Impression material

IMPRESSION MATERIALS

Dr. Raied Al-Attar
2017-2018
5th lecture

DEFINITION:

A dental impression is defined as the negative record of the tissues of the mouth . It is used to reproduce the form of the teeth and surrounding tissues.

• Or Impression: -ve replica of the oral hard and soft tissuesCast: +ve replica of the oral hard and soft tissues

DEFINITION:

Impression material:-
Any substance or combination of substances used for making an impression or negative reproduction.

Impression technique:-

A method and manner used in making a negative likeness.

Impression Trays Container used to carry the impression material into or out from the patient’s mouth
Stock trays
Special trays


Under cutAreas under the inclined planes

Ideal requirements of Impression materials

• Biologically
• Non- toxic and non-irritant
• Interfacially
• Compatible with different model and die materials
• Chemically
• Have long shelf life
• Dimensionally stable in storage

Ideal requirements of Impression materials

• Mechanically
• When set they should behave elastically
• Have sufficient mechanical properties ie. tear strength to resist tearing during impression removal from the undercuts
• Have sufficient flow under pressure that helps in recording the fine details of the oral structure
• Practicability
• Inexpensive
• Easy manipulated
• Have reasonable working and setting times


CLASSIFICATON:
There are several classification. According to philips science of dental materials impression materials are classified on the basis of setting and elasticity.

Mode of setting

rigid
Elastic
Set by chemical reaction(irreversible)

Impression plaster, zinc oxide eugenol.

Alginate, polysulfide, polyether, silicone,
Set by temperature change(reversible)

Compound, waxes

Agar hydrocolloid.

Classification of Impression Materials

• I. According to the mechanical behavior
• Elastic materials
• Used for both edentulous and dentate patients having undercuts
• 1. Hydrocolloids
• Reversible hydrocolloid (Agar)
• Irreversible hydrocolloid (Alginate)
• 2. Elastomeric Materials
• Polysulfide
• Silicones (Condensation-polymerizing & addition-polymerizing)
• Polyether


• I. According to the mechanical behavior
• B. Inelastic (Rigid) materials
• Used only with edentulous patients having no or shallow under cuts
• Plaster of Paris
• Impression compound
• Zinc oxide Pastes
• Impression waxes
Classification of Impression Materials

• II. According to the setting mechanism

• Chemically-set materials
• Because of the irreversible reaction, they are used only for one time
• Plaster of Paris
• Zinc oxide pastes
• Alginate hydrocolloid
• Elastomeric materials
Classification of Impression materials

• II. According to the setting mechanism

• B. Physically-set materials
• Because of the reversible reaction they are able to be reused
• Impression compound
• Agar hydrocolloid
• Impression waxes
Classification of Impression materials


• III. According to the usage
• Materials for making 1ry impression
• Used in stock trays, thick consistency, record poor details
• Impression compound
• (Complete denture)
• Alginate hydrocolloid
• (Removable and fixed prosthesis)
• Putty and heavy consistencies of rubber impression materials
• (Removable and fixed prosthesis)
Classification of Impression materials

• III. According to the usage

• B. Materials for making 2ry impression
• Used in special trays, thin consistency, record fine details
• Plaster of Paris (Complete denture)
• Zinc oxide pastes (Complete denture)
• Impression waxes (Complete denture)
• Agar hydrocolloid
• (Removable and fixed prosthesis)
• Medium and light consistencies of rubber impression materials
• (Removable and fixed prosthesis)
Classification of Impression materials


ELASTIC IMPRESSION MATERIALS;AGAR;
Agar hydrocolloid was the first successful impression material to be used in dentistry.
It is an organic hydrocolloid extracted from certain types of seaweeds.
Agar is a reversible hydrocolloid.
Since it is reversible can be reused.

Uses

As tissue conditioner.
For full mouth impression without deep undercuts.
Used extensively for crown and bridge impression before elastomers came to the market.
Widely used at present for cast duplication.

Supplied as;

Gel in collapsible tube(for impression)
A number of cylinders in a glass jar(syringe material).
In bulk containers(for duplication)

Composition;

INGREDIENTS
PERCENTAGE BY WEIGHT
Agar
13-17%
Borates
0.2-0.5%
Potassium sulphate
1-2%
wax, hard
0.5-1%
Thixotropic material
0.3-0.5%
Alkylbenzoates
0.1%
water
Around 84%
Coloring and flavoring agents
Traces


Function of each ingredient;
Agar-basic constituent.
Potassium sulphate-It counters retarding effects of borates.
Wax-filler.
Thixotropic material-plasticizer.
Alkylbenzoates-preservative.
Coloring agents-for patients comfort
Water-dispersion medium.
Manipulation;
Agar hydrocolloid requires special equipments ;
Hydrocolloid conditioner.
Water cooled rim lock tray.

Impression tray;

Rim lock trays with water circulating devices are used (water cooled rim lock tray).
Rim lock has a beading on the inside edge of the tray which help to retain the material within the tray.
It also has an inlet and outlet for connecting water tubes.
The tray should allow a space of 3mm occlusally and laterally and extend distally to cover all teeth.

Hydrocolloid conditioner

IMPRESSION DISINFECTION

Main disinfectants used include iodophor,bleach or glutaraldehyde.

ADVANTAGES

Accurate die can be prepared, if material is properly handled
Has good elastic properties.
Good recovery from distortion
well tolerated by patient
Cheap

Disadvantages

Not flow well compared to newly available material
Tears relatively easily
Only one model can be poured


ALGINATE
Its an irreversible elastic hydrocolloid
It is a mucous extract yielded from certain brown sea weeds
Types
type 1 – fast setting
type 2- normal setting
Applications
Used for impression making;
when there are undercuts
in mouth with excessive flow of saliva
For impression to make study models and working casts
For making preliminary impression

PROPERTIES OF ALGINATE

Alginate has pleasant taste and smell
It is highly flexible
Good elasticity and elastic recovery
Fine reproduction of tissue detail
Compressive strength – ranges from 0343-70 mpa
Tear strength- 350-700gm/cm2
Dimensionally stable
Poorly adheres to the tray
Biological properties- inhalation of silica particles cause health hazards.


MANIPULATION
steps in manipulation

for mixing a clean flexible plastic bowl and clean wide bladed stiff metal spatula is being used.
proper water powder ratio specified by the manufacturer should be used(1 measure water with two level scoops of powder)
mixing is started with a stirring motion. vigorous motion can also be used.

ADVANTAGES

Easy to mix and manipulate
Low cost
Comfortable to patient
Hygienic
Good surface detail even in presence of saliva
Accuracy if properly handled
Minimum requirement of equipment

DISADVANTAGES

It cannot be corrected
Poor dimension stability
Poor tear strength
Distortion may occur if not properly handled


GROUP A
Numerate the property of ideal gypsum material?

What is the basic component of investment material?

GROUP B
Numerate the application of gypsum material in dentistry ?

What is allotropic form in which silica exist?