DENTAL CERAMICS

1. NashathFathima (49) Naheema.K (48) Muhsina Farsana(47) Nasmeena Nasir(50) Mufeeda Ashraf(45) Mubeena Muhammad(44) DENTAL CERAMICS

2. Introduction • Dental ceramics • Structure and characteristic properties • Classification • Composition • Feld spathic porcelain • Recent technologies • Metal ceramics • All ceramic porcelain restorations • CAD CAM mechinble ceramic restorations • Copy milling technic OVERVIEW

3. Dental ceramics are non-metallic inorganic structures of simple compounds of oxygen with one or more metallic or semi metallic materials There are four varieties of ceramics • Amorphous silicate ceramics (SiO2 with small amount of glass formers i.e. Al2O3, MgO, ZrO2etc) • Crystalline oxide ceramics (MgO.Al2O3, 3Al2O3.2SiO2, Al2O3.TiO2 etc. used as refractory materials of modern investments for titanium castings) INTRODUCTION

4. Partially crystalline glass ceramics (like DICOR, glass matrix, with tetra silicfluormica crystals). Non Oxide ceramics (borides, carbides, nitrides, selenides, silicides, etc which are not used for dental restorations, but only as abrasives.

5. O l -O-Si-O- l O • tetrahedral structure of SiO2, • Has Si4+ cations at the centre and anions at each corners • This structure due to short range oxygen valency bonding is amorphous & very rigid • Very low thermal expansion, so perfect insulator • So forms a vitreous structure on solidification STRUCTURE

6. By adding metallic ions(K++,Na+,Al++,Ca++) it is possible to break the oxygen bonding, cause certain amount of crystallization, or devitrification, and increase the C.O.T.E. • These are known as glass interruptors

7. Biological • Biocompatible • Insoluble in oral fluids, but absorb water etc. and undergo slight degradation Chemical • Chemically inert • No free electrons, but only oxygen bonding and hence perfect insulators CHARACTERISTIC PROPERTIES

8. Mechanical • Brittle, non ductile. Non malleable • High compressive strength and hardness • Low tensile, shear and flexure strengths • Vitreous solidification produce microcracks • Glazing improves surface integrity and flexure strengths Thermal • Low C.O.T.E(6-12 ppm/0C) • Perfect insulators due to lack of conducting electrons

9. According to 1.Composition • Feldspathic • Leucite based • Lithia based • Aluminuous • Pure alumina, silica, zirconia CLASSIFICATION

10. 2.Processing • Condensation and sintering or firing • Partial sintering and glass infiltration • Hot pressing, casting, slip casting • (CAD CAM)-Computer Aided Designing and Computer Aided Machining • Copy milling and machining • 3.Varieties used • Core porcelain • Opaque porcelain • Body(dentin) porelain • Gingival, neck or cervical porcelain • Enamel(incisal porcelain) • Color frits(pigments) • Glaze porcelain

11. 4.Fusion temperatures • High fusing(>13000C)-used for artificial teeth • Medium fusing(1100-13000C)used for artificial teeth • Low fusing(850-11000C)-crown, bridges, veneers, metal ceramics • Ultra low fusing(<8500C)-metal ceramics, casting • 5.Microstructure • Amorphous glass • Crystal containing glass • Crystalline porcelain • Partially crystallized porcelain

12. 6.Transparency • Opaque • Translucent • Transparent • 7.Applications • Porcelain/ceramic jacket crowns • Veneers • Post and cores • Fixed partial dentures • Stains and color frits • Glazes • Metal ceramics • Anterior and posterior restoraives

13. DISPENSING METHODS • The ceramic compositions are melted, fritted (quenched to produce microcracks) and powdered into small particles of different sizes. • This helps better close packing during condensation to reduce firing volume shrinkages. • Opacifiers, shades, color frits are also incorporated.

