Week 2 Ch 6: Gypsum and Wax Products

gypsum

mainly used for making positive reproductions or replicas of oral structures; mineral found in nature in various parts around the world known as calcium sulfate dihydrate

casts

hard replicas of hard and soft tissue of the patient’s oral cavity made from gypsum products; often referred to as models

diagnostic casts

generally made from dental plaster or stone and used for patient education, tx planning and tracking the progress of tx

working casts

casts generally made from one of the dental stones that are strong enough to resist the stresses of fabricating an indirect restoration or prosthesis

dies

replicas of prepared teeth that are generally removable from the working cast

plaster

contains the most excess water; produces bigger and more numerous air voids

die stone

contains least excess water; produces fewer, small air voids

shape of particles, porosity

what are 2 factors that contribute to the strength and abrasion resistance of the final product?

plaster - 0.30%

what expands the most?

high strength stone - 0.10%

what expands the least?

silicone, polyether

what forms the best surface detail with gypsum products?

solubility

set gypsum products are not highly soluble in water; more porous the gypsum the more soluble the material is

plaster - type 1

rarely used; if used, it is used as a final impression for edentulous arches

model plaster - type 2

white in colour; powder consists of porous, irregular particles; used where strength is not a critical requirement; used to secure casts to the articulator or preliminary casts; least costly

dental stone - type 3

made by carefully controlled calcination under steam pressure in a closed container and a higher temperature; material more uniformed in shape and less porous; stone is stronger and more expensive than plaster; ideal for making casts for complete and partial denture and orthodontic models; yellow or white in colour

high strength - type 4

material is very dense and cuboidal in shape; die stone, densite; used for making casts or dies for inlay and crowns; pink or green in colour

expansion - type 5

most costly of all gypsum products; commonly used in die materials - materials very hard but they are susceptible to abrasion during carving of wax patterns; blue or green in colour

manipulation

water aids in wetting and helps the material flow; powder is sifted into the water to help prevent clumps forming; water evaporates as the gypsum product sets

1 minute

when does working time begin?

8-10 minutes

when does initial set occur?

45-60 minutes

when is final setting time?

anatomic portion

replicates the hard and soft structures - poured by vibrating small increments of flowable gypsum into the impression

art portion (base)

aids in handling and articulating the cast

casting wax

used for the construction of metal framework of partial and complete dentures; not softened in oral cavity

baseplate wax

used to produce the form on which denture teeth are set; wax must not distort at mouth temperatures

corrective impression

used in addition with other impression materials in the process of taking impressions on edentulous clients; flows at mouth temperatures

bite registration wax

used to produce wax bite registration for articulation of models; susceptible to distortion at temperatures higher than the mouth temperatures; horseshoe shaped