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Porcelines used in metal ceramics /certified fixed orthodontic courses by Indian dental academy

Porcelines used in metal ceramics /certified fixed orthodontic courses by Indian dental academy



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Porcelines used in metal ceramics /certified fixed orthodontic courses by Indian dental academy Porcelines used in metal ceramics /certified fixed orthodontic courses by Indian dental academy Presentation Transcript

  • PORCELAINS USED IN METAL CERAMICS. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com 1
  • INTRODUCTION Metal ceramic restorations combine the strength and accuracy of cast metal with the esthetics of porcelain. www.indiandentalacademy.com 2
  • Metal ceramic restoration: • "a fixed restoration that employs a metal substructure on which a ceramic veneer is fused" (Glossary of Prosthodontic Terms, 1987). • www.indiandentalacademy.com 3
  • A 13- unit metal-ceramic restoration. www.indiandentalacademy.com 4
  • • The word Ceramics is derived from Greek word “keramos” which means ‘pottery’ or ‘burnt stuff’. Porcelain in English means “china”. www.indiandentalacademy.com 7
  • Ceramics Compounds of one or more metals with a non metallic element, usually oxygen. They are formed of chemical and biochemical stable substances that are strong, hard , brittle, and inert non conductors of thermal and electrical energy(GPT-7). www.indiandentalacademy.com 8
  • Porcelain is defined as A ceramic material formed of infusible elements joined by lower fusing materials. Most dental porcelain are glasses and are used in the fabrication of teeth for dentures, pontics and facings, metal ceramic restorations, crowns, inlays, onlays, and other restorations. www.indiandentalacademy.com 9
  • Other designations of metal ceramics • Porcelain-fused to metal. • Ceramo-metal crown. • Porcelain veneer crown. • Porcelain bonded to metal crown. www.indiandentalacademy.com 10
  • Structure of ceramics •Dental porcelain are glassy materials Glasses may be regarded as a super cooled liquids or as non crystalline solids • Their atomic structure and resultant properties depend, not only on composition, but also on thermal history. www.indiandentalacademy.com 11
  • • 1850 Samuel Stockton was the first to mass produce these teeth first in America • Claudius Ash created a artificial tooth that could be placed over a post on either a complete denture of FPD. It was known as “tube” tooth. www.indiandentalacademy.com 15
  • • 1889 Dr Charles H. Land gave the idea of fusing porcelain to a thin platinum foil. – he developed low fusing porcelain in 1898. 1903 he introduced the porcelain jacket crown to dentistry www.indiandentalacademy.com 16
  • • 1907 Stockton developed dental porcelain. • 1962 –M. Weinstein, S.Katz, and A.B.Weinstein patented a method to fabricate the first metal ceramic crown. www.indiandentalacademy.com 17
  • • Two of the most important breakthroughs responsible for the long-standing superb aesthetic performance and clinical survivability of metal-ceramic restorations are the patents of Weinstein and Weinstein (1962) and Weinstein et al (1962). • One of these patents described the formulations of feldspathic porcelain that allowed systematic control of the sintering temperature and thermal expansion coefficient. www.indiandentalacademy.com 18
  • • The other patent described the components that could be used to produce alloys that bonded chemically to and were thermally compatible with feldspathic porcelains www.indiandentalacademy.com 19
  • What are ceramics? – Dental ceramics may consist primarily of glasses ,porcelains, glass-ceramics. – The properties of ceramics are customized for dental application by precise control of the type & amount of the components used in their production. www.indiandentalacademy.com 20
  • • Ceramics are more resistant to corrosion. Ceramics generally do not react with most liquids, gases, alkalies & acids. And they remain stable over long time. • Dental ceramics exhibit far to excellent flexure strength & fracture toughness. www.indiandentalacademy.com 21
  • • Although ceramics are strong, temperature-resistant & resilient these materials are brittle and may fracture when quickly heated and cooled. • Dental ceramics are non-metallic inorganic structures,primarily containing components of oxygen with one or more metallic or semi metallic elements. www.indiandentalacademy.com 22
  • Properties of ceramics. • Most ceramics are characterized by their refractory nature, high hardness, (relatively low tensile strength and essentially zero percent elongation), and chemical inertness. www.indiandentalacademy.com 23
  • • For dental applications a hardness of a ceramic less than that of enamel and an easily polishable surface are desirable to minimize the wear damage that can be produced on enamel by the ceramic surface. www.indiandentalacademy.com 24
  • 1) Strength. • Porcelain is a material having good strength. However, it is brittle and tends to fracture. • The strength of porcelain is usually measured in terms of its flexure strength or modulus of rupture. www.indiandentalacademy.com 25
  • a) Flexure strength: • It is a combination of compressive, tensile, as well as shear strength. • Glazed porcelain is stronger than ground porcelain. • Ground-75.8 Mpa (11,000 psi) • Glazed-141.1 Mpa (20,465 psi) www.indiandentalacademy.com 26
  • b) Compressive strength: • Porcelains have good compressive strength. • 331 Mpa (48,000psi) www.indiandentalacademy.com 27
  • c) Tensile strength: • Is low • 34 MPa (5000psi). www.indiandentalacademy.com 28
  • d) Shear strength: • It is low and is due to the ductility caused by the complex structure of dental porcelain. • 110 Mpa (16000psi). www.indiandentalacademy.com 29
  • Factors affecting strength. • 1) Composition. • 2) Surface integrity: Surface imperfections like microscopic cracks and porosities reduce the strength. • 3) Firing procedure: Inadequate firing weakens the structure as vitrification is not complete. Overfiring also decrease strength as more of the core gets dissolved in the fluxes, thereby weakening the core network. www.indiandentalacademy.com 30
  • 2) Modulus of elasticity: • Porcelain as high modulus of elasticity. • 69 GPa . www.indiandentalacademy.com 31
  • 3) Surface hardness: • Porcelain is much harder than natural teeth. • 460 KHN www.indiandentalacademy.com 32
  • 4) Wear resistance: • Porcelain is more resistant to wear than natural teeth. Thus, it should not be placed opposite to natural teeth. www.indiandentalacademy.com 33
  • 5) Specific gravity: • Is 2.242. • The specific gravity of fired porcelain is usually less, because of the presence of air voids. It varies from 2.2 to 2.3. www.indiandentalacademy.com 34
  • 6) Dimensional stability: • Porcelain is dimensionally stable after firing. www.indiandentalacademy.com 35
  • 7) Chemical stability: • It is insoluble and impermeable to oral fluids. Also it is resistant to most solvents. However, contact with hydrofluoric acid causes etching of the porcelain surface. www.indiandentalacademy.com 36
  • 8) Esthetic properties: • Are excellent. It is able to match adjacent tooth structure in translucence, color and intensity. www.indiandentalacademy.com 37
  • 9) Biocompatibility. • It is compatible with the oral tissue. www.indiandentalacademy.com 38
  • 10) Thermal compatibility • Refers to the ability of a metal and its veneering porcelain to contract at similar rates. • The coefficient of thermal expansion by definition is the change in length per unit of original length of a material when its temperature is raised by 1o K •. www.indiandentalacademy.com 39
  • Thermal compatibility (contd.) • When the co efficient of thermal expansion of metal and porcelain are compatible the tensile stress that develop during cooling are insufficient to cause immediate cracking of porcelain or delayed cracking after cooling at room temperature. www.indiandentalacademy.com 40
  • • Porcelains have coefficient of thermal expansion between 13.0 and 14.0 X 10-6 and metal between 13.5 and 14.5 X 10-6. • The difference of 0.5 X10-6 in thermal expansion between metal and porcelain causes the metal to contract slightly more than does the ceramic during cooling after firing the porcelain. www.indiandentalacademy.com 41
