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Fixed Prosthodontics > Principles of Tooth Preparations > Flashcards

Principles of Tooth Preparations Flashcards

1
Q

A crown preparation is a _____ surgical procedure

A

Irreversible

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2
Q

What are the seven principles of tooth design and restoration design?

A
  1. preservation of tooth structure
  2. retention form
  3. resistance form
  4. added preparation features
  5. marginal integrity
  6. structural durability of the restoration
  7. preservation of the periodontium
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3
Q

A crown preparation is an _______ surgical procedure

A

Irreversible

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4
Q

In consideration of preservation of tooth structure are biologic factors such as: (3)

(what are other things you must consider in addition to the structure you’re working on)

A
  1. dental pulp
  2. gingival tissues
  3. adjacent teeth
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5
Q

When considering preservation of tooth structure, if not careful, injury can occur such as:

A

-mechanical damage
-temperature damage
-chemical damage
-bacterial damage

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6
Q

Pulpal integrity:

any time a bur touches a tooth, the pulp is:

A

stimulated to respond

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7
Q

Pulpal integrity:

a crown preparation _______ the pulp

A

“traumatizes”

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8
Q

Pulpal integrity:

Most pulps respond with:
Some pulps respond by:
Some pulps remain:

A

A healthy healing response
Dying (pulpal necrosis)
Hypersensitive with lingering pulpal inflammation

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9
Q

Why an some pulp become/remain hypersensitive or necrotic?

A
  1. decreased thickness of dentin remaining between prepared walls and pulp
  2. heat transferred to tooth during preparation
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10
Q

When considering pulpal integrity, what is a “vital core”?

A

Leave at minimum 1mm of dentin surrounding pulp

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11
Q

How much MINIMUM of dentin should be surrounding the pulp of a prepped tooth?

A

1mm

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12
Q

If there are risks like killing the pulp, why do we prepare teeth for crowns?

A

Crowns are placed for many reasons such as:
-esthetics
-prevention of catastrophic fracturing
-protection of rooth cnal teeth
-make tooth stronger

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13
Q

What must be in balance when considering preservation of tooth structure?

(1&2 VS. 1&2)

A
  1. unnecessary destruction of sound tooth structure
  2. preservation of the structural integrity of the remaining tooth structure

VERSUS

  1. mechanical requirements the patient needs
  2. esthetic requirements the patient desires
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14
Q

When considering the preservation of tooth structure:

When preparing a tooth for a crown in a conservative manner, the operator allows for a:

A

Morphological reduction

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15
Q

Preservation of the basic primary tooth anatomy within the preparation (axial wall and occlusal anatomy):

A

Morphological reduction

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16
Q

Morphological reduction leaves the ______ of residual tooth structure surrounding the pulp

A

Maximum thickness

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17
Q

What type of features does morphological reduction leave in the tooth preparations?

A
  1. anti-rotational features
  2. retentive features
  3. resistive features
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18
Q

As we create our crown preparation, we need to form the tooth utilizing geometric form criteria we call:

A
  1. Retention
  2. Resistance
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19
Q

A seating groove in a crown preparation allows for:

A

Retention & resistance

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20
Q

Axial reduction in a crown preparation allows for:

A

Retention & resistance

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21
Q

Prevention of removal along the path of insertion:

A

Retention

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22
Q

Retention usually occurs in:

A

Patients chewing sticky foods

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23
Q

Created by two opposing vertical surfaces with converging surfaces held to within certain parameters:

A

Retention

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24
Q

Retention is created by two opposing ______ surfaces with _____ surfaces held to within certain parameters

A

Vertical surfaces; converging surfaces

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25
Q

______ is also created using cements which offer frictional resistance to dislodgement

A

Retention

(this is an example of a shear stress aiding in retention)

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26
Q

Retention is also created using _____ which offer ___ to dislodgement

A

cements; frictional resistance

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27
Q

_____ is also created through mechanical factors such as dental cements that hold through mechanical interlocking of projections of cement into irregularities of the surfaces being joined

A

Retention

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28
Q

Dental cements contribute to retention through ______ of projections of cement into _____ of the surfaces being joined

A

mechanical interlocking; irregularities

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29
Q

What are the two ways to check resistance?

