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Dental ceramics

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Dental ceramics

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Dental ceramics

  1. 1. Dental Ceramics Dr. Deepak K. Gupta
  2. 2. Introduction • Ceramic is defined as product made from non- metallic material by firing at a high temperature. • Application of ceramic in dentistry is promising – Highly esthetic – stronger, wear resistant, – impervious to oral fluids and absolutely biocompatible
  3. 3. • Spring-retained maxillary and mandibular dentures of U.S. President George Washington, – made from hippopotamus ivory by dentist John Greenwood. – Two of the first dentures made for the president using extracted human teeth
  4. 4. Advantages & Disadvatages • Advantages – Biocompatible as it is chemically inert. – Excellent esthetic. – Thermal properties are similar to those of enamel and dentine • Disadvatages – High hardness - abrasion to antagonist natural dentitions and difficult to adjust and polish. – Low tensile strength so it is brittle material
  5. 5. APPLICATIONS OF CERAMICS IN PROSTHETIC DENTISTRY • Inlays and onlays • Esthetic laminates (veneers) over natural teeth • Single (all ceramic) crowns • Short span (all ceramic) bridges • As veneer for cast metal crowns and bridges (metal ceramics) • Artificial denture teeth (for complete denture and partial denture use) • Ceramic orthodontic brackets
  6. 6. Classification: Craig • Based on the Application – Metal-ceramic: crowns, fixed partial prostheses – All-ceramic: crowns, inlays, onlays, veneers, and fixed partial prostheses. – Additionally, ceramic orthodontic brackets, dental implant abutments, and ceramic denture teeth • Based on the Fabrication Method – Sintered porcelain: Leucite, Alumina, Fluorapatite – Cast porcelain: Alumina, Spinel – Machined porcelain: Zirconia, Alumina, Spinel • Based on the Crystalline Phase – Glassy (or vitreous) phase – Crystalline phases
  7. 7. Classification: Anusavice • uses or indications – Anterior and posterior crown, veneer, post and core, – fixed dental prosthesis, ceramic stain, glaze • composition; • principal crystal phase or matrix phase • Processing method – casting, – sintering, – partial sintering – glass infiltration, – slip casting and sintering, – hot-isostatic pressing, – CAD-CAM milling, and copy milling • firing temperature – ultralow fusing, – low fusing, – medium fusing, – High fusing • Microstructure – amorphous glass, – crystalline, – crystalline particles in a glass matrix • Translucency – opaque, – translucent, – transparent • Fracture resistance : low, medium, high • Abrasiveness
  8. 8. Classification of Dental Ceramics by Sintering Temperature
  9. 9. Basic Structure • Basically porcelain is a type of glass - three dimensional network of silica (silica tetrahedral) • Since Pure glass melts at too high a temperature – Modifiers added to lower the fusion temperature – Sodium or potassium • But this weakens the strength and make it brittle
  10. 10. Composition • It mainly consist of silicate glasses, porcelains, glass ceramics, or highly crystalline solids. • Wide variety of porcelain products available in the market • So its virtually impossible to provide a single composition for them all. • So we will discuss about traditional porcelains - feldspathic porcelains
  11. 11. Composition (Percentage by Weight) of Selected Ceramics)
  12. 12. Basic Constituents: feldspathic porcelain 1. Feldspars are mixtures of (K2o. Al2o3.6SiO2) and (Na2o. Al2o3.6SiO2), fuses when melts forming a glass matrix. 2. Quartz (SiO2), remains unchanged during firing, present as a fine crystalline dispersion through the glassy phase. 3. Fluxes used to decrease sintering temperature. 4. Kaolin act as a binder. 5. Metal oxides: provide wide variety of colors
  13. 13. METAL CERAMIC RESTORATIONS • Also known as Porcelain fused to metal (PFM) • It has the advantage of being esthetic as well as adequate strength. • Most commonly used
  14. 14. Parts of PFM • Core: cast metallic framework. Also known as coping • Opaque Porcelain: first layer consisting of porcelain modified with opacifying oxides. – Mask the darkness of the oxidized metal framework – metal-ceramic bond • Final buildup of dentin and enamel porcelain
  15. 15. METAL-CERAMIC BOND • Most important requirement for good long-term performance. • The bond is a result of chemisorption by diffusion between the surface oxide layer on the alloy and the porcelain. • Roughening of surface interface also increases the bond strength – increases surface area of wetting for porcelain. – Micromechanical retention • Noble metal alloys, which are resistant to oxidizing – easily oxidising metal like indium (In) and tin (Sn): form an oxide layer
  16. 16. FAILURE OF METAL-CERAMIC BONDING • Cohesive failure: Porcelain-porcelain, metal- metal, oxide-oxide. • Adhesive failure: Porcelain-oxide, metal-oxide, metal-porcelain. • Mixed failure: Any combination of the previous failures.