  • • This puts the ceramic under slight residual compression which makes it less sensitive to applied tensile forces. www.indiandentalacademy.com 42
  • Methods of strengthening ceramics • Strengthening occurs through two mechanism, • 1) development of residual compressive stresses. • 2) interruption of crack propagation. www.indiandentalacademy.com 43
  • • Development of residual compressive stresses. • 1) Ion exchange: (chemical tempering) • exchange of potassium ions (which is 35% larger) for sodium ions. thus there is squeezing of the potassium ion into smaller spaces. This creates a residual compressive stresses on the surface of the glass. www.indiandentalacademy.com 44
  • • Thermal tempering. • By rapidly cooling the surface of the object while it is hot and in the molten state. This rapid cooling produces a layer of rigid glass surrounding a soft core. As the molten core solidifies ,it tends to shrink, creates a residual tensile stress in the core thus leaving the outer layer in residual compressive stress. www.indiandentalacademy.com 45
  • • THERMAL EXPANSION COEFFICIENT MISMATCH: • Ceramic in combination with metal are heated together .The metal which is veneered with ceramic has a higher coefficient of thermal expansion than the ceramic. Hence on cooling, the metal contracts more than the ceramics thus leaving the outer layer, of ceramic in residual compressive stress. www.indiandentalacademy.com 46
  • Interruption of crack propagation. • Two different types of dispersions used to interrupt crack propagation are: • 1) By absorption of energy by the dispersed tough particle from the crack and thus depleting its driving force for propagation. • 2) By change of crystal structure under stress to absorb energy from the crack. www.indiandentalacademy.com 47
  • 1) Dispersion of a crystalline phase. • A tough crystalline material like alumina is added in particulate form. The glass is toughened and strengthened because the crack cannot penetrate the alumina particles as easily as it can propagate in the glass. Thus the aluminous porcelains were developed for Porcelain Jacket Crown. (PJC) www.indiandentalacademy.com 48
  • Transformation toughening. • A crystalline material is incorporated that is capable of undergoing a change in crystal structure when placed under stress. The crystalline material used is termed as partially stabilized zirconia (PSZ).The refractive index of PSZ is higher than glass matrix. Thus the PSZ scatters the light producing an opacifying effect. www.indiandentalacademy.com 49
  • Terminology. Porcelain-fused-to-metal (PFM): a popular alternative designation for the metal ceramic restoration. www.indiandentalacademy.com 50
  • • Porcelain bonding: a term used to explain the mechanisms by which dental porcelain fuses or adheres to a metal substructure • Coping: the word coping can be used to identify the metal substructure of singleunit crowns designed for bonding to dental porcelain. Copings are made on a single tooth preparation, which may be a single unit or attached to pontics for a fixed partial denture. www.indiandentalacademy.com 51
  • • Framework: this term is often applied to fixed partial dentures and identifies a one-piece substructure composed on either several copings attached to a pontic or multiple single units that are joined together as a single structure. www.indiandentalacademy.com 52
  • • Degassing: the process of heat-treating a cast metal substructure in a porcelain furnace as one of the preparatory steps to applying an opaque porcelain. Subjecting the finished metal to elevated temperatures (980° to 1,050°C) in a reduced atmosphere (vacuum) or in air reportedly burns off organic surface impurities and eliminates entrapped gaseous contaminants. A newer and perhaps more appropriate term—oxidizing—has emerged in the literature to describe this procedure. www.indiandentalacademy.com 53
  • • Oxidation (or oxidizing): the process by which a metal substructure is heated in a porcelain furnace to produce an oxide layer for porcelain bonding as well as to cleanse the porcelain-bearing surfaces of contaminants www.indiandentalacademy.com 54
  • ADVANTAGES OF DENTAL PORCELAIN • Dental ceramics are attractive because of their biocompatibility, long-term color stability, wear resistance, and their ability to be formed into precise shapes. www.indiandentalacademy.com 55
  • Disadvantages. • They require costly processing equipment and specialized training. • Susceptibility to brittle fracture at relatively low stresses www.indiandentalacademy.com 56
  • The chemical components of dental porcelain. • Feldspar (K2O –Al 2O3-6SiO2 & Na2o – Al2o3-6SiO2) • Quartz (SiO2) • Alumina (Al2O3) • Kaolin (Al2O3 -2SiO2 2H2O) www.indiandentalacademy.com 57
  • Feldspar • Found as a mix of two substances . • It does not occur in pure form in nature • Mineral is crystalline and opaque • Color is indefinite and between gray and pink. www.indiandentalacademy.com 58
  • Type of feldspar Chemical Other formula names Properties uses Potassiu (K2O.Al orthocla m O3.6Si se or 2 potash aluminiu O ) feldspar 2 m silicate. 1.Reduces the fluidity of the molten materials 2.helps to maintain the form of the porcelain buildup 3.adds translucent qualities to fired restorations. Found in majority of the porcelain systems Sodium aluminu m silicate (Na2O. Al2O3. 6SiO2) 1.Lowers fusion temperature of the porcelain. Less preferred Lime feldspar CaO.2 Al2O3.2 albite or sodium feldspar . www.indiandentalacademy.com 59
  • • On heating it becomes glassy and fuses at 1290 C, on overheating it may loose its shape . • Impurities : Mica Iron –it is important to remove it as its oxides act as strong coloring agents. www.indiandentalacademy.com 60
  • Removal of impurities Iron• manually only light colored pieces of feldspar are selected • Feldspar is grounded into fine powder and vibrated down inclined planes surrounded by induction magnets www.indiandentalacademy.com 61
  • Functions • Primarily responsible for forming glass matrix www.indiandentalacademy.com 62
  • • Glass modifiers such as the oxides of potassium, sodium, and calcium acts as fluxes to increase a porcelains coefficient of thermal expansion. • The fluxes increase the porcelains coefficient of thermal expansion by breaking up oxygen crosslinking. www.indiandentalacademy.com 63
  • Silica (Quartz or Flint) SiO2 • Primarily responsible for forming glass matrix • Has a fusion temperature www.indiandentalacademy.com 64
  • SiO2 www.indiandentalacademy.com 65
  • Functions • Silica contributes stability to the mass of porcelain during heating by providing a framework for the other ingredients. • Also acts to strengthen the porcelain. www.indiandentalacademy.com 66
  • KAOLIN (Al2 o3-2sio22H2o) • It is deposited along the banks and at the bottom of streams in the form of clay. • Only purest form of clay are used for dental porcelain. www.indiandentalacademy.com 67
  • Preparation of clay • Repeated washing until all foreign materials are separated. • Allowed to settle. • Dried and screened. • Nearly white powder is obtained. www.indiandentalacademy.com 68
  • Properties of clay I. II. Its gives OPAQUENESS to porcelain MOULDABLE :On mixing with water it becomes sticky and aids in forming a workable mass of the porcelain during molding. III. Clay-water suspension maintains its shape during firing in a furnace. IV. On subjecting to high heat it adheres to the framework of Quartz particles and shrinks considerably. www.indiandentalacademy.com 69
  • • Little or no kaolin is found is modern day low fusing porcelain. • Kaolin is not used in enamel powder as it will decrease its translucency. www.indiandentalacademy.com 70
  • Alumina.(Al2o3) • The hardest and perhaps the strongest oxide. • Its CTE is similar to the low fusing porcelains. • It also strengthens the porcelain. www.indiandentalacademy.com 71
  • Manufacturing of ceramics powder www.indiandentalacademy.com 72
