Dental ceramics /certified fixed orthodontic courses by Indian dental academy


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Dental ceramics /certified fixed orthodontic courses by Indian dental academy

  1. 1. DENTAL CERAMICS  INDIAN DENTAL ACADEMYLeader in Continuing Dental Education
  2. 2. CONTENTSIntroductionHistorical aspectsClassificationCompositionCondensation and firingAesthetic propertiesMechanical propertiesMethods of strengthening ceramics
  3. 3. What are ceramics?• “Ceramic” derived from Greek words “Keramikos” = Earthen “Keramos” = Burnt stuff• Described as man made solid objects formed by baking raw materials (minerals) at high temperatures.• Defined as: An inorganic compound with non metallic properties typically composed of oxygen and metallic or semi metallic elements.(Aluminum,Calcium,Lithium,Magnesium,Potassium,Silicon,So dium, Tin,Titanium,Zirconium)
  4. 4. • Dental Ceramics contain a glassy matrix reinforced by various dispersed phases consisting of crystalline structures such as Lucite, alumina & mica.• Porcelain is a specific type of ceramic characterized by it being white & transparent• The term ‘glass ceramic’ has been introduced to classify ceramics where one or more crystalline phases have been precipitated from a glassy phase.
  5. 5.
  6. 6. HISTORICAL PERSPECTIVE• Dates back to 10 000 yearsPOTTERY IN EUROPE UPTO 1700AD:• Making usable pottery was a great challengeThe raw material was clay and it presented two major problems: 1) Consistency 2)Shrinkage on firing
  7. 7. solutions found were:• To beat the clay prior to molding to remove entrapped air.• Another development was the technique of raising temperature very gradually during firing process
  8. 8. • The most serious obstacle during this phase in the development of ceramic technology was the temperature at which the pottery could be fired.• The conversion of clay from a mass of individual particles loosely held by a water binder to a coherent solid relies on the process called Sintering In this process the point at which the individual particles are in contact fuse at sufficiently high temperatures.
  9. 9. • The need for high uniform temperatures led to invention of Kilns, that is, the oven specially designed for pottery• Initial kiln temperatures were 9000 C• Invention of Glaze to overcome surface porosities
  10. 10. Chinese Porcelain:• The Chinese had produced stoneware in 100 BC itself and by the 10th century AD they were able to produce ceramics.• Remained a secret for European countries till 18th century• The basic components of Chinese porcelain were identified as kaolin, silica and feldspar• Once the secret of Chinese porcelain was out, soon it was possible to make it in any shade or tint and the translucency gave such a depth of color that it was not long before its dental potential was recognized.
  11. 11. •1789 First porcelain tooth material patented in collaboration with a French pharmacist DuchateauAn Italian dentist Gussipangelo Fonzi launched the first singleporcelain teeth “terro metallic” tooth in 1808
  12. 12. •1808 An Italian dentist invented a “terrometallic” porcelain tooth that was held in place by platinum pin or frame
  13. 13. • 1817 Planteau, a French dentist, introduced porcelain teeth tothe US• 1822 Peacle ,an artist, developed baking process for theseteeth in Philadelphia• 1825 Commercial production of these teeth began• 1837 In England, Ash developed an improved version of theporcelain tooth.
  14. 14. •1844 The S.S.White Company was founded which further modified the design & began mass production of the denture teeth.
  15. 15. • 1903 Dr. Charles Land introduced one of the first ceramic crowns to dentistry using a platinum foil matrix and high fusing feldspathic porcelain.
  16. 16. In 1962 Weinstein use the gold alloys for porcelainAlumina reinforce crowns was developed in 1963 by Mc Leanand Hughes1n 1976 Mc Lean develop the stronger platinum bondedalumina crown
  17. 17. •1967 Restriction of uranium to 1% by wt.•1968 first use of glass ceramic by Mc Cullouch•1970 development of porcelain fused base metal alloys•1974 porcelain fused to noble metal alloys•1983 development of high expansion core material by O’Brien•1985 organic liquid binder instead of water by SANDERSON •In 1985 Logan fused porcelain to platinum post •Dr Swann Felcher did work on reinforcing the porcelain
  18. 18. 1991REPAIR OF PORCELAIN BY Ralph by using hydrofluoric acidetching silane1993 Monsenego Burdaicon studied the effect of florescencein ceramics
  19. 19. Indications• Esthetic alternative for discolor teeth• Traumatic fractures of incisal angles or buccal cusps• Congenital abnormalities• Veneers• Inlays and onlays• Crowns• Denture tooth material
  21. 21. CLASSIFICATION OF DENTAL CERAMICSAccording to Skinner:1. According to their use or indications: Anterior Posterior Crowns Veneers Post & Cores FPDs Stain ceramic Glaze ceramic Denture teeth
  22. 22. 2. According to composition:• Pure alumina• Pure zirconium• Feldspathic porcelain• Lucite based glass ceramic &• Lithia based glass ceramic
  23. 23. III. According to processing method: Sintering Partial sintering & glass infiltration Casting CAD-CAM Copy milling Machinable Pressable
  24. 24. IV. According to firing temperature: Ultra low fusing < 8500 C. Used for crown & bridge Low fusing 8500-11000 C. Medium fusing 11010-13000 C. High fusing 13000 C. Used for production of denture teeth
  25. 25. V. According to microstructure: Glass Crystalline Crystal containing glassVI. According to translucency: Opaque Translucent TransparentVII. According to resistanceVIII. According to abrasiveness
  26. 26. Based on crystalline nature• Crystalline ceramics ex: feldspathic porcelain containing Lucite [crystal phase]• Non crystalline ceramics eg:Glass
  27. 27. Based On Application• Core porcelain :• shows good mechanical properties, and provide strong base for the restoration• Opaque porcelain Body porcelain• Enamel porcelain
  28. 28. According to substrate material•Cast metal•Sintered metal•Swaged metal•Glass ionomer•CAD/CAM.
  29. 29. According to Type•Feldspathic porcelain•Aluminous porcelain•Glass infiltrated aluminous•Glass infiltrated spinell•Glass ceramicsAccording to Firing Technique•Air fired (at atmospheric pressure)•Vacuum fired (at reduced pressure)•Diffusible gas firing
  30. 30. According to Application For porcelain teeth For Ceramo-metal restorations (Metal- Ceramic Systems) For All-ceramic restorations (All-Ceramic System)
  31. 31. ALL CERAMIC SYSTEMS1) Conventional Powder – Slurry Ceramics : using condensing & sintering.(a)Alumina reinforced Porcelain e.g.. : Hi-Ceram(b) Magnesia reinforced Porcelaine.g.: Magnesia cores(c) Leucite reinforced (High strength porcelain) e.g.. : Optec HSP(d) Zirconia whisker – fiber reinforced e.g..:MirageII (Myron Int)(e) Low fusing ceramics (LFC): (i) Hydrothermal LFC e.g..: Duceram LFC (ii)Finesse(Ceramco Inc)
  32. 32. Castable Ceramics :Using casting & ceramming 1) Flouromicas e.g..: Dicor 2) Apatite based Glass-Ceramics e.g.. Cera Pearl 3) Other Glass-Ceramics e.g..: Lithia based, Calcium phosphate based
  33. 33. Machinable Ceramics : Milling machining by mechanicaldigital controlA) Analogous Systems (Pantograph systems – copying methods)1) Copy milling / grinding techniques a) Mechanical e.g.. : Celay b) Automatic e.g: Ceramatic II. DCP 2) Erosive techniques :a)Sono-erosion e.g..: DFE, Erosonicb) Spark-erosion e.g..: DFE, Procera
  34. 34. B) Digital systems (CAD / CAM):1) Direct e.g..: Cerec 1 & Cerec 22) Indirect e.g. : Cicero, Denti CAD, Automill, DCS-PresidentPressable Ceramics : By pressure molding & sintering 1) Shrink-Free Alumina Reinforced Ceramic (Injection Molded) E.g. : Cerestore / Alceram 2) Leucite Reinforced Ceramic (Heat – Transfer Molded) E.g.: IPS Empress, IPS Empress 2, Optec OPC
  35. 35. Infiltrated Ceramicsby slip-casting, sintering & glass infiltration1) Alumina based e.g.: In-Ceram Alumina2) Spinel based e.g.: In-Ceram Spinel3) Zirconia based e.g..: In-Ceram Zirconia
  36. 36. COMPOSITION OF DENTAL PORCELAINS• The quality of any porcelain depends on the choice of ingredients, the correct proportioning of each and the control of the firing procedure.• Ceramics are composed of essentially the same material as porcelain, the principal difference being in the proportioning of the primary ingredients & the firing procedure.