A
  1. wall height
  2. TOC
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30
Q

What factors contribute to retention (3):

A
  1. Two opposing vertical surfaces with converging surfaces held within parameters
  2. Cements- offer frictional resistance to dislodgement
  3. Cements- offer mechanical interlocking
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31
Q

Prevention of restoration being dislodged by apical or oblique forces:

A

Resistance

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32
Q

The apical or oblique forces that prevent the restoration fro being dislodged to ensure resistance are typically through _____ forces, but also to _____ forces which are not along the path of insertion

A

Occlusal; lateral

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33
Q

The greatest determining factor in a crown’s dislodgement:

A

Resistance

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34
Q

Resistance is the prevention of the restoration being dislodged by _____ or ____ forces

A

Apical or oblique

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35
Q

_____ is built into a preparation by forming walls to block anticipated movement due to leverage & rotation (either vertically or horizontally)

A

Resistance

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36
Q

How is resistance built into a preparation?

A

By forming walls to block anticipated movement due to leverage and rotation

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37
Q

Resistance is build into a preparation by forming walls that block anticipated movement due to:

A

-Leverage
-Rotation (either vertically or horizontally)

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38
Q

What factors can affect the resistance form of a tooth preparation? (5)

A
  1. Total occlusal convergence (TOC)
  2. Preparation wall length
  3. Tooth width after preparation
  4. Geometric forms
  5. Surface area of the tooth preparation
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39
Q

The geometric forms that affect the resistance of a tooth preparation limit:

A

Paths of insertion, grooves, boxes, vertical planes, pins & morphological reducation

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40
Q

When considering factors that affect the resistance form of a tooth preparation, what category does morphological reduction fall into?

A

Geometric forms

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41
Q

What is not a factor that affects the resistance form of a tooth preparation?

A) Geometric form
B) Total occlusal convergence
C) Surface area of the adjacent teeth
D) Tooth width after preparation

A

C) Surface area of the adjacent teeth

This should instead be: Surface area of the tooth preparation

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42
Q

Defined as the angle of convergence of taper between two opposing walls of a tooth preparation:

A

Total occlusal convergence

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43
Q

Total occlusal convergence is:

A

The angle of convergence of taper between two opposing walls of the tooth prep

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44
Q

Total occlusal convergence is the angle of convergence of taper between _________ of a tooth preparation

A

Two opposing walls

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45
Q

Defined as the angle of convergence of taper of one wall of a preparation in relationship to the long axis of the preparation:

A

Inclination

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46
Q

Inclination is:

A

The angle of convergence of taper of one wall of a tooth prep in relationship to the long axis of the prep

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47
Q

Inclination is the angle of convergence of taper of ____ of a preparation in relationship to the long axis of the preparation

A

One wall

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48
Q

Ideal TOC:

A

6 degrees

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49
Q

What can be used to accomplished a 2 or 3 degree converging angle to a tooth wall if the shank is held parallel to the intended path of insertion?

This overall contributes to:

A

Tapered diamond bur

TOC

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50
Q

A tapered diamond bur can be used to accomplish a ________ to a tooth wall if the shank of the bur is held parallel to the intended path of instertion

This overall contributes to:

A

2 to 3 degrees

TOC

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51
Q

Two opposing surfaces, each with 3 degrees of taper, add together for:

A

An overall TOC of 6 degrees

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52
Q

The angle formed between two opposing walls:

A

Total occlusal convergence (TOC)

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53
Q

Some taper is required to:

A

Seat the crown

54
Q

What is required to seat the crown?

A

Some taper

55
Q

What feature of the crown preparation is most under operator control?

A

TOC

56
Q

If on an exam when asked where to put a margin the answer is always:

A

Supragingival

*however in clinic this is not always the correct answer

57
Q

As occlusal convergence increases _____ decreases

A

Retention

58
Q

What happens to retention as occlusal convergence increase?

A

Decreases

59
Q

Maximum crown retention is around ____ degrees of TOC

A

5

60
Q

What happens when TOC is 20 degrees?

A

Retention decreases to approximately 1/5

61
Q

Describe the relationship between convergence and retention:

A

Convergence is inversely proportional to retention

62
Q

Based on evidence from clinical studies:

The average TOC of prepared teeth ends up in the range of:

A

10-20 degrees

63
Q

Based on evidence from clinical studies:

Molar tooth preps tend to have ____ TOC than premolars of anterior teeth

A

greater

64
Q

Based on evidence from clinical studies:

Mandibular tooth preps tend to have ____ TOC than maxillary tooth preps

A

greater

65
Q

Based on evidence from clinical studies:

What causes the TOC to be incorrectly greater than ideal?

