full metal and all ceramic restoration principles of tooth prep Flashcards
1
Q
marginal integrity must be?
A
closely adapted to the cavosurface finish line
2
Q
configuration of the finish line dicatates?
A
shape and bulk of material at the margin
3
Q
types of margin finish lines
A
4
Q
Knife Edge Finish Line used with
A
metal
5
Q
Knife Edge Finish Line permits
A
minimal reduction and thin material
6
Q
Knife Edge Finish Line burs
A
flame or needle
7
Q
Knife Edge Finish Line usually?
A
contraindicated
8
Q
seen? casting? fading? distortion?
Knife Edge Finish Line disadvantages
A
- Difficult to see; difficult to cast
ØThe axial reduction may fade out instead of terminating in a definite finish line.
ØSusceptible to distortion in the mouth when the casting is subjected to occlusal forces.
9
Q
can produce? contour?
knife edge difficulty casting, leads to?
A
- Produces thin margin susceptible to distortion (B)
- Leads to over-contoured surface (C)=(Poor emergence profile)
10
Q
can allow for what in this scenarios?
Knife Edge Finish Line (Metal) indications
A
very convex axial surfaces; lingual surface of mandibular posteriors; tipped teeth where the axial surface is at an angle >15o
*It will produce a distinct finish line
*Less destruction of tooth structure
11
Q
knife edge advantages
A
distinct finish line and minimal reduction
12
Q
Chamfer Finish Line usually used with?
A
metal
13
Q
metal finish line?
- Margin Geometry?
- axial depth?
- angle of margin/ internal line angle
- Margin combines?
A
- Margin Geometry – Narrow Chamfer
- (0.3mm) – 0.5mm axial depth
- Produces 30o – 45o acute metal margin / rounded internal angle
- Margin combines an acute edge (adaptability / seating) with a
nearby bulk of metal (strength).
14
Q
bur? diameter?
making the rounded chamfer margin
A
Round-end or torpedo diamond as axial wall is being produced
(1/3 – 1/2 diameter of rotary instrument).
15
Q
axial prep deeper than 1/2 diameter of the bur for rounded chamfer results in?
A
results in an acute, unsupported “lip” of tooth
structure at the margin.
16
Q
heavy chamfer marginal geometry used with what kinds of crowns
A
both metal and ceramic
17
Q
depth of the heavy chamfer, benefits?
A
- Adequate thickness for ceramic support 1-1.2 axial depth
* Internal rounded angle ↓ stresses
18
Q
bur for heavy chamfer
A
Large round/ chamfer diamond
19
Q
Shoulder Finish Line used with
A
Indications:
• Metal Ceramic Margins
• All-Ceramic Crowns
20
Q
shoulder finish line internal line angle
A
90
21
Q
•Modified (Radial) Shoulder difference from normal shoulder?
A
• Rounded internal axio-gingival
line angle
22
Q
bur for shoudler finish line
A
flat end diamond
23
Q
supports?
benefits of a shoulder finish line
A
Supports adequate thickness of ceramic
* Rounded axiogingivalline angle –decreased stresses
24
Q
what finish line is most used for ceramincs
A
shoulder
25
why would a shoulder not be used with cast metal?
unesscessary reduction
26
shoulder with bevel
•Added to a shoulder, a bevel creates an acute edge of metal
(30o– 45o) at a margin.
27
when to use shoulders with bevel
* Inlay / Onlay
* Partial Veneer Crown
* Metal-Ceramic Crown (metal collar)
28
# placement? detection? bulk/reduction?
advantages of the chamfer
*Ease of placement
*Ease of detection on impression; waxing, casting and adaptation to the tooth
*Acute in cross section while providing adequate bulk for strength
minimal destruction
minimal stress
29
roughness at the margin
• Roughness of the tooth surface finish line can prevent
close adaptation of the margin.
