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Fixed Prostodontics > Full metal & all ceramic restorations > Flashcards

Full metal & all ceramic restorations Flashcards

1
Q

• The restoration can survive in the biologic environment of
the oral cavity only if

A

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

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2
Q

The configuration of the preparation finish line dictates the

A

shape and bulk of restorative material in the margin of the
restoration.

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3
Q

Marginal Integrity
• It also can affect both

A

marginal adaptation and the degree of
seating of the restoration

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4
Q

CERVICAL FINISH LINES
Marginal Geometry – Margin Types
(5)

A

•Knife Edge
•Chamfer
•Shoulder
• Radial (Modified) Shoulder
•Bevel (Beveled Shoulder)

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5
Q

Knife Edge Finish Line (Metal)
(5)

A

• Permits very acute margin of
metal
• Most conservative preparation type
• Flame or needle diamond
• Generally contraindicated
• Difficult to see; difficult to cast

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6
Q

Knife Edge Finish Line (Metal)
Other Disadvantage’s:
(2)

A

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.

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7
Q

Knife Edge Margin
• Difficult to wax / cast →
(2)

A

• Produces thin margin susceptible to
distortion (B)
• OR Leads to over-contoured surface (C)
• (Poor emergence profile)

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8
Q

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

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9
Q

Chamfer Finish Line: Metal
• Margin Geometry – Narrow Chamfer
(3)

A

• (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).

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10
Q

Chamfer Finish Line: Metal
Round-end or torpedo diamond as axial wall is being produced
(1/3 – 1/2 diameter of rotary instrument).
• Axial preparation deeper than ½ diameter
results in

A

an acute, unsupported “lip” of tooth
structure at the margin.

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11
Q

Chamfer Finish Line: Ceramics
• Marginal Geometry

A

• Heavy Chamfer Metal-ceramic / Ceramic Crowns
- Adequate thickness for ceramic support
- Internal rounded angle ↓ stresses
- 1 – 1.2 mm axial depth
• Large round-end or chamfer diamond

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12
Q

Shoulder Finish Line
(2)

A

• 90o Cavo surface angle
• Flat-end diamond

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13
Q

Shoulder Finish Line
• Indications:
(2)

A

• Metal Ceramic Margins
• All-Ceramic Crowns

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14
Q

Modified (Radial) Shoulder

A

• Rounded internal axio-gingival
line angle

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15
Q

Shoulder Finish Line
• Cavosurface angle of 90o
(2)

A

• Supports adequate thickness of ceramic
• Rounded axiogingival line angle – decreased stresses

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16
Q

• Finish line most used for ceramic margins

A

Shoulder Finish Line

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17
Q

Shoulder Finish Line
Generally not used for cast metal
• WHY NOT?

A
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18
Q

Shoulder with Bevel

A

• Added to a shoulder, a bevel creates an acute edge of metal
(30o – 45o) at a margin.
- Inlay / Onlay
- Partial Veneer Crown
- Metal-Ceramic Crown (metal collar)

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19
Q

Chamfer is well suited for a complete cast crown:
(3)

A

• 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

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20
Q

Marginal Integrity Problems:
Roughness
(2)

A

• Roughness of the tooth surface finish line can prevent
close adaptation of the margin.
• Rough margin → plaque retention

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21
Q

• Preparation:

A

high speed handpiece / air-water
spray with diamond burs

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22
Q

• Finishing:

A

Slow speed w/ diamond or carbide
burs; hand instruments

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23
Q

• Caries removal:

A

slow speed with a #4-6 round
carbide bur; spoon excavators

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24
Q

• Raising pulp temperature 6oC ↑ pulp death by —%.