  37. 37. The various ingredients used in different formulations of ceramicsare:1. Silica (Quartz or Flint) – Filler2. Kaolin (China clay) – Binder3. Feldspar – Basic glass former4. Water – Important glass modifier5. Fluxes – Glass modifiers6. Colour pigments7. Opacifying agents8. Stains and colour modifiers9. Fluorescent agents10. Glazes and Add-on porcelain11. Alternative Additives to Porcelain
  38. 38. Feldspar 60% -80%Silica 10%Kaolin 3% -4%Fluorspar 1%Boric oxide 2%Calcium oxide 5-10%Metallic pigments >1%
  39. 39. • Other compounds such as potash, soda or lime are often added to give special properties.• Glass: is a fusible combination of silica & potash, therefore it is transparent.• Porcelain: Contains infusible elements held together by lower fusing materials and hence is less transparent.
  40. 40.
  41. 41. 2D Diagram of Oxide M2O3 2D Diagram of Oxide M2O3 In the crystalline form In the glass form
  42. 42. a) Feldspar:• Natural feldspar is a mixture of albite (Na2 Al2 Si6 O16) and orthoclase or microline (K2Al2Si6O16) with free crystalline quartz.• In its mineral state, feldspar is crystalline and opaque with an indefinite color between grey and pink.• Chemically it is designated as potassium-aluminum silicate, with a composition of K2O, Al2 O3 6SiO2.• On heating, it fuses at about 12900C, becomes glossy and unless overheated, retains its form without rounding.
  43. 43. Potassium and sodium Feldspar are normally occurringmaterials composed of potash (K2O), Soda (Na2O),Alumina (Al2O3), and Silica (SiO2).Commonly potassium feldspar is used It is used in the preparation of many dental porcelainsdesigned for metal ceramic crowns and many otherdental glasses and ceramics. When potassium feldspar is mixed with various metaloxides and fired to high temperatures, it can formleucite and a glass phase that will soften and flowslightly.
  44. 44. The softening of this glass phase during porcelain firing,allows the porcelain powder particles to coalescetogether.For dental porcelains, the process by which the particlescoalesce is called “Liquid - Phase Sintering”, a processcontrolled by diffusion between particles at a temperaturesufficiently high to forma dense solid.
  45. 45. b) Silica:• Pure quartz crystals (SiO2) are used in dental porcelains.• Silica remains unchanged at temperature normally used in firing porcelain and this contributes stability to the mass during heating by providing a framework for other ingredients.
  46. 46. It can exist in four different forms. • Crystalline quartz • Crystalline cristobalite • Crystalline tridymite • Non-crystalline fused silica 0 0   0  Si  0  Si  0   0 0
  47. 47. C) Kaolin:• It is produced in nature by weathering of feldspar during which the soluble potassium silicate is washed out by acid waters. In this process the residue is deposited and at the bottom of the streams in the form of clay.• Kaolin gives porcelain its properties of opaqueness.• It gives Consistency to mix and form a workable mass duringmolding• When subjected to a high temperature it binds the particle andmaintains the framework
  48. 48.  Color Frits:• They are coloring pigments added to the porcelain mixture.• Added in small quantities to obtain the delicate shades necessary to imitate natural teeth.• They are prepared by grinding together, metallic oxides with fine glass and feldspar, fusing the mixture in a furnace and regrinding to a powder.
  49. 49. • Metallic pigments: Titanium oxide – yellow brown shade Manganese oxide – lavender Iron oxide – Brown Nickel oxide – Brown Cobalt oxide – Blue (particularly useful for producing enamel shades) Copper or chromium oxide – Green Chromium – tin or chrome – alumina – Pink Iron oxide or platinum – Grey
  50. 50.  Opacifying Agents:• Generally consists of metal oxide (between 8% to 15%) growned to a very fine particle size (<5 µm) to prevent a speckled appearance in porcelain.• Commonest oxides are: Cerium oxide Zirconium oxide Titanium oxide Tin oxide Zircon oxide
  51. 51. Typical oxide composition of a dental PorcelainMaterial wt%Silica 63Alumina 17Boric oxide 7Potash (K2O) 7Soda (Na2O) 4Other oxides 2
  52. 52. • The opaque layer serves 3 primary functions:-a) It wets the metal surface and establishes a metal porcelain bondb) It masks the color of the metal substructurec) It initiates development of the selected shade Stains:• A stain is more concentrated than the color modifier• They can be supplied as pure metal oxides but are sometimes made from lower fusion point glasses so that they can be applied at temperatures below the maturing temperature of the enamel and dentin porcelains.
  53. 53. Generally used as a surface colorant or to provide enamel check lines, decalcification spots etc. in the body of a porcelain jacket crown. These stain products are also called as surface colorants or characterization porcelainInternal Stainingpermanent staining by using them internally. can produce a very life-like result, when built intoporcelain rather than when it is merely applied to thesurface.
  54. 54.  Glazes and add-on porcelain:• One purpose of an industrial glaze is to seal the open pores in the surface of a fire porcelain.• Dental glazes consists of low fusing porcelains which can be applied to the surface of a fired crown to produce a glossy surface.• It should mature at a temperature below that of the restoration and the thermal expansion of the glaze should be fractionally lower than the ceramic body to which it is applied.
  55. 55. Glass modifiers ∀ 0 0    0  Si  0  Si  0 + Na2O ∀ 0 0   ∀ 0 0    0  Si  • •  Si  0 + 2Na+ ∀ 0 0   Diagram showing interruption of silica tetrahedral by sodium oxide.
  56. 56. • Acts as fluxes and help in reducing the softening temperature• Decreasing the amount of cross-linking between the oxygen and the glass forming elements like silica i.e., they disrupt the continuity of the SiO4 network.• Should not be too high, because if too many tetrahedra are disrupted, there may occur crystallization during the porcelain firing operations.
  57. 57. The most commonly used are potassium, sodium calcium oxides. Introduced as carbonates that revert to oxides on heating. Other oxidesLithium oxide,Magnesium oxide,Phosphorous pentoxide etc.
  58. 58. Body Porcelain:• This term collectively describes four principal types of porcelain powders used to create the body of a restoration i.e. 1) Dentin (body or gingival) 2) Enamel 3) Translucent 4) Modifier or color frits
  59. 59. Dentin:• They correspond in color to the dentin of natural teeth.2) Enamel Porcelains:• When fired, enamel porcelains are more translucent than dentin porcelain.• Restricted range of shades – usually in the violet to grey range.3) Translucent Porcelain:• They are applied as 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.
  60. 60. 4) Body Modifiers:• These porcelains are more color concentrated and were designed to aid in achieving internal color modifications.• Modifiers are color intense, Dentin porcelains are color predominant, Enamel and translucent porcelains are color reduced
  61. 61. Other Additions to Dental Porcelains: Boric oxide (B2O3) can behave as a glass modifier• It decreases viscosity, lowers the softening temperature, and forms its own glass network. Alumina (Al2O3)• Its role in glass formation is complicated• It takes part in the glass network to alter the softening point and viscosity
  62. 62.  Lithium Oxide:• Added as an additional fluxing agent Magnesium Oxide:• May also be present but in minute quantities• It can replace calcium oxide
  63. 63.  Phosphorus Pent oxide:• Is sometimes added to induce opalescence and is also a glass forming oxide.Color Coding Dental Porcelain:• Organic dies are used to color code the porcelain powders
  64. 64. Condensation of Dental PorcelainCondensation: The process of packing the particles together and removing the liquid binder is known as condensation.• Distilled water the most common and most useful liquid binder.• Other binders: Glycerine, propylene glycol or alcohol.• “Brush Application Method”• Not recommended because the control of the powder is difficult and time consuming.
  65. 65. • “Wet Brush Technique”• is the most logical approach because: a) Wet brush maintains the moisture content in the porcelain. Metal spatula cause more rapid drying out. b) The brush can be used to introduce enamel colors, effect masses or stains without changing instruments. c) Greater control over applying small increments of porcelain. d) Blending of enamel veneers can be achieved with greater delicacy
  66. 66. Condensing Techniques:a) Vibrationb) Spatulationc) Whippingd) Mechanicale) Ultrasonic vibration
  67. 67. Volume Porosity of Powders:• The volume porosity of regular air or vacuum firing powders is in the region of 40-49%.• Vacuum firing powders generally have less shrinkage than the coarser air fire powders.• Size and shape of particles• Gap and grading system
  68. 68.
