Download DENTAL CERAMICS : INDIRECT COLURED RESTOTATION and more Study notes Endodontics in PDF only on Docsity!
INTRODUCTION
Dental ceramics are known for their natural appearance and their durable chemical, mechanical and optical properties. The word “ceramic” is derived from the Greek word “Keramos” which means “potter’s clay”. Dental ceramics are non-metallic, inorganic structures, primarily containing compounds of oxygen with one or more metallic or semi- metallic elements (aluminium, boron, calcium, lithium, magnesium, zirconium, potassium etc.) These materials are a part of systems designed with the purpose of producing dental prostheses that in turn are used to replace missing or damaged dental structures. DEFINITIONS CERAMIC: Inorganic, nonmetallic material composed of metallic or semi-metallic oxides, phosphates, sulphates or other inorganic compounds. DENTAL CERAMIC : A specially formulated ceramic material that exhibits adequate strength, durability and color that is used intraorally to restore anatomic form and function and esthetics. DENTAL PORCELAIN : A ceramic produced by sintering a mixture of feldspar, silica, alumina and other metal oxides, pigments and opacifying agents. FELDSPATHIC PORCELAIN : A specially formulated dental porcelain that contains leucite crystals (KAlSi2O6) in a glass matrix that is used for veneering the metal framework of metal-ceramic prostheses. ZIRCONIA: A partially stabilized zirconium oxide, usually in a tetragonal phase that is used primarily as a core for dental prostheses.
HISTORY
1728 Pierre Fauchard- Suggested the use of porcelain in dentistry 1789 Duchateau and DeChemant- Introduced porcelain tooth material for bridge work and denture 1808 Fonzi- Terra-metallic porcelain (held in place by platinum foil) 1903 Dr Charles Land- Introduction of first ceramic crown using platinum foil matrix and high fusing porcelain 1962 Weinstein- Introduction of porcelain fused to metal restorations 1965 Mclean and Hughes- Improved the fracture resistance by introducing aluminous porcelain 1984 Adair and Grossman- Introduction of castable glass ceramic (Dicor) 1985 – First CAD/CAM crown was publically milled and installed in the mouth. Late 1990’s – IPS Empress 2, a second generation pressable ceramic made from lithium-disilicate frame work with an apatite layered ceramic was introduced. 1999 – IPS SIGN (Ivoclar AG), a feldspar-free fluorapatite glass ceramic system for use in metal-ceramics was presented. 2001 - CERCON from Dentsply International introduced dental restorations from sintered yttrium stabilized zirconia based ceramic core material 2006 -Lithium disilicate re-emerged in 2006 as a pressable ingot and partially crystalized milling block 2007 - ITERO by Cadent as the first digital impression system for conventionally manufactured crown and bridges.
According to Processing Method:
- Casting
- Sintering
- Partial sintering and glass infiltration
- Slip casting and sintering
- CAD-CAM milling
- Copy milling USES AND APPLICATIONS:
- Inlays and onlays
- Esthetic laminates (veneers)
- All ceramic crowns
- All ceramic FPD
- Metal ceramic crowns
- Artificial denture teeth
- Ceramic post and cores
- Ceramic orthodontic brackets Advantages:
- Highly esthetic
- No display of metal
- Biocompatible
- Strong once bonded to tooth
- Does not stain
- Low thermal conductivity/ Insulation
- High abrasion resistance due to their hardness
- Long lasting
- Low coefficient of thermal expansion. Disadvantages:
- Costlier than amalgam or composite
- Accurate occlusion can be difficult to achieve
- Takes two appointments
- Intraoral finishing and polishing is a time-consuming procedure
- Fragile and brittle
- Abrasive to the opposing enamel
- Very technique sensitive
- Finishing of the margins is difficult in the less accessible
interproximal areas
- Need special and expensive laboratory equipment. COMPOSITION High Fusing Porcelains : Basic ingredients of these types of porcelains are: Feldspar Kaolin (clay) Quartz. Medium and Low Fusing Ceramics Feldspar:
- Primary constituent
- Present in concentration of 75 to 80%
- Sodium or potassium form is mainly used but in dental, potassium feldspar is preferred
- Potassium feldspar is selected because of increased resistance to pyroplastic flow and increased viscosity
- Undergoes incongruent melting at 1150°C to 1530°C to form a liquid and crystalline material, i.e potassium aluminosilicate known as leucite. Kaolin: Present in concentration of 4 to 5% Acts as binder Lowers the translucency of porcelain. Quartz: Present in concentration of 13-14 percent Acts as strengthener Increases translucency of porcelain. Medium and Low Fusing Ceramics Glass Modifiers:
This helps in maximum incorporation of porcelain powder and proper condensation of porcelain powder particles. Wet porcelain powder condensation can be done by the following methods: Vibration method: Mild vibrations help in packing the wet powder densely. This is most useful method in removing excess water from the mix. Spatulation method: In this method, a small spatula is used to smoothen the wet powder and the wet particles condense together by which the excess water comes to the surface from where it can be removed. Brush technique: In this method, dry porcelain powder is added to the surface with the help of a brush which absorbs the extra water, making the condensation of wet particles. FIRING OF PORCELAIN: Stages of Firing Porcelain undergoes different stages during firing known as bisque stages:
- Low Bisque Stage
- Medium Bisque Stage
- High Bisque Stage During firing in the first phase, the water is lost, i.e. drying takes place.
