Dental ceramics

Introduction
CERAMICS : An inorganic compound with non-metallic prosthesis typically consisting of oxygen and one or more metallic or semi-metallic elements that is formulated to produce the whole part of a ceramic based dental prosthesis. – GPT 7.
The word Ceramic is derived from the Greek word “keramos”, which literally means ‘burnt stuff’, but which has come to mean more specifically a material produced by burning or firing.

1. Dental ceramics Nishu priya 1 st year pgt

2. Contents Introduction History of dental ceramics Structure Composition Properties Classification Metal-ceramic systems: Composition and Properties Components of metal-ceramic restoration Fabrication of metal-ceramic prosthesis Bonding mechanisms Strengthening of metal ceramic Advances References

3. The word Ceramic is derived from the Greek word “ keramos ”, which literally means ‘burnt stuff’, but which has come to mean more specifically a material produced by burning or firing. Introduction DENTAL CERAMICS : An inorganic compound with non-metallic properties typically consisting of oxygen and one or more metallic or semi-metallic elements that is formulated to produce the whole part of a ceramic based dental prosthesis. – GPT 7

4. Structure Ceramics can appear as either crystalline or non- crystalline ( amorphous solids or glasses). The mechanical and optical properties of dental ceramics mainly depend on the nature and the amount of crystalline phase present. Properties of glassy phase: Brittleness Non- directional fracture pattern Translucency Surface tension Insulating properties Properties of crystalline phase: Controls coefficient of thermal expansion Increases strength

5. Non- Crystalline Ceramics These are a mixture of crystalline minerals (feldspar, silica and alumina) in an amorphous (non- crystalline matrix of glass) vitreous phase . Their structures are characterized by chains of (S i O4 ) 4 − tetrah e dra in whic h S i 4 + cations are positioned at the center of each tetrahedron with O − anions at each of the four corners . The atomic bonds in this glass structure have both a covalent and ionic character thus making it stable.

6. Alkali cations such as potassium or sodium tend to disrupt silicate chains leading to lower sintering temperatures and increased coefficients of thermal expansion.

7. Crystalline Ceramics Regular dental porcelain, being of a glassy nature is largely non crystalline and exhibits only a short range order in a tomic arrangement . The only true crystalline ceramic used in restorative dentistry is Alumina ; w hich is one of the hardest and probably the strongest oxides known. Crystalline ceramics may have ionic or covalent bonds Ceramics are reinforced with crystalline inclusions such as alumina and leucite into the glass matrix to strengthen the material and improve its fracture resistance .

8. Glass Formation This process of forming a glass is called ‘ Vitrification ’.

9. HISTORY OF DENTAL CERAMICS

10. Why dental ceramics?

11. drawbacks

12. Classification of dental ceramics Uses or indi c at i ons anterior and posterior crown veneer post and core f i xed dent a l pros t hes i s ceramic stain glaze U l t ra l ow fusing - <8 5 o C Low fusing -850-1100 o C Medium fusing- 1101-1300 o C High fusing - >1300 o C Firing te m pera t ure

13. Medium- and high-fusing porcelains are used for the production of denture teeth . The low-fusing and ultralow-fusing types are used as veneering ceramics for crown and bridge construction . Some of the ultralow-fusing porcelains are used for titanium and titanium alloys.

14. Casting Sintering Partial sintering and glass infiltration Slip casting and sintering Heat press CAD-CAM milling Copy-milling Processing method Principal crystal phase F eldspathic porcelain Leuc i t e - based gla s s ceramic Lithia - based glass-ceramic Aluminous porcelain Alumina Glass-infused alumina, Glass-infused spinel Glass-infused zir c oni a , Glass ceramic

15. Translucency Opaque Translucent Transparent Amorphous glass Crystalline Polycrystalline Based on microstructure J. Robert Kelly JADA, Vol. 139 http://jada.ada.org September 2008

16. Dental ceramics are mainly composed with crystalline minerals and glass matrix . Composi t ion Feldspar - 60 to 80% - basic glass former Kaolin - 3 to 5 % - binder Silica - 15 to 25% - filler Alumina - 8 to 20 % - glass former Oxides of Zirconium, Titanium, Tin - opacifiers Oxides of sodium, potassium, calcium - glass modifiers Metal pigments - colour matching

17. F e ld s p a r naturally occurring crystalline rocks Forms- potash feldspar and soda feldspar ( albite ). It is the lowest melting compound and melts first on firing . Pure feldspathic glass is colorless and transparent

18. Role of feldspar : Glass phase formation : During firing, the feldspar fuses and forms a glassy phase that softens and flows slightly allowing the porcelain powder particles to coalesce together . Feldspar crystals of leucite + liquid glass Exhibit liquid phase sintering Leucite formation: Potassium aluminium silicate mineral 1150 ⁰C -1530 ⁰C Incongruent melting

19. Silica : exist in many different forms -crystalline quartz, crystoballite , crystalline tridymite , non – crystalline fused silica . Quar tz cr y st a ls (non- crystalline form) are used for manu f ac t uring dental porcelain. Provides strength and hardness to porcelain during firing. It remains relatively unchanged during and after firing

20. Kaolin a type of clay material which is usually obtaine d from igneous rock containing alumina - hydrated aluminum silicate Kaolin acts as a binder and increases the moldability of the unfired porcelain . It also imparts opacity to the porcelain restoration so dental porcelains are formulated with limited quantity of kaolin.

