Metal Ceramic restoration (PFM)
_______________ refers to a process of FUSING the porcelain to metal.
"Sintering"
how to apply Opaque layer of porcelain on metal substructure:
*Done in 2 stages: 1. Slurry of opaque & liquid applied in VERY THIN layer - wets metal surface & ensure good metal-to-porcelain bonding 2. applied in THICKER layer - to mask the color of underlying metal
Location of Facial 2-plane reduction:
-@ junction of incisal 1/3 and middle 1/3 of prep
Disadvantages of metal-ceramic restorations:
-Deep tooth preparation depths -Poor resistance to TENSILE forces -Difficult to repair -Porcelain abrades opposing natural teeth
Advantages of metal-ceramic restorations:
-Esthetics -Resistance to forces of occlusion -Resistance to stain and abrasion -Biocompatible
Glazed surface can be developed by 2 methods:
-Glaze powder -Natural glaze or "Autoglaze" (Autoglaze more superior)
Which layer of porcelain requires furnace firing cycle before adding on the next layer?
-Opaque layer (but NOT DENTIN layer; enamel porcelain follows dentin application w/out firing cycle)
List the old materials used in esthetics dentistry :
-Partial veneer crown -Porcelain jacket crowns -Resin-veneered crowns
Purpose of Investment process:
-To capture all wax pattern in a solid material which is capable of maintaining accurate details during burnout procedure.
Purpose of Metal conditioning:
-To ensure clean surface for porcelain bonding -to produce oxide layer which enhances the chemical bonding between porcelain and metal
Indications of Metal-ceramic restoration:
-Uncomplicated anterior/posterior crown -Fixed partial denture restorations -Abutment retainers for removable partial dentures
Contraindications of Metal-ceramic restorations:
-Young patients with large pulps -Where the abrasiveness of porcelain would be too destructive
Removal of moisture from porcelain slurry is usually done by : Why do we need to remove water/moisture?
-absorption into tissue paper (augmented by tapping & vibrating once applied to metal) →allows for DENSE packing of porcelain particles
how to apply Dentin layer ("Body") of porcelain on metal substructure:
-applied over opaque porcelain layer -applied with 20% enlargement to compensate for shrinkage
Dental porcelains are strong against ________________ forces, but weak/ easily fractures against _______________.
-compressive forces -shear & tensile loading
After the casting is recovered, How is the porcelain-bonding surface treated differently?
-inspect for smoothness, correct collar dimension, SHARP metal/porcelain line angle -mill surface w/ clean aluminum oxide stone →→reduce all potential for grinding debris to become imbedded in porcelain-bearing surface
Explain what all are done in "Finish lines" step:
-measure the angle -measure depths of finish lines -remove irregular edges and unsupported enamel -refine, deepen, extend the finish line as necessary
What all are done in "Preparation smoothing" step:
-remove sharp line and point angles -remove prep irregularities (e.g. vertical bur marks) -Smoothen any sharp corners
At the completion of Wax cutback, the Wax forming the bonding surface with porcelain should have a thickness of not less than _________ mm
0.5 mm (area of high esthetic concerns = 0.3mm --> leaves more room for porcelain)
Height of Finish line:
0.5 mm above the gingiva
Lingual concavity is reduced ______ mm.
0.7 - 1.0 mm
Porcelain systems consist of 3 basic components for veneer construction:
1) Opaque 2) Dentin 3) Enamel porcelain
Which burs are used for Occluso-lingual reduction?
1) Round carbide bur (for depth grooves) 2) Diamond wheel bur or football-shaped bur
How to make two-plane reduction:
1. 3 x 1.0mm depth grooves on gingival 1/2 of facial surface (one groove at each line angle + middle) w/ 1DT diamond bur. 2. 3 x 1.0mm depth grooves on labial 1/2 of facial surface
Overall process of PFM fabrication:
1. Full Wax-up 2. Wax cutback on Facial areas (for porcelain veneer) 3. Investment 4. Burnout 5. Casting 6. Casting recovery 7. Porcelain veneer preparation 8. Metal conditioning 9. Porcelain application 10. Veneer finish & glazing 11. Metal polishing
Wax Cutback guidelines for anterior metal-ceramic veneer:
1. Incisal/lingual surface - 1.0 mm gingival to incisal facet and parallel to incisal edge 2. Proximal surface - Lingual to contact area 3. Facial surface - parallel to gingival margin at a 0.3 to 0.5 mm distance
2 types of Firing:
1. Main build-up Firing- firing of a crown after all 3 porcelain layers have been added 2. Correction firing - Firing of crown after any corrections (addition of porcelain, grinding) done after the main firing
Design considerations:
1. Occlusal contact with opposing teeth should NOT occur at junction of metal and porcelain 2. Adequate tooth reductions must be made to accommodate both metal and porcelain. 3. Support for porcelain veneer must be designed into metal framework (no unsupported porcelain allowed b/c weak & fracture-prone )
Wax Cutback guidelines for posterior metal-ceramic veneer:
1. Occlusal surface - Parallel to buccal-occlusal line angle & 1/2 of distance between cusp tips and central groove 2. Proximal surface - buccal to contact area 3. Facial surface - parallel to gingival margin at a 0.3 to 0.5 mm distance
Explain how to do Occluso-lingual reduction:
1. Round carbide bur is used to create depth cuts in checkerboard pattern. 2. Football-shaped bur or diamond wheel bur is used to eliminate the depth grooves and smooth it out.
