Metal-Ceramic Restorations Flashcards
Metal-Ceramic Restorations
- A metal casting (coping) which fits over the prepared tooth with
ceramic fused to it.
Metal-Ceramic Restorations
* Combines
the strength and accuracy of cast metal with esthetics of
porcelain.
Indications for Metal-Ceramic Restorations
* Need for full coverage with esthetic demands:
(3)
- Extensive tooth destruction
- Large restorations / undermined enamel
- Opposing ceramic surfaces
Advantages of Metal-Ceramic Restorations
(4)
- Natural appearance - esthetics
- Retention and resistance qualities of full crown
- More resistant to fracture than all-ceramic / dependable fabrication of FPD
- Preparation is less demanding than Partial Veneer Crown
- More resistant to fracture than all-ceramic / dependable fabrication of FPD
(2)
- Greater strength w/ less reduction than all-ceramic
- Ability to have metal occluding surfaces
Key Tooth Preparation Form
Decisions
(2)
*Finish line form (3 types have been
used: chamfer; shoulder; and
shoulder-bevel)
*Margin design
Shoulder With A Beveled Finish Line
(2)
- Some people think it makes for a better fitting
crown - It is certainly acceptable to use such a finish line
but it does not make the crown fit better and it does
not work with a porcelain margin
Shoulder Finish Lines
- Shoulder finish lines provide greater cervical space for
an esthetic thickness of porcelain without
overcontouring the crown and can be used with
porcelain margins
Why Use A Shoulder Finish Line
- Need for optimal porcelain thickness near the margin for
esthetics and particularly when optimal reduction is not
possible
Why Use A Shoulder With A Rounded
Axiogingival Line Angle
(3)
- Easier to prepare than a sharp angle
- Required for any crown that will be milled
- Produces less tooth weakening than sharp
axiogingival line angles for small teeth or RCT,
teeth that will be subjected to greater force since
they are FPD abutments, and teeth with
substantial secondary dentin where there is very
little pulp space remaining (older patients)
Margin Design
* Metal collar –
ease of fabrication for non-esthetic
situations
- Metal thinned to a fine line that is barely visible –
improved esthetics compared to metal collar but
more opacity than porcelain margin
- Porcelain (collarless metal ceramic crown)
– most
esthetic result but requires very skillful technician
Why Use A Shoulder Finish Line And Ceramic
Margin
(2)
- Enhanced cervical esthetics
- When there is gingival inflammation due to
overcontoured crowns and you want to make slightly
undercontoured crowns to improve the gingival
response
Legitimate Reasons for Extending
Margins Subgingivally…
(6)
- Existing caries
- Extensions of previous restorations
- Subgingival tooth fracture
- Root sensitivity
- Retention/ Resistance
- Esthetics
Extending a margin subgingivally…
*To hide a ceramic or metal-ceramic margin
for esthetics
(2)
- Should not extend more than ½ way into sulcus.
- Well-adapted, smooth, proper axial contour
Preservation of the Periodontium: Axial Contours
* Emergence Profile: t
he part of the axial contour that extends from the
base of the gingival sulcus past the free margin to the height of contour.
* Straight or slightly concave; not bulky or excessively convex
Problems with Porcelain / Ceramics
(3)
- Porcelain is subject to brittle fracture
- Internal stresses
- Excessive thickness (>3mm)
Problems with Porcelain / Ceramics
(2)
- Porcelain abrasiveness – wear to
opposing enamel / metal - Hardness and microscopic roughness
Metal-Ceramic Crown vs. Complete Metal
Crown
*Advantages:
(1)
- Esthetics
Metal-Ceramic Crown vs. Complete Metal
Crown
*Disadvantages:
(1)
- Increased removal of tooth structure
Metal-Ceramic Preparation
Requirements are based on:
(3)
- Fundamentals of Tooth Preparation:
- Material requirements (components):
- Esthetic requirements
- Fundamentals of Tooth Preparation:
(1)
- Retention and resistance form
- Material requirements (components):
(2)
- Porcelain
- Metal
- Esthetic requirements
(2)
- Extent of porcelain coverage
- Margin design and placement
Marginal Geometry – Cervical Finish Line
Form
(2)
- Shape and bulk of restoration margin
- Marginal adaptation and degree of seating
Geometry of Cavosurface Finish Line: Margin angles of less than 25o may produce a metal
margin that is
too thin and weak.