21. Glass modifiers are used as fluxes potassium, sodium and calcium ions- break bonds between silica tetrahedron- move easily at lower temperatures lower the softening temperature and increase the fluidity Increase thermal expansion High concentration of glass modifiers decrease chemical durability of glass Boric oxide fluxes (B2O3) can behave as a glass modifier to form its own glass network .

22. Color pigments Metal oxide frits are fused to provide the characteristic shade Metal oxides Color Titanium oxide Yellowish brown Nickel oxide or iron brown Copper oxide green Manganese oxide lavender Cobalt oxide blue Zirconium oxide, alumina, silica white

23. manufacturing

24. Metal-ceramic system Consist of cast metallic framework (core) on which at least two layers of ceramics are baked

25. COMPOSITION Feldspathic porcelain is used for metal bonding Higher alkali content- to raise the coefficient of thermal expansion- helps in bonding with metal Silicate glass The opaquer powder -high content of opacifiers - to mask the underlying metal

26. Classification 1. Cast metal ceramic restorations Cast noble metal alloys ( feldspathic porcelain) Cast base metal alloys ( feldspathic porcelain) Cast titanium (ultra low fusing porcelain) 2. Swaged metal ceramic restorations Gold alloy foil coping (Renaissance, Captek ) Bonded platinum foil coping

27. To bond to alloys suitable for the copings, porcelains must have a sufficiently Low sintering temperature CTEs closely matched to those of the alloys. Both the metal and the ceramic must have coefficients of thermal expansion and contraction that are closely matched such that the metal must have a slightly higher value to avoid the development of undesirable residual tensile stresses in the porcelain . Ceramic must wet the surface of alloy readily such that the contact angle is less that or equal to 60 degrees to prevent void formation. Requirements for metal- ceramic system

28. A good bond between metal and ceramic surfaces is required Adequate stiffness and strength of the alloy core is necessary to decrease the stress in porcelain Alloys should have high sag resistance as the distortion of alloy will compromise the fit of prosthesis Alloy should have high proportional limit and high modulus of elasticity as they share greater proportion of stress compared to porcelain

29. Alloys for metal-ceramic system Alloys - Noble metal alloys a) Gold - Platinum b) Gold – Platinum - Silver c) Gold - Palladium d) Palladium - silver e) High palladium System - Base-metal alloys a) Nickel - Chromium b) Cobalt - Chromium c) Other systems

30. Preparation of cast metal ceramic restorations Copings and frameworks for metal-ceramic prostheses are produced by: Casting of molten metal CAD-CAM machining Electrolytic deposition techniques Swaged metal processes

31. Most common method is melting and casting. • A wax pattern of restoration constructed • Cast in metal • High melting temperature of alloys-phosphate bonded investment Metal preparation • Clean metal surface essential for good bonding • Oil from fingers and other sources– possible contaminant • Cleanse surface • Finish with clean ceramic bonded stones/sintered diamonds • Final sandblasting with high purity alumina

32. Degassing and oxidizing • Heat in porcelain furnace to burn off any impurities to the form thin oxide layer. • Degas the interior structure of alloy Opaqer Mask/cover the metal frame and prevent it from being visible Bond the veneering porcelains to the underlying frame Condensed on the oxidized surface at a thickness of approximately 0.3 mm Translucent porcelain is applied Porcelain powder is applied by the condensation methods

33. manipulation

34. Methods of condensation: Porcelain for ceramic and metal-ceramic prostheses as well as for other applications is supplied as a fine powder designed to be mixed with water or binder and condensed into the desired form. The porcelain is usually built to shape using a liquid binder to hold the particles together. This process of packing the particles and removing the liquid is known as condensation. This provides two benefits: Lower firing shrinkage Less porosity in the fired porcelain. Binders Distilled water Propylene glycol Alcohol/Formaldehyde

35. Vibration: Mild vibrations are used to densely pack the wet powder upon the underlying matrix. The excess water comes to the surface and is blotted with a tissue paper. Spatulation : A small spatula is used, to apply and smoothen the wet porcelain. This action brings excess water to the surface where it is removed. Brush technique : The dry powder is placed by a brush to the side opposite from an increment of wet porcelain. As the water is drawn toward the dry powder, the wet particles are pulled together.

36. Dentin • Pink powder+distilled water/supplied liquid • The main bulk of tooth • A portion of the dentin in the incisal area is cut back for enamel porcelain. Enamel • White powder • build the restoration • Transparent porcelains used near incisal edges Gingival porcelain • D arker -cervical portion

37. Steps of condensation

38. Pre-heating • Placing the porcelain object on a tray in front of/below the muffle of a preheated furnace • at 650⁰C for 5min for low fusing porcelain • at 480⁰C for 8min for high fusing porcelains till reaching the green or leathery state. Significance of pre-heating stage: • Removal of excess water allowing the porcelain object to gain its green strength. • Preventing sudden production of steam that could result in voids or fractures. • Ceramic particles held together in the “green state” after all liquid has been dried off

39. Firing dental porcelain: After the condensation and building of a crown it is fired to high density and correct form. At this stage the green porcelain is introduced into the hot zone of the furnace and the firing starts, the glass particles soften at their contact areas and fuse together. This is referred to as sintering.

