Podcast
Questions and Answers
What is the primary risk associated with insufficient support for incisal porcelain in framework design?
How far away should the junction of the porcelain and metal be from centric occlusal contacts to prevent porcelain fracture?
What is the effect of having proximal contacts on porcelain for anterior teeth?
What compensatory method should be used for deficiencies in the incisal edges or cusps of prepared teeth?
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What is the benefit of a wrap-around effect of porcelain on metal?
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Which milling technique is primarily used for the fabrication of zirconia crowns and bridges?
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What is a significant advantage of dry milling over other milling techniques?
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Which material is necessary for wet milling processing?
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What is a drawback of using acrylic resin for temporary jacket crown construction?
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What is one of the main steps in the construction of an acrylic jacket crown?
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How does wet milling protect the milling diamond or carbide cutter?
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What is the maximum allowable difference in the coefficient of thermal expansion (CTE) between porcelain and metal for metal-ceramic restorations?
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In the construction process of an acrylic jacket crown, what is used to eliminate the wax pattern?
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Which of the following statements about base metal alloys in metal-ceramic restorations is true?
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What is a key reason for using ivory wax in the creation of the wax pattern for acrylic resin crowns?
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What property must a metal ceramic alloy possess to prevent bending in long span bridges?
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What is the minimum noble metal content required for an alloy to be classified as noble according to the American Dental Association?
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Which of the following metals is NOT typically included in base metal alloys for metal-ceramic restorations?
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Why is it important for the melting range temperature of the metal to be higher than the fusing temperature of the porcelain?
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What is the function of surface oxides in metal-ceramic restorations?
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Which of the following combinations of metals is typically found in high noble alloys?
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Which technique is specifically used for the fabrication of e.max crowns and bridges?
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What is the purpose of the staining technique in the IPS Empress II process?
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Which of the following materials is used in the Cut-Back Technique for achieving aesthetic appearance?
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What is the initial step in the Layering technique for pressed core restoration?
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Which casting option is associated with the use of DICOR?
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In IPS Empress II, which technique is utilized when building a wax pattern to the full contour for a partial restoration?
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What is a key requirement for the success of all ceramic restorations?
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What type of porcelain is used in the platinum foil technique?
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In which scenario is an all ceramic crown particularly indicated?
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Which of the following materials is primarily used in the machined casting method?
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What type of load distribution could contraindicate the use of all ceramic restorations?
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Which of these characteristics does NOT pertain to all ceramic restorations?
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Which condition is considered a contraindication for all ceramic restorations?
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Which of the following materials are commonly mentioned for high strength ceramics in fixed prosthodontics?
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What type of fracture is typically associated with improper occlusion in all ceramic restorations?
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What is typically NOT a reason to use an all ceramic crown?
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Study Notes
All Ceramic Restorations
- All ceramic restorations are made with special porcelain types and techniques that overcome the disadvantages of traditional all ceramic restorations.
- These restorations are known for their esthetic appeal, resembling natural tooth structure in terms of color and translucency.
- Success requires careful patient selection, proper tooth preparation, restoration construction, and favorable occlusion with centric contact limited to the middle third of the lingual surface.
Definition
- A non-metallic extracoronal restoration covering the prepared clinical crown that restores aesthetics, anatomy, and function.
Indications
- Where superior aesthetics are demanded.
- As a single crown or bridge retainer in short span bridges with high-strength ceramics like Inceram and Empress II.
- Fractured anterior teeth.
- Discolored anterior teeth:
- Generalised discoloration like tetracycline staining.
- Localized discoloration after root canal treatment.
- Mottled, pitted, and hypoplastic teeth.
- Bilateral proximal decay.
- To realign malposed or rotated teeth.
- To correct malformed teeth like peg-shaped teeth, diastemas, microdontia, amelogenesis imperfecta, and fluorosis.
- Restore root canal teeth needing high aesthetic requirements.
Contraindications
- Unfavorable load distribution: Deep bite and edge-to-edge relationship. Occlusion on the cervical third of the lingual surface creates tensile stress leading to a characteristic half-moon fracture.
All Ceramic Fabrication Techniques
- Platinum foil technique with feldspathic or aluminous porcelain.
- Centrifugal casting (castable ceramics) with DICOR.
- Refractory die technique with Hi-ceram.
- Hand-stacked (powder slurry) with Empress 1 and 2.
