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 Varieties • Amorphous silicate ceramics • Crystalline oxide ceramics • Partially crystalline glass ceramics • Non Oxide ceramics INTRODUCTION

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

5. Add metallic ions increase the C.O.T.E. • glass interruptors

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

7. 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

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

9. 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) porcelain • Gingival, neck or cervical porcelain • Enamel(incisal porcelain) • Color frits(pigments) • Glaze porcelain

10. 4.Fusion temperatures • High fusing(>13000C ) • Medium fusing(1100-13000C) • Low fusing(850-11000C) • Ultra low fusing(<8500C) • 5.Microstructure • Amorphous glass • Crystal containing glass • Crystalline porcelain • Partially crystallized porcelain

11. 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

12. DISPENSING METHODS • The ceramic compositions are melted, fritted and powdered into small particles of different sizes. • Better close packing during condensation to reduce firing volume shrinkages. • Opacifiers, shades, color frits are also incorporated.

13. COMPOSITION

14. TOUGHENING OF PORCELAIN • Solidification outermost layer solidifies first contracts exerting large compressive forces inside. • Micro crack formation • Decrease mechanical properties due to crack propagation

15. THIS IS REMEDIED BY • 1.Introduction of residual compressive stresses • METHODS • Ion exchange or chemical tapering • Soda feldspathic porcelain article is kept immersed in molten KNO3 solution the smaller Na+ ions are exchanged by the large K+ ions • Introduces large residual compressive stress and increase tensile strengths.

17. Thermal tapering • Ceramic article is suddenly cooled, the outer surface solidifies first • Causes contraction, introducing residual compressive stresses • Thermal compatibility or mismatching thermal expansions • Choose ceramic compositions which have slightly different COTE introduce residual compressive stresses

18. 2.Interruption of crack propagations • METHODS • Dispersion strengthening: • Introducing very hard crystalline phases before fusing the porcelain • Eg: alumina core porcelain(90-95% alumina) • aluminous porcelain(40-50% alumina)

20. Transformation toughening • Partially stabilised zirconia is introduced into ceramics at higher temperatures • At lower temperatures it transforms into monoclinic phase with an increased volume • Interrupts crack propagation • 3.Design of the article • stress raisers are avoided

21. 1.Preliminaries • Record impression • Prepare refractory die • Adapt with a thin platinum foil of 1/40 mm • Suitable shades applied over it OUTLINE OF FABRICATION OF PORCELAIN ARTICLE

22. 2.Condensation • The porcelain particles are closely packed to reduce the volume shrinkage and minimize porosity in the fired porcelain and excess water is removed. • Methods • Spatulation • The article is carefully smoothened with a spatula • Extra water comes to the surface by capillary action is removed

23. Brush technic • Dry powder is sprinkled over the article • Carefully tap with brush. • The powder absorbs water from inside • Vibration method • Vibrate the article • Excess water coming out is removed • Ultrasonic method • The ultrasonic vibrations re transmitted electrically • Excess water is removed

24. 3.Firing procedure • Porcelain firing unit is preheated to 6500C. • Place article in a fire clay tray • Placed on the platform of the instrument • Held near the door of the muffled chamber for 5 minutes. • The article slowly dries up. • Article is held inside muffle chamber for 5 minutes • The remaining water comes out as steam • The door of muffled chamber is then closed. • 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.

26. STAGES OF FIRING • Low bisque stage/ low biscuit stage • 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. • If the firing is stopped, the particles form a porous mass. • This partially sintered material is used in glass infiltrated ceramics (INCERAMS)

27. 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 • Produce complete cohesion and maximum volume contraction. • If this heating is prolonged pyroplastic flow the article looses sharp corners and shape.

28. 4.Cooling of the fired article • Firing is discontinued at high bisque stage for complete melting • The muffle chamber is gradually cooled - minimise 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 • Then firing is started

29. 2.Firing under diffusible gases • Before firing, air in the muffled camber is replaced by highly diffusible gases like H2, He etc. • 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 let inside the evacuated muffle chamber and then controlled cooling is done

30. Methods to minimize volume shrinkage • The porcelain mix is again applied over the article andfired. This may require 3-4 time repetitions. • 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

31. 5.Glazing of fired porcelain article To remove surface cracks and improve flexure strengths 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

32. 6.Shading of ceramics • To get permanent shade and imitate check lines the shades, color fris or stains are applied before glazing. • Natural appearance

33. Biological • Excellent biocompatibility • Chemically inert 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

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

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

36. 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

37. 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

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

39. METAL CERAMIC BONDING • Technics • Mechanical: • The bonding surface of the cast material is made rough by using diamond and carbide burs. • Increases surface area • 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. • Mechanical interlocking . • Chemical • Bonds with oxygen of oxide layer on metal surface

40. ADVANTAGES OF METAL CERAMICS • Higher strength and durability • Higher fracture resistance • Adequate marginal fit • Permanent aesthetics • DISADVANTAGES • Flexure strains produced may fracture ceramics • Poor aesthetics • Darker margins near the gingiva • More healthy tooth material is to be removed • Expensive

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

42. 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.

43. REMEDIES • Selection of material & proper technics of manipulations • Minimal applications of specially tensile and shearing forces.

44. OUTLINE OF METAL CERAMIC FABRICATION • Tooth preparation • Obtain elastomeric impression is obtained • Prepare refractory material die. • Suitable metal coping is formed to fit the die exactly by: • Lost wax casting procedure • CAD-CAM technic • Electro deposition of gold or other metals • Burnishing metal foils on the die and then heat treating.

45. HN or N metal alloys electrodeposition of pure gold first and then flash electrodeposition of tin • 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 furnace at about 950-1300Cfsometime for degassing • Forms a thin atomic layer of oxides of tin , indium or iron chemical bonding with ceramics. • Apply opaque porcelain, dentin porcelain, gingival porcelain and enamel porcelain • Apply color frits • Glazing • Cementation-GIC(type 1) /zinc silicophosphate/resin cement

47. ALL CERAMICS PORCELAIN RESTORATION

48. Castable glasses • Injection moulding glass ceramic technic • Hot pressable glass ceramic SUB HEADINGS

49. DICOR • Used to fabricated inlays crowns and venners by lost wax casting procedure and then cerammed • Prepare wax pattern over die • Attach short sprues • Invest the pattern with die in special phosphate bonded investment material • Dewaxing • Casting • Finishing • Ceramming • Chamelion effect improves aesthetics CASTABLE GLASSES