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Dental+ceramics

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Applied Dental Material

Applied Dental Material
Second Year

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    Dental+ceramics Dental+ceramics Presentation Transcript

    • DENTAL CERAMICS
    • Introduction  Definition of ceramic materials: The word ceramic is derived from the Greek word: Keramikos=Burnt stuff Ceramic materials are inorganic compounds formed of metallic or semi-metallic & nonmetallic elements, which are subjected to high heat treatment [firing] for a time period to achieve desirable properties.
    • Introduction  General composition: 1.    A ceramic material consists of two phases: Vitreous phase [Glassy phase]: It is the phase which is responsible for aesthetics only. It is formed by vitrification, where the molten glass has been cooled without crystallization. It is amorphous in structure. 2. Crystalline phase:  It is the phase which is responsible for strength & hardness only.  It is formed by de-vitrification, where the crystallization of the glass occurs at high temperature in the presence of nucleating agents.  It is crystalline in structure.
    • Introduction  Dental examples: 1. 2. 3. 4. 5. Dental gypsum products. Dental investment materials. Filler in dental composite resin. Powder in dental cements. Dental porcelain.
    • Dental Porcelain  Definition: Dental porcelain is a vitreous ceramic based on silica network.  Supplied form: Powder in different shades mixed with distilled water .  Applications: 1. Denture teeth. 2. Crown & bridge. 3. Inlays. 4. Onlays. 5. Laminate veneer. [Layer of ceramic bonded to the facial surface of the prepared tooth]
    • Composition:  Main components:  Feldspars – Quartz – Kaolin.  Other Components:  Glass modifier –Flux – Sugar & Starch – Pigments.
    • Main components: 1. Feldspars:  They are an-hydrated potassium & sodium aluminum silicate.  Upon firing at ~12000, they: fuse, become glassy, retain their form without roundation. N.B.:  If potassium aluminum silicate ∆treatment Leucite + Glassy phase  The precipitation of leucite [Crystalline structure] will change the properties of dental porcelain: * Increase strength. * Increase hardness. * Increase α. * Decrease aesthetics.
    • 2. Quartz [Crystalline phase]:  It is present as fine crystalline dispersion throughout the vitreous phase.  It remains unchanged during firing.  It acts as strengthening agent. 3. Kaolin:  It is hydrated aluminum silicate.  It becomes sticky during mixing  *Workable mass *Opaqueness.  During firing, it adheres to quartz & shrinks considerably. .·. Recent dental porcelain does not contain kaolin. This is known as feldspathic porcelain
    • Other components: 1. a. b. c. a. b. Glass modifier: It is an alkali metal ion, as sodium, potassium or calcium which can associate with the oxygen atoms at the corners of the silica tetrahedra of the vitreous phase, thereby: Lowering the fusing temperature of the dental porcelain to be suitable for different applications. Increasing its α. Increasing its fluidity. N.B.: Effect of high concentration of glass modifier: It reduces the chemical durability of the vitreous phase. Devitrification [Crystallization] may occur during porcelain firing.
    • 2. Flux: It is a low fusing glass e.g. boron oxide based glass Its action is similar to glass modifier. 3. Sugar & starch: They help in forming workable mix instead of kaolin. 4. Pigments & fluorescent agents: They provide different & natural shades.
    • Manufacturing: Blending the components then melting. 2. During melting, the glass modifier & the flux combine with silica tetrahedra of the vitreous phase. [thermo-chemical reactions] 3. The material, while red hot, is then quenched to obtain frit. [Powder] 4. The frit contains two principal phases: a. The vitreous phase. b. The crystalline phase. 1.
    • Manipulation:  1. 2. 3. 4. 5. Conventional technique: Tooth preparation. Elastic impression. Pouring of die. Adaptation of the platinum foil matrix, which retains the dental porcelain mix in the shape of the tooth preparation. The tooth shade is produced by three basic shades of the dental porcelain powder: opaque, dentin & enamel shades;
    • the following steps (except the glazing) are repeated for each shade application. 6. Proportioning. 7. Dental porcelain powder, in the selected shade, is mixed with distilled water to a creamy consistency 8. The mix is applied in excess [~13%oversize] to the platinum foil matrix to compensate for shrinkage during firing 9. Proper compaction of the mix is done by vibration, spatulation or addition of dry powder. Proper compaction to get rid of excess water shrinkage & porosity in the dental porcelain.
    • 10. The platinum foil matrix with the oversized mix is placed in an opened preheated electric porcelain furnace to ensure removal of excess water without steam. [Drying] 11. Firing of the mix is done at controlled time & temperature under vacuum. Firing is done : *To remove remaining water *To fuse DP powder particles at their contact areas forming a continuous mass [sintering] i.e. no melting or chemical reaction. 12. Slow uniform cooling should be done to avoid surface cracks, which are developed due to *Large α mismatch between vitreous & crystalline phases. *Thermal shock.
    • 13. Glazing: * To produce smooth, shiny & impervious surface. * To improve aesthetics & strength. Glazing is performed either by: -Self glaze: It is the flow of the glass from the D.P. restoration to its surface. [Preferred method] - Addition of low fusing glass to the surface of D.P. restoration.