After drying stage, the temperature and time is controlled till final fusing, glazing and shading stages. As the temperature is raised, the porcelain particles fuse together by sintering. By densification, volume is reduced. COOLING: After firing is done, porcelain is slowly cooled as rapid cooling may result in crazing or cracking of the surface. Slow cooling is done by placing the restoration under a glass cover to protect it from cold wind and dirt contamination. GRINDING FOR FINAL ADJUSTMENTS : Grinding of surface of the polished porcelain required for intraoral minor adjustments results in decrease in the strength, increase in the discoloration and plaque accumulation. If grinding is unavoidable, it is done using very fine diamond round bur. Afte grinding, rough surface should be polished using very fine finishing disks, porcelain laminate, polishing laminate, or polishing kit. GLAZING: Glazes, shades and stains are added to provide natural appearance. Glaze layer is kept at least 50 micron thick.
It will cause metal restorations and tooth structure to wear more rapidly; particularly when not adequately glazed or when glaze is removed during occlusal adjustment (should be smoothened by polishing). COMPRESSIVE STRENGTH OF CERAMIC IS GOOD BUT HAS A POOR TENSILE STRENGTH It is due to the surface defects like porosities and microscopic cracks. So when place under tension, stress concentrates around these imperfections resulting in fracture. Flexure strength 75.8 Mpa Compressive strength 331 Mpa Tensile strength 34 Mpa Shear strength 110 Mpa Modulus of elasticity 60-70 Mpa METAL CERAMIC RESTORATIONS All ceramic restorations, though look very natural, but are very brittle and subject to fracture. All metal restorations are very strong but they cannot be used in areas where esthetics is the main concern. In metal ceramic restoration, advantages of esthetics of porcelain and strength of metal are combined. For proper bonding between metal and porcelain, alloys and porcelain used should have the following properties:
- Porcelain and alloys should be able to form a strong bond.
- Both should have almost similar coefficient of thermal expansion so that porcelain does not crack or separate from alloy on cooling.
- Porcelain should fuse at a much lower temperature than the melting temperature of the metal.
- The alloy should not deform at porcelain fusing temperature.
- Alloy should have a high modulus of elasticity.
- Adequate stiffness, sag resistance and strength of the alloy. Composition of Metal Ceramic Alloys and Ceramics: Alloys used are:
- Noble metal alloys: High gold alloys: Gold-platinum-palladium alloys :Low gold alloys: Gold –palladium alloys Gold –palladium-silver alloys
- Silver –palladium alloys
- Base metal alloys: Nickel-chromium alloys Cobalt chromium alloy Porcelain-metal Bond: There are generally two types of bonding present between metal and ceramic:
- Micromechanical bonding
Most common failure is bond fracture at the metal oxide interface. Other reasons are: Fusion of porcelain grains inside the coping Thin margins of metal buckle due to contraction of porcelain Elastic deformation of nonrigid metal structure Casting contamination by low fusing alloy components from the metallic die Forceful fitting may result in elastic deformation of the metal and breakdown in porcelain bond. ALL CERAMIC SYSTEM To overcome the disadvantages of porcelain fused to metal, all ceramic materials have been introduced with new technique and technology. All ceramic systems have high strength and precision fit close to that of ceramo-metal in addition to esthetics.
