impression materials in denstistry

There are many impression materials used in prosthetic

dentistry and there are many different techniques employed to

obtain a true replica of the teeth and mucosa

Impression materials are used to record the shape of the

teeth and alveolar ridges

There are a wide variety of impression materials available

each with their own properties, advantages and disadvantages

2

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

1. Non toxic and non irritant

2. Acceptability to the patient:

3. Accuracy:

4. Use of material:

5. Compatible with

model materials

6. Economics of material

3

(a)Setting time,

(b)Taste,

(c)Consistency

(a) Surface reproducibility

(b) Dimensional stability

(a) Ease of mixing

(b) Working time

(c) Setting time

(d) Handling of the material (a) Cheap

(b) Long shelf life

(c) Accuracy (save redoing impression)

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

Mucodisplacive : compound, high viscosity alginates, high

viscosity elastomers - these record an impression of the mucosa

under load.

This results in a wider distribution of load during function, making

it more stable it also compensates for the differing

compressibility of the denture bearing area reducing the risk of a

fracture due to flexion.

4

The retention of the dentures may be

compromised as the soft tissues wish to

return to their original position at rest.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

Mucostatic : plaster, zinc oxide eugenol, low viscosity

alginates – since they are more fluid displace the tissues less.

These essentially record an impression of the undisplaced

mucosa. This results in better retention of the denture because

of closer adaptation to the mucosa at rest.

5

Instability of the denture may occur during

function as the tissues distort

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

6

Non-elastic impression materials

Impression compound

Impression Plaster

Zinc Oxide Eugenol

Impression Waxes

Elastic impression materials

Hydrocolloids

Agars

Alginates

Elastomers

Polysulphides

Silicones

Polyethers

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

7

These materials are rigid and

therefore exhibit little or no elasticity.

Any significant deformation

produces a permanent deformation.

Used where there are no undercuts

and are mainly used for edentulous

patient cases.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

8

Characteristics

• Thermoplastic

• Poor surface detail

• High coefficient of

thermal expansion

(contraction of up to

0.3%)

• Distorts wen removed

over undercut areas

• Mucocodisplacive

• Poor dimensional

stability

• Can be modified by re-

heating

• Non toxic and non irritant

• Good shelf life

Advantages

• Non irritant and non toxic

• Reusable (but with re-

use the constituents are

leached out)

• Can be reheated and

readapted

• Can support other

materials for wash

impressions

• Mucocompressive

Disadvantages


stability

• Poor surface detail

• Expansion coefficient

• Will distort if removed

from undercuts

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

9

Characteristics

• Excellent at recording

fine detail

• Dimensionally stable if

anti expansion solution

used

• Fractures if undercuts

present

• Mucostatic

• Needs to be treated with

a separating medium

before being cast in

stone or plaster

• Exothermic reaction

• Non toxic but may be

unpleasant due to

dryness and heat

evolved during setting

Advantages

• Good surface detail

• Excellent dimensional

stability

• Rate of the setting

reaction can be

controlled by the

clinician

Disadvantages

• Cannot be used for

mucocdisplacive

impressions

• Cannot be added to

• Properties affected by

operator handling

technique

• Taste and roughness

may cause the patient to

vomit

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

10

Characteristics

• Used for recording

edentulous ridges in a

close fitting special tray

or the patients existing

dentures

• Non toxic

• Adherence to tissues

• Mucostatic or

mucocodisplacive

• Good surface detail in

thin section

• Good dimensional

stability

• Can be added to with

fresh zinc oxide eugenol

• Stable on storage and

good shelf life

Advantages

• Dimensional stability


• Can be added to

• Mucostatic or

mucocodisplacive

Disadvantages

• Cannot be used in very

deep undercuts

• Only sets quickly in thin

section

• Eugenol allergy in some

patients

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

11

Not commonly used thermoplastic materials, which flow at

mouth temperature and are soft a room temperature.

Normally used to correct small imperfection (e.g. airblows) in

other impressions, especial zinc oxide impressions.

Combination of a low melting paraffin wax and beeswax in a

ratio of approximately 3:1 to ensure the wax flows at room

temperature.

A cast should be poured up immediately after taking the

impression to avoid distortion which readily occurs in wax.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

12

Can be stretched and bent to a fairly

large degree without suffering any

deformation.

Used for recording the patient's mouth

where undercuts are present.

Usually used for partial dentures,

overdentures, implants and crown and

bridge work.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

13

Relatively fluid materials when

the solute particles present are

dispersed throughout the liquid.

