IMPRESSION MATERIALS

IMPRESSION

IMPRESSION

MATERIALS

MATERIALS

DR ZURYATI AB GHANI

DR ZURYATI AB GHANI

BDS (WALES), Grad Dip

BDS (WALES), Grad Dip

Clin

Clin

Dent (Adelaide),

Dent (Adelaide),

Doctor in Clinical Dentistry (

Doctor in Clinical Dentistry (

prosthodontics

prosthodontics

),

),

Adelaide, FRACDS (Australia).

Adelaide, FRACDS (Australia).

18.06.07

Impression materials

Impression materials

Plaster

Compound

ZOE paste

Wax

Non Aqueous

Polysulphide Condensation Silicone Additional Silicone Polyether

Non Elastomeric

Elastomers

Aqueous

Reversible hydrocolloid (Agar)

Irreversible hydrocolloid (Alginate)

DESIRABLE PROPERTIES

ƒ Easy to mix and dispense

ƒ Dimensionally stable

ƒ Good wetting

ƒ Accuracy in detail

ƒ Accuracy after cold sterilisation

ƒ Odor and taste neutral

ƒ Good elastic recovery

ƒ Good tear strength

ƒ Compatibility with die materials

ƒ Long shelf life

ƒ Adequate working time

KEY LEARNING ISSUES

ƒ Classification of materials

ƒ Understanding setting reaction

ƒ Properties

ƒ Delivery systems

Non

Non

elastomeric

_elastomeric

impression materials

impression materials

„

Compound

Compound

„

„

Composition: 40%resin, 7% waxes,

Composition: 40%resin, 7% waxes,

3% organic acids, 50% fillers,

3% organic acids, 50% fillers,

colouring

colouring

agents

agents

„

„

Capable of

Capable of

moulding

moulding

impression at

impression at

45

45

°

°

C

C

„

„

Primary impression in the edentulous

Primary impression in the edentulous

ridge

Zinc oxide

Zinc oxide

Eugenol

Eugenol

Composition

„ „

Tube 1

Tube 1

Zinc oxide

Zinc oxide

Oils

Oils

Additives

„ „

Tube 2

Tube 2

Eugenol

Eugenol

Oil

Oil

Resin

Resin

Additives

Additives

Additives

Zinc oxide

Zinc oxide

eugenol

eugenol

„

„

Used in custom made tray to record

Used in custom made tray to record

usually edentulous arches, sometimes

usually edentulous arches, sometimes

referred as wash impression

referred as wash impression

„

„

Mixing time 30 to 45

Mixing time 30 to 45

secs

secs

„

„

Setting time 3 to 5

Setting time 3 to 5

mins

mins

„

„

Brittle, messy, sometimes irritates

Brittle, messy, sometimes irritates

patient due to

Zinc oxide

Impression waxes

Impression waxes

„

„

Useful for correction of small

Useful for correction of small

imperfection in

imperfection in

ZnOE

ZnOE

impression, or

impression, or

for recording partial lower free end

for recording partial lower free end

saddles

Aqueous

Aqueous

elastomeric

_elastomeric

impression materials

impression materials

1)

1)

Agar

Agar

-

-

Reversible hydrocolloid

Reversible hydrocolloid

2)

Alginate

Alginate

„

„

One of the most widely used

One of the most widely used

impression materials

impression materials

„

„

ADVANTAGES: Easy to mix and

ADVANTAGES: Easy to mix and

manipulate, cheap, flexibility of set

manipulate, cheap, flexibility of set

impression, minimum equipment,

impression, minimum equipment,

accuracy if handled properly.

