1. Dental Ceramics

2. Dental Ceramics - definition ceramics contain both metal and nonmetal elements bonding is either covalent or ionic crystalline or non-crystalline

3. Dental Ceramics - properties ceramics brittle thermal & electrical insulators non-reactive

4. Dental Ceramics – effects of cooling rate fast cooling: crystallization is sluggish many ceramics are amorphous – glasses fast cooling to form vitreous materials (i.e., vitrification) slow cooling: crystallization can occur

5. A silicon dioxide tetrahedra: oxygen silicon

6. Crystalline & Amorphous Silica crystalline SiO 2 amorphous SiO 2

7. Action of fluxes on glasses sodium silicate glass Fluxes interfere with ordering of tetrahedra, promote glass formation, reduce melting temperature

8. Fluxes for Glass Making soda sodium carbonate Na 2 CO 3 lime calcium carbonate CaCO 3 potash potassium carbonate K 2 CO 3

9. Dental Ceramics - definition glass-matrix composite A material that consists of crystalline filler particles within a glassy matrix. Many dental ceramic are such composites. That said, ceramics core materials marketed between 1995 and 2006 are either mostly or entirely crystalline.

10. Crystalline Fillers: Two sources: high-melting crystalline particles added to ceramic powders. If these particles have a very high fusion temperature, they might not melt when the other ingredients melt. Upon cooling, the particles will be trapped within the glass as it solidifies. new phases that precipitate within the glass when the glass is either 1) slow cooled or 2) heated to high temperatures below the glass transition temperature.

11. An important type of ceramic – glass ceramics: These are ceramics that form crystalline phases within their glassy matrix as the result of heat treatment. Note that it may be possible to form more of the crystalline phase by heating for a longer time or at a higher temperature. In most cases, the glassy phase will become a two phase mixture – one glassy and the other crystalline. In some cases, the glassy phase can completely transform, becoming 100% crystalline

12. Mg ++ Mg ++ Mg ++ Mg ++ Silicates magnesium silicate crystal Silicate minerals are often the raw materials for glasses. When melted the crystalline structure breaks down and the me- tal ions act as fluxes that lower the melting point of the glass. Traditional dental porcelain is made from a silicate mineral called feldspar.

13. Feldspathic porcelains: the matrix is a glass made form the mineral feldspar (K 2 O - Al 2 O 3 - SiO 2 ) melts above 1290 o C, if cooled fast it forms a glass fillers are leucite and sometimes quartz A family of glassy-matrix composites:

14. Traditional Fabrication of Ceramic Restorations ApplicationCeramic TypeFabrication Denture Teeth High-fusing feldspathic porcelain Sintered at high pressure Inlays Medium-fusing feldspathic porcelain Sintered Veneers Medium-fusing feldspathic porcelain Sintered Jacket Crowns Medium-fusing feldspathic porcelain many new ceramics Sintered / many new methods Metal-Ceramic Crowns Medium or low-fusing feldspathic porcelains Sintered

15. Sintering a glass-ceramic frit: high temperature partially sintered powder compacted powder shrinkage still porous

16. Glass-Ceramics – sintering rate low viscosity glass small particles a range of particle sizes high surface energy glasses vacuum firing sintering rate increased by

17. Glass-Ceramics – sintering rate low viscosity glass small particles a range of particle sizes high surface energy glasses vacuum firing sintering rate increased by

18. Glass-Ceramics – sintering rate low viscosity glass small particles a range of particle sizes high surface energy glasses vacuum firing sintering rate increased by

19. Glass-Ceramics – sintering rate low viscosity glass small particles a range of particle sizes high surface energy glasses vacuum firing sintering rate increased by

20. Glass-Ceramics – sintering rate low viscosity glass small particles a range of particle sizes high surface energy glasses vacuum firing sintering rate increased by

21. Methods of fabricating dental ceramics Sintering – the traditional method casting hot pressing (injection molding) computer-aided-machining melt infiltration

