IMPRESSION MATERIALS

Prof . Dr Amal EzzEl Din Dental Biomaterials ,Faculty of

Dentistry Alex _Univ.

o Uses Make an accurate replica of

tissues.o Impression

Single tooth.

Whole dentition.

Partially or

completely

edentulous mouth.

o Biocompatible: non toxic- non irritant.

o Acceptable to the patient: pleasant

odour, taste, esthetic colour.

o Ease of manipulation, reasonable

cost.

o Reasonable setting time.

o Adequate shelf life.

o Adequate strength: not tear or break

on removal from mouth.

o Compatible with model materials.

o Dimensionally stable: neither

expands nor contracts.

o Adequate flow properties: to

register fine details.

o Readily disinfected without loss

of accuracy.

Classification

1. According to the ability of a set material to be

withdrawn over undercuts.

Non Elastic

Elastic

According to the manner which they

harden(set):

Reversible

Sets by a physical

reaction due to temperature changes

Irreversible

Sets by a chemical reaction.

Impression materials

Impression materialImpression material

ElasticElastic

NonelasticNonelastic

HydrocolloidsHydrocolloids

Zinc oxide eugenolZinc oxide eugenol

Impression CompoundImpression Compound

PlasterPlaster

Non-aqueouselastomers

Non-aqueouselastomers

AgarAgar

AlginateAlginatePolyethersPolyethers

Additionsilicone

Additionsilicone

Condensationsilicone

Condensationsilicone

PolysulfidesPolysulfides

Impression waxImpression wax

Classification

By Setting Mechanism

By Application or Mechanical Properties

Non-elastic Elastic

Chemical reaction

(irreversible)

Plaster of ParisZOE

Alginate hydrocolloidElastomers

Temperature changes

(reversible)

CompoundWax

Agar hydrocolloid

o Thermoplastic material.

o Composition:

Natural resins e.g., shellac &

carnuba wax.

Fillers: soap or talc.

Lubricants: stearic acid.

Colouring agent: e.g., rouge.

Types (forms of Supply)

Type I: low fusing compound softens at

53-60°C

Supplied in the form of sheets, or cakes

used as: impression for edentulous

patients.

Or in the form of sticks or cones or

cylinders.

Used as: impression for a single tooth

preparation as in (crowns), known as

Copper Band Impression.

Impression Compound

Type II: High fusing compound softens at 70°°C.

Used as tray material to hold a secondary impression material

Heating: o In a water bath-soaking in water in cases

of sheets and cakes. o Over a flame in case of sticks.o Avoid over heating.o Kneading: with the fingers.o Importance: assures uniform heating

Increases the flow. Gives workability.

Manipulation The compound disc is completely immersed in a water

bath at 55-60 C for about 4-5 minutes to ensure complete softening. Gauze is placed at the bottom of the water bath to prevent adherence. However if it is left in too long some of the constituents may be leached out into the water bath, altering the properties of the material (it is often the plasticizer stearic acid that is leached out). If the compound is kneaded water will become incorporated and act as a plasticiser. Kneading of the compound will incorporate water into the mass and thus increase the flow in the material (water = plasticizer).

The compound is loaded on to the tray and firm pressure is used to seat the tray home in the mouth. After the impression has been taken it is carefully examined, a common mistake is not softening the compound enough. In this is the case the impression can be reheated in a separate bowl of water (cross infection control) and the impression is repeated.

Cooling:

oAssure uniform cooling by

spraying with water at 16-18°C

before removal from the mouth.

Flow type 1: 85% at 45°C

less than 6% at 37°C.

Type II: 70% at 45°C

less than 2% at 37°C.

Viscous material does not record fine

details.

• Low thermal conductivity.

• High expansion and contraction

coefficients.

• Linear contraction on cooling from

mouth temperature to room

temperature

(0.3%-0.4%).

o Dimensional Changes: due to relief of

internal stresses (relaxation) Warpage

distortion of the impression.

o Model should be poured as soon as

possible.

o No separating medium.

o Separation of model.

PROPERTIES

Poor surface detail High coefficient of thermal expansion

(contraction of up to 0.3% when removed from mouth to room temperature)

Distorts when removed over undercut areas

Poor dimensional stability Can be modified by re-heating Non toxic and non irritant Good shelf life

ADVANTAGES & DisADVANTAGES

ADVANTAGES 1. Non irritant and

non toxic2. Reusable (but with re-use the constituents are leached out)3. Can be reheated and readapted4. Can support other materials for wash impressions

DISADVANTAGES 1. Poor

dimensional stability2. Poor surface detail3. Expansion coefficient4. Will distort if removed from undercuts

THANK YOU