  69. 69. Air-Firing Porcelain: • In air firing methods a very slow maturation period is ideal for which to aim, in order to allow the maximum amount of entrapped air bubbles to escape. • Heating the porcelain 30o-50oC below the maximum firing temperature is recommended.Vacuum Firing Procedures:• Vacuum firing porcelains were introduced primarily to give improved aesthetics in the enamel porcelains.• Vines et al. (1958) have explained the densification of porcelain by vacuum firing.
  70. 70. Translucency:• The particle size distribution of a dental porcelain has a marked influence on the translucency of the final product.• The translucency is affected by the number and size of the entrapped air bubbles.• Larger particles – larger interstitial voids – fewer bubbles – improved translucency.• Small particles – smaller interstitial voids – more fine air bubbles – reduced translucency
  71. 71. To avoid porosities:-a) Porcelain powder must be dried slowly to eliminate all water vapor and vacuum must be applied before the porcelain enters the hot zone of the furnace. In this way, the internal pores are reduced before the surface skin seals off the interior too rapidly.b) Vacuum firing should not be prolonged, once the surface skin is sealed as it can cause surface blistering since residual air bubbles will try to rise to the surface through the molten porcelain.
  72. 72. The vacuum should be broken whilst the work is still in the hotzone of the furnace. This allows the dense surface skin ofporcelain to hydrauically compress the low pressure internal airbubbles.Vacuum firing also has its limitations. If large bubbles aretrapped in the porcelain by poor condensation techniques,these bubbles cannot be reduced in size to any significantdegree.
  73. 73. Diffusible gas firingHelium hydrogen or steam is substitutedfor the ordinary furnace atmosphereGases diffuse or dissolve in porcelein
  74. 74. Classification of Stages of Maturity: Low Bisque Medium Bisque High BisqueSurface very porous Less porous Completely sealed and smoothGrains start to soften Entrapped air becomes A slight shine appears onand “lense” sphere shaped the surfaceShrinkage is minimal Definite shrinkageBody extremely weak Body is strongand friableThermal Shock:• It is caused by uneven heating or cooling.• A crown’s surface may expand on contract more quickly than the interior and due to the differential thermal expansion, stresses will be set up.
  75. 75.
  76. 76.
  77. 77. Aesthetics of Dental PorcelainColor is a complex science that was described by Munsell in the Munsell color ordered system as having three dimensions: Hue, value, chroma (Munsell 1936; Preston and Bergen 1980). Munsell’s Color Wheel
  78. 78. The color that is seen by an observer in making a tooth shade will depend upon:• The spectral energy distribution of the light source e.g.. daylight or artificial light.• The spectral characteristic of tooth, in respect to absorption, reflection and transmission.• The sensitivity of the eye.• The conditions under which the color of the tooth is being viewed, e.g.. oral background, wet or dry conditions, angle and intensity of illumination.
  79. 79.  Optical Properties:1) Translucent objects will both reflect and transmit some light. a) Reflections a) Specular and b) Diffused b) Refractive index and dispersion2) Fluorescence
  80. 80. Areas of light reflection and transmission through the natural human tooth
  81. 81. Four Dimensions of tooth color system:a) Hue: Basic color of an object.b) Chroma: Degree of saturation of a particular hue.c) Value: Defined as brightness. • Ranging from white to black: • white being highest in value black the lowestd) Maverick: Colors seen through dentin without organization
  82. 82. The Zone System• The color of teeth is determined by the hue of the dentin and the thickness and hue of the overlying enamel.• A tooth may have more than one dentin hue present.Body or Dentin Porcelain Layer:• Gives more opportunity to make use of diffused light than the opaque layer as it has twice the latter thickness, thus permitting more light to enter.Incisal or Enamel Porcelain Layer:• It should cover the entire surface• Should be translucent and bulkiest at the incisal or cusp region and taper to a feather edge at the gingival margin• It permits the light to enter the crown, travel to its depth, and reflect color in all directions.
  83. 83. Absorption:• There is always a degree of absorption when light rays encounter any surface. Dark objects absorb more light than light objects.• An object is perceived as red because it is absorbing the blue and green rays of the incident light and reflecting red rays.
  84. 84. Light Scattering:• Dental porcelain can be regarded as optically heterogeneous, i.e. it is a transparent medium containing small particles such as metallic oxides (opacifiers), crystals or glassy grains of dissimilar refractive indices.• When a beam of light enters such a system, a portion of a beam is scattered and the intensity of the beam is reduced.• In any ceramic system, the greatest light scattering effect is obtained with an increasing difference in refractive index between the particles and the main bulk of porcelain phase.Opacity:• The important optical characteristic seen when a beam of light enters a typical dental porcelain is: a) A fraction of light is reflected (specular reflection) and this determines the degree of glaze or gloss on the surface. b) Of the remaining light, a fraction is diffusely reflected, and the remainder directly and diffusely transmitted.
  85. 85. • In opaque materials, the degree of diffuse reflection is related to the surface roughness.• It is therefore undesirable to apply dentin and enamel porcelains onto highly glazed opaques since a mirror surface is created and bright spots may appear particularly at the incisal third of the preparation.• A rougher surface can be produced by lightly blasting the surface of the opaque with 30 µm aluminum oxide grit.
  86. 86. Translucency:• Diffuse reflection of light produced by internal scattering must not be too great in dental porcelain, otherwise anterior crowns look very artificial.• We require minimal light absorption but maximum light scattering to give an effect similar to enamel prisms.Surface Gloss:• The glaze or gloss on the surface of a ceramic crown is intimately related to the relative amount of specular and diffuse reflection.• These factors are primarily determined by the index of reflection and by the surface smoothness.
  87. 87. Role of Opaque Porcelains in Obtaining Aesthetics:• It has been said that opaque porcelains are not required in dental ceramics and that the original air-fired crown could provide the best system.• However, if a porcelain crown is to simulate natural teeth, greater degree of light transmission in the enamel and dentin porcelain, consequently, may be required.• The use of opaque porcelain in the metal ceramic crown was dictated by the metal background and unfortunately, the aesthetic benefits of vacuum-firing have been partially lost.
  88. 88.  Shade Matching Guidelines:• Shade matching may be divided into two areas: Artistic - Scientific. Artistic:• Requires many years of intense study and practice Scientific:• Modern color measuring equipment can substantially reduce trial and error
  89. 89. Some common guidelines:• The patient should be viewed so that his head is at the operator’s eye level.• Use of maximum amount of day-light• For precise color matching, the clinician should use a small angular field. In addition, he must be careful not to become influenced by apparent changes in color due to “successive contrast” effects.• It is not advisable, to view colors for long periods.• The natural dentition should always be kept dry and teeth viewed from several different angles.
  90. 90. • It is better to concentrate on the middle third of the tooth since the body shade is the most important basic color in the tooth.• A shade slightly lower in value (darker) than the tooth being matched should be selected. A slightly darker shade is less conspicuous than a lighter shade.• Select the basic hue of the tooth by matching the shade of the patient’s canine, which is the most chromatic tooth in the mouth.
  91. 91. Tooth Shade Guide: The primary requirements for a tooth color guide should include:-a) Should be made from same material from which the restoration will be made.b) Backed by metalc) Has the same thickness as the restoration will have.
  92. 92. d) Employs the same overlaying techniques used to make the restorations.e) A logical arrangement in color space.f) An adequate distribution in color space.Two basic types:1) Customized shade guide2) Commercial shade guide a) Vita shade guide – the most logical of all
  93. 93. b) Vita 3D master – 3 dimensional shade guide lighter darker paler richer reddish yellowish
  94. 94. c) Digital shade guide: Accessories Software
  95. 95. Aesthetics of Metal Ceramic Crown:a) Reduction in the thickness of the metal copingb) Reduction in the light reflectivity from the metal opaque porcelain• When the thickness of the current high fusing gold alloy copings is reduced much below 0.5 mm, there is a risk of metal creep occurring during the sintering of the porcelain veneer which results in unacceptable clinical fit.• Alternatively, when a base metal alloy of higher melting point is used to overcome the problem of metal creep, the effectiveness of the bond between porcelain and metal remains in doubt. In addition, base metals are difficult to cast in thin section and obtain a good fit and they tend to induce grey color effect in the porcelain.• For these reasons, preformed copings or foil in various thickness were used with aluminous porcelain for bonding.
