IMPRESSION MATERIALS INCOMPLETE DENTURES

Under the guidance of :

Dr. MURUGESAN

Prof.

Presented by:

Dr. APARNA. N

INTRODUCTION

Impression materials are used to register

or reproduce the form & relationship of the

teeth & oral tissues. They are used to make an

accurate replica of the hard & soft oral tissues.

HISTORY

Before middle of the 18th century- Blocks of ivory & bone as IM.

During 18th century – Bees Wax, used in making impression

1848 Colburn & Blake – Gutta percha as IM. 1844 Wescott, Dwinelle & Dunning – Used Plaster

of Paris as IM. 1925 Alphous Poller – 1st suggested use of agar for

dental impressions

1922 Everett – Used Fluid wax of 3 consistencies S.S. Wilding – Patent to use algin for impression Middle 1950’s – Elastomeric impression materials introduced. 1955 Pearsen – New elastic impression material of polysulphide base. 1960’s – Polyethers introduced in Germany.

IMPRESSION DEFINITION (WINKLER) :-

Impression is defined as an imprint or negative likeness of the teeth of the edentulous areas where the teeth have been removed or of both, made in a plastic material that becomes relatively hard or sets while in contact with these tissues.

IMPRESSION DEFN (GPT)

A negative likeness or copy in reverse of the surface of an object; or an imprint of the teeth & adjacent for use in dentistry.

PRELIMINARY IMPRESSION (GPT)

A negative likeness made for the purpose of diagnosis, treatment planning or the fabrication of tray.

FINAL IMPRESSION (GPT)

The impression that represents the completion of the registration of the surface or object.

IMPRESSION MATERIAL (GPT)

Any substance or combination of substances used for making an impression or negative reproduction.

PURPOSE

Constructing a model or a cast is an important

step in complete denture fabrication. Various types of

casts & models can be made from gypsum products

using on impression mold or negative likeness of a

dental structure therefore the case must be an accurate

representation of oral structures which requires that

the impression be accurate.

IDEAL REQUIREMENTS:-

1. Desirable flow properties.

2. Set or harden at or near mouth temperature.

3. Should not distort or tear.

4. Biocompatable

5. Dimensionally stable

6. Compatable with gypsum

7. Accuracy

8. Pleasant odour, taste & esthetic colour.

9. Adequate shelf life.

10.Readily disinfected

11.No release of gas during the setting of impression or gypsum products.

12.Economic & easy to use

CLASSIFICATION

A. Based on setting mechanism.

B. Based on mechanical properties

C. Based on impression techniques

A. Based on setting mechanism.

1. Thermoplastic (Reversible)

(Ex.) Compound, Agar

2. Thermosetting (Irreversible)

(Ex.) ZOE Paste, Alginate, Elastomers

B. Based on mechanical properties

1. Elastic

(Ex.) Elastomers, Hydrocolloids

2. Inelastic

(Ex.) ZOE Paste, Impression Compound

C. Based on impression techniques

1. Mucostatic

(Ex.) ZOE Paste, Impression Plaster

2. Muco Compressive

(Ex.) Hydrocolloids, Impression Compound

MATERIALS USED:-

Plaster

Modelling Compound

ZOE Paste

Hydrocolloids

Elastomers

IMPRESSION PLASTER:

COMPOSITION

Calcium sulfate hemihydrate

Modifiers

Potassium sulfate

Pigments

Retarders

Gum tragacanth

Starch

Flavouring agents

Anti expansion solution

SETTING REACTION

The setting reaction of gypsum occurs by dissolution of calcium sulfate hemihydrate, formation of a saturated solution of calcium sulfate, subsequent aggregation of less soluble calcium sulfate dihydrate and precipitation of the dihydrate crystals.

