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Fixed Prosthodontics > Crown Preparations- margin design > Flashcards

Crown Preparations- margin design Flashcards

1
Q

Parts of a crown preparation:

A
  1. axial wall
  2. interproximal wall
  3. finish line
  4. occlusal anatomy
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2
Q

A full coverage restoration can survive in the biologic environment of the oral cavity only if:

A

the margins are closely adapted to the surface finish line of the preparation

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3
Q

The design of the preparation ______ dictates the shape and bulk of restorative material in the marginal area of the restoration

A

finish line

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4
Q

Types of finish line design include:

A
  1. knife edge
  2. chamfer (light and heavy)
  3. shoulder
  4. beveled should
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5
Q

A chamfer finish line can be described as:

A

light or heavy

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6
Q

Finish line design that is used primarily for full metal crowns only. (Especially gold crowns):

A

Knife edge

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7
Q

Most conservative preparation design for the finish line :

A

Knife edge

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8
Q

What may be used to create a knife edge finish line?

A

Flame or needle-shaped diamond bur

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9
Q

The disadvantages of knife edge finish lines include:

A
  1. difficult to see finish line in an impression or scan
  2. metal can be thin & susceptible to distortion under heavy occlusal load
  3. often leads to an over-bulking of crown material to compensate for thinness along margin
  4. easy to miss creating distinct end of finish line and instead acial wall never terminates
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10
Q

This image shows a knife edge finish line. What is the disadvantage to B?

A

Margin thin and susceptible to distortion

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11
Q

This image shows a knife edge finish line. What is the disadvantage to C?

A

To compensate for thin marginal area, labs will overbulk crown at margin

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12
Q

What are the indications for the use of knife edge margin finish lines?

A
  1. generally NOT indicated
  2. in certain instances like a tipped molar, a knife edge margin is possible to be conservative in an abnormal area
  3. must have an excellent lab technician
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13
Q

In certain instances, like a tipped molar, a _____ margin is possible to be conservative in an abnormal area

A

knife edge

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14
Q

Label the following types of margin finish lines:

A

(left to right)
1. shoulder
2. chamfer
3. knife edge

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15
Q

What is required for a knife edge finish line?

A

An excellent lab technician

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16
Q

What are the two types of chamfer margins?

A
  1. heavy chamfer
  2. light chamfer
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17
Q

What types of crowns use a light chamfer?

A

Metal crowns & zirconia crowns

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18
Q

What types of crowns use a heavy chamfer?

A

-Ceramic crowns
-Zirconia crowns
-Metal-ceramic crowns

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19
Q

What type of bur can be used to create a chamfer finish line?

A

Round-end tapered diamond

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20
Q

A heavy chamfer will work for what type of crowns?

A

Any type of crown

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21
Q

When creating a chamfer margin finish line axial depth more than 1/2 the bur, can create ____ of the margin, which leave ____ likely to chip or break leaving an open and exposed margin

A

lipped edges; unsupported enamel

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22
Q

What are the advantages of a chamfer margin finish line? (5)

A
  1. chamfer is well suited to full metal crowns & zirconia crowns
  2. ease of seating & placing crown
  3. ease of detecting margin on impression/scan
  4. if full metal, chamfer is easy to wax & cast
  5. provides adequate thickness of restoration material at margin area
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23
Q

A light chamfer is ______ deep in axial wall

A light chamfer produces a _____ degree margin with rounded internal angle

A

0.3-0.5 mm

30-45 degree margin

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24
Q

A light chamfer produces a a ____ internal angle

A

Rounded

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25
Q

Type of margin finish line that combines knife edge burnish-ability with bulk of material for all metal crowns:

A

Chamfer

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26
Q

Label the parts of the following crown prep:

A

a) chamfer finish line
b) functional cusp bevel
c) planar occlusal reduction
d) rounded angles
e) axial reduction

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27
Q

the chamfer finish line promotes:

A

marginal integrity

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28
Q

the functional cusp bevel promotes:

A

structural durability

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29
Q

the planar occlusal reduction promotes:

A

structural durability

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30
Q

the rounded line angles promote:

A

structural durability

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31
Q

the axial reduction promotes:

A

retention and resistance

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32
Q

A heavy chamfer provides room for:

A

thicker ceramic margin

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33
Q

The ______ of the heavy chamfer decreases material stress in the margin area

A

internal rounded angle

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34
Q

What is the measurements of a heavy chamfer?

(How deep)

A

1.0-1.2mm deep

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35
Q

What bur is used to accomplish a heavy chamfer?