  17. 17. CERAMICS FOR METAL-CERAMIC RESTORATIONS • Must fulfill five requirements: – simulate the appearance of natural teeth, – fuse at relatively low temperatures, – have thermal expansion coefficients compatible with alloys used for metal frameworks, – Compatible in the oral environment, – have low abrasiveness. • Composition: silica (SiO2), alumina (Al2O3), sodium oxide (Na2O), and potassium oxide (K2O) • Opacifiers (TiO2, ZrO2, SnO2), • Various heat-stable coloring oxides • Small amounts of fluorescing oxides (CeO2) - appearance of the dentin/enamel complex structure
  18. 18. METAL FOR COPING OF METAL CERAMIC RESTORATION • The alloy must have a high melting temperature to withstand high firing temp of porcelain. • Adequate stiffness and strength of the metal framework. • High resistance to deformation at high temperature is essential. • Adequate thickness of metal.
  19. 19. FABRICATION OF METAL-CERAMIC PROSTHESES • Casting of Metal Core – Wax framework is fabricated on the die. – The framework is cast by lost wax technique. – Sandblasting of the cast metal copy. – Degassing is done to form oxide layer to improve bonding to ceramic. • Processing of Porcelain over metal core – Condensation and Build-up – Firing or sintering – Glazing – Cooling
  20. 20. Condensation • The plastic mass of powder and water is applied to the metal coping. Function of condensation – Adapt the porcelain to the required shape. – Remove as much water from the material as possible to decrease firing shrinkage. Methods of condensation – Vibration – Spatulation – Brush
  21. 21. Build-up There are three types of porcelain used a. Opaque porcelain: Mask the color of the cement used for adhesion of the restoration. b. Body or dentin porcelain: Makes up the bulk of the restoration by providing most of the color or shade. c. Enamel porcelain: It provides the translucent layer of porcelain in the incisal portion of the tooth.
  22. 22. FIRING OR SINTERING • It is to fuse the particles of porcelain powder producing hard mass. Stages of firing: a. Low bisque stage: Particles lack complete adhesion, low amount of shrinkage occur, and very porous. b. Medium bisque stage: water evaporates with better cohesion to the powder particles and some porosity . c. High bisque stage: fusion of particles to form a continuous mass, complete cohesion and no more shrinkage.
  24. 24. GLAZING • The glazing is to obtain a smooth surface that simulates a natural tooth surface. • It is done either by: – Auto glazing: rapid heating up to the fusion temperature for 1-2 minutes to melt the surface particles. – Add on glazing: applying a glaze to the surface and re-firing. • Auto glazing is preferred to an applied glaze AUTOGLAZED VENEER CERAMIC
  26. 26. ALL-CERAMIC RESTORATION • All-ceramic restorations use a wide variety of crystalline phases. • Several processing techniques are available for fabricating all-ceramic restorations: – Sintering: Alumina and leucite – Heat-pressing: Inceram and IPS impress – Slip-casting: Dicor – CAD/CAM: VitaBlock, Dicor MGC Lava DVS Cross-Section
  27. 27. Sintered All-Ceramic Materials • Two main types of all-ceramic materials • Alumina-Based Ceramic – developed by McLean in 1965 – aluminous core ceramic used in the aluminous porcelain crown – high modulus of elasticity and relatively high fracture toughness, compared to feldspathic porcelains • Leucite-Reinforced Ceramic – 45% by volume tetragonal leucite – higher flexural strength (104 MPa) and compressive strength – increased resistance to crack propagation
  29. 29. Heat-Pressed All-Ceramic Materials • Application of external pressure at high temperature to sinter and shape the ceramic • Produce all-ceramic crowns, inlays, onlays, veneers, and more recently, fixed partial prostheses. • Ceramic ingots are brought to high temperature in a phosphate-bonded investment mold produced by the lost wax technique.