  96. 96. PROPERTIESCompressive strength 50,000 psiTensile strength 5,000 psiShear strength - 16,000 psiElastic modulus 10X106 psi
  97. 97. Linear coefficient of thermal expansion - 12X10-6 / °CSpecific gravity 2.2 to 2.3Linear shrinkage -High fusing - 11.5Low fusing - 14.0%Refractive index- 1.52 to 1.54
  98. 98. •Blebs are internal voids tend to reduce the specific gravityof porcelain.•Porcelains extremely hard materials and because of thisproperty offer considerable resistance to abrasion. Thiscould be a disadvantage in that it causes excessive wear ofthe opposing natural tooth structure or the restorativematerial.
  99. 99. •The brittleness → 0.1% deformation issufficient to fracture porcelain before fracture•.•Uranium oxide / cerium oxide is added to matchthe fluorescence of porcelain to that of the naturaltooth.
  100. 100. 1. Relatively inert.2. Chemically stable.3. Corrosion resistant.4. Highly biocompatible.5. Conducive to gingival health – as it prevents plaque addition.6. Solubility is less.
  101. 101.  TWO FACTORS AFFECTING THE PROPERTIES • Manner and degree of condensation / compaction of power. Degree of firing and procedure followed to fuse mass.
  102. 102. Methods of StrengtheningCeramics• Predictable strength of a substance is based on the strength of the individual bonds between the atoms in the material.• However, the measured strengths of most materials are more than 100 times lower than this theoretical value.
  103. 103.  Reasons for low strength Minute scratches and other defects present on all the material, behave as sharp notches whose tips ma be as narrow as the spacing between atoms. - A phenomenon known as “Stress concentration” at the tips of these minute scratches or flaws causes the localized stress to increase to the theoretical strength of the material at a relatively low average stress throughout the structure.
  104. 104. •The compressive strength is quite highcompare to tensile or shear strength.•The tensile strength is low because of theunavoidable surface defects.•The shear strength is low because of lack ofductility in the material.•Voids and blebs greatly reduce the strength ofporcelain.
  105. 105.
  106. 106.  Methods to Overcome the Deficiencies of Ceramics fall into 2 categories:a) Methods of strengthening brittle materials i) Development of residual compressive stresses within the surface of the material. ii) Interruption of crack propagation through the material.b) Methods of designing components to minimize stress concentrations and tensile stresses.
  107. 107. i) Development of residual compressive stresses within the surface of the material.• One of the widely used methods of strengthening glasses and ceramics• Strengthening is gained by virtue of the fact that these residual stresses must first be negated by developing tensile stresses• Net tensile stress develops
  108. 108. • Three methods of introducing these residual compressive stresses are:a) Ion exchange or chemical tempering is a process involving the exchange of larger potassium ions (K) for the smaller sodium ions (Na), a common constituent of a variety of glasses.b) Thermal tempering is a common method. It creates residual surface compressive stresses by rapidly cooling (quenching) the surface of the object while it is hot and in the softened (molten) core.c) Thermal compatibility
  109. 109.  ii) Interruption of crack propagation through the material: Two different methods:-a) One type relies on the toughness of the particle to absorb energy from the crack and deplete its driving force for propagation.b) The other relies on crystal structural change under stress to absorb energy from the crack.
  110. 110. a) Dispersion of a crystalline phase: Alumina Particles Acting as SEM of Alumina Reinforced Crack Stoppers Core showing the alumina particles embedded in a glassy matrix composed of feldspar• Dicor glass-ceramic: The cast glass crown is subjected to a heat treatment that causes micron-sized mica crystals to grow in the glass.
  111. 111.  b) Transformation Toughening:• This technique involves the incorporation of a crystalline material that is capable of undergoing a change in crystal structure when placed under stress.• The crystal material usually used is termed partially stabilized zirconia (PSZ).
  112. 112.  Reducing Stress Raisers:• Stress raisers are discontinuities in ceramic structures and in other brittle materials that causes stress concentrations. Abrupt change in shape or thickness in the ceramic contour can act as stress raiser and make the restoration more prone to failure.
  113. 113. • In porcelain jacket crowns, many conditions can cause stress concentration:a) Creases or folds of the platinum foil substrate that become embedded in the porcelain, leaves notches that act as stress raisers.b) Sharp line angles in the preparation also create areas of stress concentration.c) Large changes in porcelain thickness, a factor also determined by the tooth preparation, can create areas of stress concentration.
  114. 114.  d) Large changes in porcelain thickness, a factor also determined by the tooth preparation, can create areas of stress concentration. e) A small particle of porcelain along the internal porcelain margin of a crown also induces locally high tensile stresses. f) If the occlusion is not adjusted properly on a porcelain surface, contact points rather than contact areas will greatly increase the localized stresses in the porcelain surface as well as within the internal surface of the crown.
  115. 115.  In case of a porcelain veneer crown this can be achieved in three ways:1. Reinforcement of the inner surface by a higher strength ceramic.2. Reinforcement of the inner surface by a metal casting or foil bonded to the porcelain.3. Surface treatment of the porcelain by chemical toughening.
  116. 116. Metal Ceramic Alloys/ Technology
  117. 117. • The six basic principle features which distinguish a metal ceramic alloy from both crown and bridge and removable partial denture alloys are:• MCA be able to produce surface oxides for chemical bonding with dental porcelains.• coefficient of thermal expansion is slightly greater than that of the porcelain veneer to maintain the metal- porcelain attachment.• melting range considerably higher than the fusing of the dental porcelain fired on it. This temperature separation is needed so the porcelain build-up can be sintered to a proper level of maturity without the fear of distortion of the metal substructure.
  118. 118. • Ability to withstand, exposure to high temperatures, without undergoing dimensional change -- high temperature strength or sag resistance.• Processing should not be too technically demanding• A casting alloy should be bio-compatible.
  119. 119.
  120. 120.  Classification for Metal Ceramic Alloys: by Naylor, 1986• Based on composition• All alloys are first separated into one of two major types: Noble (precious) Base metal (non-noble or non-precious).
  121. 121. System GroupNoble metal alloys:i) Gold-platinum-palladium High silverii) Gold-palladium-silver Lower silveriii) Gold-palladiumiv) Palladium – silver Cobaltv) High palladium Copper Silver-goldBase Metal Alloys:i) Nickel-Chromium Berylliumii) Cobalt-Chromium Beryllium-freeiii) Other systems
  122. 122. Levels of Content: The designation “low”, ‘medium’ and ‘high’ are givenwith the following values in order to describe the level ofthe principle constituent on which an alloy is based(Naylor, 1986). Low - 0% to 33% Medium - 34% to 66% High - 67% to 100%
  123. 123. NOBLE METAL ALLOYSTypical Formulations:a) Gold – platinum – palladium alloys: Gold – 84% Platinum – 7.9% Palladium – 4.6% Silver – 1.3% Indium & tin addition approx. – 2%b) Gold – platinum – tantalum alloys: Same as above but palladium replaced by tantalum
  124. 124.  c) Gold – palladium – silver alloys: Gold – 50% Palladium–30% Silver 12% Indium & tin – 8% d) Palladium-silver alloys: Palladium 60% Silver-40% Addition of indium and tin to increase hardness
  125. 125. Base-metal Alloys:a) Ni-Cr without Beryllium Chromium – 12-25% Molybdenum 0% - 10% Minor amounts of Al, Fe, Si, Ga, etc.b) Ni-Cr with Beryllium Chromium – 12-20% Molybdenum 0% - 10%with aluminium, silicone, manganese and typically 1.5 to 2.0 wt% beryllium
  126. 126.  Co-Cr Chromium 20-30% Molybdenum 0% - 7% Si, Mn, Al, Tungsten, Gallium, Tantalium, Ruthenium
  127. 127. Alloy Advantages DisadvantagesGold - Excellent bonding to - Low sag or creepPlatinum porcelain resistance, can distort at - Good castability fine margins or warp onPalladium - Easily finished and long span bridges polished - High cost - Corrosion resistant and non-toxic - Excellent for producing occlusal surfacesGold - High melting range giving - Silver content may causePalladium better creep resistance greening of porcelainSilver - Yield strength can be - White color may show higher than some Au-Pt Pd through grey in the mouth alloys - High palladium content - Good castability can increase risk of H2 - Easily finished and gas absorption during polished casting - Non-toxic - Bonding to porcelain not yet proven clinically or - Low cost experimentally
  128. 128. Alloy Advantages DisadvantagesPalladium - High yield strength and - Difficult to castSilver modulus of elasticity - Does not reproduce fineAlloys - Suitable for long span margins like the high gold alloys bridges - High silver content can -Non-toxic interfere with bonding and -Low cost cause discoloration of porcelain - High palladium content increases gas absorption - Poor colorNickel - High modulus of elasticity - Very difficult to cast accuratelyChromium and yield strength allows - Margins may be short or roughalloys use in thinner section - Permanence of bond yet to be - Low cost established - Can be toxic in nickel sensitive patients - Very difficult to remove from teeth in event of repair
  129. 129. Role of Constituent Elements:a) Aluminium (Al):• It lowers the melting range of Nickel (Ni)-based alloys.• It is a hardening agent and influences oxide formation.b) Beryllium (Be):• Lowers the melting range, improves castability, improves polishability and helps to control oxide formation.c) Boron (B):• Is a deoxidizer.