  • Fritting. • The process of blending, melting and quenching the glass components is termed “fritting”. • All the raw mineral powders are mixed together in a refractory crucible and heated till a molten mass is formed. • It is then quenched in water. • It immediately breaks into fragments and this is termed the “frit”. www.indiandentalacademy.com 73
  • • Frits are ground to the specific particle size established by individual manufacturers for their particular brand of porcelain. www.indiandentalacademy.com 74
  • • Depth orientation grooves flat end tapered diamond. www.indiandentalacademy.com 76
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  • • Make at least two vertical cuts in the incisal portion of the facial surface. www.indiandentalacademy.com 78
  • • Next align the flat end tapered diamond with the gingival portion of the facial surface. www.indiandentalacademy.com 79
  • • Sink the side of the diamond into the mesiodistal center of the facial surface,maintain the instrument alignment parallel to the gingival surface of the facial segment. www.indiandentalacademy.com 80
  • • Make two incisal orientation grooves that are 2mm deep.The diamond should be parallel to the incisal edge faciolingally. www.indiandentalacademy.com 81
  • • Incisal reduction is done with the flat end tapered diamond. www.indiandentalacademy.com 82
  • www.indiandentalacademy.com 83
  • • Facial reduction; incisal half,flat end tapered diamond. www.indiandentalacademy.com 84
  • • If there sound tooth structure inter proximally, wing preparation is done. www.indiandentalacademy.com 85
  • • Begin the lingual reduction with the small round diamond with diameter of 1.4mm. Sink this instrument into the lingual tooth structure up to 0.7mm. www.indiandentalacademy.com 86
  • • Lingual axial reduction torpedo diamond and carbide finishing bur. www.indiandentalacademy.com 87
  • • Lingual reduction is done with the small wheel diamond. www.indiandentalacademy.com 88
  • • Smooth the entire facial surface with no.171 bur .Round over the any sharp angles on the incisal angle or along the edges of the incisal notches with no.171 bur. www.indiandentalacademy.com 89
  • Components of the metal ceramic restoration • Two major components: • a metal substructure and a porcelain veneer. • The surface oxide layer that lies between the metal and the porcelain veneer could be considered a separate component, but it is an integral part of the casting alloy substructure. www.indiandentalacademy.com 90
  • www.indiandentalacademy.com 91
  • The basic components of a traditional porcelain kit include 1.opaque porcelain. 2.dentin porcelains 3.enamel porcelains Modifiers, stains & glazes. Newest products has high fusing shoulder porcelains. www.indiandentalacademy.com 92
  • The metal substructure • Conventional low-fusing dental porcelain lacks the strength required of an all-porcelain restoration, so a metal substructure is added to support the porcelain veneer. • The thickness of the metal coping can vary, depending on the type of casting alloy used and the amount of tooth structure reduced by the dentist. www.indiandentalacademy.com 93
  • The oxide layer • Most metal ceramic alloys are oxidized after the porcelainbearing area of the restoration has been properly finished and cleaned. www.indiandentalacademy.com 94
  • • The metal oxides that form on the alloy's surface during this heattreatment procedure play a key role in bonding the dental porcelain to the underlying metal substructure. • Because noble elements do not oxidize, an alloy's base metal constituents are principally responsible for forming this oxide layer. www.indiandentalacademy.com 95
  • • Differences in alloy composition require that oxidation techniques be alloy specific • Ideally this oxidation should be no more than a discrete, monomolecular film on the alloy's surface for all metal ceramic alloys, irrespective of compositional differences. www.indiandentalacademy.com 96
  • Opaque porcelain layer • These porcelains are made opaque by the addition of insoluble oxides, such as • tin oxide (SnO2), • titanium oxide (TiO2), • zirconium oxide (ZrO2), • cerium oxide (CeO2), www.indiandentalacademy.com 97
  • Opaque porcelain layer contd. • • • • oxide, and rubidium oxide, barium zinc oxide. Such oxides have high refractive indices, so they scatter light. www.indiandentalacademy.com 98
  • Composition on chemical analysis www.indiandentalacademy.com 99
  • • Between 8% and 15% of an opaque powder is composed of metallic oxides, and some particles may be less than 5 um in size. • Even small differences in particle size distribution are thought to influence the ability of opaques to mask the color of a metal substructure. www.indiandentalacademy.com 100
  • • The opaque porcelains three major functions: • (1) to establish the porcelain-metal bond, • (2) to mask the dark color of the metal substructure, and • (3) to initiate the development of the selected shade of porcelain. www.indiandentalacademy.com 101
  • • A uniform thickness of 0.2 to 0.3 mm generally is regarded as ideal. • That masking power is influenced by the amount and the color of the oxidized (degassed) metal casting (Naylor, 1986) www.indiandentalacademy.com 102
  • • A casting alloy of a different composition might generate a thick, dark oxide layer (Naylor, 1986) and require a thicker opaque covering. • The thickness of the opaque layer needed to veneer the metal and mask the surface oxides differs among brands of porcelain and even varies for different shades within the same porcelain system www.indiandentalacademy.com 103
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  • Body porcelains • Body porcelain collectively describes four principal types of porcelain powders used to recreate the "body" of a restoration: dentin (body or gingival), enamel (or incisal), translucent, and modifier. • These body porcelains are mixed with either distilled water or a special liquid (provided with the porcelain kit) that helps to prevent the buildup from drying out rapidly. www.indiandentalacademy.com 105
  • • They are applied directly over the fired opaque layer . • The dentin, enamel, translucent, and modifier powders all have the same chemical and physical properties, they may be intermixed freely if custom shading is desired. • They differ in appearance in the fired state because of variations in the amount and type of metallic oxide pigments each contains. www.indiandentalacademy.com 106
  • The dentin porcelain veneer • The major color contribution is derived from the pigmented metal oxides in the dentin body porcelain • It is this initial layer of dental porcelain that imparts the dentin shade associated with, but not confined to, the gingival two thirds of a tooth. • The dentinal layer is overbuilt slightly, cut back, and overlaid with enamel porcelain in those sections of the restoration where greater translucency is desired. www.indiandentalacademy.com 107
  • • For more accurate shade duplication, estimates of the combined thickness of fired dentin and enamel porcelains range from a minimum of 0.5 to 1.0 mm to a maximum thickness of 1.5 to 2.0 mm www.indiandentalacademy.com 108
  • • For uniformity of shade and maximum strength, it is desirable to have an even thickness of porcelain covering the metal substructure. • The minimum total thickness of porcelain may be between 1.2 to 1.3 mm at the middle one third of the restoration and 1.5 to 1.6 mm at the incisal edge (Yamamoto, 1985). www.indiandentalacademy.com 109
  • ENAMEL PORCELAIN VENEER • Enamel porcelains are more translucent than dentin porcelains. • The enamel porcelains are usually in the violet to grayish range & impart a combination of true translucency & the illusion of the translucency by virtue of their grayish or some times bluish appearance. • www.indiandentalacademy.com 110
  • • When fired, enamel porcelains are more translucent than dentin porcelains (McLean, 1979). • They also have a more restricted range of shades. A typical porcelain system may provide only four or five bottles of enamel powders to cover the entire range of shades in the kit. www.indiandentalacademy.com 111
  • Translucent porcelains • Translucent porcelains are not transparent, they do not allow the transmission of all light. • They are applied as a veneer over nearly the entire surface of a typical porcelain buildup. • This veneer imparts depth and a natural enamel-like translucency without substantially altering the body shade that is overlaid. www.indiandentalacademy.com 112
