Transcript

Impression Materials

Chapter 8DAE/DHE 203

Impression Materials:

Used to make replicas of oral structures “Negative” replica made by impression Cast material is placed into impression to

yield a “positive” replica of the oral tissue Allows for the indirect restoration or dental

appliance to be fabricated without the patient present

Variety of materials for a variety of applications

Uses of Impression Materials:

Used in the fabrication of:

Indirect restorations: Crowns & bridges Dental prosthetics Temporary crowns

Orthodontic & Dental appliances

Acrylic trays Bite registration Study models

Uses of Impression Materials:

Characteristics of Impression Materials:

Fluid enough to flow around area of interest Must “set” in reasonable amount of time Can remove from mouth without distortion No harmful effects on tissues Relatively tasteless & odorless Dimensionally stable until a cast is created Give detailed reproduction Compatible with cast materials

Impression Trays:

Used to carry the material to pt’s mouth Must be sturdy enough to support the material Need to be disposed of or sterilized after use Metallic trays are autoclavable Stock trays available: full arch, quadrant Custom trays made of acrylic for most accuracy Triple trays takes impression of opposing teeth,

occlusal registration, and prep site Perforated trays have holes for retention of

material

Categories of Impression Materials:

INELASTIC

Rigid Cannot be used

with undercuts For edentulous or

bite registration

ELASTIC

Flexible & “rubbery” Used with undercuts Generally used today Two subcategories:

Hydrocolloids (Aqueous) Elastomers

Inelastic Impression Materials:

Impression Compound ZOE Impression Paste Plaster

Inelastic Impression Materials:

Impression Compound: Resins + wax Thermoplastic, solid material

Heat to soften material Cool to set material Physical change only; NO chemical reaction

Forms: plates and sticks Soften in water bath (10° warmer than body) Applied to tray and inserted in mouth to cool Used as a custom tray

Inelastic Impression Materials:

ZOE Impression Paste: Similar formulation as ZOE cements Pastes mixed together – chemical

reaction BASE + CATALYST

Applied in thin layer in custom tray for edentulous arch; or to occlusal surfaces

Sets in 4 – 5 minutes

Elastic Impression Materials:

Hydrocolloids: Reversible Hydrocolloids Irreversible Hydrocolloids

Elastomers: Polysulfides Polyethers Condensation Silicones Addition Silicones - Polyvinylsiloxanes

Elastic Impression Materials:

HYDROCOLLOIDS – “water-based” impression materials Colloid – liquid suspension of particles Particles derived from seaweed & kelp Liquid = water GEL – the rubber-like form of the

material SOL – the material in liquid solution Not dimensionally stable – must be

“poured” immediately

Hydrocolloids:

Reversible Hydrocolloid: Agar – a gelatinous material + water Thermoplastic – NO chemical reaction “Reversible” –

Goes from gel, to sol, and back to gel, by raising and lowering temperature

Dispensed in tubes & syringes Very accurate final impression material

Hydrocolloids:

Handling Reversible Hydrocolloid:Special water baths with 3 chambers are used

1) Material is immersed in boiling tank (212°F) for 10-20 minutes; turns from gel to sol

2) Place in storage bath (150°F); 10 minutes to few days; remains sol

3) Load tray; immerse in the tempering bath (110°F); 5-10 minutes; lowers temp for pt comfort

Hydrocolloids:

Handling Reversible Hydrocolloid:4) Load syringe; extrude onto prep site5) Seat tray in mouth6) Attach cooling hoses to tray7) Hold firmly in pt’s mouth until cooled

and transformed to gel state8) Remove from pt’s mouth and pour

immediately

Reversible Hydrocolloid:

Advantages:

Very accurate Excellent

compatibility with gypsum

Disadvantages:

Labor-intensive Poor tear

resistance Poor stability Need equipment

space and very organized staff

Hydrocolloids:

Irreversible Hydrocolloid: ALGINATE impression material Formed by chemical reaction Powder + water; mixed NOT reversible; SOL to GEL only Protect from inhalation Dispensed in cans or bulk packages Used when less detail is required

Hydrocolloids:

“What are indications for alginate impressions?”

Study models Opposing models of final casts Casts for mouthguards, whitening trays,

custom trays, orthodontic appliances, provisional crowns, etc.

To fabricate a direct provisional crown

Hydrocolloids:

Handling Alginate: Fluff powder and

measure accurately Measure water – temp! Mix in a flexible,

rubber bowl Stir to wet powder Strop mixture against

side of bowl to eliminate air bubbles

Mix until creamy & homogeneous; 60 sec.