14. COMPOSITION

15. TOUGHENING OF PORCELAIN • During solidification, first the outermost layer of the liquid solidifies forming a skin,which contracts exerting large compressive forces on the liquid inside. • The liquid inside solidifies slowly as there are no conducting free electrons.it forns a vitreous (liquid) solid. • The reaction exerted inside against the compressions at the outer surface causes large number of micro cracks • These decrease the mechanical properties due to crack propagation

16. THIS IS REMEDIED BY • 1.Introduction of residual compressive stresses • METHODS • Ion exchange or chemical tapering • If a soda feldspathic porcelain article is kept immersed in molten KNO3 solution for few minutes, the smaller Na+ ions are exchanged by the K+ ions which are about 30% bigger in size. • This introduces large residual compressive stress and increase tensile strengths.

17. Thermal tapering • If the ceramic article is suddenly cooled, the outer surface solidifies first and surrounds the softer molten core • This causes contraction, introducing residual compressive stresses • Thermal compatibility or mismatching thermal expansions • The residual compressive stresses can be introduced by choosing two or more layered, and bonded, ceramic compositions which have slightly different COTE

18. 2.Interruption of crack propagations • METHODS • Dispersion strengthening: • This by introducing very hard crystalline phases before fusing the porcelain • Eg: • alumina core porcelain(90-95% alumina) • aluminous porcelain(40-50% alumina) • leucite, lithiadisilicate, magnesia alumina spinel, zirconia etc • forming a crystalline phase by devitrification as in ceramming

19. Transformation toughening • Partially stabilised zirconia is introduced into ceramics at higher temperatures • At lower temperatures it transforms into more stable monoclinic phase with an increased volume • This form is harder and interrupts crack propagation • 3.Design of the article • Any abrupt changes in the thickness of the article, sharp corners, wrinkles in swagged metal copings etc are regions of high stress concentrations, called stress raisers. Such weak points are avoided while designing the article

20. 1.Preliminaries After recording the impression, a hard die of prepared tooth is made in a refractory material which is adapted with a thin platinum foil of 1/40 mm without wrinkles. Suitable shades of required amount of powder is mixed with water or special liquid to make a thick slurry which is applied over platinum foil. OUTLINE OF FABRICATION OF PORCELAIN ARTICLE

21. 2.Condensation • The porcelain particles are closely packed inorder to reduce the volume shrinkage and minimize porosity in the fired porcelain and excess water is removed. • There are 4 methods: • Spatulation • The article is carefully smoothened with a spatula when extra water comes to the surface by capillary action which is removed by blotting paper.

22. Brush technic • A small amount of dry powder is sprinkled over the article and carefully tapped with brush. • The powder absorbs water from inside whicj an be removed • Vibration method • The article is carefully vibrated and excess water coming out is removed • Ultrasonic method • The ultrasonic vibrations re transmitted electrically and excess water is removed using blotting paper

23. 3.Firing procedure • Porcelain firing unit is preheated to 6500C. • The article to be fired is placed in a fire clay tray and then placed on the platform of the instrument and held near the door of the muffled chamber for 5 minutes. • The article slowly dries up. • The platform is raised and article is held inside muffle chamber for 5 minutes. • The remaining water is converted to steam and comes out. • The door of muffled chamber is then closed. • It is evacuated by connecting it to a vacuum pump. • The temperature is gradually raised to 9500C in abou 5 minutes at the rate of 10C per second.

24. STAGES OF FIRING Low bisque stage/ low biscuit stage As the temperature gradually rises, the surface of particles begin to soften and the lose particles begin to join. There is no volume shrinkage. Firing can be stopped at any stage. At this stag if the firing is stopped, the particles just join together forming a porous mass. this partially sintered materialis used in glass infiltrated ceramics (INCERAMS)

25. Medium bisque stage On further heating more softening of particles take place and begin to melt There is better cohesion and slight volume shrinkage High bisque stage Further heating causes melting of all particles producing complete cohesion and maximum volume contraction. As the liquid is highly viscous, the shape is retained for a short time If this eating is prolonged, the liquid gradually flows under gravity i.e. pyroplastic flow and the article looses sharp corners and shape.