• Rough margin → plaque retention
30
chamfer disadvantages with ceramics
reduced strength and poor esthetics with ceramic
31
deep chamfer advantages and disadvantages
32
classic shoulder advantages and disadvantages
33
radial shoulder advantages and disadvantages
34
radial shoulder with bevel pros and cons
35
knife edge pros and cons
36
instruments of prepping, finishing and caries removal
•Preparation: high speed handpiece / air-water
spray with diamond burs
•Finishing: Slow speed w/ diamond or carbide
burs; hand instruments
•Caries removal:slow speed with a #4-6 round
carbide bur; spoon excavators
37
Effect of Temperature Increase on the Pulp
•Raising pulp temperature 6oC ↑ pulp death by 15%.
•Increases of 10oC → 95% incidence of pulp death
38
possible thermal insults to pulp
* Tooth preparation (↑5o-20oC)
* Light curing units (↑5o-20oC)
* Heat of polymerization: resins, provisional materials (↑5o-45oC)
39
how to maintain pulp with thermal threats
§Use copious water spray to cool dentin / pulp
§Use sharp burs / diamonds / high speed, light pressure
§Do NOT marginate crowns “dry”
§Prepare teeth as quickly as feasible / avoid desiccation
40
diamond burs
how they remove strucutre?
efficency?
basic shapes?
• Remove enamel and dentin by grinding
• Most efficient (2-3X faster than carbide burs)
• Basic shapes: round end, flat end, (taper or cylinder);
flame / needle, wheel, torpedo, football / egg
• Diamond cleaning stone (wet)
41
•Tungsten carbide burs
function?
used for?
•Tungsten carbide burs• milling cutters that shear tooth structure from
surface
• cut precise preparation features and smooth
surfaces in enamel and dentin
42
finish line should have what texture
smooth
43
how can we use hand instruments for our prep
* Hand instruments smoothly finish enamel finish lines
| * Refine internal line angles
44
Advantages of Full Metal Crowns
1) coverage? allows for?
2) allows for change?
3) range of application?
Advantages of Full Metal Crowns
1) Complete coverage affords greatest retention and
resistance form
2) Allows for the greatest change in esthetic tooth form
and occlusion
3) Makes it successful in a wide range of situations such as
tooth form or alignment is not ideal and therefore a less
than perfect tooth preparation will be a likely result
45
Disadvantages of Full Metal Crowns
1) esthetic?
2) prep requires?
3) subgingival finish lines?
Disadvantages of Full Metal Crowns
1) Complete metal crowns are not esthetic to many people
and therefore they are often limited to non-visible areas
of the mouth
2) They require more extensive tooth preparation than
partial coverage crowns
3) If the finish line is subgingival around the entire tooth, it
is more likely there will be a less than optimal gingival
response
46
what finish line is recomended for all metal crowns and why
• Chamfer finish lines are recommended for all –metal crowns because they are easy to form, adequately distinct on the tooth and die, and provides sufficient space that the metal is adequately rigid. A depth of 0.3 – 0.5 mm is recommended
47
slope of chamfer line
continuous in cervical direction
48
how to form the chamfer
They are formed by using a diamond
| instrument with a rounded tip and a diameter of 0.6 – 0.8 mm
49
REDUCTION FOR OCCLUSAL CLEARANCE
• Occlusal depth grooves are prepared to a uniform depth of 1.0 – 1.5 mm using a coarse grit diamond. They should follow the pathways and depths of the developmental grooves.
• A depth groove prepared along the entire mesiodistal length of the central developmental groove is very helpful in achieving adequate reduction in an area that is commonly under-reduced.
50
why are rounded line angles so important for casting
• Line angles are rounded to facilitate pouring impressions without trapping
air bubbles and investing wax patterns without air inclusions.
• Additionally, should nodules occur in the casting, they are easier to remove when the line angles have been rounded.
51
Final Finished Surface Of The
| Preparation
• The prepared surfaces and finish line are smoothed using a fine grit diamond that is the same size as the coarse grit diamond used for the initial reduction
52
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Complete Metal Crown - Tooth
Preparation Review
•finish line/depth?
•Axial reduction/ TOC?