Hydrocolloids:

Handling Alginate: Load alginate into tray

from posterior Press material into tray

to eliminate voids Smooth & indent

alginate with wet finger

Use extra alginate to wipe onto occlusal surfaces of teeth

Taking an Alginate Impression:

Bead the tray as necessary Stand behind patient for maxillary (11:00) Center tray above teeth and seat posterior Press tray down & toward anterior and allow

lip to cover tray; material should fill vestibule

Hold tray in patient’s mouth until set (2 - 3 min)

Loosen cheeks and lips with finger Remove occlusally with a firm snap

Evaluating an Alginate Impression:

Full coverage, including retromolar area Tray centered Clear & sharp impression No voids, air bubbles, or tears Has a “peripheral roll” (vestibular area)

If all is OK, rinse & disinfect impression, pour-up in stone/plaster, or store in humid

bag.

Irreversible Hydrocolloid:

Advantages:

Easy & economical Many applications Patient comfort Excellent wetting

by gypsum Disposable tray

Disadvantages:

Not enough detail for final impression

Must be poured immediately

Hydrocolloids:

SYNERESIS – shrinkage in impression due to loss of water from heat or exposure to air.

IMBIBITION – swelling of impression due to taking up moisture

To avoid these conditions (dimensional distortion), pour-up immediately!

Elastomers:

Two-paste systems: Two tubes – pastes mixed by hand Two putties – mixed/kneaded by hand Cartridge & Extruder Gun – automix tips used Cartridge & Motor-driven Mixer – automix tips

used Set by chemical reaction Warmth and moisture may slow setting Must use a tray adhesive (if tray not perforated)

Latex may inhibit set of polyvinylsiloxanes

Elastomers:

Elastomers are used in a two-step process: Preliminary Impression - the material used to

form the base or the “tray” material used in an impression; usually more viscous or heavy-body

Secondary or “Wash” Impression – the material applied through a syringe around the prep site for detail; usually less viscous;light or medium -body.

Elastomers:

POLYSULFIDE: Oldest elastomeric used in dentistry Two pastes – mix base with catalyst Liquid polymer with “sulfhydryl” group –

contains sulfur “rubber-base” impression material Used best with custom trays Other materials have replaced this one

Elastomers:

Handling Polysulfides:1. Equal lengths of pastes on pad2. Pastes are “swirled” together, then stropped3. Material placed in custom tray4. Take impression – hold in place for up to 15

min.5. Remove from pt’s mouth slow & steady force6. Rinse & disinfect7. Pour-up impression within several hours

Polysulfides:

Advantages:

Economical Good tear

resistance Good

compatibility with gypsum

Disadvantages:

Malodor Stains clothing Long setting time Fair stability Less accurate

Elastomers:

Condensation Silicones: Similar to silicone rubber products (but

non-toxic)

Setting by-product of alcohol “Hydrophobic” – results in voids in stone Shrinkage occurs as it sets Must be poured immediately Accurate, but slow setting time Replaced by improved products

Elastomers:

POLYETHERS: Developed in 1960’s No reaction by-product produced Shorter working and setting time Only come in a single viscosity Stiff material – can use a triple tray Very popular – “Impregum” No need to pour-up immediately

Elastomers:

Handling Polyether:1. Mix equal lengths of paste; or extrude

through the automix cartridge tip2. Load syringe and apply to tooth thru

tip3. Load tray and invert over area for

impression4. Allow to set; 4 – 5 minutes5. Remove from mouth6. Rinse & disinfect

Polyether: Impregum

Polyether:

Advantages:

Short setting time Single viscosity Good stability Good tear strength Clean & easy to

use

Disadvantages:

Bad taste Most difficult to

remove from mouth

Elastomers:

ADDITION SILICONES: “Polyvinylsiloxanes” – silicone polymer Two pastes or two putties Hydrophobic by nature – manufacturers

adding components to increase wettability Very accurate & fast setting Avoid contact with latex (gloves, rubber dams)

Low setting shrinkage & very stable

Elastomers:

Handling Addition Silicone: Mix equal lengths of

pastes, or automix Apply light-body

material to tooth thru syringe

Load tray with heavy-body

Set tray over prep site Set in 4 – 5 minutes Rinse & disinfect

Addition Silicone: Polyvinylsiloxane

Advantages:

Very stable Short setting time Good tear

resistance Great accuracy No bad taste

Disadvantages:

May have poor wettability

Two pastes to mix