26. 4.Cooling of the fired article • Firing is discontinued at high bisque stage for complete melting • The muffle chamber is gradually cooled • This is to minimize formation of micro cracks • Then platform is bough down and the article is removed • Methods to minimize internal porosities • 1.Firing under vacuum • The muffled chamber is evacuated connecting to a vacuum pump • This removes the air trapped in between the particles in condensed slurry • Then firing is started

27. 2.Firing under diffusible gases • Before firing, air in the muffled camber is replaced by highly diffusible gases like H2, He etc. • These occupy space in between particles instead of air • These have very small molecular size and can easily pass through and come out of molten viscous liquid envelope • 3.Cooling under pressure • Immediately after firing is discontinued, air is le inside the evacuated muffle chamber and then controlled cooling is done

28. Methods to minimize volume shrinkage • The porcelain mix is again applied over the article andfired. This may require 3-4 time repetitions. But repeated firing decreases mechanical properties • A skilled technician initially prepares an oversized article by 13-14% linear. On firing required size is obtained after contraction • Firing is done in increments of 0.5-2.0 mm thickness, like core porcelain, dentin porcelain, enamel porcelain, glazes etc. This compensates the shrinkage

29. 5.Glazing of fired porcelain article To remove surface cracks and improve flexure strengths, glazing is done Auto glazing The finished article is kept in the furnace and the temperature is quickly raised only to melt the surface particles, which flow and fill the microcracks Add on or extended glazing A special transparent glaze porcelain of lower fusion temperature is mixed in water and coated on the article as a thin layer It is then fired at lower temperature only to melt the outer layer of glaze porcelain which flows into cracks

30. 6.Shading of ceramics • To get permanent shade and imitate check lines the shades, color fris or stains are applied before glazing. • This gives more natural appearance

31. Biological • Excellent biocompatibility • Chemical inertness in oral conditions Mechanical – INADEQUATE • Highly brittle • Low shear and diametral tensile strengths • Low compressive strength • Greater surface hardness.this cause abrasion of opposing natural tooth PROPERTIES OF FELDSPATHIC PORCELAIN

32. Thermal • Low COTE nearly same as tooth enamel • Good thermal insulator • Aesthetics • Good aesthetic properties • The color parameters(hue, chroma ad values) are permanent

33. Metal ceramics To overcome the mechanical deficiencies and retain the aesthetic excellence ,the ceramic appliances are strengthened by bonding to metallic structures.

34. For selection of metals • Adequate bio compatibility, non toxicity, non carcinogenic properties. • High corrosion resistance, chemically stable • High proportional limit, yield strength, compressive, tensile and sheer strengths • High modulus of elasticity to get sag resistance. • Low creep value • High fusion temperature, more than porcelain • Low C.O.T.E. IDEAL REQUIREMENTS

35. For the selection of porcelain • High bio compatibility • Good mechanical properties • High C.O.T.E. • Ability to wet and bond with metal surface. • Fusion temperature should be lower than the metal • Good color stability

36. ALLOYS USED FOR METAL CERAMICS • H.N. alloys • N alloys • PBM alloys

37. METAL CERAMIC BONDING • Technics • Mechanical: The bonding surface of the cast material is made rough by using diamond and carbide burs. These creates an increase surface area to improve wetting and mechanical bonding. • Thermal: C.O.T.E. of alloys are decreased to about 13.5-14 ppm/oc. C.O.T.E. of ceramics is increased to 13-13.5 ppm/oc. It helps bonding by mechanical interlocking known as thermal bonding.

38. CHEMICAL BONDING This is achieved by bonding of ceramics through oxygen of thin oxide layer formed on the metal surface.

39. ADVANTAGES OF METAL CERAMICS • Higher strength and durability • Higher fracture resistance • Adequate marginal fit • Permanent aesthetics • DISADVANTAGES • Flexure strains produced in long span bridges may fracture ceramics • Slightly poor aesthetics due to metallic color reflections • Darker margins near the gingiva • More healthy tooth material is to be removed to accommodate thicker article. • More expensive due to complicated procedures.