  130. 130.  d) Chromium (Cr):• Is a solid solution hardening agent that contributes to corrosion resistance by its passivating nature in Ni and Co (Cobalt) based alloys. e) Copper (Cu):• Serves as a hardening and strengthening agent, can lower the melting range of an alloy.
  131. 131. f) Gallium (Ga):• Added to silver-free porcelain alloys to compensate for the decreased coefficient of thermal expansion created by removal of silver.g) Gold (Au):• Provides a high level of corrosion and tarnish resistance and increases an alloy’s melting range slightly.• It improves workability, burnishability and raises the density and the cost of an alloy.
  132. 132.  h) Indium (In):• Is a less volatile oxide-scavenging agent, lowers the alloys melting range and density, improves fluidity and has a strengthening effect. i) Nickel (Ni):• Its coefficient of thermal expansion approximates that of gold and it provides resistance to corrosion.• Unfortunately, nickel is a sensitizer and a known carcinogen.
  133. 133. Functions of Metal Ceramic Substructure:Two types:a) Primaryb) SecondaryPrimary Functions:i) The casting provides the fit of the restoration to the prepared tooth.ii) The metal forms oxides that bond chemically to dental porcelain.iii) The coping serves as a rigid foundation to which the brittle porcelain can be attached for increased strength and support.iv) The substructure restores the tooth’s proper profile.
  134. 134.  Secondary functions :a) Metal occlusal and lingual articulating surfaces generally can be less destructive to the enamel of opposing natural teeth.b) The occluding surfaces can be easily adjusted and repolished intra orally.c) Fabrication of a restoration with minimal occlusal clearance has more potential for success with a metal substructure than the all-ceramic materials.
  135. 135. Metal Ceramic Bond:• Four theories have been proposed to explain the processes that leads to porcelain to metal bond:i) Van der Waals forcesii) Mechanical retentioniii) Compression bondingiv) Direct chemical bonding Chemical form of attachment is the predominant and most important mechanism
  136. 136. Vander Waals Forces:• These secondary forces are generated more by a physical attraction between charged particles than by an actual sharing or exchange of electron in primary (chemical) bonding.• These forces are generally weak. Only minimal attraction exists between the electron and nuclei of atoms in one molecule and the nuclei and electron of atoms in the adjacent molecule.
  137. 137. • The better the wetting of the metal surface, the greater the Van der Waals forces.• Van der Waals forces are only minor contributors to the overall attachment process.
  138. 138. 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 aluminium oxide is believed to enhance mechanical retention further by eliminating surface irregularities while increasing the overall surface area available for bonding.• Despite its presence, mechanical retentions contribute to bonding are relatively limited.
  139. 139. 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.Chemical Bonding:• Two mechanisms may exist with the chemical bonding theory. According to one hypothesis, the oxide layer is permanently bonded to the metal substructure on one side while the dental porcelain remains on the other.• The oxide layer itself is sandwiched in between the metal substructure and the opaque porcelain.
  140. 140. • The second, and more likely, theory suggests that the surface oxides dissolves, 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 that metal and porcelain share electron.• Both covalent and ionic bonds are thought to form but only a monomolecular layer of oxide is believed to be required for chemical bonding to occur.• Chemical bonding is generally accepted as the primary mechanism in the porcelain metal attachment process.
  141. 141. Porcelain Failure:• Fracture in porcelain on a metal ceramic restoration may take place1) During fabrication2) During placement3) During service1) Fabrication fracture may be caused by:i) Thermal expansion/ contraction mismatch.ii) Improper restoration design-sharp angles, insufficient metal, or excessive unsupported porcelain and small radii.iii) Improper firing practice resulting in altered thermal expansion/ contraction of the porcelain.
  142. 142. 2) Insertion fracture: are usually associated with elastic or plastic deformation of the metal substrate. The deformation stresses are generally imposed bya) Questionable path of insertionb) The presence of undercutsc) Insufficient tooth reductiond) Difficulty of cement escape The stresses encountered in metal ceramic restoration are generally longitudinal (along the length), tangential (along the circumference), and radial (along the radius). Each of these stresses may assume the form of compression or tension, depending on whether the alloy contracts more or less than the porcelain.
  143. 143. Types of Metal-PorcelainBond Failure:• Classification of ceramo-metal failures by O’Brien (1977)1) Metal-porcelain: Generally seen 3 when the metal surface is totally depleted of oxide prior to baking the porcelain or when no oxides are available. • It may also be due to contaminated or porous metal surfaces. 52) Metal oxide porcelain: Common type of failure in the base metal alloy system.3) Metal-metal oxide: When there is over production of chromium and nickel oxide at the interface.
  144. 144. 4) Metal oxide – Metal oxide: Occurs due to over production of oxide causing a sandwich effect between metal and porcelain.5) Cohesive within metal: It is most unlikely type of fracture for the individual metal ceramic crown. Occurs in cases where the joint area in bridges break.6) Cohesive within porcelain: This is most common type of fracture in the high gold alloys.
  145. 145.  Advantages of Metal Ceramics:a) Very high strength values due to prevention of crack propagation from the internal surfaces of crowns by the metal reinforcement.b) Improved fit on individual crowns provided by cast gold collar.c) The only porcelain material that can be used in fixed bridge work and for splinting teeth.
  146. 146. Disadvantages of Metal Ceramics:a) Increased opacity and light reflectivity, particularly in tungsten filament light.b) More difficulty to create depth of translucency in the crown due to the ‘mirror’ effect of the dense opaque masking porcelain.c) The fit of long span bridges or splints may be affected by the creep of the metal during successive bakes of porcelain.d) More difficult to obtain good aesthetics than regular or aluminous porcelain.e) Porcelains used in the metal-ceramic techniques are more liable to devitrification which can produce cloudiness.
  147. 147. Indications of Metal Ceramics:a) In case of parafunctional mandibular activity where an aesthetic restoration is essential.b) Teeth requiring fixed splinting or being used as bridge abutments.c) In all posterior teeth where full coverage is necessary for aesthetic reasons.d) Where lingual clearance of less than 0.8 mm is present.
  148. 148.  Contraindications:a) Adolescent teeth where minimal tooth preparation is essential.b) Teeth where enamel wear is high and there is insufficient bulk of tooth structure to allow room for metal and porcelain.c) Anterior teeth where esthetics is of prime importance e.g. high shades of very translucent teeth.
  150. 150. Characteristic Features of All-Ceramic CrownsØ Excellent esthetic result.Ø Moderate strength for single - unit anterior toothrestorations when bonded with resin cement.Ø Lack of gray/ brown metal show through since a metalsubstructure is absent.Ø Inability to cover the color of a darkened toothpreparation or post / core, since the crowns are translucent.Ø Laboratory costs higher than those for typical PFMcrowns.
  151. 151. The advantages of All-ceramic restorationsinclude:Increased translucency Improved fluorescenceGreater contribution of colour from the underlying toothstructure Inertness Bio-compatibility Resistance to corrosion Low temperature / electrical conductivity
  152. 152. Newer types of all-ceramic restorations developed mayprove to have a lower incidence of clinical fracture for 3important reasons : stronger materials and involve better fabricatingtechniques can be etched and bonded to the underyling toothstructure with the new dentin adhesives greater tooth reduction -enough room to create thicker andstronger restorations.
  153. 153. Disadvantages Wear of opposing occluding enamel or dentin if thepressed all-ceramic crowns are a part of heavy incisalguidance or canine rise.Ø Difficulty in removing the crown and cementingmedium when replacement is necessary (Bonded pressedceramic crowns are much more difficult to remove thanstandard PFM crowns)
  154. 154. Currently available all-ceramics can be broadlycategorized according to their method of fabrication :Ø CONVENTIONAL (POWDER – SLURRY)CERAMICSØ CASTABLE CERAMICSØ MACHINABLE CERAMICSØ PRESSABLE CERAMICSØ INFILTRATED CERAMICS
  156. 156. TYPES :Alumina – Reinforced porcelain (Aluminous PorcelainMagnesia – Reinforced porcelain (magnesia coreceramics)Leucite Reinforced (Non-pressed)Low fusing ceramicsZirconia whisker- fibre reinforced,
  157. 157. ALUMINA – REINFORCED PORCELAIN(ALUMINOUS PORCELAINS )Alumina glass composites used in dental ceramic workhave been termed “Aluminous Porcelain” (McLean &Hughes, 1965).