  • BODY MODIFIERS • These porcelains are more color concentrated & were designed to aid in the achieving internal color modifications. • They are used to distinguish the dentin, enamel & translucent porcelains, because they have the same basic physical & chemical properties. • All these powders are basically same materials, they do differ in the appearance because of the modifiers. www.indiandentalacademy.com 113
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  • STAINS • Stain powders contain less silica or alumina & more sodium & potassium oxides. • They contain high concentration of metallic oxides. • They are created by mixing the metallic oxides with lower fusion point glasses www.indiandentalacademy.com 115
  • GLAZES • Glazes are generally colorless, low fusing porcelains. • They possess considerable fluidity at high temperatures. • They fill small surface porosities & irregularities. when fired helps to recreate the external glazy appearance of the natural tooth www.indiandentalacademy.com 116
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  • GLAZE (Contd.) • A glazed ceramic surface is generally considered beneficial by increasing the fracture resistance and reducing the potential abrasiveness of ceramic surfaces www.indiandentalacademy.com 118
  • Color coding • By convention dentin powders are pink and enamel powders are blue. • These organic colors burn off during firing procedure and do not affect the shade of the fired restoration in any way. • Some manufacturers color code the distilled water instead of the powder.e.g. pencraft porcelain www.indiandentalacademy.com 119
  • CLASSIFICATION OF DENTAL CERAMICS • Different types of dental ceramics are available These include core ceramic, liner ceramic, margin ceramic, opaque dentin (also, body or gingival) ceramic, dentin ceramic, enamel (incisal) ceramic, stain ceramic, glaze ceramic, and addition ceramic www.indiandentalacademy.com 120
  • • These products can be classified in several possible ways according to their: (1) use or indications (anterior, posterior, crowns, veneers, post and cores, FPDs, stain ceramic, and glaze ceramic); www.indiandentalacademy.com 121
  • • (2) composition (pure alumina, pure zirconia, silica glass, leucitebased glass-ceramic, and lithiabased glass-ceramic • (3) processing method (sintering, partial sintering and glass infiltration ,CAD-CAM, and copymilling); www.indiandentalacademy.com 122
  • • Microstructure (glass, crystalline, and crystal-containing glass); • Translucency (opaque, translucent, and transparent); Fracture resistance; or Abrasiveness www.indiandentalacademy.com 123
  • Based on the method of fabrication 1. Condensation porcelains using condensation and sintering 2. Castable ceramics –Dicor-Dentsply 3. Pressable ceramics 4. Machinable ceramics 5. Infiltrated ceramics 6. Injection molded ceramics –Cerestore www.indiandentalacademy.com 124
  • Classification (Mclean) 1) Regular feldspathic porcelain 2) Aluminous porcelain 3) Metal bonding porcelain. www.indiandentalacademy.com 125
  • Based on their fusion temperature (Phillips,1982) type Fusing temperature range uses High fusing porcelains- 1288 to 1371 C 1200-1400 used for manufacturing denture teeth . Medium fusing Porcelains- 1093 to 1260 C 1050-1200 for all ceramic restorations and prefabricated pontics. Low fusing porcelains- 871 to 1066 C for metal ceramic and all 800-1050 www.indiandentalacademy.com ceramic. Both are similar in composition and microstructure. 126
  • METAL SUB STRUCTURE DESIGN. • Majority of the porcelain-to-metal bond failures occur as a direct result of improper substructure design • Errors in the preparation of the metal ceramic sub-structure frequently go unnoticed until the brittle porcelain veneer fails in service. www.indiandentalacademy.com 127
  • METAL SUB STRUCTURE DESIGN. • TYPES • FUNCTIONS. • DESIGN. www.indiandentalacademy.com 128
  • Types of metal ceramic system. • A. Cast metal ceramic alloys: • 1.Noble-metal alloy systems: • High gold - a) Gold platinum palladium. • Low gold - b) Gold palladium silver. • Gold free - c) Palladium silver. • 2.Base metal alloys systems: • Nickel chromium alloy. • Cobalt chromium alloys ( rarely used in ceramic bonding). www.indiandentalacademy.com 129
  • • B. • Foil copings: • a) Bonded platinum foil coping. • b) Swaged gold alloy foil coping. www.indiandentalacademy.com 130
  • a) Bonded platinum foil coping: • Another method of bonding porcelain to metal is the use of tin oxide coatings on platinum foil. • The method consists of bonding aluminous porcelain to platinum foil copings. • Attachment of the porcelain is secured by electroplating the foil with a thin layer of tin and then oxidizing it in a furnace. www.indiandentalacademy.com 131
  • • The objective of this type of restoration is to improve esthetics. • The thicker cast metal coping that is normally used is replaced by a thinner platinum foil, thus allowing more space for the porcelain. www.indiandentalacademy.com 132
  • b) Swaged Gold Alloy Foil Coping: • A laminated gold alloy supplied in fluted shape is also used as an alternative to the cast metal coping. • The foil is swaged onto the die and flame sintered to form a coping. • An “interfacial alloy” powder is applied and fired and the coping is then veneered with porcelain. www.indiandentalacademy.com 133
  • Primary functions:• The casting provides fit of the restoration to the prepared tooth. • The metal forms oxides that bond chemically to the dental porcelain. www.indiandentalacademy.com 134
  • • The coping serves as a rigid foundation to which the brittle porcelain can be attached for increased strength & support. • The sub structure restores the tooth's proper emergence profile. www.indiandentalacademy.com 135
  • Secondary functions. • Metal occlusal & lingual articulating surfaces generally less destructive to the enamel of the opposing natural tooth. • Fabrication of the restoration with minimal occlusal clearance has more potential for the success with metal substructure than all ceramic alloys. www.indiandentalacademy.com 136
  • • Occlusal surfaces can be easily adjusted & repolished intraorally. • The metal axial walls can support the removable partial denture. www.indiandentalacademy.com 137
  • Metal sub structure design • Majority of the porcelain-to-metal bond failures occur as a direct result of improper substructure design • Errors in the preparation of the metal ceramic sub-structure frequently go unnoticed until the brittle porcelain veneer fails in service. www.indiandentalacademy.com 138
  • Sub structure design (contd) • Hence necessary to understand the essentials of proper substructure design, since it will help to ensure the longevity of the final prosthesis. www.indiandentalacademy.com 139
  • Principles of substructure design. • Are the occlusal contacts to be in metal or porcelain? www.indiandentalacademy.com 140
  • • Occlusion in metal requires less tooth reduction (1 to 1.5 mm). • Approximately 2 mm of occlusal reduction is necessary for posterior teeth and 1 to 1.5 mm for anterior teeth requiring porcelain on occluding surfaces. www.indiandentalacademy.com 141
  • • Metal surfaces can be more easily adjusted and repolished at chair side without adversely affecting the restoration. • On the other hand, removing the glaze of a metal ceramic restoration during intraoral adjustments weakens the porcelain greatly www.indiandentalacademy.com 142
  • • 2. Are the centric occlusal contacts 1.5 to 2mm from the porcelain-metal junction? www.indiandentalacademy.com 143
  • • occlusal contacts when placed directly on or close to the porcelainmetal junction, there is an increased likelihood the porcelain will chip or fracture at that point of contact . • Porcelain is strongest under compression and weakest under tension, so situations that induce tensile stresses in the ceramic during function are more apt to promote bond failures www.indiandentalacademy.com 144
