Chapter 18: Dental Laboratory Materials

Rigid impression materials

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

The assorted types of rigid impression materials are

• Impression plaster

• Metallic oxide paste

• Impression compound

Impression plaster

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

Metallic oxide paste

Two-paste system, zinc-oxide eugenol (ZOE) base with resin accelerator. This paste hardens through chemical reaction

ZOE stands for

Zinc oxide eugenol

Plastic impression materials

Used with or without the presence of teeth. This movable material is employed where some material flexibility is needed for the impression.

The three types of plastic impression materials are

• Thermoplastic

• Compound

• Wax

Thermoplastic

Material that 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 a solid when cool; used in copper bands for independent crown preps.

Wax

Used for registration of bites or for impression of a single tooth area

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 irreversible hydrocolloids

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 material 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.

Elastomeric impression materials

Used to make impressions of preparations and for demanding or accurate reproductions. Composed of a base and an accelator, or catalyst and can be measured, mixed, and placed in a tray or syringe for use in the mouth. Material may be hand mixed or placed in a extruder gun.

Catalyst

Substance that speeds up the chemical reaction

Extruder gun

Device that contains two independent materials to be forced mixed and dispensed into a common tip as one material, thus eliminating measuring, mixing, and cleanup time.

Polysulfide

Also known as mercaptan, rubber-based impression material. Hardens or sets by the means of chemical action.

Silicone

Putty base with a liquid accelerator or as a two paste system

Polyether

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

Modifier

Substance used to change the condition of a material

Vinyl polysiloxane

Impression material supplied in tubes, putty, paste to paste system, and cartridge styles. May be heavy, medium, or wash viscosity; impressions may be poured more than once. Stable material. Some may have bubble gum flavoring.

Calcination

Preparation of gypsum products

Gypsum: Type I plaster - impression

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

Gypsum: Type II - model

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

Gypsum: 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.

Gypsum: Type IV - improved or die stone

Stronger Class II stone used for dental dies and casts. It is dehydrated in a solution of calcium chloride to obtain a modified alpha-hemihydrate form; also known as densite.

Gypsum: Type V - casting investment

Gypsum-bonded material that can withstand extreme heat; used for casts of a prosthesis.

Model and cast

Used for a positive reproduction of the mouth and oral conditions. The gypsum model, called a diagnostic cast or study model, consists of an art portion (base) and an anatomical (tooth) portion.

Die

Reproduction of prepared tooth; usually Class II stone poured into an impression of the preparation. Can be electroplated with copper, silver, amalgam, or low fusing metals for a stronger surface and working area.

Electroplated

Thin metal covering through electrolysis

Inlay wax

Hard wax; blue, purple, green, or 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 12 X 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 premade, which saves time and is more consistent.

Bite wafer wax

Used to check occlusion relationships; supplied in a pre-formed 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 trays edges; also called rope wax.

Sticky wax

Hard, brittle wax 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.

Acrylics

Synthetic resin material used in fabrication of appliances

Monomer

small molecules that bond together to form polymers, which are used in dental materials

Polymer

Used in appliances, like the base

Polymerization

Also known as curing,

Filler

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

Inert

Not active, chemically

Initiator

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

Activator

Reacts with initiator to start polymerization

Plasticizer

Substance that causes a softening effect; changes hard, brittle resin into a flexible, tough material

Inhibitor

Substance that prevents polymerization that mantains storage life

Composite

Polymer matrix bonded to glass particles; used for dental restorations

Self-curing resins

Autopolymerization materials that perform the uniting process by means of a chemical Union; the activator is present in the polymer powder or base and does not have to be added

Heat-cured resins

Acrylic materials are united but need outside heat to set up; not as popular as self-cured but less likely to present bubbles or voids when processed correctly

Alloy

A mixture of metals

Combination of two metals

Binary

Combination of three metals

Ternary

Combination of four metals

Quaternary

Combination of five metals

Quinary

Tempered

made hard or flexible or resilient especially by heat treatment

Annealed

Purification by placement into flame; heated in flame until red

Gold casting alloy: Type I (Consistency & Use)

Consistency: Soft

Use: Used for simple, nonstress surface, inlays

Gold casting alloy: Type II (Consistency & Use)

Consistency: Medium

Use: Preferred in stress-bearing inlays or onlays

Gold casting alloy: Type III (Consistency & Use)

Consistency: Hard

Use: Used in crowns and short-span bridgework

Gold casting alloy: Type IV (Consistency & Use)

Consistency: Extra-hard

Use: Preferred for partial denture frames, saddles, and clasps

Type III is the most

Commonly used noble alloy.

