cast and die Gypsum Products dental material

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cast and die dental material

cast and die dental material

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  • 1. Cast = Model Die = Metal cast or cast for single tooth CAST AND DIE MATERIALS
  • 2. Relationship of impression to cast Cast is the opposite for impression and vice versa
  • 3. Ideal Requirements of Model and Die Materials 1. Sufficient mechanical properties (Impact strength, Hardness and tensile strength) 2. Dimensionally stable 3. Compatible with impression materials 4. Colored 5. Easy manipulated
  • 4. Types of model and die Materials Non-Metallic 1.1. Gypsum productsGypsum products model and diesmodel and dies 2.2. Investment modelInvestment model and diesand dies 3.3. Resin diesResin dies 4.4. Flexible diesFlexible dies 5. Cement dies 6. Ceramic dies Metallic 1. Electroplated diesElectroplated dies 2. Low-fusing metal dies 3. Amalgam dies
  • 5. Non-metallic Cast & Die Materials I. Gypsum Products
  • 6. Gypsum (CaSo4.2H2O) Calcination Heating the (CaSo4.2H2Oo) at 115o C in open kettle Autoclaving Heating the (CaSo4.2H2O) at 125o C with steam under pressure Boiling Boiling the (CaSo4.2H2O) in 30% CaCl2 β - Ca So4. ½ H2O α - Ca So4. ½ H2O α - Ca So4. ½ H2O Dehydration Type I gypsum (Impression plaster) Type II gypsum (Model plaster) Type IV gypsum (Extra hard stone) Type III gypsum (Hard stone) Clinical material Type V gypsum (Extra hard- high expansion stone) Laboratory materials
  • 7. Difference Model plaster Hard stone Extra hard stone Source Ca So4 .2H2 O Ca So4 .2H2 O Ca So4 .2H2 O Manufact- uring Heating Of Ca So4 .2H2 O at 115 0 C in open kettle Autoclaving Of Ca So4 .2H2 O at 125 0 C Boiling Of Ca So4 .2H2 O in 30 % Cacl2 Particles β - Ca So4 . ½ H2 O - Irregular - Non homogenous - Porous α - Ca So4 . ½ H2 O More - Regular - More homogenous - Less Porous α - Ca So4 . ½ H2 O - The most regular - The most homogenous - The least porous P/L ratio 100 gm / 50-60 ml 100 gm /35-40 ml 100 gm / 25-30 ml Excess water The largest amount Less amount The least amount Compressiv e strength The weakest More strong The strongest Tensile strength The weakest More strong The strongest Surface hardness The Least hard More hard The hardest Setting expansion 0.30% (The highest) 0.20% 0.10% (The lowest) Setting time 15 Min 15-45 Min 15 Min Uses 1. As 1ry cast 2. Mounting of Casts on 1.As 2ry cast (Working Cast) in Complete 1.As working wast for crown & bridge work
  • 8. Gypsum products SETTING REACTION: - After mixing of Ca So4.1/2 H2O powder with water - A Chemical reaction named crystallization will start during which Ca So4.1/2 H2O changes into intermeshed Ca So4.2 H2O through a series of steps as follows;
  • 9. Gypsum products (Setting reaction. Cont.d.) 1. Solubility of hemihydrate in water to form a saturated solution of dihydrate 2. Precipitation of minute dihydrate crystals (Nuclei of crystallization) 3. Crystal growth 4. Intermeshing of the growing crystals to form the set hard mass This reaction is associated with; - Heat generation (exothermic reaction) and - Dimensional changes (setting expansion)
  • 10. Ca So4. ½ H2O + 2 H2O → Ca So4. 2 H2O + ↑ Heat Nuclei of crystalization Crystal growth Intermeshing Steps of gypsum setting process
  • 11. Gypsum products (Setting reaction. Cont.d.) Controlling the setting reaction (i.e. Setting time): Role of the manufacturer 1. Particle size 2. Additives (Accelerators and retarders) Role of the operator 1. Liquid / Powder ratio 2. Mixing rate 3. Mix temperature
  • 12. Gypsum products SETTING EXPANSION: - Mechanism of setting expansion 1. Interaction between the growing crystals will result in formation of stresses 2. Release of these stresses will lead to outward thrusting of the crystals, increasing the distances in between, that permit further growth until inter-meshing occurs - Controlling the setting expansion 1. Liquid / powder ratio 2. Mixing rate 3. Additives (Anti-expansion agents)
  • 13. Gypsum products PROPERTIES: 1. Biologically - Wear gloves to avoid skin irritation 2. Interfacially - Separating medium is required if the impression is made of impression plaster - Precautions are required with hydrocolloids (Water content) and condensation polymerized rubber impressions (By-products).
  • 14. Gypsum products (properties. Cont.d) 3. Mechanically - Acceptable compressive and tensile strength (N.B. Stone > Plaster) - Low values of surface hardness 4. Chemically - Degree of setting expansion (Plaster > Stone > extra hard stone,however High exp stone > extra hard stone) - Surface of gypsum could erode by using chemical disinfectants
  • 15. Gypsum products (properties. Cont.d) 5. Practicability - Easy manipulated - Inexpensive - Long shelf life if stored in dry conditions
  • 16. Non-metallic Cast & Die materials 2. Resin die Materials
  • 17. Resin cast & Die Materials A. PMMA was an early type, but higher rate of its polymerization shrinkage is a limiting factor B. EPOXY RESIN DIES  Tougher and more abrasion resistant than extra-hard stone, but less accurate and less stable dimensionally  Used safely with polysulfide (separating medium is required), addition silicone and polyether rubber impression materials
  • 18. Epoxy resin dies Composition: (Two component system) 1. Resin monomer: Viscous material 2. Hardener: Polyamine (toxic and irritant, should not come in contact with skin) Reaction: - Chemical named Polymerization during which; the polyamine causes the resin molecules to link together into very large networks of molecules
  • 19. Characters of Epoxy resin C&D Material - Working time: 15 min, the mix becomes thicker and gradually get hard - Setting time: Several hours (1-12 hours) - Setting shrinkage: 0.03-0.3% and may continue for 3 days after mixing - Porosity: are liable to be formed as a result of the viscosity of mixed material. So, both 1. The use of Centrifuging during impression pouring… and 2. Using of Automixing system help in minimizing the porosity
  • 20. THANK YOU