40. As sintering of the particles begins, the porcelain particles bond at their points of contact and the structure shrinks and becomes dense . The thermochemical reactions between the porcelain powder components are virtually completed during the original manufacturing process . Thus some chemical reactions occur during prolonged firing times or multiple firings The initial firing temperature • The voids are occupied by the atmosphere of the furnace . • As the sintering of the particles begins, the porcelain particles bond at their points of contact. As temperature is raised • The sintered glass gradually flows to fill up the air spaces . • The particles fuse together by sintering forming a continuous mass, this results in a decrease in volume referred to as firing shrinkage

41. With progression of firing • The gaps between particles become porosities. The viscosity of the glass is low enough for it to flow due to its own surface tension. The result is that the porosity voids will gradually become rounded as firing proceeds The final firing stage • The voids slowly rise to free surfaces and disappear

42. Vacuum(negative pressure) firing Porcelain in furnace- packed powder particles and air channels around air pressure inside the furnace is reduced to about one tenth of atmospheric pressure, the air around the particles is also reduced to this pressure. As the temperature rises, the particles sinter together. Pores are compressed to one tenth of their original size, and the total volume of porosity is accordingly reduced . Advantages of vacuum-fired porcelain Decreased porosity increase in the strength of the porcelain greater translucence

43. the Stages in Maturity: Low Bisque : surface of the porcelain is very porous . At this stage the grains of porcelain will have started to soften. Shrinkage will be minimal and the fired body is extremely weak and friable. Lack translucency and glaze. Medium bisque: surface will still be slightly porous but the flow of the glass grains will have increased. A definite shrinkage but lacks translucency and high glaze. High bisque: surface of the porcelain would be completely sealed and presents a much smoother surface with a slight shine . Shrinkage i s complete. Appears glazed.

44. Porcelain surface treatment Natural/auto glaze Applied/add-on glaze Polishing Custom staining

45. Glaz i ng Porcelains are glazed to give a smooth and glossy surface . The glazing should be done only on a slightly roughened surface and never should be applied on glazed surfaces. Objectives • Life like appearance/ esthetics • Improves Strength and life • Seal surface flaws • Enhances Hygiene • Reduces wear of opposing teeth

46. Over glaze These are ceramic powders containing more amount of glass modifiers thus lowering fusion temperature Applied on to restoration Firing temperature is less than that of body porcelain Disadvantage-Chemical durability less compared to self glaze(because of the high flux content) Self glaze No separate glaze layer All the constituents on the surface are melted to form a molten ma s s about 25 μ m t h i c k Restoration subjected to controlled heating at fusion temperature Only surface layer melts and flows to form a vitreous layer resembling glaze Disadvantage-porcelain must be stripped completely if it is unacceptable

47. Polishing • Using special abrasives • Sof-Lex ( 3M,Minneapolis,MN),Fi nishing disks ( Shofu , Kyoto, Japan) porcelain laminate polishing kit, or other abrasive system. • Difficult to polish Surface staining and characterisation Stain powders + special liquid- applied and blended with brush By staining and characterization more emphasis on recreating natural look Can include 1. Defects 2. Cracks 3. Other anomalies on enamel

48. Add on porcelains The add on porcelains are made from similar materials to glaze porcelain except for the addition of opacifiers and coloring pigments. These are sparingly used for simplest corrections like correcting of tooth contour / contact points.

49. cooling • Should be well controlled • slowly • Uniformly • Rapid cooling can cause cracks • Induce stresses and weakens ceramic If it cools too slowly • Crystals form within the glass body which will degrade its optical properties, turning if from a clear glass into a cloudy one . if it is cooled too quickly • Stress build up in the glass . • To reduce the stresses ,it is kept near the glass transition temperature (its solidus) for a long time so that the atoms in the glass can rearrange just enough to relieve the stress. • When most of the stress has been eliminated, the finished glass is finally allowed to cool to room temperature

50. Swaged metal-ceramic system The most widely used product of this type has been Captek (Precious Chemicals Co., Inc., Altamonte Springs, FL), which is an acronym for “capillary assisted technology .” Developed by Shoher and Whiteman The product is designed to fabricate the metal coping of a metal- ceramic crown without the use of a melting and casting process. It is a laminated gold alloy foil sold as a metal strip.

51. CAPTEK P •Platinum/palladium/gold •Porous structure •Serves as internal reinforcing skeleton. •On heating in a furnace captek P acts as metal sponge draws hot liquid gold completely into it (capillary technique) CAPTEK G • 97.5%-GOLD • 2.5%-SILVER • Provides characteristic gold color

52. Captek P and G metals can yield thin metal copings for crowns or frameworks for metal-ceramic bridges.

53. fabrication

54. Advantages • Thinner foil alloy copings (0.25mm) • Greater thickness of ceramic • Improved esthetics • Gold color of alloy

55. Bonded platinum foil ceramic Platinum foil coping adapted on to the die Electro-deposition technique-to improve bonding and esthetics Thin layer of tin is electrodeposited on to the foil and then oxidized in a furnace

56. Platinum foil is adapted on the die Opaque porcelain Dentin porcelain Enamel porcelain Laminate is separated Gaps filled with porcelain prior to second firing Surface texture created

57. Luted platinum veneers veneers after cementation

58. BONDING MECHANISMS Chemical adhesion Primary bonding mechanism Chemisorption by diffusion of oxides between alloy and ceramic – forms an interface Base metal alloys-chromic oxide Noble metal alloys-iridium oxide Mechanical entrapment creates attachment by interlocking the ceramic into the microabrasion on the surface of the metal Air abrasion appears to enhance the wettability, provide mechanical interlocking . Compression bonding Coefficient of thermal expansion mismatch- As a result of higher metal contraction on cooling , -The fused porcelain will be sucked (attracted) more strongly into the metal surface irregularities. -Residual compressive stresses will developed in and strengthen the porcelain .

