Impression materials

Impression materials

-used to make replicas of oral structures
-allows for indirect resto or dental appliance to be made even without the patient present

negative replica

impression

positive replica

cast material is placed onto impression to produce positive replica

uses of impression material

used in fabrication of:
1. indirect resto(crowns, bridges, dental prosthetics, temp. crowns)
2. orthodontic and dental appliances
3. acrylic trays
4. bite registration
5. study models

characteristics of impression material

1. Fluid enough to flow
2. Set in reasonable amount of time
3. Can be removed w/o distortion
4. no harmful effect on tissue
5. relatively tasteless & odorless
6. dimensionally stable when cast is made
7. give detailed reproduction
8. compatible with cast mat.

impression trays

Used to carry the impression material into the patient's mouth thus they need to be sturdy enough to support the material

After use, impression trays need to be:

disposed or sterilized

Which impression tray is autoclavable?

metallic trays

stock trays are available in ___, ___

full arch, quadrant

custom trays are made of ___ for accuracy and are made ___ for patients

acrylic, especially

triple trays

takes impression of opposing teeth, occlusal registration, and prep site

Perforated tray

has holes for retention of material

types of stock trays

metallic and non-metallic

metallic stock trays

can be aluminum(can be bended/easily deformed) or stainless steel(sturdy)

non-metallic stock trays

plastic trays can be sterilized, disposable plastic trays

plastic impression trays are disposable bcs ?

it cant undergo sterilization thru boiling or dry heat

how to sterilize plastic impression trays

cold sterilization

mode of stock trays

perforated trays, non-perforated/plain trays

perforated trays are used with?

alginates

non-perforated/plain trays are used with?

impression compound

parts of the tray

floor, handle, flanges

types of impression tray

stock trays, custom trays

stock trays

various sizes and made by manufacturers

custom(Individual/special) trays

made for one patient, discarded later

classification of impression materials

1. acc. to manner in which material hardens
2. acc. to use in dentistry
3. acc. to state and condition

acc. to manner in which material hardens

thermoplastic means/physical condition
Chemical rxn

acc. to use in dentistry

1. for edentulous mouth
2. for non-edentulous mouth
3. for both edentulous and non-edentulous mouth

acc. to state and condition

rigid(for edentulous), flexible(for non-edentulous)

Categories of impression materials

1. inelastic
2. elastic

bite registration

uses wax, used to know position of maxilla in relation to mandible

Inelastic impression material

rigid, cannot be used with undercuts

inelastic impression mat is sued for?

edentulous or bite registration

inelastic materials

impression compound, ZOE impression paste, plaster

impression compound is made up of?

resin and wax

impression compound is ____, solid material

thermoplastic
*heat to soften
*cool to set
*physical change only, NO chemical rxn

impression compound are supplied in what forms

plates, sticks

impression compound manipulation

1. soften in water bath(10° warmer than body)
2. apply to tray and inserted in mouth to cool

can impression compound be used as custom tray?

yes

Dental impression compound other names

impression compound, tray compound

impression compounds is used to record ___ impression

final, referred to as corrective wash

Impression compound composition

40% - resins
50% - fillers
7% - waxes
3% organic acids

in impression compounds, stearic acid acts as a ?

plasticizer

types of impression compound

type 1 - true compound
type 2 - tray compound

type 1 - true compound

preliminary impression of edentulous mouth(stock tray)
single tooth with prepared cavity

type 2 - tray compound

used as tray to carry other materials

type 2 - tray compound's ONLY separating medium

water at room temperature

properties of impression compound

flow, thermal conductivity

requirement for impression compound

1, should not contain any poisonous/irritating ingredients
2. harden uniformly
3. harden completely at/slightly above mouth temp.
4.after setting, it should allow for trimming with sharp knife to avoid flaking, chipping, fracture
5. exhibit smooth, glossy surface after its been thru flame
6. dimensionally stable at all times
7. while soft, should take minute details or crevices and small markings important for denture construction

ZOE impression pastes

similar formula as ZOE cements
pastes mixed together - CHEMICAL rxn

ZOE has

base + catalyst

ZOE is applied in _____ in custom tarys for edentulous arch or occlusal surface

thin layer

ZOE impression paste setting time

4-6 mins

Elastic impression materials

Hydrocolloids, elastomers

hydrocolloids

reversible (agar)
irreversible (alginate)

elastomers

polysulfide, polyether, condensation silicone, addition silicone

water based impression materials

hydrocolloids
*from seaweed and kelp

colloid

liquid suspension of particles

ZOE uses

custom trays, final impression
-more detailed vs modelling compound

are hydrocolloids dimensionally stable?