  • • A substructure should be designed so the functional incisal or occlusal contacts are located at least 1 .5 mm and perhaps as much as 2 mm from the metal-porcelain junction. www.indiandentalacademy.com 145
  • • When the anterior teeth contact in the incisal region,it is often necessary to consider a design with lingual surface in porcelain to avoid functioning on or over the porcelain metal junction. www.indiandentalacademy.com 146
  • • Do not design the sub structure so contact occurs at the porcelain metal junction. www.indiandentalacademy.com 147
  • • When the anterior teeth occlude in the gingival half of the maxillary teeth or when the lingual tooth reduction is less than 1mm it is best to design the sub structure with occlusion in the metal. www.indiandentalacademy.com 148
  • • 3.Are the interproximal contacts to be restored in metal or porcelain? www.indiandentalacademy.com 149
  • • The inter proximal contact areas of anterior teeth, and at least the mesial contacts of posterior teeth, are frequently restored in porcelain • with porcelain inter proximal contact areas would be more esthetic, particularly with anterior teeth. www.indiandentalacademy.com 150
  • • It is important to provide proper metal support to a porcelain marginal ridge in the substructure design to prevent possible fracture • However, the distal inter proximal contacts of posterior teeth may be restored in either metal or porcelain because these areas are not as critical esthetically. www.indiandentalacademy.com 151
  • • 4.Are the cusp tips (or incisal edges )adequately supported by the metal substructure with no more than 2mm of unsupported porcelain? www.indiandentalacademy.com 152
  • • The ultimate goal of any substructure is to support an even thickness (1mm minimum, 2 mm maximum) of the porcelain veneer. • If this maximum thickness is exceeded, the ceramic layer may no longer be properly supported, resulting in a catastrophic failure at the cusp tip or incisal edge www.indiandentalacademy.com 153
  • • 5. Is the substructure thick enough to provide a rigid foundation for the porcelain veneer? www.indiandentalacademy.com 154
  • • Areas to be veneered with porcelain must be at least 0.3 mm thick. • with base metal alloys, the coping can be reduced to 0.2 mm or less and still be strong enough to support the porcelain www.indiandentalacademy.com 155
  • How does dental porcelain bond to metal? (1) van der Waals forces (Lacy, 1977), • (2) mechanical retention, • (3) compression bonding, and • (4) direct chemical bonding (Lacy, 1977; McLean, 1980; www.indiandentalacademy.com 156
  • van der Waals forces • The attraction between charged atoms that are in intimate contact yet do not actually exchange electrons is derived from van der Waals forces. • These secondary forces are generated more by a physical attraction between charged particles • Van der Waalsforces are generally weak. www.indiandentalacademy.com 157
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  • • The better the wetting of the metal surface, the greater the van der Waals forces. • porcelain's adhesion to metal can be diminished or enhanced by alterations in the surface character (texture) of the porcelain-bearing surface on the substructure www.indiandentalacademy.com 159
  • • van der Waals forces are only minor contributors to the overall attachment process. www.indiandentalacademy.com 160
  • Mechanical retention • The porcelain-bearing area of a metal casting contains many microscopic irregularities into which opaque porcelain may flow when fired. • Air abrading the metal with aluminum oxide is believed to enhance mechanical retention further by eliminating surface irregularities (stress concentrations) www.indiandentalacademy.com 161
  • Mechanical retention's contribution to bonding may be relatively limited. • Dental porcelain does not require a roughened area to bond to metal but some surface roughness is effective in increasing bonding forces • www.indiandentalacademy.com 162
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  • Compression bonding • Dental porcelain is strongest under compression and weakest under tension; hence, if the coefficient of thermal expansion of the metal substrate is greater than that of the porcelain placed over it, the porcelain should be placed under compression on cooling www.indiandentalacademy.com 165
  • • the metal contracts faster than the porcelain but is resisted by the porcelain's lower coefficient of thermal expansion. • This difference in contraction rates creates tensile forces on the metal and corresponding compressive forces on the porcelain. www.indiandentalacademy.com 166
  • Chemical bonding • The single most significant mechanism of porcelain-metal attachment is a chemical bond between dental porcelain and the oxides on the surface of the metal substructure www.indiandentalacademy.com 167
  • • The two hypothesis that explains chemical bonding are • 1, The sandwich theory the oxide layer is permanently bonded to the metal substructure on one side while the dental porcelain remains on the other www.indiandentalacademy.com 168
  • • The oxide layer itself is sandwiched in between the metal substructure and the opaque porcelain. This "sandwich" theory is undesirable in that a thick oxide layer might exist that would weaken the attachment of metal to porcelain www.indiandentalacademy.com 169
  • • The second, and more likely, theory suggests that the surface oxides dissolve, or are dissolved by, the opaque layer. The porcelain is then brought into atomic contact with the metal surface for enhanced wetting and direct chemical bonding so metal and porcelain share electrons. (McLean, 1980; Yamamoto, 1985) www.indiandentalacademy.com 170
  • • Chemical "bonding" is generally accepted as the primary mechanism in the porcelain-metal attachment process www.indiandentalacademy.com 171
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  • The oxidation (degassing) process • After the cast metal ceramic castings have been properly finished with uncontaminated carbide burs or ceramic abrasives the castings are heat-treated in a porcelain furnace (in air or a vacuum) to a designated temperature for a specified period of time (Naylor, 1986). www.indiandentalacademy.com 174
  • • The heat-treatment process allows specific oxides to form on the metal surface. These oxides are responsible for the chemical porcelain- metal "bond." www.indiandentalacademy.com 175
  • • A high-gold-content alloy contains oxidizable trace elements such as tin, indium, and iron to produce an adherent oxide layer. Because elements like gold and the other noble metals do not oxidize, it is often necessary to hold these castings at temperature for several minutes to permit the non noble trace elements to form the oxide layer www.indiandentalacademy.com 176
  • • The base metal alloys readily oxidize, but trace elements are still added in an effort to form a particular type of oxide for a stable bond . • The oxidation procedure may be carried out in a vacuum to minimize the amount of oxidation, and the hold time is often reduced or omitted. www.indiandentalacademy.com 177
  • • Allowing certain base metal alloys to oxidize in air, or to remain at temperature, could lead to over oxidation. An excessively thick and non-adherent oxide layer is often responsible for porcelain bond failures www.indiandentalacademy.com 178
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  • • A properly oxidized casting often has a distinctive appearance in terms of color and character (texture, thickness, etc). • That appearance of a properly oxidized metal substructure differs among alloy systems and may also differ among alloys within the same system. www.indiandentalacademy.com 180
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  • • Some manufacturers do not recommend an oxidation/ degassing step; instead, they advocate minimizing the number of firings to which the casting is subjected. www.indiandentalacademy.com 182
  • Removing the oxide layer • Two principal methods for removing oxides are – Acid treatment (chemical method) – Nonacid treatment (mechanical method). www.indiandentalacademy.com 183