ADVANTAGES

Good Detail Reproduction

Economical

Good Dimensional Stability

No distortion, it fractures before it can distort

DISADVANTAGES

Disagreeable to the patient

Rigidity, critical areas may be lost

Removal of bulky impressions

Requires usage of separating media

INDICATIONS

Wash impressions

Recording flabby tissues

IMPRESSION COMPOUND

COMPOSITION

Beeswax

Rosin

Copal resin

Carnauba wax

Plasticizers

Talc

Colouring agents

CLASSIFICATION

1. Impression Compound (Low Fusing)

2. Tray Compound (High Fusing)

LOW FUSING

In the form cakes, sticks and cones

Colour varies from red, green, white, brown,

Cakes used for preliminary impressions.

Sticks and cones for border molding.

HIGH FUSING

In the cake form, normally black in colour.

Used as tray for wash impressions with impression plaster or zinc oxide eugenol.

MANIPULATION

The compound is softened by heating, either dry heat or in a hot water bath; water bath is preferred for complete dentures.

The water bath temperature should be maintained between 60 & 65oC.

Sticks & Cones can be softened by dry heat, but should be tempered before placing it in the patients mouth.,

ADVANTAGES

Cheap

Reusable

No irritation

Can be re-modified and re-softened till accuracy is

achieved.

DISADVANTAGES

Poor surface reproduction

Poor dimensional stability.

Difficult to remove from under cuts.

Unpleasant taste.

Tempering required.

INDICATIONS

Preliminary Impressions

Border Molding

ZINC OXIDE EUGENOL PASTE:

COMPOSITION

Base Paste : Zinc Oxide 87%

Fixed Veg / Mineral Oil 13%

Accelerator Paste : Oil of cloves / eugenol 12%

Gum / polymerised rosin 50%

Filler 20%

Lanolin 3%

Resinous balsam 10%

Accelerator & colour 5%

SETTING MECHANISM

Chelation Mechanism

Chelate compound : Zinc eugenolate

Final product : Unreacted zinc oxide particles with excess free eugenol in matrix of crystals of zinc eugenolate.

DISADVANTAGES

Burning sensation

Messy

Sticks to skin & instruments

Rigid

ADVANTAGES

Good dimensional stability

Good detail reproduction

Impression can be modified by adding in deficient areas

Easy to manipulate

Sufficiently long working time

INDICATIONS :

Secondary Impressions

Bite Registrations

IMPRESSION WAX

- Waxes were first used in dentistry in the early 18th century for the purpose of recording impressions of edentulous mouths.

TYPES:- - Dental waxes are classified as:

1) Pattern wax

2) Processing wax

3) Impression wax

- Impression wax is of 2 types:

1) Corrective wax

2) Bite registration wax

COMPOSITION:-

- Waxes used in dentistry may be composed of natural & synthetic waxes, gums, fats, fatty acids, oils, natural & synthetic resins & pigments of various types.

- Particular working characteristics of each of the dental waxes are achieved by the blending of appropriate natural & synthetic waxes & resins & other additives.

ALGINATES:-

COMPOSITION

Potassium alginate - Soluble alginate - 15%

Calcium sulfate - Reactor - 16%

Zinc Oxide - Filler - 4%

K titanium fluoride - Accelerator - 3%

Diatomaceous earth - Filler - 60%

Sodium phosphate - Retarder - 2%

SETTING MECHANISM :

Sol-gel reaction, of soluble alginate with calcium

sulfate & formation of an insoluble alginate gel.

Calcium ions replace sodium or potassium ions of

adjacent molecules to produce a cross linked complex or

polymer network.

