Crown Preparations- Margin Design Flashcards
1
Q
Parts of a crown preparation: (4)
A
- axial wall
- interproximal wall
- finish line
- occlusal anatomy
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
3
Q
The design of the preparation ___ dictates the shape an bulk of restorative material in the marginal area of the restoration
A
finish line
4
Q
Types of finish line designs include:
A
- knife edge
- chamfer (light & heavy)
- shoulder
- beveled shoulder
5
Q
A chamfer finish line can be described as:
A
light or heavy
6
Q
Finish line used primarily for full metal crowns only. (especially gold crowns):
A
knife edge
7
Q
Most conservative preparation design for finish line:
A
knife edge
8
Q
What types of burs may be used to create a knife edge finish line?
A
flame or needle-shaped diamond bur
9
Q
The disadvantages of knife edge finish lines include:
A
- difficult to see the finish line in an impression or scan
- metal can be thin and is susceptible to distortion under heavy occlusal load
- often leads to an over-bulking of crown material to compensate for thinness along margin
- easy to miss creating distinct end of finish line and instead axial wall never terminates
10
Q
This image shows a knife edge finish line. What is the disadvantage to B?
A
Margin is thin and susceptible to distortion
11
Q
This image shows a knife edge finish line. What is the disadvantage to C?
A
To compensate for thin marginal area, labs all overbulk crown at margin
12
Q
What are the indications for knife edge finish lines?
A
- Generally NOT indicated
- In certain instances like a tipped molar, a knife edge margin is possible to be conservative in an abnormal area
13
Q
In certain instances like a tipped molar, a ____ margin is possible to be conservative in an abnormal area
A
knife edge margin
14
Q
What is required for a knife edge margin?
A
An excellent lab technician
15
Q
Label the following image: (left to right)
A
- shoulder margin
- chamfer margin
- knife edge
16
Q
What are the two types of chamfer margins?
A
- heavy chamfer
- light chamfer
17
Q
What type of crowns use a light chamfer?
A
metal crowns & zirconia crowns
18
Q
What type of crowns would you use a heavy chamfer?
A
- ceramic crowns
- zirconia crowns
- metal-ceramic crowns
19
Q
What type of bur can be used to create a chamfer finish line?
A
round-end tapered diamond
20
Q
A heavy chamfer will work for what type of crowns?
A
Any type of crown
21
Q
When creating a chamfer 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
22
Q
What are the advantages of a chamfer margin? (5)
A
- chamfer is well suited for full metal crowns and zirconia crowns
- ease of seating crown & placing of crown
- Ease of detecting margin on impression or scan
- If full metal, chamfer is easy to wax and cast
- provides adequate thickness of restoration material at margin area
23
Q
A light margin chamfer is ___ deep into axial wall.
A light chamfer produces ___ degree margin with ____ internal angle
A
0.3-0.5
30-45 degrees; rounded
24
Q
Type of margin finish line that combines a knife edge burnish-ability with bulk of material of all metal crowns:
A
light chamfer
25
Label the parts of the following crown prep:
A) chamfer finish line
B) functional cusp bevel
C) planar occlusal reduction
D) rounded angles
E) axial reduction
26
The chamfer finish line promotes:
marginal integrity
27
The functional cusp bevel promotes:
structural durability
28
The planar occlusal reduction promotes:
structural durability
29
The rounded line angles promote:
structural durability
30
The axial reduction promotes:
retention & resistance
31
A heavy chamfer provides room for:
thicker ceramic margin
32
The ___ of the heavy chamfer decreases material stress in the margin area.
internal rounded angle
33
What are the measurements of a heavy chamfer? (how deep)
1.0-1.2 mm deep
34
What bur is used to accomplish a heavy chamfer?