  • Acid treatment (chemical method) • Different types of acids are used to reduce or eliminate surface oxides, including hydrofluoric, hydrochloric, and dilute sulfuric acid. • The potential hazards of these acids require that they be stored and used in clearly marked, resealable plastics bottles. • It is advisable to wear protective rubber gloves and eye protection during all handling procedures. www.indiandentalacademy.com 184
  • • A rubber-tipped instrument should be used to place oxidized castings into the acid appropriate for the alloy. • Place the covered container in an ultrasonic unit for the time recommended by the alloy manufacturer. • Remove the casting and thoroughly rinse it under tap water. For the final cleaning step, put the coping in a container of distilled water and clean it ultrasonically for 10 to 15 minutes. www.indiandentalacademy.com 185
  • Nonacid treatment (Mechanical method) • Castings can be air-abraded with pure, 50um aluminum oxide (Al2o3) that is nonrecycled. • Steam clean or ultrasonically clean the casting in distilled water for 10 to 15 minutes before applying the opaque porcelain. www.indiandentalacademy.com 186
  • Porcelain-metal bond failures • Metal ceramic alloys, whether noble or base metals, all oxidize differently because of variations in their composition. • If the oxidation process is not performed properly, the subsequent porcelain-metal bond may be weak and may lead to bond failure. www.indiandentalacademy.com 187
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  • Porcelain delamination • With base metal alloys, the separation of the porcelain veneer from the metal substrate can be more a loss of the "attachment" of the oxide layer that is either too thick or is poorly adherent to the metal substructure. www.indiandentalacademy.com 189
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  • Porcelain delamination contd • Overoxidation has been a particular problem with the heavily oxidizing base metal alloys and has been linked to their increased tendency for bond failures . www.indiandentalacademy.com 191
  • • Bond failures are not caused by a loss of the chemical bond between the ceramic and the oxide layer • on the contrary, the porcelain might remain visibly attached to the oxides but the oxide layer may be so thick that the bond is lost through it . • This particular problem is caused by the formation of a thick and poorly adherent oxide layer. www.indiandentalacademy.com 192
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  • Classification of bond failures in metal-ceramics. • (Given by O’ Brien (1977). • 1) Metal – Porcelain: • Fracture leaves a clean surface of metal. Seen when metal surface is devoid of oxides. May also be due to contaminated or porous metal surface. Usually occurs in high gold alloys. www.indiandentalacademy.com 195
  • • 2) Metal oxide – Porcelain: • Porcelain fractures at metal oxide surface, leaving oxide firmly attached to metal .Seen more often in base metal alloy systems. • 3) Metal – Metal Oxide: • Metal oxide breaks away from the metal and is left attached to the porcelain. Seen commonly in base metal alloy systems due to over production of chromium and nickel oxides. www.indiandentalacademy.com 196
  • • 4) Metal Oxide –Metal Oxide: • Fracture occurs through the metal oxide. Results from overproduction of oxide causing sandwich effect between metal and porcelain. Occurs during the usage of nickel-chromium alloys. • 5) Cohesive within Metal: • More common in bridges where the joint area breaks. Rarely seen in single crowns. www.indiandentalacademy.com 197
  • • 6) Cohesive within Porcelain: • Tensile failure within porcelain. Bond strength exceeds strength of porcelain. Seen in high gold content alloys. www.indiandentalacademy.com 198
  • • Excessive absorption of oxides by the porcelain can lower the porcelain's coefficient of thermal expansion, alter the final shade (cause a graying or bluing), or do both (Naylor, 1986 www.indiandentalacademy.com 199
  • • Changes in the shade of the porcelain may not be noticeable with posterior restorations, particularly if a greater thickness of porcelain masks the dark oxides www.indiandentalacademy.com 200
  • Incompatible materials • Further more, bond failures are not always attributable to improper oxidation but may actually be caused by a physical incompatibility between the porcelain and the metal substructure. The difference in the coefficient of thermal expansion of the veneering porcelain and the metal ceramic alloy may be slight yet sufficient to be responsible for cracking of the ceramic veneer or substantial enough to result in porcelain debonding. www.indiandentalacademy.com 201
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  • Overoxidation/underoxidation • The oxidation procedure varies for alloys of different compositions. • Careful processing followed by an assessment of the postoxidation appearance of each casting will ensure that the procedure was accomplished correctly. • Castings that are either overoxidized or underoxidized should be reprocessed accordingly until a uniform oxide of the desired color and thickness recommended for the alloy involved has formed. www.indiandentalacademy.com 203
  • • Contamination – castings that demonstrate some form of contamination may not have to be remade but by simply refinishing a substructure's porcelain-bearing surface may be all that is necessary when surface debonding becomes evident. Uncontaminated finishing materials are used to prevent this. www.indiandentalacademy.com 204
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  • • Simply refinishing this casting removed the surface and subsurface contamination and resulted in an appropriate porcelain-metal bond. www.indiandentalacademy.com 206
  • Applying Porcelain to the Metal Substructure • The application of dental porcelain to the metal substructure is the single most demanding procedure in the fabrication of a metal ceramic restoration. • As a rule, the skills needed for this particular process require the most effort to perfect. www.indiandentalacademy.com 207
  • Instruments and equipment • Brushes • A variety of brush sizes and styles are available in porcelain instrument kits, the most important of which are the brushes used for building or stacking porcelain. . The size range varies from a no. 4 to a no. 8. Sable brushes are the standard because they permit easy manipulation of the porcelain. www.indiandentalacademy.com 208
  • • Another frequently used instrument is a large no.10 brush, often referred to as a whipping brush • A basic instrument kit should also include flat brushes with relatively stiff bristles. These large- and small-sized brushes should be kept dry because they are used exclusively to remove porcelain particles from non porcelain-bearing areas and from inside the substructure prior to firing. www.indiandentalacademy.com 209
  • • Very small no. 0 to no. 000 sable brushes are required for the placement of stains or small increments of porcelain. These brushes are useful anywhere maximum control is necessary www.indiandentalacademy.com 210
  • Carving Instruments • Porcelain carving instruments, designed for shaping and carving porcelain buildups. • Carving instruments serve two principal functions. • 1.Those with a serrated handle can be used to condense wet porcelain. • 2.Instruments with blades, as well as the small discoid carver, can be used to build (stack) porcelain, shape the buildup, and carve the porcelain. www.indiandentalacademy.com 211
  • Spatula • Small, flexible, metal spatula is used to dispense and mix porcelain. • Any small metal fragments generated during mixing can then be introduced into the wet porcelain as contaminants. www.indiandentalacademy.com 212
  • • This metal debris can dramatically discolor the mix as well as the fired porcelain restoration. With careful use, however, the metal mixing spatula need not be abraded. • But for added safety, a glass mixing rod is often substituted for the metal spatula to avoid this problem altogether. www.indiandentalacademy.com 213
  • Razor knives • Another necessity in the basic set of instruments is some type of razor knife, equipped with a thin, flexible blade for carving the porcelain buildup. www.indiandentalacademy.com 214
