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Fixed Prosthodontics I > Principles of Tooth Preparations > Flashcards

Principles of Tooth Preparations Flashcards

1
Q

A crown preparation is an ___ surgical procedure

A

irreversible

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2
Q

What are the 7 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

In consideration of preservation of tooth structure are biological factors such as:

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

A
  • dental pulp
  • gingival tissues
  • adjacent teeth
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4
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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5
Q

Pulpal integrity: Any time a bur touches a tooth, the pulp is:

A

stimulated to respond

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6
Q

Pulpal integrity: A crown preparation _____ the pulp

A

“traumatizes”

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7
Q

Pulpal integrity: most pulps respond with:

A

a healthy healing response

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8
Q

Pulpal integrity: some pulps respond by:

A

dying (pulpal necrosis)

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9
Q

Pulpal integrity: some pulps remain ___ with lingering pulpal inflammation

A

hypersensitive

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10
Q

Why can the pulp become/remain hypersensitive or necrotic?

A
  1. decreased thickness of dentin remaining between prepared walls & pulp
  2. heat transferred to tooth during prep
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11
Q

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

A

leave at minimum 1mm of dentin surrounding pulp

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12
Q

How much MINIMUM of dentin should be surrounding the pulp?

A

1mm

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13
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 Root Canal Teeth
- Make tooth stronger

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14
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 structural integrity of the remaining tooth structure

VERSUS

  1. mechanical requirements the patient needs
  2. esthetic requirements the patient desires
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15
Q

When considering 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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16
Q

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

A

morphological reduction

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17
Q

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

A

maximal thickness

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18
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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19
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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20
Q

A seating groove in a crown preparation allows for:

A

retention & resistance

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21
Q

Axial reduction in a crown preparation allows for:

A

retention & resistance

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22
Q

Prevention of removal along the path of insertion:

A

retention

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23
Q

Retention usually occurs:

A

in patients chewing sticky foods

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24
Q

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

A

retention

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25
Q

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

A

vertical surfaces; converging surfaces

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26
Q

____ is also created using cements with offer frictional resistance to dislodgment.

A

retention

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27
Q

Retention is also created using ___ which offer ____ to dislodgment.

A

cements; frictional resistance

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28
Q

Retention is also created using cements which offer frictional resistance to dislodgment. this is a ____ aiding in retention.

A

shear stress

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29
Q

____ is also created through mechanical factors such as dental cements.

A

retention

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30
Q

Retention is also created through ____ factors such as dental cements

A

mechanical factors

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31
Q

Retention: Dental cements hold through _____ of projections of cement into irregularities of the surfaces being joined.

A

mechanical interlocking

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32
Q

What are the 2 ways to check resistance?

A

Wall height & TOC

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33
Q

What factors contribute to retention? (3)

A
  1. two opposing vertical surfaces with converging surfaces held to within certain parameters
  2. cement- offers frictional resistance
  3. cement- offers mechanical interlocking
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34
Q

Prevention of restoration being dislodged by apical or oblique forces:

A

resistance

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35
Q

Resistance is the prevention of the restoration being dislodged by ___ or ___ forces

A

apical or oblique

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36
Q

The apical or oblique forces that prevent the the restoration from 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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37
Q

The greatest determining factor in a crown’s dislodgment:

A

resistance

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38
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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39
Q

How is resistance built into a preparation?

A

by forming walls to block anticipated movement due to leverage & rotation

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40
Q

Resistance is build into a preparation by forming walls to block anticipated movement due to ___ & ____

A

leverage & rotation

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41
Q

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

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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42
Q

TOC=

A

total occlusal convergence

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43
Q

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

A

the paths of insertion, grooves, boxes, vertical planes & pins & morphologic reduction

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44
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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45
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 of adjacent teeth

should be surface area of the tooth prep

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46
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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47
Q

Total occlusal convergence is the:

A

angle of convergence of taper between two opposing walls of a tooth preparation

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48
Q

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

A

two opposing walls

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49
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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50
Q

Inclination is:

A

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

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51
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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52
Q

Ideal TOC:

A

6 degrees

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53
Q

What can be used to accomplish a 2 to 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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54
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 insertion.

This overall contributes to:

A

2 to 3 degrees

TOC

55
Q

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

A

an overall TOC of 6 degrees

56
Q

The angle formed between two opposing walls:

A

Total Occlusal Convergence (TOC)

57
Q

What is required to seat a crown?

A

some taper

58
Q

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

A

TOC

59
Q

If on an exam, we ask you where to put a margin the answer is always:

A

supragingival (however in clinic this is not always the correct answer)

60
Q

As occlusal convergence increases, ____ decreases

A

retention

61
Q

What happens to retention as occlusal convergence increases?

A

retention decreases

62
Q

Maximum crown retention is around ___ degrees of TOC

A

5 degrees

63
Q

What happens when TOC is 20 degrees?

A

retention decreases to ~ 1/5

64
Q

Describe the relationship between convergence & retention:

A

convergence is inversely proportional to retention

65
Q

Based on evidence from clinical studies:

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

A

10-20 degrees

66
Q

Based on evidence from clinical studies:

Molar tooth preps tend to have ___ TOC than premolars or anterior teeth

A

greater

67
Q

Based on evidence from clinical studies:

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

A

greater

68
Q

Based on evidence from clinical studies:

What causes the TOC to be greater than ideal?