  30. 30. Heat-Pressed All-Ceramic Materials
  31. 31. Heat-Pressed All-Ceramic Materials • Leucite-Based Ceramic – First-generation heat-pressed ceramics contain leucite (KAlSi2O6 or K2O • Al2O3 • 4SiO2) as reinforcer – Heat-pressing temperatures: 1150° and 1180° C for 20 minutes. – ceramic ingots: variety of shades – amount of porosity in the heatpressed ceramic is 9 vol % • Lithium Disilicate–Based Materials – second generation of heat-pressed ceramics contain lithium disilicate (Li2Si2O5) – major crystalline phase: 890° to 920° C temperature range – 65% by volume of highly interlocking prismatic lithium disilicate crystals – amount of porosity after heat-pressing is about 1 vol % – Higher resistance to crack propagation
  32. 32. Slip-Cast All-Ceramic Materials • Introduced in dentistry in the 1990s • Condensation of a porcelain slip on a refractory die - aqueous slurry containing fine ceramic particles. • Porosity of the refractory die helps condensation by absorbing the water from the slip by capillary action. • Restoration is incrementally built up, shaped • Finally sintered at high temperature on the refractory die • Usually the refractory die shrinks more than the condensed slip • Restoration can be separated easily after sintering • Sintered porous core is later glass-infiltrated
  33. 33. Slip-Cast All-Ceramic Materials • Alumina and Spinel-Based Slip-Cast Ceramics – alumina content of the slip: more than 90%, with a particle size between 0.5 and 3.5 μm – 1st stage: drying at 120° C for 6 hrs – 2nd stage: sintering for 2 hours at 1120° C and 2 hours at 1180° C – 3rd stage: porous alumina coping is infiltrated with a lanthanum-containing glass during a third firing at 1140° C for 2 hours – 68 vol% alumina, 27 vol% glass, and 5 vol% porosity – Indication: short-span anterior fixed partial prostheses
  34. 34. Slip-Cast All-Ceramic Materials
  35. 35. Slip-Cast All-Ceramic Materials • Zirconia-Toughened Alumina Slip-Cast Ceramics – Zirconia-toughened alumina slip-cast – 34 vol% alumina, 33 vol% zirconia stabilized with 12 mol% ceria, 23 vol% glassy phase, and 8 vol% residual porosity. – alumina grains appear in darker contrast whereas zirconia grains are brighter • Main advantage of slip-cast ceramics: high strength; • Disadvantages: high opacity
  36. 36. Machinable All-Ceramic Materials • Machining can be done by either 2 ways • Soft Machining Followed by Sintering – Some all-ceramic materials can also be machined in a partially sintered state and later fully sintered – Requires milling of an enlarged restoration to compensate for sintering shrinkage – ceramics that are difficult to machine in the fully sintered state, such as alumina and zirconia
  37. 37. Machinable All-Ceramic Materials: Hard Machining • Milled to form inlays, onlays, veneers, and crowns using CAD/CAM technology • produce restorations in one office visit • 3M ESPE Lava Chairside Oral Scanner C.O.S., 3M ESPE; CEREC AC, Sirona Dental Systems, LLC; E4D Dentist, D4D Technologies; iTero, Cadent, Inc
  38. 38. Computer Aided Designing/Computer Aided Milling (CAD/CAM) • After the tooth is prepared • The preparation is optically scanned and the image is computerized • Restoration is designed with the aid of a computer • Restoration is then machined from ceramic blocks by a computer-controlled milling machine
  39. 39. CEREC AC, Sirona Dental System
  40. 40. SUMMARY
  41. 41.
  42. 42. References • Phillips' Science of Dental Materials- Phillip Anusavice_12th • Basic Dental Materials -2nd.ed Mannapalli • Clinical Aspects of Dental Materials Theory, Practice, and Cases, 4th Edition • Craig's Restorative Dental Material 13th edition
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