Chapter 18: Dental Laboratory Materials Part I

rigid impression materials

used where no teeth are present, and material flexibility is unnecessary

impression plaster

gypsum product, 60cc of water to 100 grams of plaster

metallic oxide paste

two-paste system, zinc-oxide eugenol base with resin accelerator. This paste hardens through chemical reaction

impression compound

supplied in cakes and sticks; color-coded for temperature flexibility; used to make a preliminary impression tray

plastic impression materials

used with or without the presence of teeth

thermoplastic

material softens when heated and hardens when cooled

compound

supplied in sheets or stick form. The material is composed of a thermoplastic resin base with filers and plasticizers. It softens when heated and returns to solid when cool; used in copper bands for independent crown preps

wax

used for registration of bites or for impression of a single tooth

elastic impression materials

used where teeth are present and material must be flexible for removal from the oral cavity or teeth. Elastic impression materials are either reversible or irreversiblehydrocolloids

reversible hydrocolloid

impression material that can change repeatedly from gel to solid states depending on the thermal condition of the substance

gel state

material is soft and pliable

solid state

material has "set" or is rigid enough to hold the form

irreversible hydrocolloid

agar impression that can be changed from gel to solid state as a result of a chemical reaction, and remain in that condition after mixing and using

elastometric impression materials

used to make impressions of preparations and for demanding or accurate reproductions.

extruded gun

a device that contains two independent materials to be forced mixed and dispensed into a common tip as one material

polysulfide

impression substance available in light, regular, or heavy-bodied; aka mercapatan, this material will harden or set by means of chemical action

silicone

first supplied as a base putty with liquid accelerator drops and termed condensation or conventional silicone type or later as a two-paste system known as addition silicone type

polyether

supplied in regular viscosity, with a thinner modifier for reduced thickness

vinyl polysuloxane

impression material supplied in tubes, putty, paste-to-paste system, and cartridge styles

calcination

preparation of gypsum products

Type I plaster- impression

used to take impression but not popular because of its weakness and replacement by better impression materials

Type II- model

aka plaster of Paris, used mostly for impression and study models. Prepared by dehydrating calcium sulfate at atmospheric pressure to beta-hemihydrate form

Type III- dental stone

white or buff colored, Class I stone, used for orthodontic, diagnostic, and working casts. Prepared by dehydrating gypsum under pressure for alpha-hemihydrate form

Type IV- improved or die stone

stronger Class II stone used for dental does and casts. It is dehydrated in a solution of calcium chloride to obtain a modified alpha-hemihydrate form; aka densite

Type V- casting investment

gypsum-bonded material that can withstabd extreme heat; used for casts of a prosthesis

model and cast

used for a positive reproduction of the mouth and oral conditions

die

reproduction of prepared tooth; usually Class II stone poured into an impression of the preparation

electroplated

thin metal covering through electrolysis

inlay wax

hand wax; blue, purple, green, ivory colors; available in 3-4 inch sticks. Type I is for direct oral use; Type II is for laboratory or indirect use for inlay, crown, and casting patterns.

baseplate wax

supplied in 3 x 6 inch sheets, pink in color and soft, medium, or hard; used for denture construction, bite registration, and prosthesis construction

casting wax

available in square sheets of various thicknesses; colors denote its softening point; used for construction of patterns for cast partial dentures

boxing wax

supplied in 1-1/2 x 12x 1/8-inch strips; used to box or wrap around an impression prior to pouring. The strips hold the plaster or stone in place to form the art base of a study model.

occlusal bite blocks

wax blocks in arch shape; used to set in teeth to be used for denture constructions. They are laboratory made by folding boxing wax and shaping, or they can be purchased remade, which saves time and is more consistent

bite wafer wax

used to check occlusion relationships; supplied in a preformed bite shape with a foil center to prevent bite through

orthodontic wax

soft, white stick wax used in orthodontics; used to line borders of impression trays

wax round wire

supplied on reels in various gauges; used to make lingual bars, sprues, and metal framework space.

utility wax

soft, adhesive wax, supplied in stick or sheet; used to mount casts and to adapt or modify impression tray edges; also called rope wax

sticky wax

hard, brittle was stick that is melted to hold dental units together

preformed wax pontic shapes

eliminates wax buildup process; supplied in various shapes and sizes of teeth

disclosing wax

also known as pressure indicator paste; painted on an appliance, inserted into the mouth, and pressure applied to indicate high, sore, or tender areas; may be used to repair wax pattern voids

miscellaneous waxes

assorted color-coded waxes with particular fine-turning properties, such as margins, sculpturing, blocking out, and dipping.

polymerization

the chemical union of the monomer and polymer substances

filler

inert substance added to the polymer to alter or modify the polymer properties

initiator

agent capable of starting polymerization process; may be light, heat, radiation, or chemicals

activator

reacts with initiator to start polymerization

inhibitor

substance that prevents polymerization; maintains storage life