ALGINATE

ALGINATE

Composition

_Function

„

„

Sodium or potassium

Sodium or potassium

alginate

alginate

„

„

Sodium phosphate

Sodium phosphate

„

„

Silicate powder

Silicate powder

„

„

Potassium

Potassium

sulphate

sulphate

or

or

potassium zinc fluoride

potassium zinc fluoride

„

„

Organic glycol

Organic glycol

„

„

Chlorhexidine

„

„

To dissolve in water

To dissolve in water

„

„

To react with alginate

To react with alginate

„

„

Control setting time

Control setting time

„

„

To aid setting of die

To aid setting of die

material

material

„

„

Min dust during

Min dust during

dispensing

dispensing

„

„

Self disinfection

„

„

Mixing time: 1 min

Mixing time: 1 min

„

„

Setting time: 2

Setting time: 2

-

-

4.5

4.5

mins

mins

„

„

Fast set: 1

Fast set: 1

-

-

2

2

mins

mins

„

„

↑

↑

Temp

_Temp

↑

↑

setting time. Do not alter powder

_{setting time. Do not alter powder}

liquid ratio to change setting time

„

„

Dimensional changes. Can be stored

Dimensional changes. Can be stored

at 100 % humidity for 1 hr without

at 100 % humidity for 1 hr without

dimensional changes

dimensional changes

„

„

Not very accurate

Not very accurate

„

Non-Aqueous Elastomers

„

Polysulfides

„

Condensation Silicones

„

Addition Curing Silicones

„

Polyethers

ƒ

Also known as thiokol rubbers or mercaptans

ƒ Provided as two pastes: Base and Catalyst Composition

Base:

Polysulfide polymer Titanium oxide or Zinc Oxide Calcium Sulfate

Catalyst:

Lead dioxide Sulfur Dibutyl phthalate

SETTING REACTION

ƒ

Condensation reaction between –SH (sulfydryl groups) with lead dioxide and sulfur to produce disulfide links and water.

ƒ

Chain lengthening and cross-linking occurs

ƒ Increase in viscosity

ƒ Elastic properties arise

ƒ Water accelerates the setting reaction

O from Pb₂O

ADVANTAGES

¾

Good tear strength and flexibility

¾ Low cost

¾ Increased working time

DISADVANTAGES

¾

Poor dimensional stability due to water loss

¾ Offensive odor

¾ Long setting time

¾ More permanent deformation on removal and less elastic recovery due to reduced degree of

DIMENSIONAL CHANGE FROM:

ƒ Temperature transition upon removal from mouth

ƒ Water loss which is a setting reaction by-product

Initial mix on pad

COMPOSITION

Base: Dimethyl polysiloxane Alkyl silicate Catalyst: Stannous octoate Setting reaction:

Cross-linking of a hydroxy terminated dimethyl polysiloxane by an alkyl silicate catalysed by stannous octoate

Dimethyl polysiloxane

ADVANTAGES

ƒ More stable than polysulfides

ƒ Good tear strength

ƒ Good working and setting times

DISADVANTAGES

ƒ Odor from alcohol byproduct ƒ Dimensional instability

Most accurate impressions with condensation silicones are generated via a putty-wash technique.

Poly-Vinyl Siloxanes

ƒSetting reaction can be inhibited via a sulfur compound in

some latex gloves by the name of zinc diethyl dithiocarbamate

ƒThis chemical interacts with the chloroplatinic acid catalyst in the PVS formulation

PolyVinyl Siloxanes

SETTING REACTION

Crosslinking reaction of a vinyl terminated dimethyl polysiloxane Catalysed by chloroplatinic acid. Hydroen gas can be released as as by-product. The more contemporary products have hydrogen gas scavengers.