A

typically a large round-ended diamond bur

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36
Q

Label which chamfer is light and which is heavy:

A

Left- light
Right- heavy

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37
Q

A ______ margin design produces a close to 90 degree angle

A

shoulder

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38
Q

A shoulder margin design produces a close to _____ degree angle

A

90

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39
Q

A shoulder margin design is used primarily for ______ crowns and ______ crowns where thickness of material is important but can also be used for ___ crowns

A

metal ceramic & all ceramic; zirconia

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40
Q

A modified shoulder produces a _____ angle

A

rounded

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41
Q

A shoulder margin is typically created with:

A

flat-end diamond burs

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42
Q

In a shoulder margin design, the angle of the axial wall and finish line is close to 90 degrees and this functions to:

A

decrease stresses on restoration material

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43
Q

A shoulder margin designs primarily used for _____ and ____ crowns

A

metal-ceramic & all ceramic

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44
Q

Label the different margins shown:

A

Left: shoulder margin
Right: beveled shoulder

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45
Q

Some shoulder finish lines can include a bevel at a _____ degree angle

A

30-45

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46
Q

A shoulder with a bevel is often used for _____ and _____

A

inlays and onlays

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47
Q

What type of margin can be used for metal ceramic crowns where there is a metal collar?

A

beveled shoulder

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48
Q

A beveled shoulder margin allows for _____ of metal to ensure marginal fit

A

adaptability

49
Q

Significant roughness of preparation finish line can prevent:

A

close adaptation of crown margin

50
Q

Rough margin = ______ = _____

A

plaque accumulation; recurrent decay

51
Q

Finish line designs vary based on: (3)

A
  1. restoration material
  2. location in the mouth
  3. desired results
52
Q

The type of tooth preparation in which the finish line forms a 90-degree angle with the unprepared tooth surface:

A

shoulder

53
Q

The advantage of this margin includes:

-less distortion of crown margins
-provides adequate bulk
-good crown contours
-can attain good esthetics

A

shoulder

54
Q

The disadvantages of this margin includes:

-marginal adaptation can be affected
-more tooth structure needs to be removed

A

shoulder

55
Q

Indications of this type of margin include:

-all ceramic crowns
-PFM crowns

A

shoulder

56
Q

This type of margin is similar to a shoulder but has a bevel placed at the border:

A

beveled shoulder

57
Q

Indications of this type of margin include:

-gingival finish line on the proximal box of inlays or onlays
-occlusal shoulder of onlays and mandibular three-quarter crowns
-the finish line for extremely short walls
-the posterior margin for metal-ceramic crowns with a supra gingival margin

A

beveled shoulder

58
Q

The advantages of this type of margin include:

-to get proper marginal adaptation
-the bulk of the material in border

A

beveled shoulder

59
Q

The disadvantages of this type of margin include:

-more tooth structure is removed
-less conservative approach
-preparation should be extended apically

A

beveled shoulder

60
Q

A finish line design for tooth preparation in which the gingival aspect meets the external axial surface at an obtuse angle:

A

chamfer

61
Q

Indications for this type of margin include:

-cast metal restorations
-lingual margin of metal-ceramic restorations

A

chamfer

62
Q

Advantages of this type of margin include:

-conservative tooth prep
-good marginal adaptation
-provides bulk to the restoration

A

chamfer

63
Q

Disadvantages of this type of margin include:

-technique sensitive
-any defect in fabrication can lead to unsupported tip of the crown

A

chamfer

64
Q

Similar to chamfer finish line but comes with a 90 degrees cavosurface angle with a large radius rounded internal angle:

A

heavy chamfer

65
Q

In cases of metal restorations using a chamfer margin, a ____ is added to the finish line

A

bevel

66
Q

Indications for this type of margin include:

-ceramic crowns
-metal crowns with a bevel

A

heavy chamfer

67
Q

Advantages for this type of margin include:

-best finish line for a ceramic crown

A

heavy chamfer

68
Q

Disadvantages for this type of margin include:

-technique sensitive
-little discrepancy can lead to the formation of a lip or unsupported fragile enamel

A

heavy chamfer

69
Q

Also considered a thin-edge margin or feather-edge:

A

knife edge

70
Q

Indications for this type of margin include:

-young patients
-metal restorations
-MOD onlay
-inaccessible areas
-when the finish line extends to the cementum
-the lingual surface of mandibular posterior teeth
-pin ledge 3/4 quarter crown

A

knife-edge/feather-edge

71
Q

Advantages for this type of margin include:

-conservative
-helps in preserving tooth structure
-ideal for marginal adaptation
-useful in gold & metal crowns/restorations as it lets you burnish it to a fine finish
-considered an ideal finish line

A

knife-edge/feather-edge

72
Q

Disadvantages for this type of margin include:

-distinct or proper finish is not visible
-waxing
-polishing and casting become critical
-overcontouring of restorations to obtain a bulk is a usual complication

A

knife-edge/feather-edge

73
Q

Crown preparation concerns:

Scientists seem to oscillate back and forth as to whether heat produced during a crown preparation will:

A

kill the pulp

74
Q

Crown preparation concerns:

It is agreed that the _____ becomes irritated and inflamed during _____

A

pulp; crown preparations

75
Q

Crown preparation concerns:

A rise in the pulp temperature by ____ degrees significantly increases the chance of _____

A

10 degrees; pulpal necrosis

76
Q

Crown preparation concerns:

Because of the concerns with overheating the pulp during a crown preparation we should: (7)

A
  1. use lots of water
  2. use sharp burs
  3. use light pressure
  4. use high speed
  5. use diamond burs
  6. avoid desiccation of the teeth
  7. if visibility is compromised, with an assistant, with water off from the hand piece, an assistant can use air and small amounts of water to help keep tooth cool.
77
Q