  158. 158. Porcelains used in an all aluminous porcelaincrown consists of : Aluminous core porcelain :40-50 % by wt fused alumina crystals fritted in a low-fusing glass.The alumina (α - alumina ) particles have very hightensile strength.They are stronger and more effective in interruptingcrack propagationstrengthening by two to three folds with the proportion ofthe crystalline phase. ·
  159. 159. Dull/ opaque porcelain with lack of translucency.used as core material (0.5 -1mm) over platinum foilveneered with feldspathic porcelain.strength still insufficient to bear high stresses.Eg: Vitadur – N(Vident) Hi – Cream (Vident)
  160. 160. AdvantagesØ Low coefficient of thermal expansion in the range of8*10-6/0C.DisadvantagesØ Requires specially formulated and compatible enameland dentin porcelains for veneering.Improvement in strength is insufficient to bear high stresses.
  161. 161. MAGNESIA – REINFORCED PORCELAINMagnesia Core Ceramics are high expansion ceramicsdescribed by O’Brien in 1984used as core material for metal ceramic veneer porcelain. dispersion strengthened core ceramics made by finedispersion of crystalline magnesia (40-60%)The magnesia crystals strengthen the glass matrix by bothdispersion strengthening and crystallization within the
  162. 162. Advantages:Increased coefficient of thermal expansion (CTE14.5x10-6/0C) Iimproves its compatibility with conventional feldspathic metalveneering porcelains . (CTE: 12 to 15x 10-6/0C).Improved strength and a high expansion property comparedsuitable for use as a core material ,substituting for a metallic core as substructure.
  163. 163. LEUCITE – REINFORCED PORCELAINS Feldspathic porcelains, dispersion strengthened bycrystallization of leucite crystals in the glass - matrix .
  164. 164. Optec HSP (Optec high Strength porcelain )(Jeneric/Pentron) leucite reinforced feldspathic porcelain - condensed andsintered like aluminous and traditional feldspathic porcelainon a refractory die instead of a platinum foil .Its moderate strength is derived from the nucleation andgrowth of fine dispersion of a higher volume fraction ofleucite crystals..Despite the increase in crystallization ,the material retains itstranslucency apparently because of the closeness of therefractive index of leucite with that of the glass matrix . Theflexure is approximately 140 Mpa..
  165. 165. Composition : It is a glass ceramic with a leucite content of 50.6 weight %dispersed in a glassy matrix . uses : Inlays ,onlays,crowns and veneers.
  166. 166. AdvantagesØ Despite lack of metal or opaque substructure, it has highstrength by leucite reinforcement, hence can be used as acore material.Ø Good translucencyØ Moderate flexural strengthØ No special laboratory equipment needed.
  167. 167. DisadvantagesØ Potential marginal inaccuracy caused by porcelainsintering shrinkage.Ø Potential to fracture in posterior teeth. Increased leucite content may contribute to highabrasive effect on opposing teeth.
  168. 168. Hydrothermal ceramicsnew dental ceramics developed from industrial ceramics byintroducing hydroxyl groups into the ceramic structure underheat and steam from which the tem ‘hyrdothermal’ ceramic isderived.The term ‘hydrothermal manufacturing processes’ introducedby Ryabov et al, Bartholomew, Bertschtein and Stepanov& Scholze in the 1970’s and 1980s
  169. 169. The hydrothermal ceramic systems- low fusing porcelainscontaining hydroxyl groups in the glass matrix.Although the melting, softening and sintering temperatureshad reduced, these materials exhibited an increase inthermal expansion and mechanical strength without acompromise in their chemical solubility.
  170. 170. Hydrothermal ceramics can be formulated as two types :Ø A single phase porcelainEg: Duceram LFC® (Degussa Dental, South Plainfield, NJ)Ø A leucite containing two phase materialEg.: Duceragod® (Degussa Dental, South Plainfield, NJ)
  171. 171. Advantage of hydrothermal ceramics overconventional porcelains:Ø Lower fusion temperature (680-7000 C)Ø Increased coefficient of thermal expansionØ Minimal abrasion of opposing dentitionØ Greater toughness and durabilityØ Stronger bond to the deep gold coloured Degunormalloy(Degussa Dental, S. Plainfield, NJ).
  172. 172. Duceram LFC:low fusing hydrothermal ceramic composed of an amorphousglass containing hydroxyl (-OH) ions.It was developed in mid 1980’s based on the ideas and studieson industrial porcelain ceramic from the early 1960’s and wasfirst introduced to the market in 1989 for use in all ceramicprostheses, ceramic / metal-ceramic inlay and partial crowns.
  173. 173. Advantages over feldspathic porcelain:Ø Greater densityØ Higher flexural strength attributed to OH ionexchange and sealing of surface microcracksØ Greater fracture resistanceØ Lower abrasion than feldspathic porcelain (wear rateequal to that of natural teeth)Ø Surface resistant to chemical attack by fluoridecontaining agents.Ø Highly polishable, not requiring re-glazing duringadjustment.
  174. 174. Disadvantages :Cannot be directly sintered on the metallic substructurebecause of the low coefficient of expansion.Thus, an inner lining of conventional high-fusing ceramic isrequired on the metal substructure because of the lowcoefficient of expansion.
  176. 176. Glass-ceramics are polycrystalline materials developedfor application by casting procedures using the lost waxtechnique, hence referred to as “castable ceramic”. Glass ceramics in general are partially crystallized glassand show properties of both crystalline and amorphous(glassy) materials.They are fabricated in the vitreous (Glass or non-crystalline/amorphous) state and converted to a ceramic(crystalline state) by controlled crystallization usingnucleating agents during heat treatment.
  177. 177. Castable dental Glass-CeramicsFluoromicas OtherGlass-Ceramics(SiOK2MgOA12O3ZrO2) Based on a) LithiaE.g Dicor b)CalciumphosphateApatite Glass-Ceramic(CaOMgOPO5SiO2 systemE.g: Cera Pearl (Kyocera Bioceram)
  178. 178. Dicor:Dicor, the first commercially available castable glass-ceramicmaterial for dental use was developed by The Corning GlassWorks (Corning N.Y.) and marketed by Dentsply International(Yord, PA, U.S.A).The term “DICOR” is a combination of the manufacturer’snames: Dentsply International & Corning glass.Dicor is a castable polycrystalline fluorine containing tetrasilicicmica glass-ceramic material, initially cast as a glass by a lost-wax technique and subsequently heat - treated resulting in acontrolled crystallization to produce a glass - ceramic material.
  179. 179. Major IngredientsSiO2 45-70%,K2O upto 20%;MgO 13-30%MgF2 (nucleating agent & flux 4 to 9%)Minor IngredientsA12O3 upto 2% (durability & hardness)ZrO2 upto 7%; Fluorescing agents (esthetics)BaO 1 to 4% (radiopacity)
  180. 180. Advantages of DicorØ Chemical and physical uniformityØ Excellent marginal adaptation (fit)Ø Compatibility with lost-wax casting processØ Uncomplicated fabrication from wax-up to casting,ceramming and colouringØ Ease of adjustment
  181. 181. Ø Excellent esthetics resulting from natural translucency, lightabsorption, light refraction and natural colour for therestoration.Ø Relatively high strength (reported flexural strength of 152MPa), surface hardness (abrasion resistance) and occlusalwear similar to enamel.Ø Inherent resistance to bacterial plaque and biocompatiblewith surrounding tissues.Ø Low thermal conductivity. Radiographic density is similar to that of enamel.
  182. 182. DisadvantagesØ Requires special and expensive equipments such asDicor casting machine, ceramming oven. (High investmentcost for the lab)Ø Although short term clinical studies, verified theefficacy of the Dicor system in laboratory studies for useas veneers and inlays, failure rates as high as 8% (# ofthe restoration) were reported, especially in the posteriorregion. In addition, failure rates as high as 35% have beenreported with full coverageDicor crowns not bonded to tooth (The poor strength isthought to be caused by porosity, especially in theoutermost "ceram layer").
  183. 183. Dicor must be shaded/ stained with low fusing feldspathicshading porcelain to achieve acceptable esthetics,however the entire stain/ colors maybe lost duringocclusal adjustment (use of abrasives), during routinedental prophylaxis or through the use of acidulatedfluoride gels.
