Metal free Castable Glass ceramics- Dicor.pptx

DICOR GLASS CERAMIC IS A CASTABLE CERAMIC

1. Glass ceramics dicor 2 nd year theory

2. Poly crystalline materials Lost wax technique Castable ceramics Partially crystallized glass Both crystalline and amorphous materials

3. Fabrication in the vitreous state Converted into a ceramic –by controlled crystallization using nucleating agents during heat treatment

4. Classification

5. Dicor First commercially available glass ceramic Corning glass works NY Castable polycrystalline flourine containing tetrasilicic mica glass ceramic material –initially cast as a glass by lost wax technique and then subsequently heat treated –controlled crystallization to produce a glass ceramic material

6. Supplied as Dicor castable ceramic Special Dicor casting crucible 4.1 gm dicor ingot Dicor shading porcelain kit

7. Fabrication of castable ceramics Casting – Glass liquefies at 1370 degree-lost wax, centrifugal casting technique Wax pattern – made on a die Castable ceramic investment Double line casting ring Burnout 900 degree celcius 30 min

8. Glass ingots – castable ceramic material Zirconia crucible Centrifugally cast in electronically controlled DICOR CASTING MACHINE

9. Transparent glass casting amorphous and fragile. After cooling, it is divested, sandblasted (25um Al2O3 particles at 40 psi) and carefully separated from the sprue .  Ceramming : The cast glass material is subject to a single-step heat treatment called as ' Ceramming ' to produce controlled crystallization by internal nucleation and crystal growth of microscopic plate like mica crystals within the glass matrix.

10. This procedure gives glass-ceramic the special physical and mechanical properties of DICOR. Method : The transparent fragile casting is embedded in castable ceramic embedment material (Gypsum-based) and placed in a Ceramming tray in the DICOR Ceramming Furnace.

11. Ceramming cycle 1 1/2hours and sustained upto 6 hours. The cerammed glass-ceramic casting is achromatic and appears as a whitish opaque semi-crystalline material; hence external colourants are required to develop the required shade ( by veneering self - glazing, pre-mixed DICOR shading porcelain provided by the manufacturer). 

12. ceramic process is adjusted so that the cast glass ceramic is composed of: Tetrasilic flouromica crystals (crystalline) - 55% by volume . Glass matrix (non-crystalline) - 45% by volume. The microstructure after ceramming consists of multiple interlocking small plate-like crystals of tetrasilicic flouromica (K2 Mg5 -Si4 O10 F2 ) approximately 1 µm thick and 5- 6mm in diameter

13. CRYSTAL FUNCTIONS Improved strength Interlocking of mica crystals – resistance to fracture Improved esthetics Reduced abrasive property

14. Chameleon effect of dicor Transparent crystals scatter the incoming light Disbursed and spread over the entire glass ceramic Enhances the esthetic properties

15. Advantages of dicor Chemical and physical uniformity Excellent marginal adaptation Compatibility with lost wax casting process Ease of adjust ment

16. Disadvantages Expensive equipments like DICOR casting machine

17. Two ceramic products   Dicor plus ( Dentsply , Trubyte division) : Consists of a cast cerammed core ( Dicor substrate) and shaded feldspathic porcelain veneer. However , as Dicor plus is a feldspathic porcelain that contains leucite , the abrasiveness is expected to be similar to other feldspathic porcelains. Willis Glass : Consists of a Dicor cast cerammed core and a Vitadur -N porcelain veneer similar in nature to that used for Dicor

18. Castable apatite glass CERAMIC Castable apatite ceramic is classified as CaO-P2 O5 - MgO - SiO glass ceramic. 1985 - Sumiya Hobo & Iwata developed a castable apatite glass-ceramic which was commercially available as Cera Pearl (Kyocera Bioceram , Japan)

19. Cerapearl   Contains a glass powder distributed in a vitreous or non-crystalline state. Composition : Approximately (By weight)  Calcium oxide ( CaO ) -45%  Phosphorus Pentoxide (P2 O5 ) -15% Aids in glass formation  Magnesium oxide ( MgO ) -5% Decreases the viscosity ( antiflux )  Silicon dioxide (SiO2 ) -35% Forms the glass matrix.  Other -

20. Trace elements Nucleating agents(during ceramming ). Chemistry : Apatite glass-ceramic melts (1460°C) and flows like molten glass and when cast (1510°C) it has an amorphous microstructure.