A

Likely due to challenges in access and visibility

66
Q

_____ preps are generally shorter with higher occlusal forces

A

Posterior

67
Q

_____ preps require more angled TOC than ____ teeth to facilitate crown seating

A

Posterior; anterior

68
Q

Summary on TOC:

  1. Ideal TOC angle =_____ degrees
  2. Acceptable TOC angle =_____ degrees
  3. If a prepared TOC angle is more than ____ degrees, the preparation would benefit from further modifications to the prep design
A
  1. 6-10 degrees
  2. 10-20 degrees
  3. 20 degrees
69
Q

Wall length=

A

Height

70
Q

The greater the height of the tooth preparation wall, the greater the _____ of the restoration

A

Retention

71
Q

increased height = increases the ______ = increased _____

A

area of cementation; retention

72
Q

How do you measure the tooth wall height?

A

Measured from incisal/occlusal surge to the margin

73
Q

What is being measured in these images?

A

Wall height

74
Q

Decreased wall length (height) creates a:

A

Disproportionate decrease in resistance

75
Q

For every 1mm increase in wall height, the retention and resistance form increases up to:

A

10%

76
Q

The wall height should be greater than the:

A

Tipping arc of displacement

77
Q

The shorter the preparations, the _____ the taper MUST be

The taller the preparation, the ____ the taper MAY be

A

less; greater

78
Q

A narrow tooth with a smaller diameter preparation can have _______ resistance than a wider, larger diameter tooth when they both have the same wall height

A

greater

79
Q

A narrow tooth with a smaller diameter preparation can have greater resistance than a wider, larger diameter tooth when they both have the same wall height.

This is because the small tooth has a:

A

Shorter rotational radius for the Arc of Rotation (tipping arc)

80
Q

For ideal and adequate resistance and retention, the height/width ratio should be greater than:

(This also implies the TOC is less than 20 degrees)

A

0.4 for all teeth

81
Q

If a molar is on average 10mm facial-lingually, and the minimal ratio is 0.4, then _____ of wall height is idea and adequate

A

4mm

(10 x 0.4)

82
Q

Wall height ideals when preparation is within TOC of _____ degrees

A

10-20 degrees

83
Q

Ideal wall height:

Molars= _____
Incisors & premolars= ______

A

Molars= 4mm

Incisors & premolars= 3 mm

84
Q

How is resistance form assessed? (3)

A
  1. measure TOC between two opposing walls
  2. Measure wall height parallel with long axis
    (3mm premolars/incisors) (4mm molars)
  3. Measure tooth width ratio
    (occlusal: facial/lingual should be at least 0.4)
85
Q

If you’re measure the tooth width ratio:

Occlusal: facial/lingual should be at least ___

A

0.4

86
Q

If the tooth preparation does not have the resistance form you desire, what modifications can you make to the prep to increase the resistance? (3)

A
  1. Decrease the TOC with axial re-shaping of prep walls
  2. addition of grooves/box forms (these must be parallel to the path of insertion)
  3. increase wall height
87
Q

-Decrease the TOC with axial re-shaping of prep walls

-addition of grooves/box forms

-increase wall height

What do all of these contribute to?

A

Modifications to increase resistance

88
Q

How might you decrease the TOC in order to increase resistance?

A

By axial re-shaping of prep walls

89
Q

When increasing resistance by the addition of grooves/box forms, these must be:

A

Parallel to the path of insertion

90
Q

If you want to increase resistance by increasing wall height, how might you accomplish this? (4)

A
  1. lower margin
  2. add wall height with core build up
  3. crown lengthening surgery
  4. orthodontic extrusion
91
Q
  1. lower margin
  2. add wall height with core build up
  3. crown lengthening surgery
  4. orthodontic extrusion

These are all mechanisms to:

A

Increase wall height (which would increase resistance)

92
Q

Resistance can be improved by adding grooves which function to:

A

Limit the path of withdrawal to only one

93
Q

T/F: There are times when leaving a crown preparation less than ideal will actually increase the resistance and retention form

A

True

94
Q

There are times when leaving a crown preparation ________ will actually increase the resistance and retention form

A

Less than ideal

95
Q

What can you do if your TOC is not ideal (more than 20 degrees) or your wall height is less than ideal?

A

Geometric box forms can be added to your preparation

96
Q

Geometric box forms include: (3)

A
  1. box
  2. groove
  3. pin hole
97
Q

Box, groove, and pin holes (geometric box forms) are examples of _____ retention:

A

Auxillary

98
Q

It is most common to use ____ for secondary retention

A

Grooves

99
Q

Using grooves as a secondary retentive feature allows for: (2)

A
  1. increases surface area
  2. limits the path of draw to one
100
Q

Retentive features should ideally be cut no deeper than ___ axially and ____ occlusally

A

1.5 mm axially; 2.0 mm occlusally

101
Q

These are examples of ______.