A

15

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25
• Increases of 10oC → --% incidence of pulp death
95
26
• Thermal Responses: (3)
• Tooth preparation (↑5o-20oC) • Light curing units (↑5o-20oC) • Heat of polymerization: resins, provisional materials (↑5o-45oC)
27
• Thermal Responses: (3)
• Tooth preparation (↑5o-20oC) • Light curing units (↑5o-20oC) • Heat of polymerization: resins, provisional materials (↑5o-45oC)
28
Effect of Temperature Increase on the Pulp how to avoid (4)
§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
29
Instrumentation: Diamond Stones (4)
• 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)
30
Tungsten carbide burs (2)
• milling cutters that shear tooth structure from surface • cut precise preparation features and smooth surfaces in enamel and dentin
31
Twist drills (2)
• cutting edges on the tip and fluted sides • bore small-diameter holes in dentin for pins
32
Preparation finish line smoothness is important to
marginal fit and longevity. (Preparation surface roughness does not affect retention.)
33
Instrumentation • Hand instruments
smoothly finish enamel finish lines • Refine internal line angles • Chisel • Hoe • Hatchet • Margin trimmer
34
Advantages of Full Metal Crowns (3)
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
35
Disadvantages of Full Metal Crowns (3)
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
36
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 --- is recommended
0.3 – 0.5 mm
37
Chamfer finish lines exhibit a ---. They are formed by using a diamond instrument with a rounded tip and a diameter of ---
continuous cervical slope 0.6 – 0.8 mm
38
The tooth is reduced until --- of the instrument diameter is located within the tooth. The rotary instrument is then moved around the tooth perimeter while maintaining the desired depth
½
39
Axial Reduction The axial surfaces (facial, lingual, mesial, distal) are reduced using a
tapered round – end diamond instrument so they converge occlusally within the range of 10 to 20 degrees of total convergence
40
REDUCTION FOR OCCLUSAL CLEARANCE • Occlusal depth grooves are prepared to a uniform depth of --- using a coarse grit diamond. They should follow the pathways and depths of the developmental grooves.
1.0 – 1.5 mm
41
REDUCTION FOR OCCLUSAL CLEARANCE A depth groove prepared along the entire --- length of the central developmental groove is very helpful in achieving adequate reduction in an area that is commonly underreduced.
mesiodistal
42
Line angles are rounded to facilitate pouring impressions without
trapping air bubbles and investing wax patterns without air inclusions.
43
Additionally, should nodules occur in the casting, they are easier to remove when the
line angles have been rounded.
44
Rounding Lines Angles for Cast Metal Crowns* (3)
• Facilitates pouring impressions without voids in the dies • Facilitates investing wax patterns without air inclusions and resulting casting nodules • When casting nodules are present, they are easier to remove.
45
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 • A coarse grit diamond that has been used multiple times for initial tooth reduction and sterilized multiple times can also be used as it will no longer create the roughness it once produced
46
Complete Metal Crown - Tooth Preparation Review •A chamfer finish line that is --- mm in depth •Axial reduction with --- degrees of total occlusal convergence •Reduction for occlusal clearance of --- mm •Auxiliary axial resistance form features as needed •Rounding of all line angles
0.3 – 0.5 10 to 20 1.0 – 1.5
47
Advantages of Glass-Ceramic Crowns (3)
1) Esthetic potential / translucency 2) Good tissue response 3) Conservative tooth preparation (??) i. Compared to MCC preparation (lingual / occlusal metal) ii. Facial versus lingual
48
Disadvantages of Glass-Ceramic Crowns (6)
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 ??)
49
Glass-Ceramic Crowns Indications (4)
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
50
Glass-Ceramic Crowns Contraindications (4)
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
51
Modified Shoulder or Heavy Chamfer (5)
marginal integrity structural durability periodontal preservation resistance esthetics
52
Axial Reduction (4)
retention and resistance structural durability esthetics
53
Vertical Lingual Wall (1)
retention and resistance
54
Concave Cingulum Reduction (1)
structural durability
55
Rounded Line Angles (1)
structural durability
56
Design Specifications: All Ceramic Crown • Incisal reduction • Facial axial reduction • Lingual axial reduction • Marginal reduction
2.0 – 2.5 mm 1.2 – 1.7 mm 1.0 – 1.2 mm 1.0 – 1.2 mm
57
The Benefits of All-Ceramic Crowns
• Enhanced esthetics due to the absence of metal and improved light transmission. Most beneficial for teeth with normally colored dentin
58
• With some dark teeth, can use --- to mask dark dentin
zirconia core
59
Ceramic Susceptibility to Fracture (2)
• Microcrack formation and propagation - Stress concentrations - Surface flaws • No mechanism for yielding to stress w/o fracture (plastic deformation).
60
Biomechanical Factors: Overcoming Deficiencies in Glass Ceramic Restorations • Methods of strengthening brittle materials: (2)
1. Reinforced Glass Ceramics; Polycrystalline - Zirconia 2. CAD-CAM
61
Biomechanical Factors: Overcoming Deficiencies in Glass Ceramic Restorations • Methods of design to optimize success: (4)
1. Management of occlusal forces 2. Restoration design and material 3. Cementation (resin bonding) 4. Tooth preparation design
62
Particle-filled Glass-Ceramics Lithium Disilicate (e.max) Layered or Monolithic • Indications: (3)
• Anterior / Posterior crowns • Anterior FDP • Inlays / Onlays, Veneers
63
Particle-filled Glass-Ceramics Lithium Disilicate (e.max) Layered or Monolithic • Strength:
360-500 Mpa (Moderate)
64
Particle-filled Glass-Ceramics Lithium Disilicate (e.max) Layered or Monolithic • --- cementation • Requires --- occlusal thickness and --- shoulder
Resin 1.5-2.0mm 1mm
65
Glass Ceramics and Opposing Occlusal Forces Anterior teeth (4)
• Lower occlusal forces / less strength requirement • Higher esthetic requirements • Unfavorable occlusion – edge-edge and cervical 1/5 • Must have adequate tooth support (long walls)
66
Zirco(YTZP): Core / Ceramic Veneer or Full Contour Crown Core thickness :
0.4mm minimum (layered with 1–2mm porcelain) Full-contour zirconia with porcelain glaze (complete metal prep requirements)
67
Glass Ceramics and Opposing Occlusal Forces Posterior teeth (3)
• Higher occlusal forces → greater strength requirements • Less esthetic requirement • Increased failure on molars (zirconia or MCC or metal)
68
Glass Ceramics and Opposing Occlusal Forces Bruxism / clenching (2)
• Contraindication for glass-ceramic crowns / FDPs • Suggest occlusal night guard with ACCs
69
50% increase in fracture strength ACC with adhesive
resin cement
70
Layers of Porcelain and High-Strength Core 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
71
ACC Preparation Design Considerations (6)
• 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
72
Sharp line angles promote fracture (3)
• A sharp incisal edge may be reduced until a flat area is obtained. • Incisal reduction should not exceed 3mm. • Incisal edge ≥ 1mm wide (CAD-CAM)
73
Adequate Tooth Preparation Length for Support 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
74
Effect of Taper on Strength (2)
• 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.
75
Shoulder Provides Support at Margin (3)
• 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
76
All-Ceramic Margin Designs (2)
• 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
77
Effect of Finish Line Form (3)
• Avoid excessive cervical slope / bevel • Avoid rapid occluso-cervical undulations • Uniformity and smoothness improves marginal fit
78
TOOTH PREPARATIONS CAD/CAM All-Ceramic Restorations
• 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

Fixed Prostodontics (19 decks)

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