22. Traditional Fabrication of Ceramic Restorations ApplicationCeramic TypeFabrication Denture Teeth High-fusing feldspathic porcelain Sintered at high pressure Inlays Medium-fusing feldspathic porcelain Sintered Veneers Medium-fusing feldspathic porcelain Sintered Jacket Crowns Medium-fusing feldspathic porcelain many new ceramics Sintered / many new methods Metal-Ceramic Crowns Medium or low-fusing feldspathic porcelains Sintered

23. High Fusing Feldspathic Porcelain* (1300 – 1400 o C) Wt. % silica15% feldspar81% Kaolin5% metal oxidesbalance * Used to make denture teeth.

24. Metal Oxide Colorants TiO 2 - yellow - brown Fe 2 O 3 - brown UO 3 - fluorescence

25. Low & Medium Fusing Feldspathic Porcelains (850 - 1100º C) less feldspar more quartz metal oxides more low fusing fluxes potassium carbonate sodium carbonate borates Note that these porcelains are used to make both porcelain jacket crowns (PJCs) and the porcelain covering on metal-ceramic crowns. In PJCs, a thin platinum foil is placed over the die. The porcelain is applied to the foil. This allows the porcelain green ware and foil to be removed from the die and carried to the furnace.

26. Making a frit fused at high temp. quenched - crazes the glass ball milling yields 7 - 70 µm powder

27. Making a paste frit water binder

28. Porcelain Processing - condensation blotting vibration dry powder Goal: to compact the powder so that the particles are as close together as possible.

29. Porcelain Processing - drying slow temperature increase is achieved by placing the green ware outside the open furnace door this process prevents boiling of the water that remains in the green ware

30. Porcelain Processing – firing (low bisque) sintering begins weak; porous shape is true

31. Porcelain Processing – firing (high bisque) porosity minimized shrinkage: High fusing :11.5 % linear, 30% volume Low fusing: 14% linear, 34% volume

32. Porcelain Processing – glazing Cover the surface with a glassy layer. Two methods: coat surface with a low-fusing feldspathic porcelain (over-glaze) extend final firing (self-glaze)

33. Effect of stress state on strength of brittle materials : tensile force 100 N compressive forces 100 N compressive forces 100 N tensile force 100 N flaws open; cracks grow flaws close; no crack growth tensile stresses in material compressive stresses in material Feldspathic porcelain Ultimate strength tensile 24.8 MPa compressive 149 MPa

34. Effect of stress state on the strength of brittle materials: tensile force 100 N tensile force 100 N Compressive internal stresses must be overcome before crack growth can occur. Compressive internal stresses at surfaces will increase the ultimate tensile and transverse (bending) strength of materials. Conversely, tensile internal stresses will assist crack opening and, therefore, decrease tensile and transverse strengths. compressive internal stresses compressive internal stresses

35. Strengthening of Dental Ceramics (specifically feldspathic porcelains) thermal tempering glazing polishing ion exchange dispersion strengthening

36. Strengthening Dental Ceramics – thermal tempering rapid cooling surface cools faster core of ceramic is molten; surface is solid as the molten core contracts it tugs at the surface placing it in compression

37. Strengthening of Dental Ceramics (specifically feldspathic porcelains) thermal tempering glazing polishing ion exchange dispersion strengthening

38. Strengthening Dental Ceramics – glazes 1.fills surface scratches, cracks, etc. (e.g., the ceramic is stronger because there fewer flaws) 2.if glaze contracts less than underlying ceramic as it cools from high temperature, compressive stresses will arise in the glaze because of the faster contracting underlying ceramic.

39. Strengthening of Dental Ceramics (specifically feldspathic porcelains) thermal tempering glazing polishing ion exchange dispersion strengthening

40. Strengthening Dental Ceramics – polishing polishing strengthens ceramics by reducing the size of cracks at the surface

41. Strengthening of Dental Ceramics (specifically feldspathic porcelains) thermal tempering glazing polishing ion exchange dispersion strengthening

42. sodium silicate glass Ion exchange replaces Na ions near the material’s surface with slightly larger K ions

43. Strengthening Dental Ceramics – ion exchange the glassy phase of many dental ceramics contains the relatively small sodium ion apply a potassium-rich slurry to the ceramics surface and heat to 450 o C for 30 min some of the sodium ions in the glassy phase are replaced by the 35% larger potassium ions (diffusion) compressive stresses arise in the surface layer where the exchange has occurred.