  • Hemostat • A small, straight or curved hemostat is needed to hold the work during the opaquing process and during porcelain additions and condensation. • Hemostats can be modified to hold the metal substructure securely without damaging the metal margins. However, an 18-gauge handle added to the lingual collar provides a convenient, safe, yet secure grip for removing the restoration from the working cast and holding it during condensation www.indiandentalacademy.com 215
  • Glass or ceramic mixing slab • Finally, either a glass slab, ceramic tile, or ceramic tray can serve as a plate for mixing and storing the porcelain during the buildup procedure. Initially, a small mixing slab will suffice (Fig 8-9a). www.indiandentalacademy.com 216
  • • As modifiers are added and more complex buildups are attempted,a larger working surface will be required to accommodate all the different porcelain mixtures www.indiandentalacademy.com 217
  • PORCELAIN CONDENSATION. • Condensing dental porcelain actually refers to any procedure that results in the unfired porcelain particles being tightly packed on to themselves. • As the particles moves closer together, the air and moisture previously occupying the space between the individual particles move to the surface of the buildup. www.indiandentalacademy.com 218
  • • Any liquid or air that remains trapped in the unfired porcelain will form voids in the unfired ceramic. • The presence of porosity in fired porcelain weakens the restoration and impairs its esthetic qualities. www.indiandentalacademy.com 219
  • • In well-condensed porcelain there is reduction in the amount of firing shrinkage. • Methods of porcelain condensation. • 1) capillary action. • 2) vibration • 3) spatulation • 4) whipping • 5) dry powder addition. www.indiandentalacademy.com 220
  • Capillary action. • The technique of blotting a wet built up with absorbent paper uses surface tension. www.indiandentalacademy.com 221
  • Vibration. • Is created by passing a serrated instrument over the neck of a hemostat in which the restoration is held. • Vibration is a means to mechanically draw additional moisture to the surface where it can then be removed by blotting paper. www.indiandentalacademy.com 222
  • Spatulation. • A spatula is used to apply , then rub the porcelain built up to force the liquid to the surface. www.indiandentalacademy.com 223
  • Whipping. • A no. 10 sable brush is rapidly moved over the porcelain surface with a whipping motion. The whipping motion brings the liquid to the outer surface for blotting. www.indiandentalacademy.com 224
  • Dry powder addition. • Requires dry porcelain powder be sprinkled on an area of wet porcelain, using the existing liquid to moisten the powder addition. www.indiandentalacademy.com 225
  • Opaquing the metal substructure • The areas of the substructure that will be veneered with porcelain must not be touched and should be protected from dust, oils from the skin, and any other forms of contamination www.indiandentalacademy.com 226
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  • Applying opaque porcelain— glass rod technique • First wet the oxidized metal substructure to be veneered with distilled water and gently vibrate the casting to thoroughly wet the surface. • A wet surface makes porcelain application easier and reduces the possibility of trapping air between the porcelain and the metal. The thin film of water also will draw the opaque particles onto the metal www.indiandentalacademy.com 228
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  • Glass rod technique. • Use the pointed end of the glass rod to apply the opaque porcelain. Begin by opaquing the most convex portion of the coping Move the opaque toward the porcelain-metal junction from one interproximal area to the other and cover the incisal edge. www.indiandentalacademy.com 230
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  • • Then move the opaque over the incisal edge to cover the porcelain-bearing surface on the lingual aspect. Once the porcelain-bearing areas are completely covered, lightly tap the hemostat and the porcelain will settle into any concavities www.indiandentalacademy.com 232
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  • • If, during the opaque application, areas of opaque appear rough and irregular, lightly tap the hemostat handle or move the serrations on a carver across the hemostat in a sawing motion. • The vibrations created by either of these procedures will act to condense the wet porcelain into a more uniform layer. • www.indiandentalacademy.com 234
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  • • Excess moisture should be removed before the opaque is applied to the metal. Gently blend the opaque at the porcelainmetal junction. • Lightly tap the hemostat and dry the opaque by placing it in front of an open porcelain furnace muffle. www.indiandentalacademy.com 236
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  • • Dry the opaque layer by exposing it to the heat radiating from the porcelain muffle. www.indiandentalacademy.com 238
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  • • A properly fired (sintered) opaque layer should have a sheen or eggshell glisten. www.indiandentalacademy.com 240
  • • If a second application of opaque porcelain is required, lightly wet the opaqued surface with opaque liquid. • Apply the second opaque porcelain layer in the same manner as the first. • Keep this second layer as thin and uniform as possible. www.indiandentalacademy.com 241
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  • Applying opaque porcelain— brush technique • Simply mix the opaque porcelain .Use the tip of porcelain brush to lift a portion of the mixed opaque www.indiandentalacademy.com 244
  • • Apply the porcelain on the most convex part of the oxidized coping. Repeat the process several times until the porcelain-bearing area is completely covered with porcelain. www.indiandentalacademy.com 245
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  • Mixing dentin porcelains – The technique for mixing body porcelains is same as that used to mix opaque porcelains in that a glass rod is preferred to a metal spatula and the liquid is carefully added to the powder to prevent the entrapment of air. www.indiandentalacademy.com 248
  • • Mix the body powders (dentin and enamel) with the recommended liquid (Vita VMK 68 porcelain and modeling liquid ) www.indiandentalacademy.com 249
  • • When properly mixed, dentin porcelain should have a smooth,cream consistency. www.indiandentalacademy.com 250
  • • If too much liquid is added to the mix, use a tissue or blotting paper to remove excess liquid until the proper consistency is achieved. www.indiandentalacademy.com 251
  • Appling dentin porcelain. • The dentin porcelain buildup procedure is to apply and condense enough porcelain to create a restoration that is 10% to 15% large than normal. www.indiandentalacademy.com 252
  • • This overbuilding will accommodate the enamel veneer that will be placed over the dentin layer and help to compensate for shrinkage of the porcelain. A high quality sable brush is preferred to create the porcelain buildup www.indiandentalacademy.com 253
  • The dentin built up technique. • Return the cleaned, opaqued coping to the master cast. www.indiandentalacademy.com 254
  • • To minimize the entrapment of air in the porcelain, move the tip of the pointed brush through the mixed dentin porcelain and remove the brush with the dentin porcelain captured on the brush www.indiandentalacademy.com 255
  • • Apply the porcelain to the most convex surface (midfacial area) on the restoration. www.indiandentalacademy.com 256
  • • Coax the porcelain toward the interproximal and incisal areas. Add more porcelain to the facial surface and use a light tapping motion to move the porcelain along the porcelain-metal junction. www.indiandentalacademy.com 257
  • • Move the porcelain down to the incisal edge and lightly blot the buildup to condense the porcelain on the substructure. place the additional dentin porcelain in the incisal region and move it from one interproximal area to the other. www.indiandentalacademy.com 258