ADVANTAGES

Good tear strength

Biocompatible

Adequate shelf life

Economic & easy to use

DISADVANTAGES

Cannot record fine surface details

Dimensionally unstable

Incompatibility with gypsum

Distortion

AGAR

COMPOSITION

Agar - Brush heap structure - 13-17%

Borate - Strength - 0.2-0.5

Sulfate - Gypsum hardener - 1-2%

Wax - Filler - 0.5-1%

Thixotropic materials Thickener - 0.3-0.5%

Water - Reaction medium - Balance

FINAL IMPRESSION WITH AGAR

SETTING MECHANISM

Sol-gel reaction

ADVANTAGES

Moist field OK

Accurate and pleasant

Hydrophilic

Low cost

Long shelf-life

DISADVANTAGES

Requires special equipment

Thermal discomfort

Tears easily

Pour immediately

Difficult to see margins and details

INDICATIONS:

Final impressions

Duplicating procedures

ELASTOMERS

POLYSULFIDES

COMPOSITION

BASE PASTE : Polysulfide polymer 80.85%

Titanium dioxide, Zinc Sulfate 16.18 %

Copper carbonate, silica

ACCELERATOR PASTE : Lead dioxide 60.68 %

Dibutyl phthalate 30.35 %

Sulfur 3 %

Other substances 2 %

SETTING REACTION

The terminal & pendant mercaptan groups of the adjacent molecules are oxidised by the accelerator to produce chain extension & cross linking.

ADVANTAGES

Long Working Time

High tear resistance

Modest cost

DISADVANTAGES

Requires custom tray

Stretching leads to distortion

Stains clothing

Obnoxious odor

Pour within 1 hr.

CONDENSATION SILICONE

COMPOSITION

Base Paste : Polydimethyl Siloxane

Fillers

Accelerator Paste : Accelerator

Alkyl Silicate

SETTING REACTION

The formation of elastomer occus through the cross linking of terminal groups of silicone polymers & the alkyl silicates to form a 3 dimensional network.

Ethyl alcohol – byproduct

ADVANTAGES

Putty for custom tray

Clean and Plesant

Good working time

DISADVANTAGES

High polymerization shrinkage

Volatile by-product

Low tear strength

Hydrophobic

Pour immediately

ADDITION SILICONE (Polyvinyl Siloxanes)

COMPOSITION

Base Paste : Polymethyl hydrogen siloxane

Hybrid silicone

Fillers

Catalyst Paste : Divinyl polydimenthyl siloxane

Platinum salt activator

Retarders

Fillers

SETTING REACTION

Does not produce low molecular weight by product.

Secondary reaction can occur with production of hydrogen gas if OH groups are present.

ADVANTAGES

Putty for custom tray

Automix dispense

Clean and pleasant

Ideally elastic

Pour repeatedly

Stable: delay pour

DISADVANTAGES

Hydrophobic

Low tear strength

Putty displaces wash

Putty too stiff

Difficult to pour cast

High cost

POLYTHER

COMPOSITION

Base Plate : Ethylene oxide & Tetrahydrofuran

Filler

Plasticizer

Accelerator Paste : Alkyl Aromatic Sulfonate

Fillers

Plasticizers

SETTING MECHANISM

The elastomer is formed by cationic polymerization by opening

of the reactive terminal rings, under the influence of cation initiators.

ADVANTAGES

Fast setting

Clean

Automix dispense

Least hydrophobic

Good stability

Delay pour

Good shelf life

DISADVANTAGES

Stiff, high modulus

Bitter taste

Needs to block undercuts

Absorb water

Leaches components

High cost

COMPARATIVE STUDY

Properties Good Poor

Flexibility Elastomers Inelastic

Hydrocolloids

Accuracy Elastomers Alginates

Agar Impression Compound

ZOE Poly Sulfides

Tear Strength - Agar

Dimensional Stability Elastomers Hydrocolloids

ZOE

Dimensional Changes - Condensation Silicones

REFERENCES

1. Phillips’ Science of Dental Materials

2. Restorative Dental Materials

Craig & Powers

3. Dental Materials : Properties & Manipulation

Craig, Powers, Wataha

4. Materials in Dentistry : Principles & Applications

Ferracane

5. Dental Materials & Their Selection.

William J.O’ Brien

6. Essentials of Complete Denture Prosthodontics

Sheldon Winkler

7. The Glossary of Prosthodontic Terms

Thank You