Alternatively, the particles can

become attached to each other,

forming a loose network which

restricts movement of the solute

molecules. The colloid becomes

viscous and jelly like, and is called

a gel.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

14

Some colloids have the ability to change reversibly from

the sol state to the gel state. A sol can be converted into a

gel in one of two ways:

1. Reduction in temperature, reversible because

sol is formed again on heating (eg agar).

2. Chemical reaction which is irreversible (eg

alginates). A gel can lose (syneresis which results

in shrinkage) or take up (imbibition which results

in expansion) water or other fluids.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

15

Hydrocolloids are placed in the mouth in the sol state

when it can record sufficient detail, then removed when it

has reached the gel state.

Hydrocolloid materials especially the alginates, may

display a lack of incompatibility with some makes of dental

stones. The resultant model may show reduced surface

hardness and possibly surface irregularities and

roughness.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

16

Characteristics

• Good surface detail –

can be used for crowns

and bridges

• Can be used on

undercuts, but liable to

tear on deep undercuts

• Evaporation or imbibition


• Slow setting time

• Poor tear resistance

• Adequate shelf life

• Can be sterilised by an

aqueous solution of

hypochlorite.

Advantages


• Reusable and easily

sterilised

Disadvantages

• Need special equipment

(water bath) and special

technique

• Dimensional instability

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

17

Characteristics

• Good surface detail –

used for study models

and for removable partial

dentures

• Reaction is faster at

higher temperatures

• Elastic enough to be

drawn over the

undercuts, but tears over

the deep undercuts

• Not dimensionally stable

on storing due to

evaporation


• Setting time can depend

on technique

Advantages



• Ease of use and mix

• Cheap and good shelf

life

• Setting time can be

controlled with

temperature of water

used

Disadvantages


stability

• Incompatibility with some

dental stones

• Setting time very

dependent on operator

handling

• Messy to work with

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

18

On mixing the powder with water a sol is formed, a chemical

reaction takes place and a gel is formed. The powder contains

1. Alginate salt (e.g. sodium alginate)

2. Calcium salt (e.g. calcium sulphate)

3. Trisodium phosphate

SODIUM

ALGINATE

SODIUM

SULPHATE

+ +

CALCIUM

SULPHATE

CALCIUM

ALGINATE

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

19

Clinical considerations: Powder and water should be measured to manufactures

instructions.

Water at room temperature should be used, this gives a

reasonable working time of a couple of minutes. Faster or slower

setting times can be achieved by using warm or cold water

respectively.

The material nearer the tissues sets first

Retention is needed to the impression tray and is provided by

perforations in the tray and/or adhesives.

Once removed, it should be covered in a damp gauze/napkin to

prevent syneresis (not placed in water which would cause

imbibition-expansion).

The impression should be soaked in hypochlorite for 60 seconds

and then cast as soon as possible.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

20

Used where a high degree of accuracy is needed,

especially in crown and bridge work.

Two main advantages over the Hydrocolloids - good

tear resistance and dimensional stability.

Hydrophobic rubber based materials.

Come in different viscosity's ranging from low to high

viscosity. The light bodied material maybe used as a wash

impression over a medium or heavy-bodied material.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

21

ONE STAGE IMPRESSION

Light bodied impression material is placed in a syringe, and placed over the areas

where high detail is required (e.g. over a crown preparation). Some is then

squirted over the heavy-bodied impression material which has been loaded into an

impression tray. The impression is then taken as normal.

This technique saves time, but it can be very labour intensive because

the two need to mixed at the same time.

TWO STAGE IMPRESSION

An impression is taken with the heavy-bodied material. This is then removed from

the mouth and inspected. The light bodied material is then prepared and again

placed in a syringe. This is then squirted over heavy-bodied material and then

impression relocated in its original impression.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

22

Characteristics

• Used for complete

denture, crown and

bridge work mainly, but

also used for partial

dentures, overdentures

and implants


• Excellent surface detail

• Varying viscosity

• Very small setting

contraction

• Contraction on cooling

from mouth to room

temperature

• Very good tear

resistance

• Viscoelastic

Advantages


• Accuracy

• Comes in a number of

different viscosity's

• Long working time

(although this may be a

disadvantage in some

clinical situations)

• Long shelf life

Disadvantages

• Lead oxide in base paste

may have toxic effects

• Staining of clothes due

to the Lead oxide

• Messy to work with -

unpleasant rubbery

smell

• Can only be used in a

special traY

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

23

Characteristics

• Used for crown, bridge

and bite registration

• Hydrophillic

• Good shelf life of up to 2

years

• Good elastic recovery

• Non toxic

• Low setting contraction

• Low tear strength


• Good dimensional

stability

Advantages

• Accuracy

• Good on undercuts

• Ease of use

Disadvantages

• May cause allergic

reaction due to the

sulphonic acid ester

• Poor tear strength

• Rapid setting time (short

working time)

