Modeling materials

Impression materials Impression materials are used to make an accurate replica of the hard and soft tissues. The impression gives a negative reproduction of the tissues.

1.1 Definition What is the modeling materials? Model material is a material with which we can fill the impression , a positive cast is made that can be removed after the model material has set.

1.2 Classify of Gypsum products 1. Dental plaster 熟石膏 2. Dental stone 人造石 3. High-strength / low expansion dental stone 高强度/低膨胀人造石 4. High-strength /high expansion dental stone 高强度/高膨胀人造石

What is the Gypsum products? 生石膏 CaSO4. 2 H2O The dihydrate form of calcium sulfate ,called gypsum, is usually white to milky yellowwish in color and is found in a compact mass in nature. Deposits of gypsum, however, are found in most countries.

1. Dental plaster 熟石膏 2. Dental stone 人造石 3. High-strength dental stone These 3 types have identical chemical formulas of calcium sulfate hemihydrate,CaSO4.1/2 H2O, but they posses different physical properties, which makes each of them suitable for a different dental purpose.

2. Dental plaster 2.1 Manufacture dehydration by heat Gypsum Plaster CaSO4. 2 H2O CaSO4. 1/2 H2O+ 11/2H2O 110~120°C Gypsum Plaster

Manufacture of dental plaster, stone,and high-trength stone dehydration by heat or formulation Mineral other means Plaster Model plaster Gypsum Lab plaster Hydrocal Dental stone Densite High-strengt dental stone

2.2 Composition of plaster: 1) Calcium sulfate hemihydrate 75~85% 2) Gypsum (CaSO4.2H2O) 5~8% 3) Calcium Sulfate (CaSO4) 5~8% 4) A few of other materials 4%

2.3 Mechanism of Setting CaSO4.1/2 H2O+11/2H2O CaSO4.2H2O+3900cal/g.mol The reaction is exothermic, and whenever 1 g mol of CaSO4.1/2 H2O is reacted with 1.5 g mol of water, 1 g mol of CaSO4.2H2O is formed, and 3900 calories of heat are developed.

2.4 Properties 1) Control of Setting Time: Atmosphere (water), Temperature , Water/powder ratio, Rate of mixing, Time of mixing, Accelerator and retarder

2) Viscosity High-strength dental stones Impression plaster

3) Compressive strength 4) Surface hardness and abrasion resistance 5) Tensile strength 6) Reproduction of dental 7) Setting expansion

2.5 Manipulation Mixing : 1. Using a metal spatula with a stiff blade Using a hand-mechanical spatulator 1 minute / 2 revolutions per second 3. By a power-driven mechanical spatulator 20 seconds / low-speed drive

Pouring: vibration Separated: 45~60 minutes Disinfect the models: