Seminar 1
Basic dental materials
Gypsum – properties and mixing
Carving: the upper incisor of the gypsum block
Teeth identification
Basic dental materials
• Main
Preventive materials
Resine composite restorative materiels
Amalgam
Cements
Noble dental alloys
Cast base-metal alloys
Ceramics (ceramic-metal systems)
Polymers for prothesis
Basic dental materials
• Auxiliary
Gypsum
Waxes
Impression materials
Grinding and Polishing Materials
Gypsum
• Main source: gypsum rock
• Dihydrate of calcium sulfate
(CaSO4). 2 H2O
Gypsum
• Dihydrate of calcium sulfate
(CaSO4). 2 H2O
Heating
• Calcium sulfate hemihydrate
(CaSO4). H2O
Gypsum
• Calcium sulfate hemihydrate
(CaSO4). H2O
Water
Calcium sulfate dihydrate
• (CaSO4). 2 H2O
Gypsum
• Exothermic reaction :
• 1,5 g mol water …….1 g mol of calcium
sulfate dihydrate …… 3900 calories of
heat
Gypsum
• Die material – model
• Impression material
• Binder material in casting investment
Gypsum
Three types of base raw materials derived
from partial dehydratation of gypsum rock
Plaster (Fluffy, soft)
Hydrocal (higher density, more crystalline)
Densite (the densist material)
Gypsum
Plaster (Fluffy, soft)
Hydrocal (higher density, more crystalline)
Densite (the densist material)
The same chemical bases, different physical
properties
Gypsum
Plaster (Fluffy, soft)
Gypsum mineral heated in an open kettle at
a temperature 110°C – 120°C
β– calcium sulfate hemihydrate
Lab plasters, formulating models
Gypsum
Hydrocal (higher density, more crystalline)
Gypsum mineral dehydrated under pressure
and in presence of water vapour at 125°C
α − calcium sulfate hemihydrate
Low-moderate dental stones
Gypsum
Densite (the densist material)
Gypsum rock is boiled in a 30% calcium
chloride solution after that the chloride is
washed with hot water and the material is
ground – powder.
Gypsum
Modifying chemicals
(handling characteristic, properties)
Potassium sulfate (K2SO4), terra alba: accelerators
Sodium chloride – shortens setting reaction,
increases expansion
Sodium citrate – retarder
Borax both retarder and accelerator
Calcium oxide, gum arabic- reduces the amount of water
necessary to mix gypsum products.
Gypsum
Water/powder ratio
100g of powder:
Model plaster 37 - 50
Dental stone 28 - 32
High strength dental stone 19 – 24
Expansion during setting
Spatulation
Gypsum
• Water
• Powder untill it sucks (draws) water
• Spatulate – paste, mash
• Put into the form – check setting