  184. 184. Two ceramic products were introduced to overcome theabove problem:Ø Dicor plus (Dentsply, Trubyte division) : Consists ofa cast cerammed core (Dicor substrate) and shadedfeldspathic porcelain veneer. However, as Dicor plus is a feldspathic porcelain thatcontains leucite, the abrasiveness is expected to be similarto other feldspathic porcelains. Willis Glass : Consists of a Dicor cast cerammed coreand a Vitadur-N porcelain veneer similar in nature to thatused for Dicor Plus.
  185. 185. CASTABLE APATITE GLASS CERAMICCastable apatite ceramic is classified as CaO-P2O5-MgO-SiO glass ceramic.1985 -Sumiya Hobo & Iwata developed a castable apatiteglass-ceramic which was commercially available as CeraPearl (Kyocera Bioceram, Japan).
  186. 186. CERA PEARL (Kyocera San Diego, CA): contains aglass powder distributed in a vitreous or non-crystallinestate.Composition: Approximately (By weight)Ø Calcium oxide (CaO) -45%Ø Phosphorus Pentoxide (P2O5) -15% Aids in glassformationØ Magnesium oxide (MgO) -5% Decreases the viscosity(antiflux)Ø Silicon dioxide (SiO2) -35% Forms the glassmatrix.Ø Other -Trace elements Nucleating agents(duringceramming).
  187. 187. Desirable characteristics of Apatite CeramicsØ Cerapearl is similar to natural enamel in composition,density, refractive index, thermal conductivity, coefficient ofthermal expansion and hardness.Similarity in hardness prevents wear of opposing enamel.
  188. 188. Bonding to tooth structure –Glass ionomer cements adhere to tooth structure (dentinand enamel) primarily bonding to the apatite component,and thus should also bond to the apatite phase within theglass-ceramic.To enhance this possibility, Cerapearl surface is activatedby air abrading (to provide mechanical interlocking effect)or treatment with activator solution (etching of with 2N HCIpreferentially removes the glassy phase from the surface,thus exposing the apatite phase).The glass ionomer can then bond to this apatite phaseboth chemically (ion-exchange) and mechanically(interlocking effect).
  189. 189. Lithia Based Glass-Ceramic Developed by Uryu; and commercially available as-Olympus Castable Ceramic (OCC)Composition:It contains mica crystals of NaMg3 (Si3AlO10) F2 andBeta Spodumene crystals of LiO.AI2O3.4SiO2 after heattreatment.
  190. 190. Calcium Phosphate Glass-CeramicReported by Kihara and others, for fabrication of all-ceramic crowns by the lost wax technique. It is a combination of calcium phosphate andphosphorus pentoxide plus trace elements.The glass ceramic is cast at 1050°C in gypsuminvestment mold. The clear cast crown is converted to a crystallineceramic by heat treating at 645°C for 12 hours.Reported Flexural strength (116 Mpa);Hardness close to tooth structure.
  191. 191. Disadvantages Weaker than other castable ceramics; Opacity reduces the indication for use in anteriorteeth.
  192. 192. Advantages of castable glass ceramicsØ High strength because of controlled particle sizereinforcement.Ø Excellent esthetics resulting from light transmissionsimilar to that of natural teeth .and convenient proceduresfor imparting the required colour.Ø Accurate form for occlusion, proximal contacts, andmarginal adaptation.Ø Uniformity and purity of the material.Ø Favorable soft tissue response.Ø X-ray density allowing examination by radiograph
  193. 193. Colour control, optical effects allow predictable andesthetic results. Cast glass ceramics are thermal resistant. Bacterial plaque adherence on the surface is inhibited,thus maintaining the tissues surrounding the restoration. Radiolucency allows for a dimension of depth in theobservation of marginal integrity. Wear rate values are similar to that of human enamel.
  194. 194. MACHINABLE
  195. 195. CAD/CAM is an acronym for Computer Aided Design /Computer Aided Manufacturing (or Milling).French systemSwiss systemMinnesota system
  196. 196. Triad of fabrication: Fabrication of a restoration whether with traditional lost-waxcasting technique or a highly sophisticated- technology suchas a CAD/CAM system has three functional components: Data acquisition Restoration design Restoration fabrication
  197. 197. Machinable Ceramic system (MCS) for dentalrestorations:Ø Digital Systems (CAD/CAM):DirectIndirectThree steps :§ 3-dimensional surface scanning§ CAD -Modelling of the restoration§ Fabrication of restoration.
  198. 198. Ø Analogous systems (Copying methods)Copy Milling / Copy Grinding or Pantography SystemsTwo steps :§ Fabrication of prototype for scanning;§ Copying and reproducing by milling
  199. 199. DIGITAL SYSTEMSComputer aided design and computer aided manufacturing(CAD/ CAM) technologies have been integrated into systemsto automate the fabrication of the equivalent of castrestorations.CAD/CAM milling uses digital information about the tooth preparation or apattern of the restoration to provide a computer-aided design(CAD) on the video monitor for inspection and modification.The image is the reference for designing a restoration on thevideo monitor. Once the 3-D image for the restoration designis accepted, the computer translates the image into a set ofinstructions to guide a milling tool (computer-assistedmanufacturing [CAM]) in cutting the restoration from a block ofmaterial.
  200. 200.
  201. 201. Stages of fabrication Although numerous approaches to CAD/CAM forrestorative dentistry have evolved, all systems ideallyinvolve 5 basic stages:Ø Computerized surface digitizationØ Computer - aided designØ Computer - assisted manufacturingØ Computer - aided estheticsØ Computer - aided finishing
  202. 202. CEREC SYSTEMThe CEREC (Ceramic Reconstruction) system( Siemen/sirna corp) originally developed by Brains AG in Switzerland andfirst demonstrated in 1986, but had been repeatedlydescribed since 1980. Identified as CEREC CAD/CAM system, it wasmanufactured in West Germany and marketed by theSiemens group.
  203. 203. Cerec System consists of :Ø A 3-D video camera (scan head)Ø An electronic image processor (video processor) withmemory unit (contour memory)Ø A digital processor (computer) connected to,Ø A miniature milling machine (3-axis machine)
  204. 204. Machinable ceramics ( Ceramics used in machiningsystems)are pre-fired blocks of feldspathic or glass - ceramics.Composition :Modified feldspathic porcelain or special fluoro-alumino-silicate composition are used for machining restorations.PropertiesØ Excellent fracture and wear resistanceØ Pore-freeØ Possess both crystalline and non-crystalline phase (a2-phase composition permits differential etching of theinternal surface for bonding).
  205. 205. Ceramic CAD/ CAM restorations are bonded to toothstructure by :Ø Etching for a bond to enamelØ Conditioning, priming and bonding (when appropriate)Ø Etching (by HF acid) and priming (silanating)Ø Cementing with luting resin.
  206. 206. Machinable CeramicsThe industrially prefabricated ceramic ingots/ blank usedare practically pore-free which do not require hightemperature processing and glazing, hence have aconsistently high quality.The blanks measure approximately 9 x 9 x 13 mm and areindustrially fabricated using conventional dental porcelaintechniques. Eg: Vitadur 353N (Vita Zahnfabrik, BadSackingen, West Germany) frit powder is mixed withdistilled water, condensed into a 10 x 10 x l5 mm steel dieand fired under vacuum (the temperature is increased at arate of 60OC/min to 950oC and held for one minute).
  207. 207. Two classes Fine-scale feldspathic porcelain Glass-ceramics
  208. 208. Cerec Vitabloc Mark I :This feldspathic porcelain was the first composition usedwith the Cerec system (Siemens) with a large particle size(10 - 50µm). It is similar in composition, strength, and wearproperties to feldspathic porcelain used for metal-ceramicrestorations.Cerec Vitabloc Mark II : This is also a feldspathicporcelain reinforced with aluminum oxide (20-30%) forincreased strength and has a finer grain size (4µm) thanthe Mark I composition to reduce abrasive wear of
  209. 209. Dicor MGC (Dentsply, L.D. Caulk Division) :This is a machinable glass-ceramic composed offluorosilica mica crystals in a glass matrix.The micaplates are smaller (average diameter 2 um) thanin conventional Dicor (available as Dicor MGC - light andDicor MGC - dark). Greater textural strength than castable Dicor and theCerec compositions.Softer than conventional feldspathic porcelain. Lessabrasive to opposing tooth than Cerec Mark I, and morethan Cerec Mark II (invitro study results).
  210. 210. Other machinable ceramics being developed include:Ø Bioglass (Alldent Corp., Rugell, Liechtenstein)Ø DFE -Keramik/Krupp Medizintechnir GmbH, Essen,Germany; Bioverit / Mikrodenta CorpØ Empress / Vivadent –lvoclar Corp, Schaan,Liectenstein.
