Restorative Material Ceramics PDF

Restorative Material Ceramics Dr. Malak Bamigdad BDS KAU, Saudi Board in Prosthodontic dentistry  Ceramic is any product made from a nonmetallic inorganic material usually processed by firing at a high temperature to achieve desirable properties. What is Porcelain? A type of g...

Restorative Material Ceramics Dr. Malak Bamigdad BDS KAU, Saudi Board in Prosthodontic dentistry  Ceramic is any product made from a nonmetallic inorganic material usually processed by firing at a high temperature to achieve desirable properties. What is Porcelain? A type of glass three-dimensional network of silica. feldspathic glasses modified with feldspars( K2O,Al2O3,6SiO2) and (Na2O,Al2O3,6SiO2) Glass matrix. Quartz(SiO2) fine crystalline dispersion through glass. fluxes sintering temperature , kaolin(binder), metal oxides( colors) The more restrictive term porcelain refers to a specific compositional range of ceramic materials originally made by mixing kaolin. Dental ceramics for metal-ceramic restorations belong to this compositional range and are commonly referred to as dental porcelains. ✓ Classification of Dental Ceramics ✓ General Applications of Ceramics in Prosthetic Dentistry ✓ Mechanical and Thermal Properties of Dental Ceramics ✓ Optical Properties of Dental Ceramics ✓ All-Ceramic Restorations Classification of Dental Ceramics Classification by Application Classification by Fabrication Method Classification by Crystalline Phase  Classification by Application Ceramics have two major applications in dentistry: (1) ceramics for metal-ceramic crowns and fixed partial prostheses. (2) all-ceramic crowns inlays, onlays, veneers, and fixed partial prostheses. Additional ceramic for orthodontic brackets, dental implant abutments, and ceramic denture teeth are available.  Classification by Fabrication Method 1.Sintering: The most common fabrication technique for metal ceramic restorations is called sintering. Sintering is the process of firing the compacted ceramic powder at high temperature to ensure optimal densification. 2.Slip-casting 3.Heat-pressing 4.CAD/CAM machining  Classification by Crystalline Phase After firing, dental ceramics are composed of a glassy (or vitreous) phase and one or more crystalline phases, together with various amounts of porosity. Depending on the nature and amount of crystalline phase and porosity present, the mechanical and optical properties of dental ceramics vary Increasing the amount of crystalline phase may lead to crystalline reinforcement and increase the resistance to crack propagation but also can decrease translucency ( decease esthetic ) Materials for all-ceramic restorations have increased amounts of crystalline  Zirconia (between 35% for leucite- reinforced ceramics and up to 99% for polycrystalline zirconia ceramics such as 3Y-TZP) for better mechanical properties, but they are usually more opaque than dental porcelains for metal-ceramic restorations with low crystallinity. Summary of ceramics Classifications Summary of ceramics Classifications  General Applications of Ceramics in Prosthetic Dentistry Metal-Ceramic Crowns and Fixed Partial Prostheses All-Ceramic Crowns, Inlays, Onlays, and Veneers  Mechanical and Thermal Properties of Dental Ceramics Toughening Methods: Toughening methods for glasses and ceramics can be “built-in” or intrinsic to the material composition or crystalline phase. Crystalline reinforcement and transformation toughening are examples of built-in toughening mechanisms. Specific processing steps, such as tempering, chemical strengthening, or glaze application can also be involved to obtain strengthening. The principle of toughening by crystalline reinforcement is to increase the resistance of the ceramic to crack propagation Transformation toughening (Zirconia) Zirconia presents in three crystallographic shapes at different temperatures: 1. Cubic Phase(from 2680°C to 2370°C) 2. Tetragonal phase (from 2370°C to 1170°C) 3. Monoclinic phase(from 1170°C to room temperature) Tetragonal form of Zirconia can be retained at room temperature by addition of yttrium oxide (Y2O3) Yttrium Partially stabilized tetragonal Zirconia)  Transformation toughening Crack occurs in the Yttria zirconia changes from the tetragonal to monoclinic phase ( increase the size of the crystals ) Compressive stress leading to closing of the crack ( Yattria Zirconia strength (900-1400 Mpa)  The transformation is also called stress-induced and is accompanied by a volume increase with associated compressive stresses in the vicinity of the crack tip, eventually leading to a closing of the crack in the transformed zone Transformation toughening is responsible for the excellent mechanical properties of 3Y-TZP. Tempering and chemical strengthening are extrinsic strengthening techniques based on the creation of a compressive stress layer at the surface of a glass or a ceramic. Tempering is obtained by using rapid but controlled cooling rates whereas chemical strengthening relies on the replacement of small ions with larger ions by diffusion from a molten salt bath in which the ceramic or glass is immersed..  