44. Strengthening of Dental Ceramics (specifically feldspathic porcelains) thermal tempering glazing polishing ion exchange dispersion strengthening

45. Strengthening Dental Ceramics – dispersion strengthening the glassy matrix of many dental ceramics can be strengthened by adding crystalline ceramic particles these particles toughen the ceramic by blocking the crack paths rather than go through these particles, cracks go around them

46. Types of crowns: no core foil core electroformed core gold impregnated sintered alloy core cast metal core ceramic core best esthetics must hide metal color good esthetics

47. Distribution of posterior crowns made in large dental laboratory December 2013 : metal-ceramic crowns - 10% zirconia ceramic – 62% lithium disilicate - 14 bare metal alloy – 3% Glidwell Labs 2013; in 2007 65% of their crown were metal- ceramic.

48. Study of 515 metal-ceramic FPD’s: survival rate 5 years – 96% 10 years – 87% 15 years – 85% Walton TR. An up to 15-year longitudinal study of 515 metal- ceramic FPDs: Part 1. Outcome. Int J Prosthodont 2002;15(5):439-45. NOTE: This is in a private practice.

49. Study of 515 metal-ceramic FPD’s: causes of failure tooth fracture – 38% periodontal breakdown – 27% loss of retention – 13% caries – 11% Walton TR. An up to 15-year longitudinal study of 515 metal- ceramic FPDs: Part 2. Modes of failure and influence of various clinical characteristics. Int J Prosthodont 2003;16(2):177-82. NOTE: This is in a private practice. Note that failures are NOT associated with the metal-ceramic FPD itself.

50. Types of crowns: no core foil core electroformed core gold impregnated sintered alloy core cast metal core ceramic core best esthetics must hide metal color good esthetics

51. Porcelain Crowns feldspathic porcelain high leucite glass ceramic* castable glass ceramic* lithium disilicate filled glass ceramic* No Core * Note that all these are glass ceramics. That traditional feldspathic porcelain is also a glass ceramic was not known until the mid 1980s.

52. Coreless Porcelain Crowns - Alternatives High-leucite feldspathic porcelains sintered - 41 vol. % leucite (Optec HSP) Injection-molded porcelain (IPS Empress)

53. Feldspathic Porcelains – Leucite crystalline phase formed when feldspathic porcelains are heated above 710 o C is a potassium aluminum silicate ( K 2 O  Al 2 O 3  4SiO 2 ) transparent

54. Van Noort, Introduction to Dental Materials, 2 nd edition. Feldspathic porcelain reinforced by leucite.

55. Feldspathic Porcelains – roles of Leucite increases thermal expansion double that of feldspathic glass strengthens feldspathic porcelain bending strength 1.5 – 3 X

56. Porcelain Crowns feldspathic porcelain high leucite glass ceramic* castable glass ceramic* lithium disilicate filled glass ceramic* No Core * Note that all these are glass ceramics. That traditional feldspathic porcelain is a glass ceramic was not known until the mid 1980s.

57. Cores for Porcelain Crowns - Alternatives Castable Glass-Ceramics ceramming to form fluoromica crystals (Dicor)* ceramming to form hydroxyapatite crystals (CerePearl)** * No longer sold. ** Can find no evidence that this is on the market (2015)

58. Cores of ceramic crowns – pressable ceramics Examples: Empress Empress 2 Ceramic is heated to a temperature at which it will flow under stress. It is not liquified.