TRADITIONAL POWDER SLURRY CERAMIC
These are supplied in powders which are mixed with water to form ‘slurry’. This slurry formed can be built up in different layers on a die to form the restoration. This type of ceramic can be classified into following types: Alumina Reinforced Ceramic It is based on dispersion strengthening. Alumina crystals are dispersed uniformly in glass matrix to increase strength, toughness and elasticity of the material. The concentration of alumina crystals and glass powder are mixed and prefritted at 1200°C. Then this crystal glass mixture is grounded and incorporated into glass matrix, e.g. Hi-ceram. Leucite Reinforced Ceramic: In it, leucite crystals (potassium aluminosilicate) are dispersed in glassy matrix. Leucite is added in feldspathic porcelain to match the thermal contraction of ceramic to the metal but it also acts as reinforcing filler because of very high tensile strength.
Procedure : Alumina powder is mixed with water to form slurry known as ‘Slip’ which is painted on die. It leaves a layer of solid alumina on the surface. Sintering is done at 1120°C for 10 hours to form porous core. Glass is selected and applied on the porous core and firing is done at 1100°C for 3 to 5 hours. The molten glass infiltrates by capillary action into core. This results in high strength composite structure, i.e. In ceram. In Ceram Spinel: In this spinel (aluminum and magnesium oxide) is used as the core material. It has better translucency than In ceram. It can be used for both anterior and posterior crowns. CASTABLE CERAMIC Castable ceramic was first introduced in 1984. In this, glass ceramic is modified into the desired shape and size as a glass and heat treatment is given to induce crystallization. The process of crystallization is known as ceramming. In 1984, castable ceramic was marketed under the trade name DICOR. Composition: After ceramming, the material contains:
- 55 percent—Tetrasilicic fluoride crystals
- 45 percent—Glass ceramic.
Advantages :
- Satisfactory marginal fit
- High strength
- Higher surface hardness
- Wear resistance similar to enamel
- Dicor inlays are stronger than procelain inlays made on refractory dies. PRESSABLE CERAMIC This type of ceramic is available as core ingot which is heated at high temperature and pressed into a mold. Pressing process is done for 45 mintues at high temperature to get ceramic substructure which further can be shaded with stains or by glazing. Two Types of Pressable Ceramics are Available:
- IPS Empress 1: Contains 35 vol. percent of leucite crystals
- IPS Empress 2: Contains 70 vol. percent of lithia disilicate crystals. Advantages
- Lack of metal
- High flexural strength
- Excellent fit
- Excellent esthetics. Disadvantage
- Prone to fracture in posterior areas
2. IPS Empress II Indicated in all ceramic bridges ,anterior and posterior crowns It is similar except that the core contains Lithia disilicate crystals in a glass matrix and veneering ceramics contains apatite crystals It has ideal strength because the needle like crystals cause cracks to deflect, blanch or blunt thus propagation of cracks through this material is arrested by lithium disilicate crystals, providing substantial increase in flexural strength. A second crystalline phase containing of a lithium ortho phosphate ( li3po4) of a much lower volume is also present Due to its high strength, it is used in creating anterior and posterior crowns and posterior bridges. IPS e. Max The new all ceramic system (lithium disilicate) from ivoclar vivadent which is marketed under the brand name IPS e .max. COMPOSITION:
- phosphor oxide, alumina,
- potassium oxide other components
- 70% needle like crystals embedded in glass matrix approximately 3- μm in length. PROPERTIES:
- Highly aesthetic
- Highly thermal shock resistant glass ceramic due to the low thermal expansion.
- High strength material that can be cemented or bonded.
- Offers a full contour restoration fabricated from one high-strength ceramic, thereby eliminating the challenge of managing 2 dissimilar materials. MACHINABLE CERAMIC These ceramics are supplied in the form of ceramic blocks under various shades. Later, these blocks are fabricated into inlays, onlays and crown with the help of CAD-CAM or copy milling. Computer Generated Ceramic Restorations : Indirect computer generated ceramic restorations can be made chairside in CEREC® SYSTEM–CAD (Computer aided design), CAM (Computer aided manufacturing). The CEREC® system was the first commercially available CAD/CAM system developed for the rapid chairside design and fabrication of ceramic restorations. Machined ceramics do not require the addition of glasses to achieve proper morphology.