21. Apatite glass ceramic molten glass CaPO4 (CaO-P2O5 -MgO-SiO2) (Amorphous) The amorphous CaPO4 formed after melting and casting changes into a crystalline oxyapatite on heat treatment ( ceramming ) at 870°C for 1 hour.

22. The chemically unstable oxyapatite when exposed to moisture (water) further converts to crystalline hydroxyapatite (HA crystals). CaPO4 Oxyapatite Hydroxyapatite (Amorphous) (Crystalline) (Crystalline) Ca10 (PO4 )8 20H Strength is dependent on these crystals and the bond between the 1460°C melting 1510o C casting 1460°C Ceramming

23. Other physical properties Coefficient of thermal expansion : 11.0 x 10-6 /°C  Young's Modulus : 103Gpa  Casting Shrinkage : 0.53%  Flexural strength similar to Dicor  Biologic properties : Dense material, Chemically stable, pH similar to natural enamel, Non toxic/ biocompatible

24. Fabrication Casting : The   wax pattern of the proposed restoration is invested in phosphate-bonded high heat investment developed exclusively for this system (CTE to match Cera Pearl's casting shrinkage of 0.53 %). Following burnout, the investment is transferred to an automatic casting machine designed especially for this system.

25. The Cera Pearl crystals (8-10gms) are placed in the ceramic crucible, melted under vacuum (at 1460o C) and cast (at 1510o C) into the mold. Annealing is done one hour after the casting in an automatic furnace to release the inner stresses of the cast structure. The investment material around the cast structure is removed by sandblasting (25-30um Al2 O3 beads) and ultrasonically cleaned. The annealed casting is reinvested (CP crystal mold, Kyocera Corp.) for ceramming .

26. C eramming oven is preheated at 750°C for 15 minutes. After the cast glass ceramic is place in the oven the temperature is raised at the rate 50o C/min until it reaches 870°C and held for 1 hour.  

27. After crystallization, the casting is dis-invested, and cleaned by sandblasting (201µm Al2 O3 powder). It appears white in comparison with natural enamel and requires the application of an external stain. Eg , Cerastain ( Bioceram ), which consists of B2 O3 -SiO2 -Al2 03 -K2 O glass, traces of various metal oxides

28. Desirable characteristics of apatite ceramics Cerapearl is similar to natural enamel in composition, density, refractive index, thermal conductivity, coefficient of thermal expansion and hardness. Similarity in hardness prevents wear of opposing enamel. Bonding to tooth structure - Glass ionomer cements adhere to tooth structure (dentin and enamel) primarily bonding to the apatite component, and thus should also bond to the apatite phase within the glass-ceramic.

29. To enhance this possibility, Cerapearl surface is activated by air abrading (to provide mechanical interlocking effect) or treatment with activator solution (etching of with 2N 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

30. Advantages of castable 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 . Accurate form for occlusion, proximal contacts, and marginal adaptation . Uniformity and purity of the material . Favorable soft tissue response. X-ray density allowing examination by radiograph www.indiandentalacademy.com

31. Advantages of cast glass ceramics over metal ceramics The component chemical compounds are standardized, eliminating any inaccuracies, The forming procedures can be quality controlled. Superior compressive strength because of its semi- crystalline form and is also a machinable material Crack propagation's are interrupted by the crystalline structure. Utilized conventional lost-wax technique similar to casting alloys. Hence , casting and finishing can be easily done.

32. Colour control , optical effects allow predictable and esthetic results.  Cast glass ceramics are thermal resistant.  Bacterial plaque adherence on the surface is inhibited, thus maintaining the tissues surrounding the restoration.    Radiolucency allows  for a dimension of depth in the observation of marginal integrity.  Wear rate values are similar to that of human enamel.