Gypsum Flashcards
What is Gypsum material used for?
model/ die material
What properties does gypsum have?
dimensional accuracy
fluid when poured
good wetting
compatible with all materials
What products are used for models/dies?
dental plaster
dental stone
densite
What has highest porosity and particle size?
plaster
How is gypsum used to make plaster?
heated at 120 degrees
How is gypsum used to make densite?
boiled in calcium chloride
How is gypsum used to make dental stone?
steam pressured
What are the stages of setting re. gypsum?
1st stage: water becomes saturated with hemihydrate 0.8% sol
2nd stage: conversion of hemihydrate to dehydrate
3rd stage: dihydrate crystalises out
What is setting accompanied by?
increased viscosity
exothermic- up to 30 degrees
expansion
What is a retarder of gypsum setting?
Borax
What is an accelerator of gypsum setting?
K2So4
What is colour code re. dyes?
white: plaster
yellow: stone
blue/pink: die stone