•Reduction for occlusal clearance?
•Auxiliary axial resistance form?
•line angles?
```
Complete Metal Crown - Tooth
Preparation Review
•A chamfer finish line that is 0.3 – 0.5 mm in depth
•Axial reduction with 10 to 20 degrees of total
occlusal convergence
•Reduction for occlusal clearance of 1.0 – 1.5 mm
•Auxiliary axial resistance form features as needed
•Rounding of all line angles
53
Advantages of Glass-Ceramic Crowns
1) Esthetic?
2) tissue?
3) tooth preparation?
Advantages of Glass-Ceramic Crowns
1) Esthetic potential / translucency
2) Good tissue response
3) Conservative tooth preparation (??)
i. Compared to MCC preparation (lingual / occlusal metal)
ii. Facial versus lingual
54
Disadvantages of Glass-Ceramic Crowns
1) strength? why?
2) tooth reduction required?
3) Technique?
4) Opposing tooth wear?
5) fracture potential?
6) Fixed partial dental prostheses limitations?
1) Reduced strength
i. No metal substructure
ii. Brittle nature of material
2) Substantial tooth reduction required
3) Technique sensitive
i. Clinical tooth preparation
ii. Resin cementation
4) Opposing tooth wear
5) Greater fracture potential – posteriors ( Zirconia ?)
6) Fixed partial dental prostheses limitations (Zirconia ??)
55
indications for ceramic crowns
1) High esthetic requirement
2) Favorable distribution of
occlusal load
3) Optimal tooth preparation is
possible
i. Ceramic support
ii. Circumferential shoulder or
heavy chamfer
4) When a more conservative
restoration is not indicated
56
finish lines for ceramic
circumferential shoulder or heavy chamfer
57
contraindications of ceramic crowns
1) Molar teeth (FC Zirconia)
i. Increased occlusal load
ii. Decreased esthetic demand
2) Unfavorable occlusion
i. Anterior: edge-edge or cervical 1/5
ii. Bruxism / clenching
3) Inadequate tooth length for
support
i. Ceramic thickness >2-3 mm
ii. Short clinical crowns
4) Inability to produce uniform
circumferential margin
58
Modified Shoulder or Heavy Chamfer provides what qualities for a ceramic crown?
(margin, durable, perio, resistance, esthetics)
marginal integrity
structural durability
periodontal preservation
resistance
esthetics
59
axial reduction provides what qualities for ceramic crowns
retention and resistance
structural durability
esthetics
60
purposes of rounded line angles for ceramic crowns
structual durability
61
concave cingulum reduction purpose
structual durability
62
vertical lingual wall purpose for ceramic crown
retention and resistance
63
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Design Specifications for anterior cermaic crown
• Incisal reduction
• Facial axial reduction
• Lingual axial reduction
• Marginal reduction
```
* Incisal reduction 2.0 – 2.5 mm
* Facial axial reduction 1.2 – 1.7 mm
* Lingual axial reduction 1.0 – 1.2 mm
* Marginal reduction 1.0 – 1.2 mm
64
The Esthetic Benefits of All-Ceramic Crowns
light transmission? \
dentin colors
• Enhanced esthetics due to the absence of metal and improved light transmission. Most beneficial for teeth with normally colored dentin.
With some dark teeth, can use zirconia core to mask dark dentin
65
Ceramic Susceptibility to Fracture
Ceramic Susceptibility to Fracture
• Microcrack formation and propagation due to Stress concentrations and Surface flaws
• No mechanism for yielding to stress w/o fracture (plastic deformation).
66
•Methods of strengthening brittle materials (ceramic)
1. Reinforced Glass Ceramics; Polycrystalline - Zirconia
| 2. CAD-CAM
67
•Methods of design to optimize success of ceramic
1. Management of occlusal forces
2. Restoration design and material
3. Cementation (resin bonding)
4. Tooth preparation design
68
```
Particle-filled Glass-Ceramics
name?
indications?
strength?
cement?
req what occ reduction and shoulder demensions?