- Glass infiltrated with In-ceram spinell, In-ceram alumina, and In-ceram zirconia.
- Machined with CAD/CAM using zirconia blocks, Empress 2 blocks, and Celay System.
Heat Pressed Casting
- Used for fabrication of e.max crowns and bridges using e.max ingots.
IPS Empress II (e-max Ingot) Processing Techniques
- Staining technique: A full contour wax pattern is built, which is then pressed and finished with staining materials (IPS e.max ceramic shade, Essence) and glazing materials (IPS e.max ceram glazing paste or powder).
- Cut-back technique: A full contour wax pattern is built and then the incisal and/or occlusal area is cut back. The anatomical shape and esthetic appearance are completed by applying IPS e.max ceram layering materials (Impulse, Transpa, Transpa Incisal).
- Layering technique: A wax pattern is built to form the framework of the restoration to gain a pressed core restoration.
Dry Milling
- Used for fabrication of zirconia crowns and bridges.
- Advantages: pressurized air, vacuum, easier cleaning, decreased shrinkage after firing, less time and cost.
Wet Milling
- Used for fabrication of e.max crowns and bridges with IPS e.max CAD.
- The cutting tool and milling stock are continuously bathed in cool liquid, removing material from the milling disc or block.
- Necessary for all metals and glass ceramic materials.
- Recommended for zirconium oxide ceramic with a higher degree of pre-sintering.
- Higher pre-sintering reduces shrinkage factor and enables less sinter distortion.
- Longer bur lifespan but more cleaning time.
Acrylic Jacket Crown Construction
- Used for temporary jacket crown construction.
- Advantages: easy construction, inexpensive, suitable for young patients.
- Disadvantages: low wear resistance, low abrasion resistance, discoloration.
- Steps: Impression, cast, die, tin matrix, wax pattern, flasking of wax pattern, wax elimination, packing (wet or dry), flasking, curing, cooling, deflasking, finishing, and polishing.
Metal Ceramic Restorations
- Complete coverage cast metal crown veneered with a layer of fused porcelain.
Alloys Used in Ceramo-Metallic Restorations
- Classified by the American Dental Association (ADA) according to their noble metal content:
- High Noble: Gold content > 40 wt% and noble metal content > 60 wt%.
- Noble: Noble metal content > 25 wt%.
- Base Metal: Noble metal content < 25 wt%.
- Dental alloys fused to porcelain:
- High Noble Metal Alloys: Au-Pd-Ag, Au-Pd, 60% noble metal, 40% gold.
- Noble Metal Alloys: Pd-Ag, Pd-Cu-Ga, Pd-Ga.
- Base Metal Alloys: Ni-Cr, Co-Cr, Ti.
Requirements of Alloys for Metal-Ceramic Restorations
- Difference in coefficient of thermal expansion between porcelain and metal should be less than 1 x 10^-6 0C to avoid shear stress during cooling and failure of the bond.
- Melting range temperature of the metal should be higher than the fusing temperature of the porcelain by 170-280 0C to avoid metal flow, creep, and deformation.
- High yield strength to decrease coping thickness.
- High modulus of elasticity to avoid bending in long span bridges.
- High sag resistance to avoid thermal distortion.
- Surface oxides must be produced for chemical bonding with dental porcelain. Base metal alloys oxidize readily, while noble alloys do not, so trace amounts of base elements are added to noble alloys for oxidation.
Considerations for Metal Ceramic Restorations
- Unsupported thick porcelain can lead to sub-surface porosity.
- No occlusal contacts on the porcelain/metal interface: Porcelain must be away from all centric occlusal contacts by 1-1.5 mm to avoid metal flow and fracture.
- Proximal contacts on anterior teeth should be on porcelain for better aesthetics and translucency. Contact on metal blocks light transmission and creates poor aesthetics.
- Facilitates the wrap-around effect: Metal is designed to allow porcelain wrap-around for resistance against splitting and better translucency and aesthetics.
- Compensates for deficiencies in tooth preparation: Metal is used to compensate for deficiencies in the incisal edges or buccal and lingual cusps, maintaining even and minimal porcelain thickness.
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Description
This quiz covers the fundamentals of all ceramic restorations, focusing on their composition, advantages, and clinical indications. Learners will explore the importance of aesthetics, tooth preparation, and occlusion in achieving successful restoration outcomes. Understand the diverse applications of these materials in dental practices.