    • Properties:  Generally the properties of D.P. are related to:
    • 1. Biological properties:  D.P. is inert. i.e. Tissue friendly & biocompatible 2. Solubility & Disintegration:  D.P. is indestructible in oral fluids.  Only strong chemicals e.g. Hydrofluoric acid can dissolve D.P. 3.  a. b. c. Dimensional changes during firing: A considerable amount of shrinkage & porosity occurs due to: Densification as result of sintering. Evaporation of excess water. Loss of binder(kaolin) if present.  To decrease the shrinkage & porosity, the following should be done: a. Proper proportioning. b. Oversize. c. Proper compaction. d. Use of small & large powder particles for proper compaction. e. Firing under vacuum.
    • 4. Mechanical properties:  High compressive strength. [Strong bond]  High hardness.  D.P. is even harder than enamel causing wear of the opposing natural teeth; To reduce this risk: *Use ultra-low fusing ceramic (less abrasive) *Glazing to produce smooth surface (less abrasive)  Brittle i.e. Low tensile strength, Low fracture toughness. [Ionic bond].·. Bulk thickness is required necessitates more tooth reduction.  The strength of DP is usually measured in terms of flexure strength. [Combination of compressive, tensile & shear strength]  D.P. is stiff material [High modulus of elasticity Only limited elastic deformation(0.1% strain) can be tolerated before fracture..
    • 5.    Optical properties: D.P. is a translucent material. Three basic shades of D.P. powder are used: opaque, dentin & enamel shades to recreate the color of the tooth. Once the exact color is obtained, it is quite satisfactory & stable 6.  Bonding to tooth structure Since D.P. restorations are of indirect type, thus their bonding depends on: *The type of the used cement. *The surface treatment of the tooth & restoration 7.  Thermal properties D.P. is electrical & thermal insulator. [No free electrons] It has low α. [Strong bond] 
    • Strengthening: [Toughening]  Purpose:  The strength values of D.P. << the predicted strength values based on the    1. 2. 3. 4. strength of their primary interatomic bond. Since DP *Contain unavoidable fabrication defects & surface cracks. * Is a brittle material & fractures by crack propagation. These cracks cause the localized stress at their tips; narrow as the interatomic spacing in the material; to increase reaching the theoretical strength of the material at a relatively low average stress. These cracks propagate leading to catastrophic failure of the material. The methods of strengthening: Designing components. Reducing the surface defects. Interruption of crack propagation. Development of residual compressive stresses within the surface of the material.
    •  The methods of strengthening: 1. 2. Designing components of the restoration with no sharp line or point angles to reduce stress concentration. Reducing the surface defects [Stress raisers] to reduce stress concentration by: a. Use of powder with large & small particles. b. Proper proportioning. c. Proper compaction. d. Proper drying. e. Firing under vacuum. f. Slow cooling. g. Glazing.
    • Interruption of crack propagation: As the D.P. is a brittle material, it fractures by crack propagation. There are two methods for crack interruption: a. Dispersion of tough particles to absorb energy from the crack& deplete its driving force for propagation [Crack deflection] e.g. Alumina. b. Crystal structural changes under stress: [Crack healing] The energy at the crack tip is absorbed to be used for phase transformation of zirconia from tetragonal to monoclinic structure. This phase transformation is accompanied by6%volume expansion, which will close the crack. [Crack healing] But the refractive index of zirconia >>than that of the surrounding structure leading to opacity. 3.
    • 4. Development of residual compressive stresses within the surface of the material: These developing compressive stresses should be first negated by induced tensile stresses before any net tensile stress occurs. Example: Developed compressive strength =40MPa Normal tensile strength =60MPa Strengthening =100MPa i.e. The material would take a total tensile stress of 100 MPa to fracture.
    • Development of residual compressive stresses within the surface of the material: a. Ion exchange: It involves the forcing of the larger potassium ion into the place previously occupied by the smaller sodium ion creating residual compressive stresses in the surface of the material during the chemical treatment. b. Thermal tempering: It involves the rapid cooling of the material while it is hot producing a skin of rigid glass surrounding a molten core which is going to solidify later. c. Thermal compatibility: Ceramometallic restoration consists of metal coping & fired ceramic veneer. It is three times stronger than the ceramic alone. Strengthening depends on slight mismatch in the coefficient of thermal expansion & contraction between metal &ceramic i.e. α of metal>α of ceramic. 4.
    • Classification  According to: 1. Fusion temperature. 2. Type of restoration.
    • fusion temperature: The fusion temperature is that temperature, at which the powder particles of dental ceramic fuse together during firing. a. b. c. d. High fusing ceramic Medium fusing ceramic Low fusing ceramic Ultra low fusing ceramic ~1300ºC. ~1100_1300ºC. ~850_1100ºC. <850ºC.
