Chapter 15 Gypsum Products
Terms in this set (41)
what material is used for making dental casts since 1756?
what are dental casts and dies used for?
replicas of the hard and soft tissues of the patient's oral cavity
an impression taken in the dental office is what?
when the impression is filled with gypsum and hardened it is what?
what are the hard replicas used for?
used to plan and track the progress of treatment
the mineral gypsum is a dihydrate of what?
how is gypsum turned into powder?
the dihydrate is heated, which causes it to lose water. it is then ground to produce a hemihydrate
what happens when the hemihydrate is mixed with water?
a product with a viscosity capable of flowing is produced
what happens after the chemical reaction is complete?
the hemihydrate is converted back to a dihydrate and is again a solid mass
what is the by-product of this chemical reaction?
heat, making it an exothermic reaction
what is formed when the heating process occurs at a temperature of 115 degrees Celsius?
the resulting hemihydrate is porous and irregular in shape forming model plaster
what is model plaster used for?
diagnostic casts, study models
what is formed when the heating process is done under pressure and a higher temperature?
uniformly shaped and less porous form of hemihydrate forming a dental stone
what is dental stone used for?
working casts, master casts
what is formed when there is a further increase in pressure and further refining of the powder by grinding?
high-strength or die stone
what are gypsum products manufactured as?
plaster, stone, high strength stone, and gypsum bonded investment
what happens when particles of powder are large, irregular, and porous?
the final product is weaker and less resistant to abrasion
what type of casts are placed under little stress and are usually produced from less expensive materials such as plaster or stone?
what type of materials have lower properties of strength and abrasion resistance?
plaster and stone
what type of casts require greater properties of strength and abrasion resistance?
working casts and dies
what two factors contribute to the strength and abrasion resistance of a final product?
shape of the particles and porosity
the strength of gypsum products is related to what?
the amount of water used in producing the study or working cast
the more water that is used...
the weaker the cast will be
a product with less water has what?
a higher density of crystals and is a denser and stronger product
plaster particle are what?
porous and irregular, requiring more water to mix
what material has the highest amount of expansion?
what material has the lowest amount of expansion?
high strength stones
what is setting expansion?
a result of the growth of crystals as they join, it is critical for accurate models and dies
expansion should be held to a...
when does setting expansion occur?
during hardening of gypsum products
what happens when a final gypsum product has great porosity?
less surface detail is produced
what impression materials form the best surface detail with gypsum products?
silicone and polyether impressions
set gypsum products are...
not highly soluble in water
what is solubility directly related to?
the porosity of the material
is plaster or stone more soluble?
plaster is more soluble than stone
what type of material would be used as a final impression wash for edentulous arches?
impression plaster, type 1
what type of material would be used for diagnostic casts and articulation of stone casts?
model plaster, type 2
what is the least expensive of all the gypsum products?
what type of material is ideal for making full or partial denture models, orthodontic models, and casts requiring high strength and abrasive resistance?
dental stone, type 3, yellow or white in color
dental stone is approximately how much stronger than plaster?
2.5 times stronger
what type of material is used for fabricating wax patterns of cast restorations?
dental stone, high strength, type 4, pink or green in color