  211. 211. The clinical advantages of the Cerec system:Ø The restorations made from prefabricated andoptimized, quality-controlled ceramic porcelain can beplaced in one visit.Ø Transluency and color of porcelain very closelyapproximate the natural hard dental tissues.Ø Further, the quality of the ceramic porcelain is notchanged by the variations that may occur duringprocessing in dental laboratories.Ø The prefabricated ceramic is wear resistant.
  212. 212. CICERO SystemComputer Integrated Crown Reconstruction (Elephantindustries).This Dutch system was marketed with the Duret (French)system, Sopha Bioconcept and the Minnesota system(Denti CAD) as the only three systems capable ofproducing complete crowns and FPDs.The Cicero CAD/CAM system developed for theproduction of ceramic-fused-to-metal restorations, makesuse of :Ø Optical scanningØ Nearly net -shaped metal and ceramic sinteringØ Computer-aided crown fabrication techniques. Alloysintering eliminates casting and therewith many processingsteps in the fabrication of metal-ceramic restorations.
  213. 213. COMET System(Coordinate M Easuri ng Technique, Steinbichler Optotechnik,GmbH, Neubeurn, Germany)This system allows the generation of a 3-dimensional datarecord for each superstructure with or without the use of awax-pattern. For imaging, 2 - dimensional line grids are projected onto anobject, which allows mathematical reproduction of the toothsurfaces. It uses a pattern digitization and surface feedback technique,which accelerates and simplifies the 3-dimensionalrepresentation of tooth shapes while allowing, individualcustomization and correction in the visualized monitor image.
  214. 214. Advantage of CAD/CAM (Cerec system)over othersystemsØ Eliminates impression model making and fabricationof temporary prosthesis.Ø Dentist controls the manufacturing of the restorationentirely without laboratory assistance.Ø Single visit restoration and good patient acceptance.Ø Alternative materials can be used, since milling isnot limited to castable materials.Ø The use of CAD/ CAM system has helped providevoid free porcelain restorations, without firing shrinkageand with better adaptation.
  215. 215. Ø CAD - CAM device can fabricate a ceramicrestoration such as inlay/ onlay at the chair-side.Ø Eliminates the asepsis link between the patient, thedentist, operational field and ceramist. The shapes created in the CAD unit are well defined,and thus a factor such as correct dimensions can beevaluated and corrections/modifications can be carried outon the display screen itself .
  216. 216. Glazing is not required and Cerec inlay onlays caneasily be polished. Minimal abrasion of opposing tooth structurebecause of homogeneity of the material (abrasiondoes not exceed that of conventional and hybridposterior composite resins). The mobile character of the entire system enableseasy transport from one dental laboratory to another.
  217. 217. Disadvantages:Ø Limitations in the fabrication of multiple units.Ø Inability to characterize shades and translucency.Ø Inability to image in a wet environment (incapable ofobtaining an accurate image in the presence of excessivesaliva, water ore blood).Ø Incompatibility with other imaging system.Ø Extremely expensive and limited availability.Ø Still in early introductory stage with few long-termstudies on the durability of the restorations.
  218. 218.  Lack of computer-controlled processing supportfor occlusal adjustment. Technique sensitive nature of surface imagingthat is required for the prepared teeth. Time and cost must be invested for masteringthe technique and the fabrication of severalrestorations, to develop proficiency in the operator.
  219. 219. PROCERA System :The Procera System (Nobel Biocare, Gioteborg, Sweden)embraces the concept of CAD/CAM to fabricate dentalrestorations.It was developed by Andersson .M & Oden .A in 1993,through a co-operative effort between Nobel Biocare AB(Sweden) and Sandvik Hard Materials AB (Stockholm,Sweden).It consists of a computer controlled design station in thedental laboratory that is joined through a moderncommunication link to Procera Sandvik AB in Stockholm,Sweden, where the coping is manufactured with advancedpowder technology and CAD/CAM technique.
  220. 220. Procedure requires 3 steps for fabrication: Scanning : At the design station, a computer controlledoptical scanning device maps the surface of the master dieand is sent via modem to the Procera production facility. Machining : At the production facility, an enlarged die isfabricated that compensates for the 15-20% sinteringshrinkage of the alumina core material.High-purity alumina powder is pressed onto the die undervery high pressure, milled to required shape, and fired at ahigh temperature (1550°C) to form a Procera coping.
  221. 221.  veneering :The sintered alumina coping is returned to the dentallaboratory for veneering thermally compatible low fusingporcelains (All Ceram veneering porcelain) to create theappropriate anatomic form and esthetic qualities.All Ceram veneering porcelain (Ducera) has a coefficient ofthermal expansion adjusted to match that of aluminium oxide(7x10-6 /°C).
  222. 222. It also has the fluorescent properties similar to that ofnatural teeth and the veneering procedures require nospecial considerations.The reported flexural strength of the Procera All Ceramcrown (687 Mpa) is relatively the highest amongst all theall-ceramic restorations used in dentistry (attributed to the99.9% alumina content).
  223. 223. This system can be used to fabricate two types of dentalrestorations : A Porcelain-fused-to-metal restoration made oftitanium substructure with a compatible veneeringporcelain using a combination of machine duplication andspark-erosion (The Procera Method, Noble Biocare). An all-ceramic restoration using a densely sinteredhigh-purity (99.9%) alumina coping combined with acompatible veneering porcelain.
  224. 224.
  225. 225. PRESSABLE CERAMICSShrink-free Ceramics Leucite-reinforced Glass-ceramicsCerestore IPSEmpressAl-Ceram Optec Pressable Ceramic (OPC)
  226. 226. SHRINK FREE ALUMINA CERAMICS The shortcomings of the traditional ceramic material andtechniques; like failures related to poor functional strengthand firing shrinkage limited the use of "all-ceramic" jacketcrowns.The development of non-shrinking ceramics such as systenl was directed towards providing analternate treatmentShrink-free ceramics were marketed as two generation ofmaterials under the commercial names :Ø Cerestore (Johnson & Johnson. NJ, USA) Al-Ceram (Innotek Dental Corp, USA)
  227. 227. CERESTORE Non-Shrink Alumina Ceramic (CoorsBiomedical Co., Lakewood, Colo.) shrink-free ceramic with crystallized magnesium aluminaspinel fabricated by the injection molded technique to form adispersion strengthened core.Composition Of Shrink Free CeramicFired Composition (Core)A12O3 (Corundum) 60%MgA12O4 (Spinel) 22%BaMg2A13(Barium Osomilite) 10%
  228. 228. Unfired CompositionA12O3 (small particles) 43%A12O3 (large particle) 17%MgO 9%Glass frit 13%Kaolin Clay 4%Silicon resin (Binder) 12%Calcium Stearate 1%Sterylamide 1%
  229. 229. Advantages :Ø Innovative feature is the dimensional stability of thecore material in the molded (unfired) and fired states. Hence,failures related to firing shrinkage are eliminated.Ø Better accuracy of fit and marginal integrity.Ø Esthetics enhanced due to depth of colour due to thelack of metal coping.Ø Biocompatible (inert) and resistant to plaque formation(glazed surface).
  230. 230. Ø Radiodensity similar to that of enamel (presence ofBarium osumilite phase in the fired core allowsradiographic examination of marginal adaptation andvisualization under the crown).Ø Low thermal conductivity; thus reduced thermalsensitivity. Low coefficient of thermal expansion and high modulusof elasticity results in protection of cement seal.
  231. 231. Disadvantages :Ø Complexity of the fabrication process.Ø Need for specialized laboratory equipment(Transfer molding process) and high cost.Ø Inadequate flexural strength (89MPa) compared tothe metal-ceramic restorations.Ø Poor abrasion resistance, hence not recommendedin patients with heavy bruxism or inadequate clearance.
  232. 232. Limitations and high clinical failure rates of the Cerestoreled to the withdrawal of this product from the market. Thematerial underwent further improvement and developedinto a product with a 70 to 90% higher flexural strength.This was marketed under the commercial name Al Ceram(Innotek Dental, Lakewood, Colo.).
  233. 233. LEUCITE REINFORCED PORCELAINS ( Transfer-molded )Leucite reinforced porcelains can be broadly divided intotwo groups:Ø Pressed –· IPS Empress & IPS Empress 2 (Ivoclar)· Optec Pressable Ceramic / OPC (Jeneric/Pentron)Ø Non-Pressed· Optec HSP & Optec VP (Jeneric / Pentron)· Fortress (Mirage)