cast and die gypsum products dental material
DESCRIPTION
cast and die dental materialTRANSCRIPT
Cast = Model
Die = Metal cast or cast for single tooth
CAST AND DIE MATERIALS
Relationship of impression to cast Cast is the opposite for impression and vice
versa
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
Types of model and die Materials
Non-Metallic
1.1. Gypsum products Gypsum products model and diesmodel and dies
2.2. Investment model Investment model and diesand dies
3.3. Resin diesResin dies4.4. Flexible diesFlexible dies5. Cement dies6. Ceramic dies
Metallic
1. Electroplated diesElectroplated dies2. Low-fusing metal dies3. Amalgam dies
Non-metallic Cast & Die Materials
I. Gypsum Products
Gypsum (CaSo4.2H2O)
CalcinationHeating the (CaSo4.2H2Oo) at
115oC in open kettle
AutoclavingHeating the (CaSo4.2H2O) at
125oC with steam under pressure
BoilingBoiling the (CaSo4.2H2O) in 30%
CaCl2
- 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
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 0C in
open kettle
Autoclaving Of Ca So4.2H2 O at 125 0C
Boiling Of Ca So4.2H2 O in 30 % Cacl2
Particles - Ca So4. ½ H2O
- Irregular - Non homogenous- Porous
- Ca So4. ½ H2O More -
Regular- More homogenous- Less Porous
- Ca So4. ½ H2O
- 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
Compressive 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 cast2. Mounting of Casts on the articulator3. In flasking
1.As 2ry cast (Working Cast) in Complete Denture work2.In flasking
1.As working wast for crown & bridge work
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;
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 growth4. 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)
Ca So4. ½ H2O + 2 H2O Ca So4. 2 H2O + Heat
Nuclei of crystalization
Crystal growth Intermeshing
Steps of gypsum setting process
Gypsum products(Setting reaction. Cont.d.)
Controlling the setting reaction (i.e. Setting time):
Role of the manufacturer1. Particle size2. Additives (Accelerators and retarders)
Role of the operator 1. Liquid / Powder ratio2. Mixing rate3. Mix temperature
Gypsum products
SETTING EXPANSION: - Mechanism of setting expansion1. 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 expansion1. Liquid / powder ratio2. Mixing rate3. Additives (Anti-expansion agents)
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).
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
Gypsum products(properties. Cont.d)
5. Practicability
- Easy manipulated- Inexpensive- Long shelf life if stored in dry conditions
Non-metallic Cast & Die materials
2. Resin die Materials
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
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
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
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