1. Ceramics for Dental Restorations

2. Definitions The term Ceramic is defined as any product made essentially from a nonmetallic material by firing at a high temperature to achieve desirable properties The term Porcelain refers to a family of ceramic materials composed essentially of Kaolin, Quartz, and Feldspar, also fired at high temperature 3. Classification of Dental Ceramics 4. Classification of Dental Ceramics Dental ceramics can be classified according to: 1. Fusion Temperature 2. Application 3. Fabrication Technique 4. Crystalline Phase 5. 1. Fusion Temperature Fusion temperature can be classified to: 1. High-fusing ceramics (1315 to 1370 C) 2. Medium-fusing ceramics (1090 to 1260 C) 3. Low-fusing ceramics (870 to 1065 C) 4. Ultra-low-fusing ceramics (below 870 C) 6. 1. Fusion Temperature The medium- and high-fusing ceramics are used for denture teeth Dental ceramics for ceramic-metal or all- ceramic fixed restorations belong to the low- or medium-fusing categories 7. 2. Application Ceramics have three major applications in dentistry: 1. Ceramics for metal crowns and fixed partial dentures 2. All-ceramic crowns, inlays, onlays, and veneers, when esthetics is a priority 3. Ceramic denture teeth 8. Dental Crowns 9. 3. Fabrication Technique 10. 3. Fabrication Technique One of the most common fabrication techniques for dental ceramics is called Sintering Sintering is the process of heating the ceramic to ensure densification. This occurs by viscous flow when the firing temperature is reached 11. 4. Crystalline Phase After firing, dental ceramics are composed of two phases: 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 12. Ceramic-Metal Restorations (or) Porcelain Fused to Metal (PFM) 13. Ceramic-Metal Restorations Ceramic-metal restorations consist of: 1. Cast metallic framework (or core) 2. Opaque layer, consisting of ceramic rich in opacifying oxides (esthetics & bond) 3. Dentin and enamel ceramics (translucent) 14. Ceramic-Metal Restorations 15. Ceramic-Metal Restorations Composition: 1. In its mineral state, feldspar, the main raw ingredient of dental porcelains, is crystalline and opaque with an indefinite color between gray and pink. Chemically it is designated as Potassium Aluminum Silicate, with a composition of K2O . Al2O3 . 6SiO2. The fusion temperature of feldspar varies between 1125 & 1170 C, depending on its purity 16. Ceramic-Metal Restorations Composition: 2. Pure Quartz (SiO2) crystals are used in dental porcelain and ground to the finest grain size possible. Silica is added, and contributes stability to the mass during heating by providing a glassy framework for the other ingredients 17. Ceramic-Metal Restorations Manufacture: 1. Feldspathic dental porcelains in recent years are made mainly with potash feldspar (K2O, Al2O3, 6SiO2) and small additions of Quartz (SiO2) 18. Ceramic-Metal Restorations Manufacture: 2. After the manufacturing process is completed, feldspathic dental porcelain consists of two phases. One is the vitreous (or glass) phase, and the other is the crystalline (or mineral) phase 19. Ceramic-Metal Restorations Processing: 1. Porcelain Application & Condensation 2. Drying 3. Firing/Sintering 4. Glazing 5. Cooling 20. Ceramic-Metal Restorations 21. Ceramic-Metal Restorations 22. Ceramic-Metal Restorations 23. Ceramic-Metal Restorations 24. All-Ceramic Restorations 25. All-Ceramic Restorations 26. All-Ceramic Restorations Several processing techniques are available for fabricating all-ceramic crowns: 1. Sintering 2. Heat-pressing 3. Slip-casting 4. Machining 27. All-Ceramic Restorations 1. Sintering: Two main types of all-ceramic materials are available for the sintering technique: A. Alumina-based ceramic B. Leucite-reinforced ceramic 28. All-Ceramic Restorations 1. Sintering: A. Alumina-based ceramic: Aluminous core ceramic is a typical example of strengthening by dispersion of a crystalline phase. Alumina has a high modulus of elasticity (350 GPa) and high fracture toughness (3.5 to 4 MPa . m 0.5) Aluminous core porcelains have flexural strengths of about 138 MPa and shear strengths of 145 MPa 29. All-Ceramic Restorations 1. Sintering: B. Leucite-reinforced ceramic: Leucite acts as a reinforcing phase; the greater leucite content (compared with conventional feldspathic porcelain for ceramic-metal applications) leads to higher flexural strength (104 MPa) and compressive strength 30. All-Ceramic Restorations 2. Heat-pressed: Heat-pressing relies on the application of external pressure to sinter and shape the ceramic at high temperature. Heat-pressing is also called high- temperature injection molding. The advantages of heat- pressed ceramics include good esthetics, high strength (but higher opacity). Processing times are short and margin accuracy is within an acceptable range 31. 2. Heat-pressed 32. All-Ceramic Restorations 3. Slip-casting: Slip-casting involves the condensation of an aqueous porcelain slip on a refractory die Materials processed by slip-casting tend to exhibit reduced porosity, fewer defects from processing, and higher toughness than conventional feldspathic porcelains 33. 3. Slip-casting 34. All-Ceramic Restorations 4. Machinable: Machinable ceramics can be milled to form inlays, onlays, and veneers using special equipment. One system uses CAD/CAM (computer assisted design/computer assisted machining) technology to produce restorations in one office visit 35. 4. Machinable 36. General Applications of Ceramics in Restorative Dentistry 37. Veneer 38. Inlay 39. Onlay 40. Thank you