dental ceramic

• Ceramic


  Any product made essentially from a nonmetallic material by firing at a high temperature to achieve desirable properties
• Ceramics


  • Brittle, hard, inert, insulating (electric and thermal)
• Porcelain


  A family of ceramic materials composed essentially of Kaolin, Quartz, and Feldspar, also fired at high temperature
• Classification of dental ceramics by fusion temperature

  • High fusing porcelain (1300–1400°C)
  • Medium fusing porcelain (1100–1300°C)
  • Low fusing porcelain (850–1100°C)
  • Ultra-low fusing porcelain (less than 850°C)
• Classification of dental ceramics by use

  • Artificial or denture teeth (mainly made from high fusing porcelain)
  • Jacket crowns, bridges, inlays (medium fusing porcelain)
  • Veneers over cast metal crowns (low fusing ceramics)
  • Used for titanium and titanium alloys (ultralow fusing)

  
• Classification of dental ceramics by processing methods

  • Condensation and sintering
  • Pressure molding and sintering
  • Casting and ceramming
  • Slip casting
  • Machining (milling by computer control) – CAD-CAM ceramics

  
• Classification of dental ceramics by type

  • Feldspathic porcelain
  • Leucite reinforced
  • Aluminous porcelain
  • Glass infiltrated porcelain
  • Glass infiltrated alumina porcelain
  • Glass ceramic
  • CAD – CAM ceramics
  • Sintered ceramic core

  
• Classification of dental ceramics by substructure or core material


  • Cast metal
  • Swaged metal
  • Glass ceramic
  • CAD – CAM ceramic

  
• Medium- and high-fusing ceramics


  • Used for denture teeth

  
• Dental ceramics for ceramic-metal or all-ceramic fixed restorations

  • Belong to the low- or medium-fusing categories

  
• Major applications of ceramics in dentistry

  • Ceramics for metal crowns and fixed partial dentures
  • All-ceramic crowns, inlays, onlays, and veneers, when esthetics is a priority
  • Ceramic denture teeth

  
• Aluminous-core ceramics


  • Have a high modulus of elasticity and high fracture toughness, 40% stronger than traditional feldspathic porcelain
• Aluminous-core fabrication


  Fabricated a platinum matrix on the die and build up a high alumina content ceramic on the matrix then baked in ceramic furnace
• Aluminous-core restorations are now being replaced by heat-pressed or machined all-ceramic restorations with better-controlled processing steps
• Slip casting


  1. Slip is an aqueous suspension of fine ceramic particles in water

  2. The slip is applied on to a porous refractory die that absorbs water from the slip by capillary action and leads to condensation of slip on the die

  3. The die with the slip are fired at high temperature

  4. The die shrinks more than the condensed slip which allows easy separation after firing

  5. The fired porous core is then glass infiltrated
• In-Ceram alumina


  • The alumina content of the slip is more than 90%, short-span anterior fixed partial prostheses can be made using this process
• In-Ceram spinel


  • Contains Magnesium spinel as a major crystalline phase with traces of alumina, more translucent, slightly lower flexural strength than alumina-based, indicated for anterior crowns, inlays and onlays
• In-Ceram zirconia


  • Contains zirconia and alumina, highest opacity and flexural strength, should only be used in posterior regions as crowns or bridges
• Heat pressing


  Relies on the application of external pressure to sinter and shape the ceramic at high temperature, also called high-temperature injection molding
• Sintering


  The process of heating the ceramic to ensure densification, occurs by viscous flow when the firing temperature is reached
• Types of all-ceramic materials for sintering

  • Alumina-based ceramic
  • Leucite-reinforced ceramic
• Aluminous core ceramic


  • Strengthening by dispersion of a crystalline phase, high modulus of elasticity and high fracture toughness, flexural strengths of about 138 MPa and shear strengths of 145 Mpa
• Leucite-reinforced ceramic


  • Leucite acts as a reinforcing phase, higher flexural strength (104 MPa) and compressive strength than conventional feldspathic porcelain
• Machinable all ceramic restorations

  1. Milled to form inlays, onlays, crowns, bridges and veneers by using CAD/CAM technology

  2. Intraoral camera (direct technique) to take an optical impression of the prepared tooth, the image is computerized, the restoration is designed with the aid of a computer, then machined from ceramic blocks by a computer-controlled milling machine
• Advantages of CAD/CAM restorations

  • Digital scans are faster and easier than conventional impressions
  • Patients can receive their permanent restoration the same day
  • No need for provisional restorations
  • High quality due to precise measurements and fabrication
  • Natural appearance due to translucent ceramic blocks and wide range of shades
• Disadvantages of CAD/CAM restorations

  • High initial cost of equipment
  • Expensive software and updates
• Dental ceramics after firing

  • Composed of a glassy (or vitreous) phase surrounding a crystalline phase
  • Increasing the amount of glassy phase lowers the resistance to crack propagation but increases translucency
  • Materials for all-ceramic restorations have increased amounts of crystalline phase (between 35% and 90%) for better mechanical properties