  • • Control the flow of the material and condense the buildup by periodically blotting the wet porcelain with the tissue. use light gingival-toincisal strokes on the facial surface to create the desired facial contour. www.indiandentalacademy.com 259
  • • Add additional porcelain to the incisal aspect of the incisal edge. www.indiandentalacademy.com 260
  • • Add additional porcelain to complete the mesial and distal corners. www.indiandentalacademy.com 261
  • Cutting back the dentin buildup • With the buildup complete, dentin porcelain as to be removed from those areas of the crown where you would like to have enamel porcelain. The procedure of removing dentin porcelain for enamel placement is referred to as the "dentin cutback." www.indiandentalacademy.com 262
  • If dentin porcelain is overbuilt(A), the amount of dentin remaining after the cutback may also be incorrect. www.indiandentalacademy.com 263
  • When the restoration has the correct anatomical contours and is slightly overbuilt(A) by 10% to 15%, the dentin cutback will also be correct. www.indiandentalacademy.com 264
  • Dentin cut back technique • With a razor knife cut back the incisal edge from between 1 to 1.5 mm. www.indiandentalacademy.com 265
  • • Remove dentin porcelain at the mesial interproximal line angle. Extend the cut to the junction of the middle and gingival one thirds for younger patients. www.indiandentalacademy.com 266
  • • Cut across the middle one third. Stop the cut back at the distal interproximal area. www.indiandentalacademy.com 267
  • • At the distal interproximal line angle, make a cut from the incisal edge toward the gingival one third as far as required for the esthetics .Then cut back the middle one third of the facial surface as necessary. www.indiandentalacademy.com 268
  • • Examine the restoration from an incisal view for symmetry and adequacy of the cutback. www.indiandentalacademy.com 269
  • • Smooth the cutback areas with the porcelain brush so the transitions from dentin to enamel porcelain are gradual. www.indiandentalacademy.com 270
  • • For younger patients ,develop mamelons.With a pointed brush ,create two depressions on the facial surface with vertical strokes from incisal to gingival. www.indiandentalacademy.com 271
  • Mixing the enamel porcelain. www.indiandentalacademy.com 272
  • • Glass rod is used to mix the powder and liquid .The enamel mix is slightly wetter than the dentin mix to facilitate its addition to a previously applied and condensed dentin layer. www.indiandentalacademy.com 273
  • • The mixed enamel porcelain should have a consistency that permits it to be readily picked up by a properly pointed porcelain brush. www.indiandentalacademy.com 274
  • • With a pointed brush, apply enamel porcelain to one corner of the cutback. www.indiandentalacademy.com 275
  • • Add more enamel porcelain and move it across the facial surface in the incisal one third. Push the wet mix toward the middle one third of the crown and work it into the opposite interproximal line angle. www.indiandentalacademy.com 276
  • • Blend the enamel porcelain at the junction of the middle and gingival one thirds and begin to establish the incisal edge and condense the porcelain by blotting periodically. www.indiandentalacademy.com 277
  • • With additional enamel porcelain, complete the incisal edge length and the mesialincisal line angle. Work your way along the incisal edge to create more of a distalincisal line angle. www.indiandentalacademy.com 278
  • • Blend the enamel porcelain into the gingival one third on the facial surface. Re-create the interproximal contours and line angles. www.indiandentalacademy.com 279
  • • Shape the mesialincisal corner as required for each case. Examine the builtup from an incisal view and evaluate the overall shape. Make certain the restoration is slightly over built. www.indiandentalacademy.com 280
  • • Condense the built up. www.indiandentalacademy.com 281
  • • Use your thin razor knife to cut and shape the mesial and distal interproximal areas. This procedure also removes any unwanted porcelain below the interproximal contact areas. www.indiandentalacademy.com 282
  • • Carefully remove the crown from the master cast. Add enamel porcelain to the small dimples in each interproximal contact area. www.indiandentalacademy.com 283
  • • Remove excess porcelain from the porcelain-metal junction and clean the facial metal collar of any porcelain with a small brush or your pointed porcelain buildup brush. www.indiandentalacademy.com 284
  • Firing procedure. • The large bulk need more time to dry and pre-heat. • Adhere to manufacturers recommended drying time. • A properly fired porcelain body bake should have a pebbly or “orange peel appearance”. www.indiandentalacademy.com 285
  • Adjusting and finishing the metal ceramic restoration. • Applying and firing the porcelain veneer to a metal substructure only approximates the shape, contour, occlusion, and surface finish restoration. • The porcelain application process requires slight overbuild of the ceramic, this results in a bulky restoration. www.indiandentalacademy.com 286
  • • Consequently, the fired porcelain requires additional adjustments to reduce any overcontouring and recreate a lifelike ceramic surface finish before the characterizing (staining) and glazing stages. • Adjusting , contouring, and finishing procedures for metal ceramic restorations play a critical role in achieving both proper function and optimal esthetics. www.indiandentalacademy.com 287
  • Armamentarium. • 1. Equipment – Handpiece with speeds of 50,000 rpm or below. • 2. Instruments – Iwanson metal caliper. • 3. Materials – Diamond abrasives, Prepolish wheels, diamond disks. www.indiandentalacademy.com 288
  • • The iwanson metal calipers can be used for thickness measurements of metal or metal and porcelain. www.indiandentalacademy.com 289
  • • Diamond abrasive instruments. www.indiandentalacademy.com 290
  • • Porcelain prepolish wheel .Designed for smoothening and polishing ceramic surfaces. www.indiandentalacademy.com 291
  • • Diamond disks • For adjusting and contouring interproximal areas. www.indiandentalacademy.com 292
  • Procedures in adjusting and finishing the metal ceramic restoration. • 1. To ensure the casting completely seats on the die. www.indiandentalacademy.com 293
  • 2.Adjusting the interproximal contacts. • a) Mark the mesial interproximal contact using thin double – sided marking film. www.indiandentalacademy.com 294
  • • b) Marking identifies the location and intensity of contact. www.indiandentalacademy.com 295
  • • Adjustments in the contact area with pre-polish wheel. www.indiandentalacademy.com 296
  • • The thickness of the restoration is periodically checked to ensure that it is not over contoured. www.indiandentalacademy.com 297
  • • The desired characterization is marked and with an abrasive the appropriate shape is created with desired effect. www.indiandentalacademy.com 298
  • Staining and glazing. • After a restoration has been adjusted and finished, it is necessary to make color corrections or additions and create a lifelike surface luster. www.indiandentalacademy.com 299
  • • Surface stains should be applied with a small sable brush. www.indiandentalacademy.com 300
  • • Stain is placed in area where the characterization is intended. Blend or dilute the effect of the stain www.indiandentalacademy.com 301
  • • The glaze is picked up with a staining brush and applied to the ceramic surface where desired. www.indiandentalacademy.com 302
  • • Dry the restoration in the porcelain furnace. www.indiandentalacademy.com 303
  • • The restoration is fired according to the porcelain manufacturers direction. www.indiandentalacademy.com 304
  • • Typically glazed restoration. www.indiandentalacademy.com 305
  • Mechanical polishing. • Mechanical polishing of the restoration after glazing gives the restoration a natural life like appearance. www.indiandentalacademy.com 306
  • A diamond polishing paste. www.indiandentalacademy.com Pumice flour 307
  • • After mechanical polishing. A life like luster is created in the ceramic yet the surface characterizatio n remains. www.indiandentalacademy.com 308
  • www.indiandentalacademy.com Leader in continuing dental education www.indiandentalacademy.com 309