59. Advantages of metal ceramic system A properly made metal-ceramic crown is more fracture resistant and durable than most all-ceramic crowns and bridges . Low fracture rate Less removal of tooth structure Better marginal fit Long term clinical durability

60. Disadvantages of metal ceramic system Potential for metal allergy Poor esthetics(Can not be used when a relatively high degree of translucency is desired .) Abrasive damage to opposing dentition Potential for fracture metal framework sometimes shows through gingiva resulting in dark margins

61. All ceramic system “All-Ceramic” refers to – Any restorative material composed exclusively of ceramic, such as feldspathic porcelain , glass ceramic , alumina core systems and certain combination of these materials. ( J.Esth Dent 1997, 9 (2 ):86)

62. classification Conventional ceramics Castable glass ceramics Injection moulded glass ceramics Glass infiltrated core ceramics Machinable ceramics

63. Conrad et al. (2007) JPD; 85: 5 classified all ceramic materials under three categories

64. Conventional ceramics Alumina – Reinforced porcelain ( Aluminous Porcelain ) Hi-Ceram Vitadur – N core Leucite Reinforced Optec HSP Optec VP

65. Aluminious core ceramics The high-strength ceramic core was first introduced to dentistry by McLean and Hughes in 1965. It is composed of aluminum oxide crystals (40-50%) dispersed in a glassy matrix . Examples : – Hi-Ceram ( Vident ) – Vitadur – N core ( Vident ) Why Alumina? Good Mechanical properties. Interfacial region between alumina and porcelain virtually stress free. High modulus of elasticity High fracture toughness Significant strengthening of the core

66. FABRICATION

67. VITA HI-CERAM Similar to traditional alumina c ore , with increased alumina. Fired directly on the refractory die – rough surface which aids in retention.

68. DISADVANTAGES Alumina is opaque, ceramic layers have to be applied to mask it High shrinkage, compromised fit ADVANTAGES withstand torque better than conventional porcelains with fracture rates slightly less than 0.5% (McLean) Pure alumina is 6 times stronger than standard porcelains Low thermal conductivity Both alumina and porcelain show the same co-efficient of expansion and contraction

69. INDICATIONS Single anterior & posterior crowns Anterior 3-unit FPD s CONTRAINDICATIONS Low fracture toughness- not indicated as posterior FPD Not indicated for patients with bruxism Vitadur N

70. Leucite reinforced porcelain feldspathic porcelain with a higher leucite crystal content ( leucite reinforced). Leucite increases flexural strength, compressive strength and cofficient of thermal expansion. Its manipulation, condensation and firing is quite similar to the alumina reinforced porcelain jacket crowns (using platinum foil matrix). Increase resistance to glassy phase to crack propagation Eg . Optec HSP

71. Advantages more esthetic - core is less opaque (more translucent) compared to the aluminous porcelain Higher strength No need of special laboratory equipment Disadvantages Fit is not as good as metal ceramic crowns High abrasiveness due to leucite content Not strong enough for posterior use. Uses: 1. Inlays 2. Onlays 3. Low stress crowns.

72. Magnesia based core porcelain Used high expansion magnesia based core material compatible with porcelain Similar to leucite reinforced ADVANTAGES Easy to veneer with widely available ceramics DISADVANTAGE Highly opaque Not used for fixed partial dentures.

73. CASTABLE glass CERAMICS Glass-ceramics are polycrystalline materials developed for application by casting procedures using the lost wax technique , hence referred to as “ castable ceramic ”.

74. dicor The first commercially available castable glass-ceramic. Developed by ‘The Corning Glass Works’ (Corning N.Y .) and marketed by Dentsply International ( Yord , PA,U.S.A ). Cast glass ceramic is composed of: Tetrasilicic flouromica crystals (crystalline) - 55% by volume . Glass matrix (non-crystalline) - 45% by volume.

75. CHAMELEON EFFECT Dicor glass-ceramic was capable of producing remarkably good esthetics because of the “chameleon” effect- part of the color of the restoration was picked up from the adjacent teeth as well as from the tinted cements used for luting the restorations. Transparent crystals scatter the incoming light as if light is bouncing off a large number of small mirrors that reflect the light and spread it over the entire surface of ceramic. Thus dicor glass change color according to their surroundings.

76. FABRICATION Casting : The glass liquefies at 1370⁰C to such a degree that it can be cast into a mold using lost-wax and centrifugal casting techniques. Ceramming : The cast glass material is subject to a single-step heat treatment called “ Ceramming ” to produce controlled crystallization by internal nucleation and crystal growth of microscopic plate like mica crystals within the glass matrix. Advantages of ceramming : Increase strength and toughness Increase resistance to abrasion Thermal shock resistance Increase chemical durability D ecreased translucency

77. Advantages Ease of fabrication Good esthetics(greater translucency and chameleon effect) Improved strength and fracture toughness Good marginal fit - low processing shrinkage Low abrasion of opposing teeth Disadvantages Inadequate strength for posterior use High fracture rate of veneers H as to be stained externally to improve esthetics Indications: Used for anterior single crown (low stress area) Used in situations where high translucency is required. Contraindications: Not used as posterior crowns . Not used in high stress bearing areas.

