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• Metal-ceramic restorations


  Restorations that consist of a metal framework with a ceramic coating
• Wildman reformulated porcelain to reduce opacity and increase translucency and color

  1838
• Addition of alumina (aluminum oxide, Al2O3)


  • Helped resolve the problem of restoration breakage by increasing strength
• Brecker's method


  Bonding low-fusing feldspathic porcelain to a metal substructure using a gold-based alloy
• After Brecker's development, the range of metal-ceramic alloys increased rapidly with the introduction of the patented Weinstein porcelain
• Porcelain


  Ceramic materials initially derived from a combination of kaolin, quartz, and feldspar sintered at high temperatures
• Metal-ceramic porcelains


  • Elimination of kaolin, addition of alumina, introduction of vacuum firing, and incorporation of a leucite-containing component
• These changes


  Vastly improved the esthetics, increased the strength, and raised the CTE of metal-ceramic porcelains to ensure metal–dental porcelain compatibility, enabling them to be used for numerous dental applications

  
• Classification of porcelain crowns

  • All-ceramic crowns
  • Porcelain Fused Metal (PFM)
• All-ceramic crowns


  • Feldspar ceramic
  • Cast glass ceramics
  • Core reinforced — Aluminous — Injection – molded — Magnesia high expansion
• Porcelain Fused Metal (PFM)

  • Cast alloy
  • Wrought alloy
• Ceramic-metal restorations


  Consist of a cast metallic framework (or core), an opaque layer of ceramic rich in opacifying oxides, and dentin and enamel ceramics (translucent)
• Feldspar


  The main raw ingredient of dental porcelains, is crystalline and opaque with an indefinite color between gray and pink, and is chemically designated as Potassium Aluminum Silicate (K2O . Al2O3 . 6SiO2)

  
• Fusion temperature of feldspar

  Varies between 1125° & 1170° C, depending on its purity
• Building porcelain


  Pack the porcelain which has been spatulated with a liquid binder, in order to minimize inclusion of air in the porcelain particles before firing
• Amount of abutment prepared

  • Should be greater than that in a full porcelain crown to obtain translucency and avoid direct reflection from the opaque layers
• Thickness of porcelain layers

  • Greater than 1.3–1.4 mm in the body portion and 1.5–1.6 mm in the incisal portion to produce a natural shade, with greater thickness required for more translucent shades
• Instruments used for building porcelain

  • Glass plate
  • Kneading spatula
  • Brush
  • LaCron carver
  • Porcelain cutter
  • Locking tweezers
  • Small hammer
  • Tissue paper

  
• Preparing the metal surface

  Grind the metal surface, microblast with 50–100 micron alumina particles
• Applying the flash coating (wash)

  Apply the opaque porcelain in one thin layer on the metal surface, thin enough to see through to the metal
• Opaque porcelains


  Serve three primary functions: wet the metal surface and establish a metal-porcelain bond, mask the color of the metal substructure, and initiate development of the selected shade
• Metal-porcelain bond


  Established when the opaque layer is fired, causing chemical bonds to form with oxides on the metal surface
• Masking power of opaque porcelain

  Influenced by small differences in particle-size distribution and by the amount and color of the oxidized metal casting
• Body porcelain


  Collective term for dentin porcelains, enamel porcelains, translucent porcelains, and body modifiers, mixed with distilled water or a special liquid to prevent rapid drying
• Applying the opaque porcelain

  Use a glass rod rather than a metal instrument to avoid abrasion and contamination
• Dentin and enamel porcelain build-up

  Use a large amount of porcelain, absorb excess moisture with tissue paper or gauze, add small amounts of porcelain like enamel or translucent, condense with light vibration
• Final condensation


  Use the Hot-Air Technique to reduce the build-up time
• Dental glazes


  Composed of colorless glass powder mixed with liquid, applied to the fired crown surface to produce a glossy appearance

  
• Stain powders


  Contain less silica or alumina and more sodium and potassium oxides in combination with special colorant oxides, making them more fluid at high temperatures
• Glazes


  Low-fusing porcelains with considerable fluidity at high temperature, filling small surface porosities and irregularities to re-create the glossy appearance of a natural tooth