MODEL AND DIE MATERIAL - PowerPoint Presentation

Slide1

MODEL AND DIE MATERIALSlide2

Definition of model or cast

It a positive replica of the teeth and adjacent structures.

Definition of die

It is a positive replica of the individual prepared tooth on which the inlays and crowns are made.Slide3

Requirements for model and die

materials

1.

Should have high strength to resist breakage 

during use.

2. Should be hard to resist scratching during use.

3. It should be able to reproduce fine details of the impression.4. It should have little dimensional change on  setting and should remain dimensionally stable during storage.Slide4

5.Compatibility with impression materials. 

There should be no interaction between the surface of impression and the model and die.

6. Good color contrast with other 

materials being used.

7. Ease of use and cheap.Slide5

Ideal requirements of die system

1. Easy to remove and replace in its original position.

2. Stable when placed in the cast.

3. Easy to mount in the articulator. Slide6

Types of model & die materials

Metallic dies

Non-metallic casts

Electroplated Dies

Copper plated

Silver plated

Amalgam used die materialLow fusing metal die

GypsumType I-Impression plasterType II-Model plasterType III-Hard stoneType IV-Extra hard stoneType V –Extra hard, high expansions stoneResinEpoxy ResinPolyurathane Flexible die materialsCeramic diesCement dies Slide7

Gypsum products

Most gypsum products are obtained from natural gypsum rock.

Because gypsum is the

dihydrate

form of calcium sulfate (CaSO

4

· 2H

2O), on heating, it loses1.5 g mol of its 2 g mol of H2O and is converted to calcium sulfate hemihydrate (CaSO4

· ½H2O).When calcium sulfate hemihydrate is mixed with water, the reverse reaction takes place, and the calcium sulfate hemihydrate is converted back to calcium sulfate dihydrate.Slide8
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Gypsum products are chemically the same (CaSO4.1/2 H

2

O) but they differ in:

1. Method of manufacturing.

2. Particle size and shape.

3. Water/powder ratio.

4. Physical and mechanical properties.

5. Uses. Slide10

Extra hard stone IV, V

Hard stone

III

Model Plaster

I, II

Difference

CaSO

4

· 2H2OCaSO4 · 2H2OCaSO4 · 2H2OSource

Boiling of CaSO4 · 2H2O in 30% CaCl2Autoclaving of CaSO4 · 2H2OAt 125 ᵒCHeating of CaSO4 · 2H2O in open airAt 115 ᵒC

ManufacturingCaSO4 · ½H2OMost regularLeast porousMost homogenousα-CaSO4 · ½H2OMore regularLess porousMore homogenousβ-CaSO4 · ½H2OIrregularPorousNon homogenous

Particles100 gm ̸25-30 mL100 gm ̸35-40 mL100 gm ̸50-60 mLP/L ratioThe strongestMore strong

The weakest

Strength

The hardest

More hard

The least hard

Surface

hardness

15 min

15-45 min

15 min

Setting time

Working cast for crown, bridge & metallic denture base

Secondary cast

In

flasking

Primary cast

Mounting of cast

In

flasking

UsesSlide11

high-strength stone dieSlide12
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Setting reaction

When

hemihydrate

is mixed with water, the reaction is reversed and the

dihydrate

is formed.

The reaction is exothermic and depends on:

1. Solubility differences Where hemihydrates are more soluble in water than the formed dihydrates. Slide14

2. Nuclei of crystallization

Where the reaction proceeds leading to precipitation of excess dehydrates in the form of nuclei of crystallization.

3. Crystal growth

During which more

dihydrates

will be precipitated around the nuclei of crystallization leading to crystal growth.

The reaction continues till all the hemihydrates are transformed into

dihydrates. Slide15

Factors affecting setting time

W/P ratio

Increasing water /powder ratio, decreases nuclei of crystallization and retards the setting time.

Spatulation

Rapid and prolonged

spatulation

accelerates setting and also increases setting expansion by breaking up some of dihydrate which increases the nuclei of crystallization. Temperature Increasing water temperature to a certain level will accelerate setting.Slide16

Impurities

Impurities will accelerate the setting time by providing nuclei of crystallization.

Fineness

The finer the particle size, the faster the mix will set by increasing nuclei of crystallization.

Accelerators and retarders

Accelerators

Such as potassium sulfate or set gypsum where they act as sites for

crystallization and increasing the rate of solubility of hemihydrates. Retarders Such as blood, saliva, alginate. Borax as a retarder forms a coat around the hemihydrate particles and this decreases the rate of solubility or around dihydrates (nucleating sites).Slide17

Manipulation

Water is dispensed into a mixing bowl.

The powder of gypsum products is added and mixed with water to obtain a smooth mix.

Spatulation

by hand using a spatula with a stiff blade with the bowl on a vibrator or a power-driven mechanical

spatulator

.Slide18
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Metallic materials: Electroplated dies

Electroplated dies are made by

electrodeposition

of metal ions into the fitting surface of an impression material.

It produces a die with

a very hard and smooth surface

registration of fine details Slide21

Copper electroplatingSlide22

Silver-plated die

Copper-plated die

Difference

Polysulfide imp.

Silicone imp.

Polyether

imp.

Compound imp.Silicone imp.CathodeSilver barCopper barAnode

Silver cyanidePotassium cyanidePotassium carbonate waterCopper sulfateSulfuric acidSulphonic acidwaterElectrolytic solution5-10 amp15-35 ampElectric current12-15 hours10-15 hoursTime requiredSlide23
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Dental waxesSlide25

Classification of dental waxes

According

to their use and

application

1. pattern

waxes

Inlay

CastingBaseplate2. Processing waxesBoxing UtilitySticky

3.Impression waxesCorrectiveBite Bite waxSlide26

Inlay pattern

wax

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Casting

wax Slide28
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Baseplate

wax Slide30

Boxing wax or carding

wax

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Utility

wax Slide32

Sticky

waxSlide33

Write short notes on

Requirements and types of model and die materials.

Differences between types of gypsum products.