VISCOSITIES

ƒ Putty ƒ Monophase ƒ Heavy ƒ Intermediate ƒ Light

PVS – Setting Reaction

PolyVinyl Siloxanes

ADVANTAGES

ƒ Very stable dimensionally

ƒ Impression re-pours possible

ƒ Odor and taste neutral

ƒ Good elastic recovery

ƒ Good tear strength

ƒ Good wetting of prep surface

ƒ Good working and setting times

Poly-Vinyl Siloxanes

DELIVERY SYSTEMS

Automix System

Poly-Vinyl Siloxanes

PROBLEMS

ƒ

Setting retardation via sulfur in latex gloves

ƒ Setting retardation from sulfur in Astringident solution

ƒ Tearing of wash material away from tray material

ƒ Hydrogen gas release

ƒ Locking into undercuts and open embrasures

COMPOSITION

Base:

ƒPolyether polymer

ƒColloidal silica filler

ƒGlycol ether or phthalate plasticizer

Catalyst:

ƒAlkyl aromatic sulfonate

ƒPlasticizers and fillers as above

PENTAMIX

delivery system can be used for dispensing Polyether impresssion material

Polyether based polymer cured by reaction between aziridine rings which branch off a copolymer of ethylene oxide and tetrahydrofuran

Aromatic ester (Initiator)

Cross-linking occurs via cationic Polymerisation of imine end groups

ADVANTAGES

ƒ

Excellent accuracy and wetting

ƒ Good dimensional stability

ƒ Very good shelf life (~ 5years, less in warm conditions)

PROBLEMS

ƒ Very stiff when set / problem in undercuts, embrasures

ƒ Cold disinfection

ƒ Poor tear strength

ƒ Odor

ƒ Paste-paste mixing (messy, porosities)

ƒ Shorter working time than PVS silicones

ƒ Sensitivity to aromatic sulfonate

θ

₁

θ

₂

A

B

B = Material has superior wetting, a desirable property

PVS silicones have good wetting properties and are advertised as having high hydrophilicity when in fact they are HYDROPHOBIC

CLINICAL TIPS TO AVOID PROBLEMS

ƒ Use correct adhesive on tray

ƒ Block out locking embrasures and undercuts prior to impression

ƒ Tooth surface must be clean

ƒ Preparation margins must be well defined and clear

ƒ Margins free of fluids and blood

ƒ Mix impression material correctly

ƒ Do not overload stock trays

ƒ Have a high velocity suction handy

ƒ Apply material efficiently without delays

ƒ Leave in place without tray movement for correct time

ƒ Remove tray carefully

ƒ Wash away any blood on impression surface

ƒ Disinfect

ƒ Inspect marginal detail

Mandikos MN. Polyvinyl siloxane impression materials: An update on clinical use. Aust Dent J 1998;43:428-34

Wassel RW, Barker D, Wall AWG. Crowns and other extra oral restorations.

Impression materials and technique. British Dental Journal 2002;192:679-690

References

References

1.

1. MandikosMandikos MN. Polyvinyl siloxaneMN. Polyvinyl siloxane impression materials: An updateimpression materials: An update on clinical use.

on clinical use. AustAust Dent J 1998;43:428-Dent J 1998;43:428-3434 2.

2. WasselWassel RW, Barker D, Wall AWG. Crowns and other extra oral RW, Barker D, Wall AWG. Crowns and other extra oral restorations.

restorations.

Impression materials and technique. British Dental Journal Impression materials and technique. British Dental Journal

2002;192:679

2002;192:679-690-690 3. Mc

3. Mc CabeCabe JF, Wall AWG. (1998) Applied dental materials, 8th edition. JF, Wall AWG. (1998) Applied dental materials, 8th edition. Blackwell Science

Blackwell Science 4.

4. ShillingburgShillingburg HT, SumiyaHT, Sumiya H, WhittsettH, Whittsett 3rd edition. Fundamentals of 3rd edition. Fundamentals of fixwd

fixwd prosthodontics. Quintessence booksprosthodontics. Quintessence books 5.

5. RosenstielRosenstiel, Land, Fujimoto. Contemporary fixed , Land, Fujimoto. Contemporary fixed prosthodonticsprosthodontics 3rd 3rd edition

edition

6. Lectures from Dr tom

6. Lectures from Dr tom BerekallyBerekally. Consultant . Consultant prosthodontistprosthodontist/lecturer /lecturer University of Adelaide, South Australia