Preservation of the Periodontium
Location of the Margin
* Subgingival margins are difficult to evaluate
(2)
- Christensen: 120μ marginal gaps undetected
- Bjorn: 40-50% with 0.2-0.3mm defects
“Biologic Width”
- The combined connective tissue-epithelial attachment from the alveolar
crest to base of the gingival sulcus (approximately 2 mm). - (+ 1 mm for a healthy gingival sulcus = 3mm free gingival margin to alveolar crest.)
Anterior Metal-Ceramic Preparation
* Resistance Form: Facial – Lingual Preparation
- Parallel to the facial cervical 1/3 - 2/3 of prep
- Lingual wall height is limited:
- need “ideal” taper for resistance form in F-L direction
- prevents dislodgment in protrusive and lateral
Anterior Metal-Ceramic Preparation
* Proximal Axial Wall Preparation:
- Longest opposing axial walls
- Most of the retention form comes from the parallel M-D surfaces
Material Requirements
* Adequate room for restorative materials
* Porcelain
(2)
* Metal
(2)
* Masking of metal
(2)
- Opaque, body, incisal
- Support (shoulder)
- Substructure strength
- Restoration fit
- Porcelain thickness
- Optimum esthetics
Components of the Metal-Ceramic Restoration
* Metal coping:
* Opaque porcelain:
* (Shoulder porcelain)
* Gingival, body, and incisal porcelain:
0.3-0.5 mm veneered areas
0.8-1.0 mm un-veneered areas
~ 0.1-0.2 mm
~ 0.8 mm
0.8 – 1.5 / 2 mm
Two-Plane Facial Reduction (Morphologic Reduction):
Allows adequate reduction for uniform color / contours and resistance.
Inadequate reduction → bulky contour or opaque “bright spot”
Over-reduction → decreased resistance / pulpal insult.
Single Plane Under-reduction: “Bright spots”
Inadequate reduction results in light reflection from the
opaque porcelain
Single-Plane – Over-reduction
(3)
- Pulpal “blush” / pulpal exposure
- Axial reduction → approaches pulp quickly
- 1.2 – 1.5mm at cervical is often too much
- Amount removed ↑ with ↑ TOC preparation
- ↑TOC = ↓Resistance form
Uniform facial
reduction
(multi-plane)
provides space
for
uniform
color and
normal crown
contours
DEPTH GROOVES: Uniform tooth reduction
(2)
- Select / measure the diamond with diameter that equals desired
reduction depth ~ 1.2 mm. - Form depth grooves using the full instrument diameter in both facial
planes.
Uniform proximal reduction facilitates
the development of
normal appearing
proximal color and translucency
Porcelain proximal surface allows light transmission
Adequate reduction through — is necessary
interproximal
*Proximal wing of preparation → metal in proximal → blocks light
transmission
Elimination of proximal wings with gradual
transition from facial to lingual allows more
esthetic
proximal porcelain surface.
Extension of facial shoulder reduction slightly
greater than — lingual to contact; gradual blend
to lingual
1mm
Anterior Metal-Ceramic Design
Porcelain Shoulder
(Collarless M-C Crown)
Depth:
* Finish Line Geometry:
1.2 mm
* Modified (Radial)
Shoulder
Anterior Metal- Ceramic Design
* Margin framework
design:
* Margin Geometry
- Disappearing Margin
- Heavy Chamfer
- (Modified Shoulder)
Margin Placement Anterior Teeth:
(3)
- facial is often subgingival for esthetics
- supragingival if no significant esthetic contraindication
- may depend on the type of ceramic restoration used and framework design
Metal-Ceramic Coping Design: Margin
* Metal Collar
* Width:
(3)
* Finish Lines used:
(2)
0.3-0.5mm
* Marginal integrity
* Finish
* Compromised esthetics
- Shoulder with bevel
- Heavy chamfer
- Why use a metal collar?
(3)
- Ease of fabrication
- Include thin, unsupported tooth structure
- Extend margin apically with less tooth reduction
Components of Metal-Ceramic Crown
Coping Design: Posterior Occlusal
— thickness – porcelain
+ — thickness – metal
— mm total
1.5 mm
0.5 mm
2.0
Metal Occlusion
(4)
- less tooth reduction
- less opposing tooth wear
- stronger restoration
*1.5mm occlusal reduction
Porcelain Occlusion
(4)
- Esthetic zone
- Generally NOT 2nd Molars
- Opposing ceramic surfaces
- 2.0mm occlusal reduction