typically a large round-ended diamond bur
35
Label which chamfer is light and which is heavy:
left: light
right: heavy
36
A ___ margin design produces a close to 90 degree angle
shoulder
37
A shoulder margin design produces a close to ___ degree angle
90
38
A shoulder margin design is primarily used for ____ crowns and ____ crowns where thickness of material is important bur can also be used for ____ crowns
metal ceramic crowns and all ceramic crowns; zirconia
39
Modified shoulder produces a ___ angle
rounded
40
A shoulder margin is typically created with:
flat-end diamond burs
41
In a shoulder margin design, the angle of axial wall and finish line is close to 90 degrees and this functions to:
decrease stresses on restoration material
42
A shoulder margin design is used mostly for ____ and __ crowns
metal-ceramic & all ceramic
43
label the different margins shown:
left: shoulder margin
right: beveled shoulder
44
Some shoulder finish lines can include a bevel at a ___ degree angle
30-45
45
A shoulder with a bevel is often used for ___ & ___
inlays & onlays
46
What type of margin can be used for metal ceramic crowns where there is a metal collar?
beveled shoulder
47
A beveled shoulder allows for ____ of metal to ensure marginal fit
adaptability
48
Significant roughness of preparation finish line can prevent:
close adaptation of crown margin
49
Rough margin = ____ = ____
plaque accumulation; recurrent decay
50
Finish line designs vary based on: (3)
1. restoration material
2. location in the mouth
3. desired results
51
The type of tooth preparation in which the finish line forms a 90-degree angle with the unprepared tooth surface:
shoulder
52
The advantage of this type of margin includes:
- less distortion of crown margins
- provides adequate bulk
- good crown contours
- can attain good esthetics
shoulder
53
The disadvantages of this margin includes:
- marginal adaptation can be affected
- more tooth structure needs to be removed
shoulder
54
Indications of this type of margin include:
- all ceramic crowns
- PFM crowns
shoulder
55
This type of margin is similar to a shoulder but has a bevel placed at the border:
beveled shoulder
56
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 facial margin of posterior metal-ceramic crowns with a supragingival margin
beveled shoulder
57
The advantages of this type of margin include:
- to get proper marginal adaptation
- the bulk of the material in border
beveled shoulder
58
The disadvantages of this type of margin include:
- more tooth structure is removed
- less conservative approach
- preparation should be extended apically
beveled shoulder
59
A finish line designs for tooth preparation in which the gingival aspect meets the external axial surface at an obtuse angle:
chamfer
60
Indications for this type of margin include:
- cast metal restorations
- lingual margin of metal-ceramic restorations
chamfer
61
Advantages of this type of margin include:
- conservative tooth prep
- good marginal adaptation
- provides bulk to the restoration
chamfer
62
Disadvantages of this type of margin include:
- technique sensitive
- any defect in fabrication can lead to unsupported tip of the crown
chamfer
63
Similar to chamfer finish line but comes with a 90 degrees cavosurface angle with a large radius rounded internal angle:
heavy chamfer
64
In cases of metal restorations using a heavy chamfer margin, a ___ is added to the finish line
bevel
65
Indications of this type of margin include:
- ceramic crowns and metal crowns with a bevel
heavy chamfer
66
Advantages of this type of margin include:
- best finish line for a ceramic crown
heavy chamfer
67
Disadvantages of this type of margin include:
- technique sensitive
- little discrepancy can lead to the formation of a lip or unsupported fragile enamel
heavy chamfer
68
Also considered a thin-edge or feather-edge margin:
knife-edge
69
Indications of 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
knife-edge/feather-edge
70
Advantages of this type of margin include:
- Conservative
- Helps in preserving tooth structure
- Ideal for marginal adaptation
- Useful in gold and metal crowns/restorations as it lets you burnish it to a fine finish
- considered an ideal finish line
knife-edge/feather-edge
71
Disadvantages of this type of margin include:
- distinct or proper finish is not visible
- polishing and casting become critical
- overcontouring of restorations to obtain a bulk is a usual complication
knife-edge/feather-edge
72
Crown preparation concerns:
Scientists seem to oscillate back and forth as to whether heat produced during a crown preparation will:
kill the pulp
73
Crown preparation concerns:
It is agreed that the ___ becomes irritated and inflamed during ___.
pulp; crown preparation
74
Crown preparation concerns:
A rise in the pulp temperature by ___ degrees significantly increases the chance of ____.