Steps of Anterior metal-ceramic crown prep:
1. Step through, isolate 2. Incisal reduction 3. Facial axial reduction 4. Axial reduction 5. Occluso-lingual reduction 6. Finish-lines 7. Prep smoothing
What is the purpose of doing 2-plane reduction on facial surface of #9?
1. To accommodate the 2-plane contour of the facial surface of maxillary anterior teeth - this will create uniform thickness of porcelain coating later. 2. To prevent encroaching upon the pulp
Why was Resin considered subpar compared to porcelain?
1. poor abrasion resistance 2. concomitant loss of esthetics
From the full wax-up of a crown, _____________ is cut away from facial surface; and ___________ is cut away from incisal edges or buccal cusp tips.
1.0 mm ; 1.5 mm
gingival-facial surface is reduced ______ mm.
1.0- 1.3 mm
Incisal-facial surface is reduced ______ mm.
1.2 mm
Which bur is used for step through, isolation?
169L bur in (high speed handpiece)
Which bur is used for facial axial reduction?
1DT diamond bur
Which bur is used to make shoulder finish line at interproximal and facial surface?
1DT diamond bur
Amount of reduction @ -Incisal areas of facial surface: -Facial surface near finish line:
2 mm ; 1.0 - 1.3 mm
Incisal surface is reduced ______ mm.
2.0 mm
Tooth preparation for PFM involves reduction of __________ on supporting cusp and ___________ on guiding cusp.
2mm; 1~1.5 mm
Convergence angle should be ______°
3 ° per side
The shoulder finish line should be ________ wide.
> / = 1.0mm
The ideal porcelain-to-metal junction is placed at :
@ 1/2 the distance between center of occlusal surface and buccal-occlusal line angle.
Define Frit:
A mass of fused porcelain obtained by firing the basic constituents and plunging them into water while hot. -It's a ground to make porcelain powders
_______________ material is used for casting high-fusing ceramic alloys.
Alumina casting crucibles
In the wax cutback, finish lines should be ______________
CHAMFER w/ large radius of curvature
Good bonding between metal and porcelain requires ______________.
Clean surface
Well-supported porcelain keeps transmitted forces in ______________ mode, where porcelain strength is GREATEST.
Compressive mode (porcelain is strong against compressive force, and weak against tensile and shear forces)
Explain how Enamel porcelain is added on top of dentin layer:
Cut back some of dentin layer → remaining dentin re-moistened slightly →Apply enamel layer
What causes porcelain to have show-through or "headlight" effect?
Cutting the labial surface straight, without two-plane reduction.
(Opaque/ dentin/ enamel) porcelain layer restores the full crown contour as carved earlier in wax.
DENTIN
(Enamel /dentin) porcelain slurry is slightly more watery and contains more fluid/ moisture.
Enamel
(T/F) When applying Enamel porcelain layer, dentin should act like a sponge, removing enamel moisture.
FALSE ; It should not act like a sponge. Moisture in enamel porcelain is to be retained.
Which finish line is used in facial vs. lingual vs. proximal side?
Facial - > 1.0mm wide- shoulder w/ mildly rounded internal line angle - 90~110° Lingual - chamfer Proximal - shoulder
Typical metal-ceramic crown designs have porcelain covering _____________ surfaces of teeth and a narrow facial collar of ____________ that forms the gingival margin.
Facial surfaces (incisal edge+ buccal cusp tip) ; metal
Which bur is recommended to use for refining the Finish line?
Fine diamond burs
Which instrument is use for the last step, Preparation smoothing?
Finishing burs on slow-speed handpiece
______________ is a ground to make porcelain powders
Frit
(High/ Low) -fusing alloys are required for casting process. Explain why:
HIGH (High-fusing alloys= melt at a very high temperature) →b/c porcelains are sintered & fired at a VERY high temperature. But you want to melt metal at a MUCH HIGHER temperature, b/c metals tend to deform & sag at elevated temperatures.
