only the ___ should be used as a solo abutment with a cantilever FPD

A

canine

135
Q

Why should the only solo abutment used with a cantilever FPD be a canine?

A
  1. long root
  2. easier esthetics
  3. occlusal forces more lateral and therefore protective of pontic
136
Q

In order for a cantilever FPD to replace a first premolar, there should be:

A

super light occlusion

137
Q

What should be used on the 2nd premolar and 1st molar instead of a cantilever?

A

full veneer retainers

138
Q

With a cantilever FPD replacing a premolar, we MUST limit:

A

occlusion on the Pontic

139
Q

When a cantilever is used on premolar, ___ is used to support the premolar cantilever pontic

A

mesial rest

140
Q

When using a rest on a cantilever pontic (by placing a rest seat in a restoration on the abutment), what is the biggest problem?

A

caries due to inadequate cleanse ability

141
Q

What can be seen in the following image?

A

rest seat on cantilever Pontic

142
Q

Describe the prognosis of a first molar replacement with a cantilever:

A

unfavorable

143
Q

Why is there an unfavorable prognosis with a first molar replacement with a cantilever?

A

-extreme leverage forces generated by posterior position
- occlusal forces place tensile stress on secondary retainer

144
Q

If a first molar must be replaced with a cantilever FPD, it is absolutely necessary that:

A
  1. pontic size is small (premolar size)
  2. light occlusal contact with no excursive contact
  3. pontic and connector need maximum OG height for rigidity
  4. good C:R ratio of abutments
  5. clinical crowns have maximum preparation length and resistance form
145
Q

Describe the prognosis for a central incisor replacement with a cantilever FPD:

A

unfavorable

146
Q

Why is there an unfavorable prognosis for central incisor replacement with a cantilever FPD?

A
  1. lateral incisor abutment
  2. severe vertical overlap
147
Q

Why is a lateral incisor abutment for a central incisor replacement with a cantilever FPD a bad idea?

A

Due to the root shape of the lateral incisor and occlusal forces

148
Q

A cantilever FPD for replacement of a central incisor #9yields a poor prognosis. This is partially due to severe vertical overlap which causes heavy occlusal forces. What are some other options for replacement of #9

A
  • conventional bridge from #8-#10
  • single implant
149
Q
A

Fixed Prosthodontics II (5 decks)

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