40. Further improvements Swaged gold foil metal ceramics Bonded platinum foil Electro deposition technics

41. METAL CERAMIC BOND FAILURES • CAUSES • Ceramic failure due to strength of ceramics. • Ceramic metal oxide bond failure due to inadequate oxide formation. • Metal oxide failure due to too thick or poor strength of metal oxide layer. • Metal oxide metal bond failure. • Metal failure due to low strength or porous defects of metal coping.

42. REMEDIES • Selection of material & proper technics of manipulations for better bonding are to be used. • Patient also should be instructed to minimize the applications of specially tensile and shearing forces.

43. OUTLINE OF METAL CERAMIC OR PORCELAIN FUSED TO METAL FABRICATION • After preparing the tooth, an accurate elastomeric impression is obtained and a ceramic refractory material die is prepared. Suitable metal coping is formed to fit the die exactly by: • Casting a pure metal CpTi, or alloys of HN,N, or PBM, by the usual lost wax casting procedure • CAD-CAM technic from a cast alloy ingot. • Electro deposition of gold or other metals on the duplicate die. • Burnishing metal foils on the die and then heat treating.

44. In case of HN or N metal alloys, electrodeposition of pure gold first and then flash electrodeposition of tin are done. In case of PBM alloys, presence of small amounts of Sn, In or Fe, results in such a thin atomic layer. • The articles are then kept in a furnish at about 950-1300C for sometime for degassing, that is to drive away gases or air trapped inside. But actually this forms a thin atomic layer of oxides of tin , indium or iron. This helps chemical bonding with ceramics. The surface of bonding should be perfectly clean. • Then apply a thin layer (.3mm) of opaque porcelain (opaquer), on this and fired. This is to prevent reflection from white color PBM alloys. In case of yellow colored alloys this opaque layer is not given, as yellow colored surface reflecting light makes it more life like(vital)

45. Over this, the translucent, body (or dentin) porcelain slurry is applied to build the tooth form and condensed. Gingival porcelain with slight red tint is also applied near the gingiva and fired together. • Then more transparent enamel porcelain of thin layer is applied and fired. The article is finished with diamond points , discs or carbide burs. • Next apply the color shades and stains. Over this glaze porcelain thin coating is applied and then fired. This finished article is finally cemented to the tooth structure with GIC (type 1) or zinc silico phosphate or resin cement.[ Note: the fusion temperatures of these different varieties should be successively in the decreasing order from the metal coping to the glaze layer.]

46. ALL CERAMICS PORCELAIN RESTORATION

47. castable glasses • injection moulding glass ceramic technic • hot pressable glass ceramic SUB HEADINGS

48. castable ceramics were first developed and manufactured by the famous corning glass works and supplied by dentsply international and hence it is known as dicor • these are used to fabricated inlays crowns and venners by lost wax casting procedure and then cerammed CASTABLE GLASSES

49. prepare a hard ceramics die and form the wax pattern of inlay or venner or crown with inlay wax.thick short are attached to allow the viscous ceramics liquid to enter the mould • invest the pattern with die in special phosphate bonded investment material.after the wax burnout,melt the casting lass ceramic pelletsc in the crucible in the centrifugal casting machine.aftercastin, slowly cool it(overniht)recover the article and finish with diamond points or disc and then staining and glazing are done • ceramming the finished casting is embedded in a protective material and subjected to heat treatment about 8oo degree celcius for abt 10-12 hrs, below its fusion temperature • lorparameter.this is known as chameleon effect STEPS OF FABRICATION OF CASTABLE CERAMIC RESTORATION

50. devitrification takes place in the middle of the article forming mica crystals well inside.the improves the strength as it is interrupts crack propagation and also aesthetics.the nucleation and crystal growth is known as ceramming. the crystal layer formed has higher refractive index or optical density.due to this, the inner layer reflect light.surprisingly this shows excellent aesthetics property as light reflected from neighboring teeth, enter into this and get reflected and refracted out, with almost same co