59. Pressable ceramics: composition Empress – leucite-filled feldspathic porcelain (40 – 50 % leucite by mass) Empress 2 – lithium disilicate-filled feldspathic porcelain (~70 vol % lithium disilicate) Note that the lithium disilicate-filled porcelain is the strongest translucent coreless ceramic currently on the market

60. Types of crowns: no core foil core electroformed core gold impregnated sintered alloy core cast core ceramic core best esthetics must hide metal color good esthetics

61. Porcelain Crowns – Types of cores Pt foil backed alumina- filled feldspathic core noble-metal foil covered with feldspathic porcelain foil copings

62. Foil-backed porcelain crowns - tin-plated platinum foil: tin oxide helps porcelain wet the foil tin oxide may also bond with porcelain an alumina-filled feldspathic porcelain used as core (opaque) layers of feldspathic porcelain (translucent) are added to bring the crown to final shape

63. Foil-backed porcelain crowns - noble metal foils: foils are laminated & pleated Au – 5% Pt – 7% Pd – 3% Ag + inside layer of Pt – 10% Ir (Renaissance / Ceplatec) Au – Pt – Pd – Ag – Rh (Flexobond) coated with gold solders

64. Foil-backed porcelain crowns - noble metal foils: a bonding agent is painted on the swaged coping to promote bonding with porcelain layers of feldspathic porcelain are added to produce final form

65. “Crunch the Crown” tests (3 mm occlusal thickness) N Pt-foil backed alumina reinforced feldspathic porc. 11 Noble alloy foil (Renaisance)14 Noble alloy foil (Flexibond)20 metal-ceramic crown34

66. Types of crowns: no core foil core electroformed core gold impregnated sintered alloy core cast core ceramic core best esthetics must hide metal color good esthetics

67. Porcelain Crowns – Types of cores Pt foil backed alumina noble-metal foil covered with feldspathic porcelain foil copings gold composite copings gold impregnated sintered alloy covered with feldspathic porcelain No longer marketed ?? Captek

68. Porcelain Crowns – gold composite copings artwork by Joe Jacobson © PJ’s Dental Lab, Inc.

69. Alloy powder impregnated wax is pressed on silicon refractory die Powder: Au-Pt-Pd, 30% of each Sintered 1075 o C for 4 minutes

70. Sintered porous Captek P Gold foil loosely wrapped around sintered Captek P coated die. Gold is drawn into sintered alloy by capillary forces Final structure is a metal matrix composite

71. 50 µm Captek P: Au – Pt – Pd porous sintered alloy Final coping after porous alloy is impregnated with gold. The final structure is 88% Au.

72. Captek coping after gold has penetrated the sintered alloy 1 – with adhesive 2 – one layer of body porcelain 3 & 4 – two layers of body porcelain 1 23 4

73. Types of crowns: no core foil core electroformed core gold impregnated sintered alloy core cast core ceramic core best esthetics must hide metal color good esthetics

74. Porcelain Crowns – Types of cores aluminous core (sintered) high density aluminous core very high density aluminous core zirconium oxide core ceramic cores

75. Aluminous porcelain Feldspathic glass + 50% Al 2 O 3 particles (1970s) twice as strong as feldspathic porcelain particles inhibit crack propagation very opaque particles are 10 – 15 µm

76. Porcelain Crowns – Types of cores aluminous core (sintered) high density aluminous core very high density aluminous core zirconium oxide core ceramic cores

77. Porcelain Crowns – Ceramic cores - In-Ceram artwork by Joe Jacobson © PJ’s Dental Lab, Inc.

78. Ceramic cores - In-Ceram Condense fine alumina - water slurry on a porous ceramic mold Partially sinter for 2 hr at 1000 o C Apply a lanthanum aluminosilicate (LaAl 2 O 3 SiO 2 ) glass to fill the pores in the alumina - slip casting

79. Ceramic cores - In-Ceram Flexure strength of the core up to 600 MPa Recommended for posterior all ceramic restorations Fixed partial dentures ???