Optical Properties of Dental Ceramics Shade matching is a critical problem in replacing natural teeth Ultraviolet (UV) and visible light rays are reflected and absorbed in different manners by the combination dentin/enamel, compared to porcelain, Translucency is another critical property of dental ceramics. The translucency of opaque, dentin (body), and enamel (incisal) porcelains differs considerably. Opaque porcelains have very low translucency, allowing them to mask metal substructure surfaces. Tin oxide (SnO2) and titanium oxide (TiO2) are important opacifying oxides for dental ceramics. The translucency of materials for all-ceramic restorations varies with the nature of the reinforcing crystalline phase Alumina- and some zirconia-based systems are opaque leucite-reinforced systems are more translucent. Recently, translucent zirconia systems have become available. Dental enamel also exhibits fluorescence. This characteristic is achieved in dental porcelains by adding rare earth oxides (such as cerium oxide). Because the outer layers of a ceramic crown are translucent, the apparent color is affected by reflectance from the inner opaque or core ceramic.  All-Ceramic Restorations Materials for all-ceramic restorations use a wide variety of crystalline phases as reinforcing agents and contain up to 99% by volume of crystalline phase. The nature, amount, and particle size distribution of the crystalline phase directly influence the mechanical and optical properties of the material. Techniques available for fabricating all-ceramic restorations sintering heat-pressing slip-casting CAD/CAM Sintered All-Ceramic Materials Alumina-based ceramic Leucite-reinforced ceramic. Alumina-Based Ceramic The core was baked on a platinum foil and later veneered with matched-expansion porcelain. Aluminous core ceramic is now baked directly on a refractory die. Aluminous core porcelains have flexural strengths approximately twice that of feldspathic porcelains (139 to 145 MPa). Leucite-Reinforced Ceramic: Leucite-reinforced ceramics containing up to 45% The greater leucite content (compared with conventional feldspathic porcelain for metal-ceramic restorations) leads to higher flexural strength (104 MPa) and compressive strength.  Sintered all-ceramic restorations are now being replaced by heat-pressed or machined all- ceramic restorations with better-controlled processing steps. Heat-Pressed All-Ceramic Materials: ceramic ingots are brought to high temperature in a phosphate-bonded investment mold produced by the lost wax technique. Better mechanical properties of many ceramic systems excellent crystal dispersion higher crystallinity, and smaller crystal size compared to sintered all-ceramics. Leucite-Based Ceramic First-generation heat-pressed ceramics contain Leucite (KAlSi2O6 or K2O Al2O3 4SiO2) as a reinforcing phase, in amounts varying from 35% to 55% by volume.  Heat Pressing Lithium Disilicate–Based Materials: The second generation of heat-pressed ceramics contain lithium disilicate (Li2Si2O5) as a major crystalline phase. The final microstructure consists of about 65% by volume of highly interlocking prismatic lithium disilicate crystals Slip-Cast All-Ceramic Materials The term slip refers to an aqueous slurry containing fine ceramic particles. The porosity of the refractory die helps condensation by absorbing the water from the slip by capillary action. The restoration is incrementally built up, shaped, and finally sintered at high temperature on the refractory die. Three types of ceramics are available for slip- casting: alumina-based (Al2O3), spinel-based (MgAlO4), and zirconia-toughened alumina (12Ce-TZP-Al2O3). The main advantage of slip-cast ceramics: ✓ high strength Disadvantages: o high opacity (with the exception of the spinel-based materials) o long processing times. Hard Machining: Fully sintered Material state The restoration is machined directly to final size. Example: CEREC & LAVA Soft Machining: Partially sintered material state Milling of an enlarged restoration to compensate for sintering shrinkage E.g. The CAD/CAM and copy-milling systems (alumina, spinel, or zirconia-toughened-alumina blocks) Thank You