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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 two 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 canines
  • 1, 3 or greater than 3 abutments
  • splinters, pier, or cantilever
  • non-parallel abutments
  • combined anterior & posterior FPD
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6
Q

Would the following image be classified as simple or complex?

A

simple

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7
Q

Would the following image be classified as simple or complex?

A

complex

(replacing more than 3 teeth)

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8
Q

Would the following image be classified as simple or complex?

A

complex

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9
Q

Would the following image be classified as simple or complex?

A

complex

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10
Q

Abnormal stress created by torque and average create:

A

material failure & tooth failure

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11
Q

Failure in FPDs 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 case 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 broke, this 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, _________ is directly proportional to ______

A

deflection; cube of the length of its span

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18
Q

FPD flexures varies directly by x^3 where x 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; 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

Deflection varies inversely by the _____

A

cube of its height (thickness)

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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

27

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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 may 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 3-4mm

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31
Q

The minimum height x width for 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 has an adequate O-C 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 material with intermediate yield strength

A

False- high yield strength

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37
Q

If concerns exist with connector strength, considers 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 the 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 connector design?

A

In response to direction of anticipated torque

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41
Q

Occlusal forces on pontics can cause:

A

mesial-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 oblique angle or out center of rotation 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 dislodgement

A

Increase

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45
Q

When placing boxes and grooves to increase resistance to dislodgment, places them in response to:

A

direction 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 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

FL grooves

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53
Q

What would the 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

buccally; 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 forced _____ , 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 maxillary canine replacement the pontic lies outside the inter-abutment axis

A

True

63
Q

For canine replacement the adjacent teeth (lateral & 1st 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

Canines + 2 contiguous teeth = poor prognosis, so you should instead try to restoree with:

A

implants if 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

Double abutments (splinting)

69
Q

Double abutments (splinting) help 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 second abutments:

A
  1. root surface area and C:R must equal to the primary abutments
  2. secondary retainers must have greater than or equal to retention of primary retainers
  3. 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

Cause of fail 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 creating movement of teeth
  2. TENSILE STRESSES between terminal retainers and abutments (intrusion of abutments under loading)
  3. DIFFERENCES IN RETENTIVE CAPACITIES between abutments (relative to size)
77
Q

The following image shows a:

A

pier abutment bridge

78
Q

______ in non-rigid connectors can minimize the transfer of stress from the particular loaded segment 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; 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 forces as well as removes stress

81
Q

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

A

distal

82
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 keyway

83
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

84
Q

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

A

unseat the key

85
Q

If a non-rigid connector is placed on the _____ side of the middle abutment, medially-directed movement will unseat the key

A

mesial

86
Q

What does the arrow indicate in the following image, why might we see this?

A

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

87
Q

Non-rigid connector indications: (4)

A
  1. pier abutment FPD
  2. long span FPD with multiple abutments
  3. non-parallel abutments (tipped molar)
  4. planning for failure
88
Q

Non-rigid connector contraindications: (3)

A
  1. long span FPD with two abutments
  2. excessively mobile teeth
  3. unopposed teeth
89
Q

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

A

no occlusal so you wouldnt need a key way

90
Q

The following 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

91
Q

The following 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

92
Q

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

A

Non-rigid connector

93
Q

-Long span FPD with multiple abutments
-Combined anterior & posterior FPDs

These would be reasons to choose a:

A

Pier abutment with non-rigid connectors

94
Q

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

A

Metal framework try in

95
Q

What is seen in the following image?

A

Pier abutment

96
Q

What is seen in the following image?

A

Pier abutment with non-rigid connector

97
Q

What can be noted in this case?

A

Pretty significant difference in path of insertion due to tipped molar)

98
Q

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

A

25-30 degrees

99
Q

Tilted molars are generally ____ abutments

A

poor

100
Q

With a tilted molar as an abutment tooth, ______ must be over-reduced/overtapered which results in ____

A

mesial wall; decreased resistance

101
Q

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

A

adjacent tooth

102
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 & adjacent teeth)

A
  1. orthodontic uprighting of tilted molar abutment
  2. mesial surface recontouring of distal adjacent tooth
  3. extraction of adjacent tooth (esp. 3rd molars)
103
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

104
Q

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

A

provide necessary space for the restoration

105
Q

By removing only enough tooth structure to provide necessary 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

106
Q

What can be compromised with tilted molar abutments?

A

retention

107
Q

An FPD distributes forces favorable by directing forces in:

A

the long axis of the abutment teeth

108
Q

______ abutment teeth provide better support than ____ abutment teeth

A

well-aligned; tipped

109
Q

______ (horizontal) often leads to proximal crestal bone loss

A

non-axial loading

110
Q

Non-axial loading (horizontal) often leads to:

A

proximal crestal bone loss

111
Q

In the following image, what does the color indicate?

A

Bone loss associated with tilted molar

112
Q

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

A

molar uprighting

113
Q

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

A

molar uprighting

114
Q

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

A

molar uprighting

115
Q

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

A

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

116
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
117
Q

When might you use a proximal half crown?

A

On a tipped molar in a patient with optimal homecare

118
Q

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

A

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

119
Q

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

A

Copings & crown on tilted molar abutment

120
Q

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

A

over-reduction

121
Q

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

A
  • design for failure
  • protect tooth (reduced fracture of crown with tooth and bridge stresses)
122
Q

What is primarily only for patients contraindicated for implants?

A

Cantilever FPD

123
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 create GUARDED PROGNOSIS
124
Q

Criteria for cantilever:

A

Replace only 1 tooth and have at least 2 abutments

125
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
126
Q

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

A
  • Resistance form for preparations
  • O-C height for connectors without impinging on interdental papilla
127
Q

What can be seen in the following image?

A

Cantilever FPD

128
Q

What can be seen in the following image?

A

Tilted molar abutment copings & crowns

129
Q

Because most of us do not have laterals in occlusion, this makes it one area where a ______ is a more ideal option

A

cantilever FPD

130
Q

Occlusal forces on a STANDARD FPD direct forces along the:

A

long axis of abutment teeth

131
Q

Cantilever pontic without abutment root directs occlusal forces _____ putting both ______ & ____ forces on abutments

A

apically; vertical & lateral

132
Q

What tooth is commonly replaced with a cantilever FPD?

A

Lateral incisor

133
Q

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

A

canine

134
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 & therefore protective of pontic
135
Q

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

A

super light occlusion

136
Q

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

A

Full veneer retainers

137
Q

With a cantilever FPD replacing a premolar we must limit:

A

occlusion on the pontic

138
Q

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

A

mesial rest

139
Q

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

A

caries due to inadequate cleansability

140
Q

What can be seen in the following image?

A

Rest seat on cantilever pontic

141
Q

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

A

unfavorable

142
Q

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

A
  1. extreme leverage forces generated by posterior position
  2. occlusal forces place tensile stress on secondary retainer
143
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 & connector need maximum O-G height for rigidity
  4. good C:R ratio of abutments
  5. clinical crowns have maximum preparation length and resistance form
144
Q

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

A

unfavorable

145
Q

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

A
  1. lateral incisor abutment
  2. severe vertical overlap
146
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

147
Q

A cantilever FPD for replacement of a central incisor #9 yields 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
148
Q
A

Fixed Prosthodontics II (15 decks)

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