The main cause of postoperative inflammation or necrosis of the pulp is probably the injury of ______, a tissue in direct functional and physiological connection with the pulp

A

dentin

78
Q

Margin design instrumentation:

For the preparation, what is used? (3)

A
  1. high-speed handpiece
  2. air/water spray
  3. diamond burs
79
Q

Margin design instrumentation:

For finishing the preparation, what is used? (3)

A
  1. slow-speed handpiece
  2. fine diamond burs (possibly some carbide burs)
  3. hand instruments
80
Q

Margin design instrumentation:

For caries removal of the crown preparation, what is used? (2)

A
  1. slow-speed with 2, 4 or 6 round bur
  2. spoon excavators
81
Q

Burs that function to remove enamel and dentin by grinding it away:

A

diamond burs

82
Q

Burs that function to remove tooth by shearing it away:

A

carbide burs

83
Q

______ burs are most efficient, 2-3x faster than _____ burs

A

diamond; carbide

84
Q

What type of bur is being described?

-cut precision prep features with smooth surfaces
-often used to place extra retentive features in a crown preparation such as a seating groove

A

Carbide burs

85
Q

_____ can be used to help smooth finish lines

A

hand instruments

86
Q

Hand instruments that can be used to help smooth finish lines include: (4)

A
  1. chisel
  2. hatchet
  3. hoe
  4. margin trimmer
87
Q

Advantages of full metal crowns:

Gold and many metal crowns are:

A

soft metals

88
Q

Full metal crowns are _____ to opposing teeth

A

gentle

89
Q

Advantages of full metal crowns:

metal is strong so:

A

material can be quite thin

90
Q

Describe the preparations involving a full metal crown:

A

very conservative preparations

91
Q

Advantages of full metal crowns:

Metals have some antibacterial properties making:

A

recurrent decay less likely

92
Q

Describe the effects of most gold and full metal crowns on the gingiva:

A

gentle

93
Q

______ crowns are very durable even if worn through or with an endo access

A

metal crowns

94
Q

In metal crown if the contact is missing:

A

you can add material to the contact to re-establish it

95
Q

List the disadvantages of full metal crowns:

A

ESTHETICS

96
Q

Discuss the margin design for a full metal crown preparation:

A

Can use knife-edge margin, but usually a light chamfer is recommended (0.3-0.5 mm)

97
Q

In a full metal crown preparation, axial walls are reduced to create a tapered wall between ____ to ____ degrees ideally, but can have TOC up to ____ degrees

A

6 to 10; 20

98
Q

In a full metal crown preparation, axial walls can be reduced as little as ___ but can be reduced more if needed

A

0.5 mm

99
Q

Discuss the occlusal reduction in a full metal crown preparation:

A

uniform occlusal reduction depth of 1.0 to 1.5mm following tooth anatomy

100
Q

Nothing is _____ in dentistry except for our tools

A

sharp

101
Q

In a full metal crown preparation, line angles and corners need to be rounded to prevent:

A

pressure points and possible fracturing of a restorative material

102
Q

In a full metal crown preparation, rounded preparations make the:

A

crown fabrication process easier

103
Q

In a full metal crown preparation, prepared surfaces and finish line are smoothed with a fine grit diamond bur, what does this ensure?

A

Preparation walls are scored, but with a smoother more consistent shape for seating and longevity of the restoration

104
Q

Full metal crown summary:

A) Chamfer finish line: _____
B) Axial reduction: _____
C) Total occlusal taper: _____
D) Occlusal clearance: _____
E) _____ of all line angles

A

A) 0.3-0.5mm
B) as little as 0.5mm
C) 6-10 degrees
D) 1.0-1.5mm
E) rounding

105
Q

Label the various tooth preparations:

A

(Left to right)
Metal or all-zirconia
PFM
All-ceramic

106
Q

A relatively new material that is tooth-colored and ceramic-like:

A

zirconia

107
Q

Zirconia is considered _____ free

A

metal

108
Q

Zirconia can have similar properties to:

A

metal

109
Q

Zirconia can be described as very:

A

hard and tough

110
Q

Compare the appearance of zirconia to natural teeth:

A

less translucent

111
Q

What material is seen in the following crown?

A

Zirconia

112
Q

The original zirconia that was very tough and very ugly:

A

Bruxir

113
Q

Why have new iterations of zirconia been created?

A

to make zirconia more esthetic

114
Q

What is the problem with making new iterations of zirconia that are more esthetic?

A

In order to make them more esthetic the strength of the zirconia is reduced

115
Q

Depending on the type of zirconia crown, the preparation can be:

A

as minimal as a full metal crown prep or as extensive as an all ceramic crown prep

116
Q

Zirconia is rapidly changing still so what is extremely important?

A

knowing which kind of zirconia your lab is using so you can prep appropriately

117
Q

The more esthetic your zirconia is, the more ______ will be needed

A

reduction

118
Q
A

Fixed Prosthodontics (13 decks)

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