    • type of restoration Any ceramic restoration is divided into two parts:
    • type of restoration According to type of restoration: Porcelain Fused to Metal All Ceramic
    •        A. Porcelain fused to metal restoration: [Ceramometallic restoration] It consists of metal core & sintered ceramic veneer. It is three times stronger than ceramic alone. Requirements of ceramic for successful restoration: Firing temperature of ceramic<Melting temperature of metal to avoid melting or sag of metal. α of ceramic < α of metal [Slight mismatch] to develop residual compressive stresses at their interface for - Strengthening of ceramic. - Compressive bonding between ceramic & metal. Strong interfacial bonding between ceramic & metal is obtained by: - Compressive bonding. - Ceramic bonds chemically to the surface oxides of the metal [Adhesive bond]. - Ceramic enters into the surface irregularities of the metal[mechanical interlocking]. Ceramic should be strong. Ceramic should mask the color of the underlying metal
    • Composition of the ceramic fired to metal: Leucite [crystalline phase]:  α of ceramic to be slightly < the higher α of metal.   Strength of ceramic. Glass modifier:  Firing temperature of D.P. < Melting temperature of metal.   α of ceramic to be slightly < the higher α of metal. Opacifier:  In the opaque shade to mask the color of metal.
    • B. All ceramic restoration:  It consists of ceramic core & veneer.  The ceramic core consists of a variety of crystalline phases up to 99% by volume. Factors affecting the properties of all ceramic restoration: i. The nature, amount & particle size distribution of the crystalline phase influence the mechanical & optical properties of all ceramic restoration. ii. The match between the refractive indices of the crystalline & glassy phases of the ceramic core controls the translucency of all ceramic restoration. iii. The α of ceramic core > the α of ceramic veneer to obtain compressive bonding. Types of all ceramic restorations according to the processing techniques: - Sintering - Slip casting - Heat pressing - Machinable
    • Sintered all ceramic material:  The all ceramic crowns have been known since 1900s.  However, they were brittle & fractured easily [half moon fractures]  In order to increase the fracture resistance, the content of the crystalline phase of the ceramic core is increased by: - Alumina. - Leucite. i.
    • Heat- Pressed all ceramic material: [High temperature injection molding] Heated ceramic ingot is injected under air pressure into a refractory mold. After solidification & divesting, the ceramic core is ready for veneering. ii. Types : *IPS Empress: Glass ceramic + leucite crystals for inlay , onlay, veneer & crown *IPS Empress 2: Glass ceramic + lithium disilicate crystals for crown & bridge
    • iii. Slip-Cast all ceramic material:  It is supplied as one of the three core ceramics: Inceram Alumina, Inceram Spinell , Inceram Zirconia. Steps:  A slurry[slip]of one of these materials is deposited on the refractory die.  The water from the slurry is absorbed by the capillary action of the porous die leaving a layer of either Alumina , Spinell or Zirconia on the surface.  This fragile layer is dried & fired (sintered) at certain temperature for certain time according to the used Inceram.  During firing the refractory die shrinks more than the deposited layer so that it can be separated easily from the die.  This fired porous core is subjected to glass infiltration process ,where molten glass is drawn into these pores by capillary action at high temperature.  The excess glass is trimmed off.  The ceramic core is now ready for veneering.
    • Indications:  Alumina Inceram for short span anterior bridge. [Intermediate translucency & strength]  Spinel Inceram for short span anterior bridge. [Highest translucency but lowest strength]  Zirconia Inceram for short span posterior bridge. [Lowest translucency but highest strength] Advantages: - High strength - Luting with any cement except Spinel Inceram Disadvantages: -High opacity except Spinel Inceram -Long processing time -Inability to be etched to aid in cementation
    • Machinable ceramics: -CAD/CAM [Computer assisted design/Computer assisted machining] It is used to produce ceramic inlay, onlay or veneer in one visit. iv. Steps: -Tooth preparation -The preparation is optically scanned [Optical impression] -The image is computerized. -The restoration is designed by the aid of the computer -The restoration is then ground from dense ceramic blocks by a computer controlled milling machine according to the computerized image. -Early models ground only the internal surface of the restoration and the external surface is ground manually. -Recent models grind both surfaces.
    • Copy milling :  It is used to produce ceramic core for crown & bridge. Steps:  Tooth preparation  Impression  Preparation of stone die  Preparation of resin pattern.  The resin pattern is placed on a machine similar to a pantographic device used for duplicating house keys.  A tracing tool passes over the pattern guiding a milling tool which grinds a copy of the pattern from Inceram block.  The milled ceramic core is then glass infiltrated.  The glass infiltrated core is built up with veneering porcelain &fired  Type of used ceramic:  Dense Inceram (Alumina, Spinell or Zirconia) block
    •  Advantages of machinable ceramics:  Reduced chair time  Single appointment (in CAD/CAM restoration)  High strength due to less porosity  Disadvantages of machinable ceramics:  Expensive  Poor marginal accuracy
    • Advantages of all ceramic restoration:  Better aesthetic, as no metal collar, subgingival grayish shadow or poor translucency  More hygienic ,as no metallic hypersensitivity or allergy Disadvantages of all ceramic restoration:  Less strength than ceramometallic restoration  In a bridge, the connectors should be sufficiently thick to resist the high tensile stresses.