The basic combination for Type III alloy is

• 75% gold

• 10% silver

• 10% copper

• 3% palladium

• 2% zinc

75% gold

Resists tarnish/corrosion, nontoxic, hypoallergenic, docile, malleable, low melting point, and burnishes (smooths out) well

10% silver

Lessens the red cast from copper and gold, increases ductility and malleability; gives strength to the alloy

10% copper

Hardens in heat and high temperature; adds flowability

3% palladium

Increases hardness, whitens gold, and prevents tarnish and corrosion.

2% zinc

Prevents porosity of surface areas, and provides smoothness

Slurry

Thin, watery mixture; plaster in the mix speeds up the set

Aluminum oxide (Supplied As, Agent, & Use)

Supplied As: mounted stone, slurry

Agent: abrasive/polish

Use: acrylic resin

Carborundum (Supplied As, Agent, & Use)

Supplied As: stones, points, disc

Agent: abrasive

Use: metal, resin, tooth

Chalk (Supplied As, Agent, & Use)

Supplied As: soft powder

Agent: polishing

Use: gold, resins

Chromium oxide (Supplied As, Agent, & Use)

Supplied As: powder

Agent: polishing

Use: stainless steel

Cuttle (Supplied As, Agent, & Use)

Supplied As: powder of fish shell

Agent: abrasive

Use: gold alloys

Diamond (Supplied As, Agent, & Use)

Supplied As: various size particles

Agent: abrasive

Use: tooth structure

Emery (Supplied As, Agent, & Use)

Supplied As: particle or luted to cloth

Agent: abrasive

Use: trim acrylic

Garnet (Supplied As, Agent, & Use)

Supplied As: stone, points

Agent: abrasive

Use: resin, composite

Pumice (Supplied As, Agent, & Use)

Supplied As: powder, slurry

Agent: abrasive

Use: metal, enamel, resin

Quartz (Supplied As, Agent, & Use)

Supplied As: grits, luted to paper, discs

Agent: abrasive

Use: general use

Rogue (Supplied As, Agent, & Use)

Supplied As: powder, brick

Agent: polishing

Use: gold, denture resin

Tin oxide (Supplied As, Agent, & Use)

Supplied As: powder, slurry

Agent: polishing

Use: metals

Tripoli (Supplied As, Agent, & Use)

Supplied as: stone, brick

Agent: polishing

Use: gold alloy

Zirconium silicate (Supplied As, Agent, & Use)

Supplied As: powder

Agent: polishing

Use: enamel

Polycarboxylate

Permanent cementation for crowns, inlays, onlays, and bridges

Use of zinc phosphate

Permanent luting of casting, orthodontic appliances. Type II is used as a base.

Use of ZOE

Temporary luting for castings, pulp capping, cavity liner, periodontal dressing, temporary restoration, insulating base, and wash.

Use of ZOE and EBA (orthoethoxybenzoic acid)

Type II permanent cement for inlays, onlays, crowns, and bridges.

Use of polycarboxylate

Luting for castings, stainless steel crowns, orthodontic cement.

Use of silicophosphate

Luting for orthodontic appliances.

Use of resin (light & self-cured), ESPE

Luting for castings, porcelain restorations, Maryland bridge.

Use of glass ionomer

Type U cementation of metal castings, direct bond Ortho bands, and core buildup. Type II is for anterior restorative.

Bonding

Force of the Union of one substance with another substance

Coefficient of thermal expansion

Amount of form change that takes place in a dental material and tooth during heat exposure in the oral cavity