These function as _____.

A

Grooves; secondary retentive feature

102
Q

Grooves or box forms must have a definitive wall perpendicular to the:

A

direction of the displacing force

103
Q

_____ is increased with increasing surface area

A

retention

104
Q

Increasing surface area helps with retention, but its not as vitally important as ______ and the _____

A

TOC parameters; Height/width ratio

105
Q

What makes a good margin? How do you define marginal integrity? (3)

A
  1. Fits as closely as possible to minimize cement film width (25 microns)
  2. sufficient strength to withstand forces of mastication
  3. located where dentist can finish and inspect and patient can clean
106
Q

Sufficient strength to withstand forces of mastication describes:

A

High marginal integrity

107
Q

What can be seen in the following image?

A

A good margin

108
Q

The crown margin should fit as closely possible to:

A

Minimize cement width (25 microns)

109
Q

Margins should be closely adapted to the _____ of the preparation

A

Finish line

110
Q

If margins are NOT closely adapted to the finish line of the preparation what might occur? (3)

A
  1. microleakage
  2. recurrent caries
  3. possible de-cementation of restoration
111
Q

What is wrong with the following image?

A

Margins are not closely adapted to the finish line

112
Q

What might the crowns in this image lead to?

A
  1. microleakage
  2. recurrent caries
  3. possible de-cementation of restoration
113
Q

What are the three requirements of the tooth prep finish line?

A
  1. needs to be conservative of tooth structure
  2. readily identifiable on tooth (you should be able to see it on impression)
  3. provides sufficient bulk for restorative material
114
Q

The size of you finish line determines: (2)

A
  1. the bulk of material at the margin
  2. the fit of the restoration
115
Q

Label the following types of finish lines (margins):

A

(Left to Right):

  1. feather-edge
  2. knife-edge
  3. chamfer
  4. bevel
  5. shoulder
  6. beveled shoulder
116
Q

-Adequate occlusal/incisal reduction and clearance without excessive removal
-uniform thickness of restoration material
-parallels the Mario planes of the tooth

These are all factors of:

A

Morphological reduction

117
Q

Label the following images regarding morphological reduction:

A

a) correct
b) flat (inadequate)
c) excessively flat

118
Q

The morphological reduction should parallel the _____ of the tooth

A

Major planes of the tooth

119
Q

When considering morphological reduction, you should have adequate occlusal/incisal reduction and clearance without:

A

Excessive removal

120
Q

When considering morphological reduction, there should be no ________

A

Pulpal involvement

121
Q

Preparation features that contribute to structural durability: (3)

A
  1. occlusal/incisal reduction
  2. functional cusp bevel
  3. axial reduction
122
Q

Creates a space for an adequate bulk of material within normal contours of the tooth:

A

Axial reduction

123
Q

Not enough axial reduction leads to ________ which causes ______

A

Thin restoration walls; difficulty to finish and possible loss of strength

124
Q

Too much axial reduction leads to ________ which causes ______

A

Thick over contoured walls; plaque trap and periodontal inflammation

125
Q

Label the axial reduction as the following:

-too thick
-too thin
-ideal

A

A) ideal
B) too thin
C) too thick

126
Q

What happens if our preparation does not leave room for structural durability?

A
  1. fracture of restoration
  2. grind through porcelain to adjust occlusion
  3. crown worn through due to thin material
127
Q

Our crown preparation and final restorations should promote periodontal health by: (3)

A
  1. placement of margin for cleanse-ability
  2. marginal smoothness and crown adaptation
  3. axial contours and emergence profile
128
Q

Margin guidelines:

  1. place margin where dentist can ___ and ___
  2. place margin where patient can ____
  3. place margin where margin can be recorded during ______
  4. place margin on ___ when possible
  5. place margin ____ when possible
  6. make margin as _____ as possible
A
  1. finish and evaluate
  2. clean
  3. impression taking
  4. enamel
  5. supra-gingival
  6. smooth
129
Q

Although a margin guideline is to “place margin supra-gingival when possible” there are many factors that come into play when deciding where to place you crown preparation margin. For lab, we are asking you to place it ideally ____

A

0.5 mm supragingival

130
Q
A

Fixed Prosthodontics (13 decks)

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