```
```
Lithium Disilicate (e.max)
Layered or Monolithic
•Indications:
•Anterior / Posterior crowns
•Anterior FDP
•Inlays / Onlays, Veneers
•Strength: 360-500 Mpa(Moderate)
•Resin cementation
•Requires 1.5-2.0mm occlusal thickness and 1mm shoulder
```
69
```
anterior teeth
occlusal forces? strength req?
what is highly req?
unfavorable occ for ceramics here?
must have?
```
Lower occlusal forces / less strength requirement
• Higher esthetic requirements
• Unfavorable occlusion – edge-edge and cervical 1/5
• Must have adequate tooth support (long walls)
70
posterior teeth
occ forces? strength req?
esthetics?
ceramic failure rates on posteriors?
* Higher occlusal forces → greater strength requirements
* Less esthetic requirement
* Increased failure on molars (zirconia or MCC or metal)
71
what paranormal habit can contraindicate ceramics? possible suggestion?
* Contraindication for glass-ceramic crowns / FDPs
| * Suggest occlusal night guard with ACCs
72
```
All-Ceramic Tooth Preparations
Lithium Disilicate (E.Max) reduction deminsions on posterior and anterior
```
73
Layers of Porcelain and High-Strength Core and necessary reduction
Necessary reduction for thickness:
0.4mm zirconia core +1.0 –2.0 mm porcelain
≈1.2-1.4mm (axial) –2.0-2.5mm (incisal) reduction
74
```
ACC Preparation Design Considerations
• planes?
• margin?
• Avoid what line angles?
• Avoid what proximal angles in finish line?
• Adequate length?
• Uniform?
taper?
```
* Flat planes at right angles to forces
* Modified shoulder (or heavy chamfer) margin
* Avoid sharp line angles (no grooves)
* Avoid steep proximal angles in finish line
* Adequate length of preparation for support
* Uniform axial reduction and minimal taper
75
Sharp line angles promote?
fracture
76
• Incisal reduction should not exceed ___mm.
• Incisal reduction should not exceed 3mm.
77
Short preparations cause considerable _______ and may lead to _________
Short preparations cause considerable stress and may lead to fracture.
• When a load is applied from a lingual direction, the facial shoulder is placed under compression and only the incisal-lingual length of the preparation provides significant resistance to this force.
78
Effect of Taper on Strength
• Excessive porcelain bulk?
• what gives strength to crown?
Effect of Taper on Strength
• Excessive porcelain bulk decreases strength.
• It is not the bulk of porcelain that gives strength to the crown, but the resistance to flexure provided by support from the tooth preparation and
accuracy of fit.
79
shoulder support at margin for ceramics
cause?
what provides support?
excessive slope finish lines?
• Occlusal loading → tensile/shear stress → fracture
• 90o shoulder helps provide support for porcelain
• Heavy Chamfer adequate with resin bonded cementation
• Excessively sloped finish line or bevel creates thin unsupported margin of
porcelain –prone to fracture
80
All-Ceramic Margin Designs
• A rounded internal angle on the modified shoulder
decreases stress at the axiogingival line angle.
• A heavy chamfer is relatively simple to form.
• Supragingival(subgingival difficult to avoid “lip”)
• Enamel/ resin bonding
81
Effect of Finish Line Form
• Avoid?
• Uniformity and smoothness?
* Avoid excessive cervical slope / bevel
* Avoid rapid occluso-cervical undulations
* Uniformity and smoothness improves marginal fit
82
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TOOTH PREPARATIONS
CAD/CAM All-Ceramic Restorations
occ reduction?
inciso-cervical height?
finish lines?
shoulder finish line?
line angles?
```
* Adequate occlusal reduction (2 mm) and lingual reduction (1 mm)
* Inciso-cervical height should not be greater than 10.5mm – length of milling diamond)
* Well-defined, smooth finish lines
* Shoulder finish lines with rounded axio-gingival line angles
* Rounded line angles: Incisal edge and internal angles ≥ 1mm wide