No! so must pour immediately

gel

rubber like form of hydrocolloid material

sol

material in liquid solution

Agar (Reversible Hydrocolloid)

made of gelatinous material + water
*very accurate final impression mat.

How does agar set?

thermoplastic, no chemical rxn

how is agar reversible?

goes from gel to sol, sol to gel thru raising and lowering temp

agar is dispensed in?

tubes, syringes

what is sued to handle agar

special water baths with 3 chambers

3 chambers

boiling tank, storage bath, tempering bath

boiling tank chamber

immersed in boiling water 212°F for 10-20 mins, turns gel to sol

storage bath

150°F, storage can last for 10 mins to few days, keeps agar in sol form

tempering bath

loaded tray is tempered(110°F) for 5-10 mins
-lowers temp for patient comfort

Handling Reversible Hydrocolloid:

1. Load syringe; extrude onto prep. site
2. Seat tray in mouth
3. Attach cooling hoses to tray
4. Hold firmly in pt's mouth until cooled and transformed to gel state
5. Remove from pt's mouth and pour immediately

Agar advantages

1. Very accurate
2. Excellent compatibility with gypsum
3. Low cost
4. Long shelf life

Alginate(Irreversible Hydrocolloid)

Powder+water, mixed
-NOT REVERSIBLE:from sol to gel only
-formed by chemical rxn
-in cans or bulk packages
-used when less detail in needed

Indications for alginate impressions

1. Study models
2. Opposing models of final casts
3. Casts for mouthguards, whitening trays, custom trays, ortho appliance, provisional crown
4. Fabricate direct provisional crown

Handling Alginate(Mixing)

1. Fluff powder, measure accurately
2. Measure water
3. Mix in flexible, rubber bowl
4. Stir to wet powder
5. Strop mixture against side of bowl to remove air bubbles
6. Mix well until creamy and homogenous(60 sec)

Handling alginate

1. Load alginate into tray from posterior
2. Press mat. into tray to remove voids
3. Smooth and indent alginate with wet fingers4.use extra alginate to wipe onto occlusal surface of teeth

Evaluating alginate impression

1. Full coverage (inc. retromolar area)
2. Tray is centered
3. Clear & sharp impression
4. No voids, air bubbles, tears
5. Has "peripheral roll"(vestibular area)

After evaluating alginate impression, if all is okay:

Rinse and disinfect impression, pour-up in stone/plaster or story in humid bag

advantages of irreversible hydrocolloid

1. Easy and economical
2. Many applications
3. Patient comfort
4. Excellent wetting by gypsum
5. Disposable tray

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 dimensional distortion in alginate, what must be done?

Pour-up immediately

Elastomers two paste systems:

Two tubes
Two putties
Cartridge and extruder gun
Cartridge and motor driven mixer

Elastomers set by

-set by chemical rxn

What can slow setting of elastomers

Warmth and moisture

If tray used for elastomer is not perforated, you must use?

Tray adhesive

Latex

May inhibit setting of polyvinylsiloxane

Elastomers are used in a two step process

1. Preliminary impression
2. Secondary or Wash impression

Preliminary impression

Material used to make the base or "tray" material, more viscous/heavy body

Secondary/ wash impression

Material applied thru syringe around prep site for detail; less viscous, light or medium body

oldest elastomer

Polysulfide

Polysulfide

Liquid polymer with SULFHYDRL grp- has sulfur
-2 pastes(base/catalyst)
-"rubber-base" impression mat
-replaced

Polysulfide advantage

Economical, good tear resistance, good compatibility with gypsum

Condensation silicone

Similar to rubber products(non-toxic)
-accurate but slow setting time
-replaced with better products

by product of condensation silicone

Alcohol

Condensation silicone is "hydrophobic"

-results in voids in stone
-shrinkage occurs as it sets, so poured immediately

Polyethers

-dev. 1960s
-shorter working and setting time
-single viscosity
-stiffer mat, can use triple tray

Polyether by product

None, no need to pour immediately

Very popular polyether

Impregum

Handling polyether

1. Extrude equal lengths of paste, extrude thru automix cartridge tip
2. Load syringe, apply to tooth
3. Load tray, invert over area of impression
4. Allow to set
5. Remove from mouth
6. Rinse & disinfect