80. Other slip-cast cores In - Ceram SPINELL - core based on magnesium aluminate (MgAl 2 O 4 ) - more translucent, but not as strong In - Ceram Zirconia - zirconia core (ZrO 2 ) - very strong - less translucent

81. Porcelain Crowns – Types of cores aluminous core (sintered) high density aluminous core very high density aluminous core zirconium oxide core ceramic cores

82. Porcelain Crowns – High Denisty Ceramic cores - Procera artwork by Joe Jacobson © PJ’s Dental Lab, Inc.

83. High density alumina - Procera near 100% alumina oxide sold as solid blocks die is digitized by copy milling

84. Current ceramics: flexural strength

85. Current ceramics: fracture toughness.

86. Clinical Fracture of All-ceramic Crowns ceramicyr.no. dur yrs anter. (no.) poster. (no.) brand (author) castable glass 20001737 17.3% 95 30% 78 Dicor (Erpenstein) melt-infiltrated alumina 19953353 4% ? 3% ? In-Ceram Huls melt-infiltrated alumina 20001973 2% 100 6% 97 In-Ceram (Mclaren)

87. Porcelain Crowns – Types of cores aluminous core (sintered) high density aluminous core very high density aluminous core zirconium oxide core ceramic cores

88. Porcelain Crowns – High Denisty Ceramic cores - Lava artwork by Joe Jacobson © PJ’s Dental Lab, Inc.

89. Zirconia Ceramics – pure zirconia ZrO 2 – zirconium oxide powder is the metal oxide of zirconium. Monoclinic at room temperature; Is tetragonal at high temperature; & cubic at even higher temperature On cooling either the cubic phase or the tetragonal phase transforms back to the monoclinic. The monoclinic phase forms with a 3 – 5 % expansion – producing many cracks As a result of the cracks, pure zirconia is very weak at room temperature.

90. Only 14 types of unit cells are found in nature Transformation under tensile stress

91. Zirconia Ceramics – PSZ Melting zirconia with small amounts of other oxides (e.g., CaO, MgO, CeO 2, Y 2 O 3 ) stabilizes the cubic phase at room temperature. These ceramics with mostly cubic zirconia but also contained small about of tetragonal and monoclinic zirconia. The cubic zirconia was found to be metastable: when stress was applied it transforms to monoclinic zirconia. As a result, this modified zirconia was call partially stabilized zirconia (PSZ).

92. Zirconia Ceramics - Y-TZP ZrO 2 – zirconium oxide powder (97 mol %) Y 2 O 3 – yttrium oxide powder (3 mol %) sintered together form nearly 100% tetragonal zirconia product is call Yttrium-stabilized Tetragonal Zirconia Polycrystals or Y-TZP. as is the case for the PSZ, Y-TZP transforms to monoclinic zirconia when stress is applied.

93. Y-TZP Ceramics – transformation toughening the tetragonal to monoclinic transformation is accompanied with a 3 – 5 % local increase in volume the transformation takes place locally; surrounding crystal is still tetragonal – consequently it resists the volume expansion as a result, compressive stresses are generated around cracks and crack tips these compressive stresses increase the fracture toughness significantly – this type of toughening is called “transformation toughening.”

94. Y-TZP Ceramics – transformation toughening as a result, compressive stresses are generated around cracks and crack tips Note that stresses are higher near cracks. Consequently, the transformation takes place around cracks. The transformed material (monoclinic crystal) is squeezed by the nontransformed crystal (tetragonal) that is farther from the crack.

95. Effect of stress state on the strength of brittle materials: tensile force 100 N tensile force 100 N Compressive internal stresses must be overcome before crack growth can occur. Compressive internal stresses at surfaces will increase the ultimate tensile and transverse (bending) strength of materials. Conversely, tensile internal stresses will assist crack opening and, therefore, decrease tensile and transverse strengths. compressive internal stresses compressive internal stresses

96. Current ceramics: flexural strength

97. Current ceramics: fracture toughness.

98. Y-TZP: problems with veneering veneers applied to achieve better esthetics sintering of veneers performed at high temperature; may also be exposed to moisture during sintering Y-TZP unstable? affected by heat, water vapor