78. Products introduced to overcome the disadvantages: Dicor plus: consists of a cast cerammed core and a shaded feldspathic porcelain veneer Willis glass: consist dicor cast cerammed core and Vitadur N porcelain veneer

79. Castable apatite glass ceramic 1985 - Sumiya Hobo & Iwata developed a castable apatite glass-ceramic which was commercially available as Cera Pearl (Kyocera Bioceram , Japan). CERA PEARL (Kyocera San Diego, CA): contains a glass powder distributed in a vitreous or non-crystalline state Chemistry : Apatite Glass-Ceramic Molten glass CaPO4 CaPO4 Oxyapatite Hydroxyapatite moisture ceramming casting

80. Desirable characteristics of Apatite Ceramics Cerapearl is similar to natural enamel in composition, density , refractive index, thermal conductivity, coefficient of thermal expansion and hardness. Bonding to tooth structure : Cerapearl surface is activated by air abrading (to provide mechanical interlocking effect ) or treatment with activator solution (etching of with HCI preferentially removes the glassy phase from the surface, thus exposing the apatite phase). The glass ionomer can then bond to this apatite phase both chemically (ion-exchange) and mechanically ( interlocking effect ). cerapearl enamel

81. fabrication

82. Advantages of castable apatite glass ceramics High strength because of controlled particle size reinforcement . Excellent esthetics resulting from light transmission similar to that of natural teeth and convenient procedures for imparting the required colour . Favorable soft tissue response . Dimensional stability regardless of any porcelain corrective procedure and subsequent firings.

83. PRESSABLE CERAMICS Can be heated to a specific temperature and forced under pressure to fill a cavity in a refractory mold.

84. Shrink free Ceramics The development of non-shrinking ceramics such as the Cerestore system was directed towards providing an alternate treatment. 1987 - Hullah & Williams described the formulation of shrink free ceramics Injection moulded /heat pressed Shrink-free ceramics were marketed as two generation of materials under the commercial names : Cerestore (Johnson & Johnson. NJ, USA) Al-Ceram (Innotek Dental Corp, USA)

85. COMPOSITION The shrink free ceramic material essentially consists of alumina and MgO mixed with Barium glass frits . CHEMISTRY On firing a combination of chemical and crystalline transformation produces Magnesium aluminate spinel, which occupies a greater volume than the original mixed oxides and thus compensates for the conventional firing shrinkage of ceramic . During firing Chemical transformation crystalline transformation 160⁰C-800 ⁰C alumina SiO SiO2 aluminosilicate + incorporated magnesia Mg aluminate spinel

86. Advantages : Innovative feature is the dimensional stability of the core material in the molded (unfired) and fired states. Hence, failures related to firing shrinkage are eliminated. Better accuracy of fit Low thermal conductivity; thus reduced thermal sensitivity . Low coefficient of thermal expansion and high modulus of elasticity results in protection of seal. Disadvantages : Inadequate flexural strength compared to the metal-ceramic restorations. Poor abrasion resistance, hence not recommended in patients with heavy bruxism or inadequate clearance . The material underwent further improvement and developed into a product with a 70 to 90% higher flexural strength. This was marketed under the commercial name Al Ceram.

87. Leucite reinforced porcelains Leucite reinforced porcelains can be broadly divided into: IPS Empress ( Ivoclar Williams) Optec Pressable Ceramic / OPC ( Jeneric / Pentron )

88. IPS EMPRESS ( Ivoclar Williams ) pre- cerammed , pre- coloured leucite reinforced glass-ceramic formed from the leucite system by controlled surface crystallization It is a type of feldspathic porcelain containing a higher concentration of leucite crystals, which increases the resistance to crack propagation . 30%-35% leucite content

89. A special furnace Empress EP500 designed for this system is capable of high temperatures . FABRICATION Crucible former placed in furnace that has an alumina plunger

90. Ceramic ingot &an Alumina plunger is inserted in to the sprue Compatible veneering porcelains are added to core to build up final restoration Divesting

91. Advantages : Lack of metal Excellent fit (low-shrinkage ceramic) Improved esthetics (translucent, fluorescence) Etchable Less susceptible to fatigue and stress failure Unlike previous glass-ceramic systems IPS Empress does not require ceramming to initiate the crystalline phase of leucite crystals (They are formed throughout the various temperature cycles ). Disadvantages : Potential to fracture in posterior areas. Need for special laboratory equipment such as pressing oven and die material (expensive ). Inability to cover the colour of a darkened tooth preparation or post and core, since the crowns are relatively translucent. Compressive strength and flexural strength lesser than metal-ceramic or glass-infiltrated (In-Ceram) crowns. Uses : Laminate veneers and full crowns for anterior teeth Inlays , o nlays and partial coverage crowns

92. Lithia reinforced porcelains IPS Empress 2 ( Ivoclar Vivadent ) and Optec OPC 3G contain more than 70 % by volume of lithia disilicate as the principal crystal phase . IPS Empress 2 is a recently introduced hot-pressed ceramic

93. Advantages: Improved fracture resistance. Very high chemical resistance of both framework and layering ceramics. High translucency. Outstanding optical properties due to apatite (also a component of natural teeth). Wear behavior similar to that of natural enamel. Ingots available in the most popular Chromoscope shades . INDICATIONS Thin veneers (0.3 mm) Inlays , onlays , occlusal veneers Crowns in the anterior and posterior region Bridges in the anterior and premolar region Implant superstructures Hybrid abutments and abutment crowns

94. GLASS INFILTRATED CERAMICS/SLIP CAST CERAMICS Specialized ceramics reinforced by an unique glass infiltration process Involves condensation of an aqeuous slip on a refractory die

95. In- ceram alumina Developed by a French scientist and dentist Dr. Michael Sadoun (1980 ) Composition: In-Ceram ceramic consists of two 3- D interpenetrating phases : Alumina crystalline- 99.56 wt % An Infiltration glass lanthanum aluminosilicate with small amounts of sodium and calcium.