10 degrees; pulpal necrosis
75
Crown preparation concerns:
Because of the concerns with overheating the pulp during a crown preparation we should: (7)
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 handpiece, an assistant can use air and small amounts of water to help keep tooth cool
76
The main cause of postoperative inflammation and necrosis of the pulp is probably the injury of ____, a tissue in direct functional and physiological connection with the pulp
dentin
77
Margin design instrumentation:
For the preparation what is used? (3)
1. high-speed handpiece
2. air/water spray
3. diamond burs
78
Margin design instrumentation:
For finishing the preparation, what is used? (3)
1. slow-speed handpiece
2. fine diamond burs (possible some carbide burs)
3. hand instruments
79
Margin design instrumentation:
For caries removal of the crown preparation, what is used? (2)
1. slow-speed with 2, 4, or 6 round bur
2. spoon excavators
80
Burs that function too remote enamel and dentin by grinding it away
diamond bur
81
Burs that function to remove tooth by shearing it away:
carbide burs
82
___ burs that are most efficient, 2-3 time faster than ___ burs
diamond; carbide
83
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
carbide burs
84
___ can be used to help smooth finish lines:
hand instruments
85
Hand instruments that can be used to help smooth finish lines include: (4)
1. chisel
2. hatchet
3. hoe
4. margin trimmer
86
Advantages of full metal crowns:
gold and many metal crowns are:
soft metals
87
Full metal crowns are ____ to opposing teeth
gentle
88
Advantages of full metal crowns:
Metal is strong so:
material can be quite thin
89
Describe the preparations involving a full metal crown:
very conservative preparations
90
Advantages of full metal crowns:
metals have some antibacterial properties making:
recurrent decay less likely
91
Describe the effects of most gold and full metal crowns on the gingiva:
gentle
92
_____ crowns are very durable even if warn through or with an endo access
metal crowns
93
In a metal crown, if the contact is missing:
you can add material to the contact to re-establish it
94
List the disadvantages of full metal crowns:
ESTHETICS
95
Discuss the margin design for a full metal crown preparation:
Can use knife edge margin but usually a light chamfer is recommended (0.3-0.5mm)
96
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
6-10; 20
97
In a full metal crown preparation, axial walls can be reduced as little as ____, but can be reduced more if needed.
0.5mm
98
Discuss the occlusal reduction in a full metal crown preparation:
uniform occlusal reduction depth of 1.0-1.5 mm following tooth anatomy
99
Nothing is ___ in dentistry, except for our tools
sharp
100
In a full metal crown preparation, line angles and corners need to be rounded to prevent:
pressure points and possible fracturing of a restorative material
101
In a full metal crown preparation, rounded preps make the:
crown fabrication process easier
102
In a full metal crown preparation, prepared surfaces and finish line are smoothed with a fine grit diamond bur, what does this ensure?
preparation walls are scored but with a smoother more consistent shape for seating and longevity of the restoration
103
Full metal crown summary:
A) Chamfer finish line:
B) Axial reduction:
C) Total occlusal taper:
D) Occlusal clearance:
E) ____ of all line angles
A) 0.3-0.5 mm
B) as little as 0.5mm
C) 6-10 dgrees
D) 1.0-1.5 mm
E) Rounding
104
Label the various tooth preparations: (left to right)
Metal or All-Zirconia
PFM
All-Ceramic
105
A relatively new material that is tooth-colored and ceramic-like:
zirconia
106
Zirconia is considered _____ free
metal
107
Zirconia can have similar properties to:
metal
108
Zirconia can be described as:
very hard and tough
109
Compare the appearance of zirconia to natural teeth:
less translucent
110
What material is seen in the following crown?
zirconia
111
The original zirconia that was very tough and very ugly:
bruxir
112
Why have new iterations of zirconia been created?
to make zirconia more esthetic
113
What is the problem with making new iterations of zirconia that is more esthetic?
In order to make them more esthetic, the strength of zirconia is reduced
114
Depending on the type of zirconia crown, the preparation can be:
as minimal as a full metal crown prep or as extensive as all ceramic crown prep
115
Zirconia is rapidly changing still so what is extremely important?
knowing which kind of zirconia your lab is using so you can prep appropriately
116
The more esthetic your zirconia is, the more ____ will be needed
reduction
117
