All Ceramic Restoration By Dr- Tayseer Mohamed Feldspathic porcelain Porcelian fused to metal All ceramic restoration Porcelian baked on platinm foil. Composed of 90% amorphous phase. Used only for anterior crown. Porcelain baked on cast metal framework Porcelian baked on Ceramic crystalline core. Used for anterior and posterior restoration. Used for anterior and posterior restoration. Very brittle if used posteriorly occlusal forces subject them to tensile stress. Strong ductile metal Crystalline phase copy withstand high provids good strength forces but fracture and ideal esthetic. and lack good esthetic. Ceramic restoration was developed to over come the dis-advatages of ceramometal restoration as. 1. lack of natural translucency. 2. Bond failure. It contains about 90 % by volume crystalline phases as reinforcing agents. Advantages of all ceramic restorations 1. Superior esthetics. 2. High biocompatible because it is inert. 3. Low thermal conductivity: no thermal shock to the prepared tooth. 4. No electrolytic corrosion. 5. No metal preparation: no metal inhaled during metal finishing. 6. Excellent bonding between the porcelain veneer and ceramic coping. 7. No repeated firing: no distortion of infra-structure. 8. Resistant to degradation to oral fluids. All ceramic systems according to various manufacturing techniques. 1. 2. 3. 4. 5. Sintered all ceramic restoration. Castable or glass ceramic. Heat pressed all ceramic. Slip cast all ceramic. Machinable all ceramic SINTERED ALL CERAMIC 1. Alumina-based Ceramics: • Alumina has a high modulus of elasticity and high fracture toughness. It redistributes stresses concentrated by the crack and absorbs the stress • 40% stronger than traditional feld-spathic porcelain. • It contains an opaque inner core containing 50% by weight alumina for high strength. • Core is veneered with matched expansion porcelain due to its inadequate translucency. 2. Leucite-based Ceramics: • Leucite(45%) in feldspathic porcelain increases the flexural and compressive strength. • The mismatch in thermal contraction between leucite and the glass matrix causes development of compressive stresses in glass around the crystals so resistance to crack propagation. • Sintered all-ceramic restorations are now being replaced by heat-pressed or machined all-ceramic restorations with better-controlled processing steps. • Glass ceramic is formed into the desired shape as a glass then subjected to heat treatment to induce crystallization of glass. • They are supplied as solid ceramic ingots, used for fabrication of cores or full crowns using lost wax and centrifugal casting technique. 2. Dicor glass ceramics • This material is 55% by volume tetrasilicic fluorimica glass ceramic material and the remaining 45% is glass. • It is initially formed as amorphous glass and then heat treated under controlled crystallization conditions to produce a crystalline glass ceramic material by ceramming process. • Ceramming process is the crystals formation. • The mica crystals give the material its characteristic physical and mechanical properties act as crack stoppers. HEAT PRESSED ALL CERAMIC 1. Leucite- based ceramics . 2. Lithium disilicate based ceramics. • Heat-pressing requires a specially designed automated pressing furnace. • Heat-pressing relies on the application of external pressure at high temperature to sinter and shape the ceramic. • Ceramic ingots are brought to high temp in a phosphate-bonded investment mold produced by the lost wax technique. • A pressure of is then applied through a refractory plunger. This allows filling of the mold with the softened ceramic. • Increase in strength can be explained by the fact that these ceramics possess a higher crystalline and that the heat-pressing process generates an excellent dispersion of these fine crystals. • The main disadvantages are the initial cost of the equipment and relatively low strength compared with other all-ceramic systems 1. Leucite- based ceramics Ex: IPS Empress. This type contains leucite as a major reinforcing crystalline phase dispersed in a glassy matrix. Ceramic ingots are pressed at a higher temperature into a refractory mold made by lost wax technique. 2. Lithium disilicate based ceramics Ex: IPS Empress-2 The major crystalline phase of the core material is Lithium disilicate. The material is pressed and layered with a glass containing some dispersed apatite crystals. Their translucency is less than leucite-based ceramics and both have higher translucency than alumina based ceramics. SLIP CAST ALL CERAMIC MATERIALS 1. 2. 3. In-ceram alumina. In-ceram spinell . In-ceram zirconia. Slip casting technique • Slip is an aqueous suspension of fine ceramic particles in water. • 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. The die with the slip are fired at high temperature. The die shrinks more than the condensed slip which allows easy separation after firing. • The fired porous core is then glass infiltrated (a process in which molten glass is drawn into the pores by capillary action at high temperature). • Materials processed by slip-casting tend to exhibit lower porosity and fewer processing defects than do traditionally sintered ceramic materials. • The strength of In-Ceram is about three to four times greater than that of earlier alumina core materials. B A c Slip casting technique a. In-ceram alumina The alumina content of the slip is more than 90% . First firing the slip, then porous alumina coping is infiltrated with glass during a second firing . This processing leads to a highstrength material because of the presence of densely packed alumina particles. The restoration is veneered using matchedexpansion veneering ceramic. • Because of the high strength of the core, short-span anterior fixed partial prostheses can be made using this process. However, the presence of alumina crystals with a high refractive index, together with 5% porosity, account for some degree of opacity in this allceramic system. b. In-ceram spinel • It contains Magnesium spinel as a major crystalline phase with traces of alumina. • Spinel-based slip-cast ceramics are more translucent, because the spinel phase allows better sintering, but the flexural strength is slightly lower than that of the alumina-based system • It is indicated for anterior crowns, inlays and onlays . c. In-ceram zirconia Contains zirconia and alumina. It has the greatest levels of opacity and should only be used in posterior regions as crowns or bridges. It has the highest flexural strength among in-ceram types. Machinable all ceramic restorations • Machinable ceramics can be milled to form inlays, onlays and veneers using two systems: 1. CAD/CAM technology . 2. Copy milling . a. CAD/CAM technology . The system refers to computer aided design/computer aided machining). The system has an intraoral camera to take an optical impression of the prepared tooth. The image is computerized. The restoration is designed with the aid of a computer. Then, the restoration is machined from ceramic blocks by a computer-controlled milling machine which takes only few minutes. • Advantages: 1. Obtaining an indirect restoration in one visit without impression taking or need for temporary restoration. 2. No need for the dental lab to fabricate the restoration. 3. No porosity as there is no firing. • Disadvantages: 1. Expensive equipment. 2. Inadequate marginal inaccuracy . b. COPY MILLED CERAMIC The primary difference between this and the earlier system (CAD- CAM) is the manner in which the tooth dimensions are picked up. Coy milling scans the object whereas the CadCam need digital impression. In this system, a hard resin pattern is fabricated on a traditional stone die. The pattern is placed in the machine. A tracing tool passes over the pattern and guides a milling tool which grinds a copy of the pattern from a block of ceramic. Then it is veneered with porcelain and fired to complete the restoration.