What does it mean to say a "preparation has been blocked out" ?
It's an unfinished, quickly done product
In Anterior PFM, The Porcelain veneer should extend as far as (Facial / Lingual) to the contact area.
LINGUAL to contact area (you WANT the contact areas to be covered with porcelain) - for Esthetics!
Fro Anterior metal-ceramic veneer outline, the wax is cut back so that proximal surface is (lingual/ buccal) to contact area. Fro Posterior metal-ceramic veneer outline, the wax is cut back so that proximal surface is (lingual/ buccal) to contact area.
Lingual ; Buccal
In the CONTACT area of Posterior PFM, should there be porcelain veneer or metal?
METAL (porcelain veneer in POSTERIOR PFM extends buccal to contact area)
What is the very last step of PFM crown fabrication?
METAL polishing (removal of oxide layer and shine/luster alloy)
2 methods of doing Incisal reduction:
Make depth cuts with: 1) 2.0 mm burr -or- 2) (1.0mm burr) X 2
_______________ refers to a process where a casting is placed in a porcelain furnace and processed under vacuum at 100F temperature above porcelain firing temperature.
Metal conditioning
Compared to other conventional dental alloy investment procedures, it is (easier/ more difficult) to recover castings from phosphate investments.
More difficult
You should position the porcelain-metal junction to where there's no _______________ occurring here.
Occlusal contact
Which step of the tooth preparation is intended to ensure minimum of 0.7mm of clearance between the preparation and the opposing dentition?
Occluso-lingual reduction
Since porcelains and metal are bonded at very high temperature, a heavy layer of ____________ accumulates on metal surfaces.
Oxide layer
_____________ is a special type of investment indicated for metal ceramic alloys that require HIGH melting temperature.
Phosphate-bonded investments (phosphate investments do NOT deteriorate at normal casting and burnout temperature and can withstand high temp)
Where is the transition point between shoulder and chamfer finish line?
Point between mid-proximal and proximal-lingual line angle
BUCCAL cusp tips of both maxillary and mandibular cusp tips are covered with (metal/ porcelain).
Porcelain (Buccal/ facial surface as well as BUCCAL CUSP TIPS are included in the porcelain veneer)
The REMOVAL of oxide layer accumulated on metal surface should be deferred until after ________________.
Porcelain applications are complete.
If you can't perfectly match the coefficient of thermal expansion of ceramic alloy to that of porcelain, It is SAFEST to have a (metal/ porcelain) to have a slightly lower coefficient of thermal expansion.
Porcelain; As the alloy and ceramic cool after sintering, the alloy will shrink the most, placing thin layer of porcelain in a state of compression. → beneficial compression
________________ is an important consideration when porcelain powders are mixed and applied on the metal.
Removal of WATER or moisture.
Which step comes first, staining or glazing?
STAINING
A very tenacious layer of ________________ remaining on the casting makes it difficult to be recovered from investment. This layer can be removed with the aid of ________________.
Silica ; Acid -or- Gritblaster
Stains are applied to a dry surface as you would watercolor paints, except _________________ .
Stain slurry must be MIXED THICK /viscous (to prevent colors from running together or pooling in depressed areas)
Removal of irregular edges and unsupported enamel are accomplished in which step of preparation? Removing SHARP line and point angles are done in which step?
Step6 - " Finish lines " Step7 - "Preparation smoothing"
You don't want to do too much wax removal and resultantly make (thin/ thin) porcelain, because this would be easily prone to fracture. Too (Thin/ Thick) porcelain would have esthetic problems.
Thick Thin
Fracture resistance is best if the porcelain layer is relatively (thin / thick)
Thin
Porcelain bonding to ceramic alloys is enhanced by small amounts of ________________ elements incorporated in alloy formulas.
Tin & Indium
The thermal expansion of Ceramic alloys need to closely MATCH to that of _________________.
Veneering porcelain
As a way of strengthening porcelain restorations, _________________ method has proven remarkably effective.
bonding porcelain to a metal substructure
Primary reason for using Porcelain in dentistry is _______________
esthetics
Strengths and weaknesses of dental porcelain are similar to that of _____________.
glass
Porcelain particles will settle into a DENSE COMPACT state only if there's adequate ________________.
liquid to allow particle movement. (moisture removal is done after porcelain powders settled)
To overcome the esthetic limitations of a poor tooth preparation, the lab technician may _______________.
over-bulk the porcelain, to hide the "show-through" or "head-light" effect of porcelain.
Define Sinter:
to cause or become a coherent mass by heating without melting