96. Slurry of alumina Capillary action

97. Uses: Single anterior & posterior crowns Anterior 3-unit FPD's Advantages : Minimal firing shrinkage, hence an accurate fit. High flexure strengths (almost 3 times of ordinary porcelain ) makes the material suitable even for multiple-unit bridges . Aluminous core being opaque can be used to cover darkened teeth or post/ core. Disadvantages : Requires specialized equipment to fabricate the restoration, hence laboratory expense is more . Poor optical properties or esthetics (opaque alumina core reduces the translucency of the final restoration ). Slip casting is a complex technique and requires considerable practice.

98. In-Ceram Spinell The porous core is fabricated from a magnesium alumina powder after sintering. This type of material has a specific crystalline structure referred to as spinell . The primary difference is a change in composition to produce a more translucent core.

99. Indications: Anterior crowns, particularly in clinical situations where maximum translucency is needed . Contraindications: Posterior restorations. Anterior and posterior FPDs. In discolored preparations and cast posts as the level of translucency is excessive and leads to an overly glassy low value appearance . Advantage: The translucency closely matches that of dentin and is twice more than Inceram alumina. Disadvantage : Decreased flexural strength Incapable to be etched

100. In- ceram zirconia A second-generation material based on In ceram fabrication technique . Core is 30% glass and 70% zirconia high degree of opacity but has good modulous of elasticity and fracture toghness Crystalline oxide of zirconium Zirconia is a nonmetal extremely low thermal conductivity It is chemically inert highly corrosion resistant

101. Advantages: Highest flexural strength Highest fracture toughness Metal free prosthesis Disadvantages: High opacity Less aesthetics Indications: Posterior crown Posterior bridges

102. MACHINABLE CERAMICS From 1998 , machined ceramics came into being. There are two major systems for the fabrication of this technique. 1. Digital systems • CAD CAM technology 2. Analogous systems • Copy milling / grinding technique • Erosive techniques

103. Strengthening of ceramics

104. Methods of strengthening ceramics

105. Ion exchange mechanism : This technique is called as chemical tempering and is the most sophisticated and effective way of introducing residual compressive stresses . This process is best used on the internal surface of the crown, veneer/inlay as the surface is protected from grinding and exposure to acids.

106. Thermal tempering This is the most common method of strengthening glass. I n dentistry silicone oil and other special liquids are used for quenching ceramics instead of water/air

107. Interruption of crack propagation- DISPERSION OF CRYSTALLINE PHASE Crystalline reinforcement: A method of strengthening glasses and ceramics is to reinforce them with a dispresed phase of different material that is capable of hindering crack propagation through the material. The crystalline phase with greater thermal expansion coefficient than the matrix produces tangential compressive stress (and radial tension) near the crystal matrix interface. Such tangential stresses divert the crack around the particle.

108. Examples of dispersed crystalline phases Leucite Lithium disilicate Alumina Magnesia alumina spinel Zirconia T etra silicic flouromica

109. Transformation toughening A newer technique of strengthening glasses involves the incorporation of a crystalline material that is capable of undergoing a change in crystal structure when placed under stress . The crystalline material usually used is termed partially stabilized Zirconia (PZC ). Pure zirconia would be useless for dental restorative applications as Tetragonal phase is not stable at room temperature and it can transform to the monoclinic phase leading to a corresponding volume increase.

110. High-temperature tetragonal phase can be stabilized at room temperature by : Doping with Mg, Ca , Sc , Y, or Nd Reduce the crystal size to less than 10 nm Yttria stabilized zirconia ceramics is known as ceramic steel(due to transformation toughening) stabilizing oxides magnesium oxide yttrium oxide calcium oxide cerium oxide

111. The energy required for the transformation of PSZ is taken from the energy that allows the crack to propagate. When sufficient stress develops in the tetragonal structure and a crack in the area begins to propagate, the metastable tetragonal crystals (grains) precipitates next to the crack tip can transform to the stable monoclinic form.

112. Crack propagation

113. Methods of designing components to minimize stress MINIMIZING TENSILE STRESSES: The design should avoid exposure of ceramics to high tensile stresses. It should also avoid stress concentration at sharp angles or marked changes in thickness.

114. reducing Stress raisers How to avoid stress raisers Sufficient bulk Minimum sharp angular changes Proper proportioning Proper compaction Proper drying Firing under vacuum Non rapid cooling Glazing

115. Machinable ceramics- Advances

116. Dental ceramics and processing technologies have evolved significantly in the past few decades, with most of the evolution being related to new microstructures and CAD-CAM methods. We shall discuss the main advantages and disadvantages of the new ceramic systems and processing methods. Dental ceramics: a review of new materials and processing methods- SILVA L et al. Braz. Oral Res. 2017;31(suppl):e58

117. Multilayered dental prostheses metal/ceramic bilayers are still considered the gold standard for FPDs development of a series of ceramic materials with high crystalline content are able to withstand the mechanical stresses : alumina-based zirconia-reinforced glass infiltrated ceramic polycrystalline alumina Y-TZP chipping fractures of the veneering ceramic were frequently reported Multilayered restorations made from CAD-CAM blocks showed significantly higher fracture strength values

118. Monolithic zirconia restorations Among polycrystalline ceramics, yttria stabilized tetragonal zirconia polycrystal (Y-TZP) for monolithic restorations has been developed more recently to overcome problems related to chipping of porcelain layers applied over zirconia Y-TZP shows superior performance among dental ceramics due the high strength superior fracture toughness The better translucency of the new zirconia materials