• Stiff set material

(sometimes hard to

remove from mouth)

• Bad taste

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

24

Two kinds, depending on the chemical reaction: Addition Silicones

Excellent dimensional stability

Cannot be manipulated with latex gloves

The cast can be done up to a week after the impression

Condensation Silicones Releases ethanol molecules upon setting

Contraction after ethanol's evaporation

Inlays, partial fixed prosthesis

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

25

Characteristics

• Used for complete

dentures, crown and

bridge work mainly, but

also for partial dentures,

implants and

overdenture

• Hydrophobic

• Ethenol release

• Moderate shelf life

• Moderate tear strength


• Shrinking of impression

over time


• Very elastic (near ideal)

Advantages

• Accurate

• Ease of use

• Can be used on severe

undercuts

Disadvantages

• Ethenol release

• Liquid component of

paste/liquid system may

cause irritation

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

26

Characteristics

• Used for crown and

bridge, denture, bite

registration

• Good shelf life

• Dimensionally stable

• Moderate tear strength


• No gas evolution


Advantages

• Accurate

• Ease of use

• Fast setting

• Wide range of viscosities

Disadvantages

• Hard to mix

• Sometimes difficult to

remove the impression

from the mouth

• Cannot be manipulated

with latex gloves (may

prevent setting)

• Hidrogen release

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

27

Impression Material Usage by General Dentists

Crown & Bridge

–addition silicone 81%

–alginate 38%

–polyether 28%

Inlays and Onlays


–polyether 22%

–alginate 20%

DPR 2001

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

28

Impression Material Usage by General Dentists

Complete dentures

–alginate 58%


–polyether 27%

Partial dentures

–alginate 78%


–polyether 15%

DPR 2002

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

29

Handling Properties

Agar Alginate Polysulfide Condensation

Silicone

Addition

Silicone Polyether

Preparation Boil, temper,

store Powder, water 2 pastes

2 pastes or

paste/liquid 2 pastes 2 pastes

Ease of use Technique

sensitive Good Fair Fair Excellent Good

Patient

Reaction Thermal Shock Pleasant, clean

Unpleasant,

stains Pleasant, clean Pleasant

Unpleasant

clean

Ease of

Removal Very easy Very easy Easy Moderate Moderate

Moderate to

difficult

Disinfection Poor Poor Fair Fair Excellent Fair

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

30

Handling Properties

Agar Alginate Polysulfide Condensation

Silicone

Addition

Silicone Polyether

Working

Time (min) 7 – 15 2.5 5 – 7 3 2 –4.5 2.5

Setting

Time

(min)

5 3.5 8 – 12 6 – 8 3 – 7 4.5

Stability 1 hour Immediate pour 1 hour Immediate pour 1 week 1 week kept dry

Wettability

and

castability

Excellent Excellent Fair Fair Fair to good Good

Cost Low Very low Low Moderate High to very

high Very high

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

31

Comparison of proprieties

Working time

–longest to shortest

agar > polysulfide > silicones > alginate = polyether

Setting time

–shortest to longest

alginate < polyether < agar < silicones < polysulfide

Stiffness

–most to least

polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids

Tear strength

–greatest to least

polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

32

Comparison of proprieties

Cost

–lowest to highest

alginate < agar = polysulfide <condensation silicone < addition silicone < polyether

Dimensional stability

–best to worst

addition silicone > polyether > polysulfide > condensation silicone > hydrocolloid

Wettability

–best to worst

hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic

addition silicone = condensation silicone

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

33

Materials for Study Models

Alginate most widely used

•inexpensive

•displaces moisture

•lower detail reproduction

•dimensionally unstable

Materials for Prosthodontics

Addition silicones most popular

•accurate

•dimensionally stable

•user friendly

•expensive

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

• Phillips’ Science of Dental Materials, edited by K Anusavice, 11th ed., 2008,

Saunders Publishing.

• Dental Materials and their Selection, edited by WJ O’Brien, 4th ed., 2008,

Quintessence Publishing.

• Dental Products Report, 2001, 2002, 2005.

• CW Caswell, AS von Gonten, and TR Meng, Volumetric proportioning techniques for

irreversible hydrocolloids: a comparative study, J Am Dent Assoc 1986 112:859-861.

• MN Mandikos, Polyvinyl Siloxane Impression Materials: An Update on Clinical Use,

Australian Dental Journal, Dec 1998, 43(5): 428-434.

• RG Craig, Review of Impression Materials, Advance in Dental Research, Aug 1988,

2,51-64.

Introduction

Properties

Mucostatic vs

Mucodisplasive

Classification

Non-elastic

Elastic

Summary

References

impression materials in denstistry

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