A

likely due to challenges in access and visibility

69
Q

____ preps are generally shorter with higher occlusal forces

A

posterior preps

70
Q

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

A

posterior; anterior

71
Q

Summary on TOC:

  1. Ideal TOC angle = ____ degrees
  2. Acceptable TOC angle= ____ degrees
  3. If a prep 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
72
Q

Wall length =

A

height

73
Q

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

A

retention

74
Q

Increased height= increases the _____ = increased ____

A

area of cementation; retention

75
Q

How do you measure the tooth wall height?

A

measured from incisal/ occlusal surface to the margin

76
Q

What is being measured in these images?

A

wall height

77
Q

Decreased wall length (height) creates a:

A

disproportionate decrease in resistance

78
Q

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

A

10%

79
Q

The wall height should be greater than the:

A

tipping arc of displacement

80
Q

The shorter the preparation, the ____ the taper MUST be

The taller the preparation, the ____ the taper MAY be

A

less; greater

81
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

82
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)

83
Q

For ideal and adequate resistance and retention, the height/width ratio should be greater than ____ for all teeth.

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

A

0.4

84
Q

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

A

4mm (10x 0.4)

85
Q

Wall height ideals when preparation is within TOC of ___ degrees

A

10-20 degrees

86
Q

Ideal wall height:

Molars:

Incisors & premolars:

A

molars = 4mm

incisors & premolars= 3mm

87
Q

How is resistance form assessed? (3)

A
  1. Measure TOC between opposing walls
  2. Measure we all height parallel with long axis (3mm for incisors and premolars & 4 mm for molars)
  3. Measure tooth width ratio (Occlusal: facial/lingual should be atleast 0.4)
88
Q

If you measure the tooth width ratio, occlusal: Facial/Lingual should be at least:

A

0.4

89
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
90
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

91
Q

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

A

By axial re-shaping of prep walls

92
Q

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

A

parallel to the path of insertion

93
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
94
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)

95
Q

Resistance can be improved by adding grooves which function to:

A

limit the path of withdrawal to only one

96
Q

True or False: There are times when leaving a crown preparation less than ideal will actually increase the resistance and retention form:

A

true

97
Q

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

A

less than ideal

98
Q

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

A

geometric box forms can be added to your preparation

99
Q

Geometric box forms include: (3)

A
  1. box
  2. groove
  3. pin hole
100
Q

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

A

auxillary

101
Q

Most common to use ___ for secondary retention

A

grooves

102
Q

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

A
  1. increases surface area
  2. limit the path of draw
103
Q

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

A

1.5mm axially; 2mm occlusally

104
Q

These are examples of ____.

These function as _____.

A

grooves; secondary retention feature

105
Q

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

A

direction of the displacing force

106
Q

____ is increased with increasing surface area

A

retention

107
Q

Increasing surface area helps with retention but its not as vitally important as ____ and the ____

A

TOC parameters; height/width ratio

108
Q

What makes a good margin? How do you define high 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
109
Q

Sufficient strength to withstand forces of mastication describes:

A

high marginal integrity

110
Q

What can be seen in the following image?

A

a good margin

111
Q

Crown margin should fit as closely as possible to:

A

minimize cement width (25 microns)

112
Q

Margins should be closely adapted to the ___ of the preparation

A

finish line

113
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
114
Q

What is wrong with the following image?

A

margin is not closely adapted to the finish line of prep

115
Q

What might the crowns in this image lead to?

A
  1. microleakage
  2. recurrent caries
  3. possible de-cementation of restoration
116
Q

What are the 3 requirements of the tooth preparation finish line?

A
  1. needs to be conservative of tooth structure
  2. readily identifiable on tooth, impression and die
  3. provides sufficient bulk for restorative material
117
Q

The size of you finish line determines: (2)

A
  1. The bulk of material at the margin
  2. The fit of the restoration
118
Q

Label the following types of finish lines (margins) (left to right)

A
  1. feather-edge
  2. knife-edge
  3. chamfer
  4. bevel
  5. shoulder
  6. beveled shoulder
119
Q
  • adequate occlusal/ incisal reduction and clearance without excessive removal
  • uniform thickness of restoration material
  • parallels the major planes of the tooth

These are all factors of:

A

morphological reduction

120
Q

Label the following images regarding morphological reduction:

A

A) correct
B) flat (inadequate)
C) excessively flat

121
Q

The morphological reduction should parallel the ____ of the tooth

A

major planes of the tooth

122
Q

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

A

excessive removal

123
Q

When considering morphological reduction, there should be no ___

A

pulpal involvement

124
Q

Preparation features that contribute to structural durability include: (3)

A
  1. occlusal/incisal reduction
  2. functional cusp bevel
  3. axial reduction
125
Q
  • creates a space for an adequate bulk of material with normal contours of the tooth:
A

axial reduction

126
Q

Not enough axial reduction leads to ___ which causes ____.

A

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

127
Q

Too much axial reduction leads to ___ which causes ____.

A

thick over-contoured walls; plaque traps and periodontal inflammation

128
Q

Label the axial reduction in the following image:

A

A) ideal
B) too thin
C) too thick

129
Q

What happens if our preparation does not leave room for structural durability? (3)

A
  1. fracture of restoration
  2. grind through porcelain to adjust occlusion
  3. crown worn through due to thin material
130
Q

Our crown preparations 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
131
Q

Margin guidelines:

  1. place margin where dentist can ___ & ___
  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 & evaluate
  2. clean
  3. impression taking
  4. enamel
  5. supra-gingival
  6. smooth
132
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 your crown preparation margin. For lab, we are asking you to place it ideally ____.

A

0.5mm supra-gingival

133
Q
A

Fixed Prosthodontics I (13 decks)

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