119. ADVANTAGES processing methods are simplified in comparison to traditional multilayered restorations less time consuming. much less invasive preparations since this ceramic material has relatively high mechanical properties thinner structures can be constructed transformation toughening, hinder crack propagation monolithic zirconia showed relatively low fracture rates causes minimum wear of the antagonists, this wear rate is within the physiological range marginal adaptation of the monolithic restorations of Y-TZP improved over the years due to the evolution of CAD-CAM systems

120. New glass-ceramics new glass-ceramics were designed to contain lithium silicate as the main crystalline phase in a vitreous matrix reinforced with zirconium dioxide crystals (10%). commercial examples of lithium silicate glass-ceramics are: Suprinity (Vita Zahnfabrik , Bad Sachingen , Germany), a material marketed in a partially crystallized state and that requires an additional thermal cycle in a furnace CELTRA Duo ( Dentisply-Sirona , Bensheim , Germany), a material that is already in its final crystallization

121. ADVANTAGES lithium silicate crystals are up to 6 times smaller than lithium disilicate crystals present in lithium disilicate glass ceramic- due to the presence of zirconia particles in the material these new zirconium-reinforced lithium silicate materials maintain good optical properties attain good surface finishing as they have a high amount of glass matrix have good mechanical properties faster to be milled in CAD-CAM machines than lithium disilicate glass-ceramics and are already offered in their fully crystallized or need a very short crystallization cycle superior polishability due to the smaller crystal sizes in the microstructure.

122. Polymer infiltrated ceramic networks (PICNs) Recently , a new material has been developed by Vita which is marketed as a polymer infiltrated in a porous ceramic The material is considered a resin-ceramic composite material, composed of two interconnected networks: a dominant ceramic and a polymer . final shrinkage of the polymer after infiltration is much greater than the shrinkage experienced upon cooling of the infiltration glass. PICN is based on initial sintering of a porcelain powder followed by infiltration with a monomer mixture.

123. ADVANTAGES: easier to mill and can be easily repaired by composite resins . lower elastic modulus and higher damage tolerance . The fracture toughness value was similar to that of the feldspathic ceramic. the stain resistance of PICN was superior to Lava Ultimate and inferior than that reported for IPS e.max INDICATIONS Based on the reduced elastic modulus of Enamic , this material is especially indicated for prosthetic treatments on stiff implants. Due to the inferior optical properties, PICNs are more suitable in the molar than in the anterior region DISADVANTAGE the shrinkage of the curing resin results in interfacial stresses occurring between the ceramic framework and the polymer results in debonding and a higher opacity because of the gaps developed at the interface.

124. Cad-cam Development of CAD-CAM systems for the dental profession began in the 1970‘s with Duret in France, Altschuler in the US and Mormann and Brandestini in Switzerland .

125. Essentials of cad cam

126. The cad cam process A CAD CAM system utilizes a process chain consisting of scanning, designing and milling phases.

127. Machinable ceramic blanks: Feldspathic porcelain blanks - Vitablocs Mark II (Vita) Glass ceramic blanks - Dicor MGC,( tetrasilicis flouromica ) -Pro Cad,Everest G( Kavo )( leucite ), -IPS emax CAD( Kavo )( lithia disilicate ) Glass infiltrated blanks -Alumina ,(Vita InCeram Alumina ) -spinell ,(Vita InCeram Spinell ), -zirconia(Vita In Ceram Zircona ) Pre-sintered blanks -Alumina (Vita InCeram Al) -Yttria stabilized zirconia (Vita In Ceram VZ) Sintered blanks -Yttria stabilized zirconia (Everest ZH blanks)

128. HARD MACHINING Machined in fully sintered state Restoration is machined directly to final size SOFT MACHINING FOLLOWING SINTERING In partially sintered state - later fully sintered Requires milling of an enlarged restoration to compensate for sintering shrinkage Used for alumina,spinell,zirconia (difficult to machine in fully sintered state) Copings are furthur glass infiltrated

129. ADVANTAGES Dentists control the manufacturing of restoration without laboratory assistance Reduced porosity & greater strength Single appointment Decreases fabrication time by 90 % Minimal abrasion of opposing tooth structure due to homogenieity of material DISADVANTAGES Expensive and limited availability Technique sensitive Inability to build layers of porcelain Decreased marginal accuracy

130. MOST COMMON CAD CAM SYSTEMS

131. Direct cad cam system

132. cerec system CEREC- Chair Side Economic Reconstruction of Esthetic Ceramic First demonstrated in 1986 Cerec System consists of : A 3-D video camera (scan head) An electronic image processor (video processor) with memory unit (contour memory) A digital processor (computer ) A miniature milling machine

133. Materials used with CEREC Dicor MGC: mica based machinable glass ceramic containing 70% vol of crystalline phase Vita Mark II ( Vident ):contain sanidine as a major crystalline phase within a glassy matrix. ProCad ( Ivoclar ):Like Ivoclar's popular Empress™ material, ProCAD is reinforced with tiny leucite particles, and has been referred to as: "Empress on a stick". Vita IN-Ceram Blanks (Vita Zhanfabrik): IN-Ceram Spinell . IN-Ceram Alumina. IN-Ceram Zirconia

134. Clinical Procedure:

135. Clinical shortcoming of Cerec 1 system : Although the CEREC system generated all internal and external aspects of the restoration, the occlusal anatomy had to be developed by the clinician using a flame-shaped, fine-particle diamond instrument and conventional porcelain polishing procedures were required to finalize the restoration. Inaccuracy of fit or large interfacial gaps. Clinical fracture related to insufficient depth of preparation. Relatively poor esthetics due to the uniform colour and lack of characterization in the materials used.

136. Cerec 2 The CEREC 2 unit (Siemen/ Sirona ) was introduced in 1992 The changes include : Enlargement of the grinding unit Upgrading allows machining of the occlusal surfaces for the occlusion and the complex machining of the floor parts. The improved Cerec 2 camera to improve accuracy and reduce errors Magnification factor increased from x8 to x12 for improved accuracy during measurements. Improved accuracy of fit

137. Cerec 3 Software still easy and user friendly which uses windows as operating system. Two compatible cameras available- SIROCAM 2 / SIDEXIS. Precise restorations. Extra-oral and intra-oral measuring. Rapid production. The imaging unit and the milling unit can be linked via cable Supported with online help and design.

138. Pro-cad It is a new CEREC ceramic material based on leucite reinforced glass ceramic with increased strength. Indications: Veneers Partial crowns Anterior and posterior crowns

139. Advantages of CEREC System One or two appointments. Optical impression, max time required is 5 sec. Wear hardness similar to enamel. Less fracture due to single homogenous block. Excellent polish. Improved esthetics. Good occlusal morphology in relation to antagonist.

140. INDIRECT CAD - CAM System that consists of several modules with at least, two distinctive CAD & CAM stations The optical impression is taken in the dental office, where CAD is done; data are transmitted to CAM station for restoration fabrication. Duret system. Procera system (Noble Bio-Care). Cicero system(Elephant Industries). President system (DCS Dental). CEREC SCAN & CEREC InLAB ( Sirona Dental company

141. Procera All Ceram System introduced in 1994. first system which provides outsourced fabrication using a network connection. Developed by Dr. Matts Anderson for Nobel Biocare embraces the concept of CAD CAM. The Procera AllCeram Crown involves a densely sintered high-purity alumina core combined with a low fusing veneering porcelain fabricated by the pressed powder technology. Procera scanner Procera optical probe

142. Consists of computer controlled design station in dental laboratory that is joined through a modern communication link to Procera , where the coping is manufactured

143. CICERO system computer integrated crown r econstruction was introduced by Denison et al in 1999, it includes optical scanning, metal and Ceramic sintering and computer assisted milling to obtain restoration. t he aim of CICERO is mass production of ceramic restorations at one integrated site. It includes rapid custom fabrication of high strength alumina coping and also partially finished crowns to be delivered to dental laboratories

144. The CICERO method of crown fabrication consists of optically digitizing a  gypsum   die designing the crown layer buildup subsequently pressing, sintering milling consecutive layers of a shaded high-strength alumina-based core material Final finishing is performed in the  dental laboratory.  

145. Lava system introduced in 2002 mainly used for fabricating zirconia framework for the all ceramic restorations. uses a laser optical system to transfer and digitize information received from the preparation. The Lava CAD software suggests a pontic automatically according to the margin .

146. CEREC SCAN CEREC SCAN (inclusive of both scanning and milling device)with lap top(imaging device). Tooth preparation. Conventional impressions. Die preparation. Works upon CEREC 3 software. Intra oral scanning device is not present.

147. Copy milling Mechanical shaping of an industrially prefabricated material Wax pattern of restoration is scanned and replica is milled out of the ceramic blank Copy milling takes about 20-30 minutes

148. Celey systems Uses copy milling technique- first available in 1992 Resin pattern fabricated directly on master die and pattern is used for milling porcelain restorations Sorenson 1994 : marginal fit of CELAY is better than CEREC

149. Pattern mounted for probing Copy milling pattern out of ceramic blank As the tracing tool passes over the pattern, a milling machine duplicates these movements as it grinds a copy of the pattern from a block of ceramic material

150. Cercon system It is commonly called as a CAM system as it does not have a CAD component. This system scans the wax pattern and mills a zirconia bridge coping from presintered zirconia blanks, which is sintered at 1,350⁰C for 6-8 hrs. Veneering is done later on to provide esthetic contour.

151. Ceramill system Based on pantograph type of copy milling Probe tip traces the resin build up Milling handpiece simultaneously mills a duplicate coping out of zirconia block Zirconia reinforced lithium disilicate

152. Advantages Precisely fitting ceramic restorations can be developed without a lab technician The grains are finer than conventional In-Ceram, therefore the strength is more than conventional. Disadvantages marginal quality of crowns made from the copy-milling technique is likely to be inferior to that of copings made from the hot pressing method.

153. Although the CAD-CAM systems described above are already well established in the dental market, they present a major drawback related to the great waste of material upon machining . Therefore, new technologies have been developed to overcome this problem. These techniques are: Selective Laser Sintering or Melting (BEGO Medifacturing ® System, BEGO Medical GmbH, Bremen, Germany) Direct 3D Printing/rapid prototyping Stereolithography .

154. conclusion It is apparent that ceramics as a material group would continue to play a vital role in dentistry owing to their natural aesthetics and sovereign biocompatibility with no known adverse reactions. However, there will always remain a compromise between aesthetics and biomechanical strength.

155. References Phillips science of dental materials – 11 th edition Craig’s Restorative dental materials –13th edition . Mannapallil – 3 rd edition W . Patrick Naylor,Introduction to Metal – Ceramic Technology –Second edition William J.O Brien, Dental materials and their selection- 3 rd edition. Kelly JR. Nishimura I. Campbell SD. Ceramics in dentistry: Historical roots and current perspectives. J prosthet dent 1996:75 18-32 . Kelly J. Dental ceramics : current thinking and trends. Dent Clin N Am 2004(48):513-530 . Dental ceramics: a review of new materials and processing methods- SILVA L et al. Braz. Oral Res. 2017;31(suppl):e58